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Fuddled Frequencies: Newsletter Challenge (January 2018)

Posted December 31, 2017 5:01 PM
Pathfinder Tags: challenge question frequency

This month's Challenge Question: Specs & Techs from GlobalSpec:

Suppose your preferred AM radio station is located at 800 kHz on your radio dial, and you have a very special, perfect radio receiver that can only tune exactly at 800 kHz, excluding all other frequencies. Would you hear the music more clearly using such a radio receiver, or there is no difference between it and a standard receiver? Can this be true if you have an FM receiver with the same characteristics?

And the answer is:

If the radio receiver is limited to exactly one frequency it cannot receive modulated waves, and without modulation no information can be transmitted – only hum. This is true for FM radios as well.

In order for a radio transmission to carry information (music in this case), the main signal (music) has to be modulated so it can make “different expressions.” AM waves are modulated by “adding” a high frequency (the carrier; this is the frequency at which you should tune your receiver) to the original signal (modulating signal). The result is a signal with highs and lows is shown in the figure.

The amplitude-modulated signal contains more than one frequency and the radio receiver must be able to receive all frequencies, including the frequency of the original signal.

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#1

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

12/31/2017 5:41 PM

No you may likely have some variance in the phase of the frequency according to distance and atmospheric conditions, modern tuners usually have some sort of phase lock loop strategy employed to match the receiver signal....

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#3
In reply to #1

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

12/31/2017 6:51 PM

Agreed. Radio waves bump into things between the transmitter and receiver.

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#13
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 9:21 AM

But, is this receiver able to reproduce the signal coming from the transmitter?

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#2

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

12/31/2017 6:49 PM

No, the bandwidth of an AM signal is about twice the modulation frequency. For example, to transmit a signal modulated by a 5000 Hz sound would require a bandwidth of 10000 Hz.

http://www.ni.com/example/30146/en/

The lower the bandwidth, the lower the maximum frequency of the modulating signal. If the bandwidth were zero, then there could be no signal received by the receiver.

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#26
In reply to #2

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 1:54 PM

Let's not confuse the modulation frequency bandwidth

With the carrier wave bandwidth ?

The modulating frequency controls only the carrier's amplitude, not the carrier's bandwidth. ( for AM )

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#32
In reply to #26

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 4:04 PM

Little known secret. Modulator forms a product of the waves, and so does FM modulator. Do the math. It produces side frequencies.

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#33
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 4:27 PM

You are right! But, you did not answer the main question.

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#38
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/03/2018 9:01 AM

To directly answer the main question:

No, Little Johnny, you cannot hear the music better or the same, in fact, you will not hear the music, you may not hear the music, and you need to go back to your seat and be seated. Basic answer no, detailed answer no way.

Secondary question: This does not work at all with FM.

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#34
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 5:09 PM

Agreed, outside the perfect case we are discussing. Even so, the frequency tolerance of the standard carrier detector ( being imperfect ) allows the standard radio to synchronize to a large degree with the incoming carrier. In effect the receiver ignores small frequency anomalies and calls it 800khz. Our perfect receiver in theory has maximum INtolerance. I believe we are dancing around the same table, sir.

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#39
In reply to #34

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/03/2018 9:15 AM

..and what a fine table it is, sir.

No sharp corners to poke us.

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#37
In reply to #32

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/03/2018 6:22 AM

Without disagreeing with what the transmitter modulator does, can I ask whether this is relevant to what the perfect receiver receives? Is not all the information available on the centre frequency, irrespective of what is duplicated on side bands?

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#40
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/03/2018 9:21 AM

This so-called "perfect" receiver as described by OP, is absolutely perfect (perhaps meaning no signal loss at center frequency), but is also perfectly monochromatic, meaning that Q=0, at any arbitrary frequency non-identical with 800.000...kHz.

No information can be encoded upon this except very slow on/off information content, and only the center frequency has any gain in the RF pre-amplifier or amplifier.

There would be a slight loss of 800.0000...kHz signal due to switching the carrier on/off (at the transmitter) in attempts to convey information.

This will never work as there is no audio modulation of carrier amplitude at precisely carrier frequency.

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#60
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/09/2018 4:28 PM

I agree with you! You won't hear anything except a 'hum'

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#77
In reply to #26

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/10/2018 3:08 PM

The <...carrier's bandwidth...> is zero. It's the modulakers on the carrier thrroom that produces the deep vibrail on the eardroves.

https://www.youtube.com/watch?v=R2nI_3VBEtA

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#4

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

12/31/2017 7:54 PM

Can this be true if you have an FM receiver with the same characteristics?

For a given modulation frequency, the FM bandwidth is even larger than it would be for an AM signal. It depends not only on the frequency of the modulating signal but also on the amount the FM frequency carrier varies with the amplitude of the modulating signal.

http://www.cdt21.com/resources/Modulation/modulation_FM.asp

In either case, you need bandwidth on your receiver to demodulate a signal.

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#10
In reply to #4

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 4:25 AM

...and that is why FM is used in the VHF and UHF regions, rather than in LF and MF, because there is more space in the frequency domain there for the wider sidebands for an FM signal compared to an AM one.

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#27
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 2:13 PM

Yes, for an FM transmission the modulated frequency would be constantly moving back and forth across the channel's centre frequency. The single point receiver would only see the instantaneous energy as the carrier moved across its focus frequency. This would be at max amplitude, as the carrier amplitude is not modulated. Thus we would demodulate a series of events that crossed the centre frequency, at some modulation frequency. This would be enough to create a raw tone of varying frequency in the audio output. The amplitude of the demodulated FM is a function of how far from centre the modulated frequency deviates, so does not come into play in a single point crossing receiver. The single point receiver will demodulate at full intensity the instant of crossing; unlike the AM case. We cannot forget that this is a perfect receiver and does not care about anything other than the energy detected at it's focal frequency.

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#5

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/01/2018 12:45 AM

The ONLY "on-frequency" transmit & reception of intelligible information is good-old fashioned (Morse) CODE, ie: ON & OFF carrier.

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#6
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/01/2018 3:54 PM

Anything you do to add intelligence (modulation) to the signal, even Morse code, widens the bandwidth. A zero bandwidth signal carries no information. It's just a sine wave that lasts forever. Just sayin'.

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#11
In reply to #6

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 4:43 AM

State 1. The transmitter oscillator is switched off. The perfect receiver receives nothing.

State 2. The transmitter oscillator is switched on. The perfect receiver detects the carrier wave and switches a buzzer and a signal light on.

The transmitter operator, using a Morse key to switch between states 1 and 2, transmits information.

The receiver operator reads the information obtained via a zero-bandwidth receiver.

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#29
In reply to #11

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 2:40 PM

A zero BW receiver?

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#7

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/01/2018 11:26 PM

If you had a perfect radio ta accept ONLY 800KHZ then it would have a bandwidth of only 1 hz. Anything else would be 799999 or 800001 hz etc. So the question of AM reception would be similar to single track digital audio provided the amplitude resolution of the perfect radio was also perfect. EXCLUDING external influences affecting apparent frequency, the radio should produce a similar output to a .wav file; only with infinite dynamic resolution within the AM envelope recieved.

Taking external influences into account, only that portion of the shifting frequency that passed thru the 1 hz window would be converted to sound as well as externally influenced variance of amplitude.

As for FM, your radio would only process the single frequency as the modulation swept across it. The resulting sound would theoretically be a variable monotone whistle, each tone corresponding to the crossing frequency at your given perfect point. The amplitude of the tone would also be maximum since FM does not theoretically modulate amplutude.

Adding external influences to the FM would be indistinguishable from the above, apart from minor variations in reception due to external signal fade, since almost any crossing would produce a reaction in the perfect receiver. A signal too low in amplitude would drop out of the detection and produce no sound at all.

Apart from all of that, the FM receiver would not consider 800khz to be a valid signal; being well below the mhz range of reception.

Finally, all of the above refers to a perfect receiver, not a perfect transmitter at 800khz.

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#24
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 1:20 PM

As long as others are picking at hairs, let me point out that OP stated ONLY that he has a perfect 800,000 hz receiver. In this single case one must assume that the internal workings of this device do not bear any resemblance to those of a real receiver; and dispense with an evaluation which would take those real circuits in hand. The perfect receiver does not care about any transmission or intermediate characteristics of the signal; it only does one thing, perfectly. It accepts any and all energy it finds at 800,000(.0 repeated) hz. And converts it to audio, the desired function of the receiver. Thus we can dispense with issues about whether it has or needs a dial, or cares about the source bandwidth, which for the point of argument in a non-perfect transmitter is much greater than 1 hz. We need only deal with the concept of perfect reception at a single point of the RF spectrum, which in this case lies within the AM band. In fact, we might even assume less than one hz bandwidth; the transmitted signal crossing that point being perfectly received would still be perfectly processed at the full intensity received. The same perfect theoretical principles would be considered for FM reception, but the bandwidth would cripple the receivers ability to faithfully reproduce the source.

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#41
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/03/2018 10:13 AM

A zero bandwidth receiver, AFAIK, does not exist. It would be a circuit with an infinite Q, meaning that energy could only be stored and could not enter or exit. But you can approximate it by a very high Q circuit, having a very narrow bandwidth. Such a circuit will respond very slowly to an input signal.

Such circuits are used in sweeping spectrum analyzers. The narrower the analyzing bandwidth, the better the resolution, but also the slower it has to be swept across the frequency band to give it time to respond to signals.

"For a swept-tuned architecture, this relation for sweep time is useful:

Where ST is sweep time in seconds, k is proportionality constant, Span is the frequency range under consideration in hertz, and RBW is the resolution bandwidth in Hertz.[3] Sweeping too fast, however, causes a drop in displayed amplitude and a shift in the displayed frequency.[4]"

https://en.wikipedia.org/wiki/Spectrum_analyzer

"

This month's Challenge Question: Specs & Techs from GlobalSpec:

Suppose your preferred AM radio station is located at 800 kHz on your radio dial, and you have a very special, perfect radio receiver that can only tune exactly at 800 kHz, excluding all other frequencies. Would you hear the music more clearly using such a radio receiver, or there is no difference between it and a standard receiver? Can this be true if you have an FM receiver with the same characteristics?"

If you plan on listening to music with a narrow bandwidth as is used in a spectrum analyzer, you will only hear very low notes. If the bandwidth were truly zero, you would hear no music at all. The music is in the sidebands.

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#45
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/04/2018 9:38 AM

I would have given you an order of magnitude good answer, but my "dial" is set up for either "1" or "0".

Precisely what I have stated about ten times already.

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#8

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 1:47 AM

This must be a Trick question.

If your radio can only tune 1 station, why would the radio need a Dial ?

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#9
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 4:21 AM

Quite.

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#12
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 9:19 AM

Well, this is not the point of the question!

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#20
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 11:24 AM

Correct use of wording is the point of the question. A Dial allows variance such as solar eagle describes, where a switch allows the control of a single hz as longintooth describes. If the Dial is akin to a varistor, then the switch is akin to a potential divider.

A Dial allows an approximate control, whereas a switch allows control such as 70AARCuda describes. There is no mention in the question about the transmitted signal, only the received signal.

The way I understand it is the wiper across a plate allows for variance, or approximation of the signal, some degree of + or - of the attenuation of the signal.

If my understanding is in error, please correct me.

If I understand this equation :

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#21
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 11:38 AM

Read the question more carefully:

"Suppose your preferred AM radio station is located at 800 kHz on your radio dial, and you have a very special, perfect radio receiver that can only tune exactly at 800 kHz."

(I added the bold to "and".) This implies two receivers, one with a dial that can receive the standard AM frequency range (to identify the frequency required), and a second fixed-tuned one to avoid other frequencies.

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#14

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 9:49 AM

I think this question is simply trying to get at the difference between amplitude modulation and frequency modulation.

So I believe the answer they want is that the perfect 800 kHz tuner will work really well with the AM transmitter but will be next to useless with the FM transmitter.

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#15
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 10:09 AM

Why is so? Please, explain!

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#22
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 11:50 AM

What does this mean?

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#30
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 3:01 PM

Amplitude modulation "mixes" the carrier frequency with the signal.

The receiver is tuned to the carrier frequency and demodulates the filtered output to reproduce the original signal. The trouble is if anything interferes with the radio signal: say halves the power, then the demodulated signal is also affected.

Frequency modulation uses the voice/music signal to slightly change the transmitted carrier frequency around the nominal frequency. Demodulation uses a frequency to voltage converter, so as long as the signal is not too badly affected the receiver can always exactly reproduce the original signal even if the carrier signals power fluctuates due to interference.

Most of the other posts here contain valid points, but, I think the question is aimed at finding out if you understand this basic difference between these two kinds of modulation.

Incidentally the "change in frequency" in the above FM picture is shown very exaggerated; in practice you would not be able to "see" the difference in frequency in a real transmission. This enables far more "stations" in a given bandwidth.

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#31
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 3:14 PM

What you describe is correct, but you are not answering the main question.

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#16

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 11:08 AM

Why would you own such a useless radio?

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#19
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 11:19 AM

Good question! But this does not answer the original question.

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#17

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 11:15 AM

I suppose it is possible for AM signal reception only, however, the receiver Q is infinite for this perfect receiver, having stated nothing about the Q of the transmitter.

Thus if the transmitter Q is not infinite, i.e. - the frequency is a delta function (except with varying amplitude), the received signal will be intermittent and non-intelligible.

If the transmitter drifts off band even by 1 Hz, no signal will be intercepted. This could be due to temperature induced drift in oscillator components.

It will not work for FM either, since FM required frequency bandwidth.

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#28
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 2:27 PM

Ah, but the bw of AM station frequencies are much more than 1 hz, are they not ?

For this example, the carrier would have to drift a long way to either side of centre to see the bw edge; and the entire bw would have the same relative intensity.

So moving the bw window back and forth across the centre frequency should theoretically have little effect on the demodulated signal, as long as the window stayed between the rolloff ends.

We are perfectly receiving the energy at the 800khz frequency ONLY.

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#18

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 11:17 AM

For an AM signal, he perfect receiver and a standard AM receiver would hear the same thing. In theory, the AM signal is at only 800 kHz and the amplitude of the signal carries the signal information. The issue is that any "noise" that mimics the slope of the 800 kHz frequency will add or subtract from the overall amplitude and degrade the signal.

The issue of sideband is not really relevant to the discussion as it is a parasitic energy cost at the transmitter.

A perfect single frequency receiver in FM is an oxymoron. FM stands for frequency modulation. The transmission is sent with an AVERAGE frequency and varied at frequencies either side of that average to send the signal. The amplitude of an FM signal does not intentionally carry signal information. The perfect receiver you describe would generate only clicks as the varying frequency passed through 800 kHz with the loudness of the click being proportional to signal amplitude.

As mentioned by others, FM typically uses much higher frequencies. At 800 kHz, if you vary the carrier frequency by the signal frequency 1:1, to transmit a 16 kHz audio signal, you would need to use a transmission signal range that varies from 792 to 808 kHz to carry the information, which is a lot of space on the radio dial. If you were at 100MHz instead, the frequency range would be 99.992 to 100.008 MHz

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#23

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 12:08 PM

"Suppose your preferred AM radio station is located at 800 kHz on your radio dial, and you have a very special, perfect radio receiver that can only tune exactly at 800 kHz, excluding all other frequencies. Would you hear the music more clearly using such a radio receiver, or there is no difference between it and a standard receiver? Can this be true if you have an FM receiver with the same characteristics?"

Pardon me, folks. The question made no mention of bandwidth. If I drill a hole in my radio dial and secure it with a screw at 800kHz, it will receive just the same as before at 800kHz. A perfect radio (as the question says) will have the proper bandwidth to receive the music. Can WHAT be true for an FM receiver? As usual the question is ambiguous.

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#25
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/02/2018 1:26 PM

I tend to agree with you, although I must yield to those who have already pointed out that amplitude modulation of a very pure carrier frequency (at the transmitter) will result in a bandwidth due to mixing of wave-forms. Any single frequency detector will be totally and completely useless, other than to note that some signal on the 800.000..kHz carrier will "randomly" appear, possibly during zero crossings of the amplitude signal.

This question is not appropriate to our understanding of telecommunications of signals, other than very slow Morse code. Actually, even if the Morse code were keyed automatically at a very rapid rate (above what human capabilities are), there would still be detected the carrier wave, albeit at a much lower amplitude, and this carrier frequency would be continuous in the limit of the highest rate of switching of dots and dashes, but would have a lessened amplitude, similar to how PWM causes and "average" voltage to appear at an Arduino output.

At low switching frequencies, the signal would decidedly be deemed to be discontinuous, and information could be transmitted that way.

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#42
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/03/2018 11:28 AM

Sorry, have to disagree with the mixed waveform guys. In AM, the signal is carried by the amplitude variation and not the variation in the frequency. The described perfect receiver would receive the complete signal plus any transmitted noise at specifically 800 kHz from other sources. Bandwidth is irrelevant in AM except that no transmitter is perfect and you get parasitic sideband crap as a side effect of the process of transmitting that spills over into adjacent frequencies.

Saying you can't receive the main AM signal without also including the parasitic crap is like saying you can't ride a pony without filling it's saddlebags with it's manure before you can ride it.

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#44
In reply to #42

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/03/2018 4:19 PM

I have to disagree. A carrier signal amplitude modulated in the time domain is mathematically equivalent to a carrier frequency and symmetrical sidebands in the frequency domain. (The sidebands are not a defect of the transmitter.)

It's basic math, the product of two sinewaves is the equivalent to two other sinewaves with the frequencies of the sum and difference.

http://www.sosmath.com/trig/prodform/prodform.html

By Fourier analysis, the audio can be broken down into the sum of many sinewaves. Each of these sinewaves is part of the sideband, so you get the symmetrical frequency sidebands centered about the carrier frequency.

Time domain:

https://en.wikipedia.org/wiki/Amplitude_modulation

Frequency domain:

Demodulation (recovery of the audio signal) for AM is very simple since the carrier amplitude is a copy of the audio. In fact, a simple diode can do it.

My point is that if your receiver only received the carrier and removed the sidebands, it would also remove the modulation and it would remove the music.

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#47
In reply to #44

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/04/2018 9:45 AM

You said what I have been saying, but most eloquently.

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#48
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/05/2018 12:09 PM

Let's try to simplify this a bit to begin with and suppose that the transmitter's carrier frequency is exactly 800KHz, and as stated in the question the receiver is a " perfect" 800KHz filter and demodulator.

Forget about the frequency domain for a minute and just look at the time domain AM signal, which is exactly what you'd see with an oscilloscope. What do you claim that signal would look like after is had passed through the filter?

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#49
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/05/2018 3:15 PM

A totally pure sine wave, carrying 0 information content, other than it is on (or off sometime later, maybe). The amplitude is this signal is invariant, since the spectrum is pure.

The frequency spectrum is a dirac delta function: {1,800.0000kHz} (of course it is zero at all other frequencies).

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#50
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/05/2018 3:33 PM

Exactly!

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#51
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/06/2018 9:30 AM

"A totally pure sine wave, carrying 0 information content"

I did say forget about the frequency domain. Just imagine that you are looking at the signals with an oscilloscope.

Suppose that the signal above is what you see before the filter. What do you see after the filter?

A totally pure sine wave? Of what amplitude?

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#52
In reply to #51

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/06/2018 11:46 AM

An AM modulated signal is the product of two things:

  • The carrier
  • The audio signal plus a DC offset

The audio signal would have a mean value of zero. The DC offset is large enough so that audio plus dc offset never goes negative. Removing the sidebands leaves just the carrier times the DC offset.

So, to answer your question, since the average of the audio is zero, the amplitude of the pure sine wave would be the average amplitude of the modulated signal.

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#53
In reply to #52

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/08/2018 6:10 AM

Huh, that’s odd I thought I sent a reply on Saturday: must have failed to submit it.

___________________________________________________________________

the average amplitude of the modulated signal

So, suppose you have a 1KHz signal at 0dB for one minute followed by a 1KHz signal at minus 6dB for one minute. How does the filter “know” about the second minute 10 seconds after the start of the first?

The trouble with the frequency domain is that it destroys/ignores “time”.

The above example is clearly extreme, so just think about a 1KHz signal at a nominal amplitude. There are 800 cycles of the carrier for every one cycle of the signal. Imagine that you’ve got a scope probe on the input to the filter and one on the output, and you capture 10 cycles of the carrier around 60° past the maximum amplitude (so about ½ peak amplitude); what do you see on the scope for the probe on the output of the filter?

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#55
In reply to #53

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/08/2018 9:56 AM

That is not entirely true. If the phase of the signal is encoded in the freq domain, all is well. It can inverse transformed and with zero loss of information, it is just math.

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#72
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/10/2018 1:26 PM

First, let me say that it has been well over 50 years since I formally studied modulation, and I may not have ever 'done the math' regarding sidebands in AM.

Randall's post #30 perfectly illustrates my understanding of AM and FM.

I have read most, if not all, of the posts in this thread (many of them multiple times, as I am wont to do). Obviously this 'perfect' receiver can not detect the sidebands, but it can detect the presence of an 800kHz signal. If it can detect the 800kHz signal, then it can certainly detect the absence thereof, and there must be some signal intensity below which the signal is considered absent. Above that minimum signal strength, I assume that it can also detect changes in the strength (amplitude) of the signal. Surely a stronger signal will produce a higher output voltage than a weaker signal (I'm thinking specifically of crystal radios; I built several back in the '40s and early '50s. The only 'filter' was the mass of the earphone diaphragm.).

If a stronger signal produces a greater output, then it is responding to amplitude modulation. No sidebands needed! I can't agree with those who say you'd hear nothing or just a hum.

If I'm wrong, please educate me...

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#74
In reply to #72

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/10/2018 2:16 PM

...then the thread is questioning the meaning of the word <...exactly...> in the original post: the width of <...exactly...> in the frequency domain determines what information gets through the filter for interpretation by the listener.

In principle, if the bandwidth of the filter were exactly zero, then not even the carrier wave will get through, as the rise of this wave from zero amplitude to any value and its fall again also has a frequency. When one mixes together two signals in the frequency domain one gets the sum and the difference of those two frequencies, which are labelled 'sidebands' in that domain.

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#79
In reply to #72

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/10/2018 3:36 PM

Nope. All you get after "demodulation" block is "static". About like trying to communicate on this forum.

Yes, the dB level of carrier may go up and down, depending on distance from XMTR, XMTR radiated power, atmospherics, etc., etc. That is not what "we" are talking about, now is it.

What you are talking about, I think, is that reduction of the carrier (in some transmitter modes that are used) reduces overall XMTR power, with more power being present (information quality) in the side-bands.

If you turn the carrier up and down using a knob, good luck reaching something resembling an audio frequency. People need to stop arguing with the very clear mathematics on this.

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#84
In reply to #79

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/10/2018 4:43 PM

It is beginning to sound like I've been carrying, and occasionally spreading, a basic misconception for around 70 years.

I have always assumed that Amplitude Modulation meant that the amplitude (radiated power) of the carrier changed according to the modulating signal. Is that not true?

"People need to stop arguing with the very clear mathematics on this." Unfortunately, I have no idea exactly what math you are referring to! I changed to Physical Science after three years studying Electronic Engineering, when I found I couldn't get a teaching credential with an electronics degree.

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#85
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/11/2018 9:07 AM

The result of multiplying one signal by another takes place in AM, FM, and PM.

The result is that the information is in the side-bands. Suppose you put the modulation for AM on the control electrode of an RF amp tube. The result is a change in gain of the carrier as it passes through the tube, right? This ends up being the mathematical product of the two sine waves.

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#86
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/11/2018 11:38 AM

Thanks. I vaguely understand the concept of multiplying producing the sidebands, but as in Rixter's excellent post #44, "A carrier signal amplitude modulated in the time domain is mathematically equivalent to a carrier frequency and symmetrical sidebands in the frequency domain." (My emphasis on the "and")

or, from the same post:

The carrier is still there, and it is still changing in amplitude according to the modulating signal, isn't it?. The carrier voltage is still crossing through zero twice every 800,000th of a second, isn't it? Thus passing the received signal through a simple diode and either mechanically or electronically removing the high carrier frequency results in a voltage based on the original modulating signal, if not identical to it. Is that statement false?

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#87
In reply to #86

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/11/2018 1:48 PM

The carrier is there, and only changes amplitude transmitted to the extent of whatever portion of the energy spectrum is still in that center frequency. Now there can be equipment that somewhat filters out the unchanged carrier wave before broadcast, thereby greatly increasing transmitted efficiency.

Demodulation is the result of the diode (detector), and some LRC filtration that only passes the low frequency (information) modulation signal...so you can listen to that L.
A. Dodgers game on the AM radio.

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#88
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/11/2018 2:57 PM

With all due respect, I cannot agree. The modulating signal changes the entire BW of the carrier. The entire BW of the modulating frequency is present at every point across the carrier BW. 20 hz of modulation occurs at every frequency within the 800khz BW, as does a 20khz modulating frequency. We are modulating amplitudes not frequency. The fact that the modulation changes the carrier by the sum of components does not alter the fact that the entire carrier is modulated. For the purposes of discussion, sidebands should also be ignored because they fall outside the target 800khz "only". We agree that the real world is not simple nor pure, but that is not the OP's question.

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#89
In reply to #88

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/11/2018 3:03 PM

I am sorry, but this is not correct information.

I think we see two different animals, not even the different ends of the elephant on this one.

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#90
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/11/2018 3:21 PM

So for an 800khz AM radio transmitter, if I want to transmit a 20hz tone, I must use a different portion of the carrier than if I choose to transmit a 200 hz tone ? Enlighten me please.

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#91
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/11/2018 3:42 PM

James Stewart, I apologise.

It is not your purpose to educate me;

And it was rude of me to address you that way.

Consider me enlightened by other sources.

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#92
In reply to #90

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/11/2018 3:49 PM

Not at all. The carrier is a relatively pure sine wave oscillator of much higher Freq than the tones to be transmitted, right? If you made a spectrum of it, you would see a flat line with a single spike in it at the carrier freq, in this case 800 kHz.

Now if you modulate that with say two tones, one is your 20 Hz, and the other is 200 Hz, you will see a total of five lines (spikes) in the spectrum, two on the low side, the middle (carrier) freq, and two on the high side. If you added 2 kHz and 20 kHz modulation tones, you would then have a total of four on the low band, the carrier, and four on the high band, a total of nine lines (spikes).

The only problem with this odd note being transmitted would be that it violates FCC bandwidth rule for AM (10 kHz allotment).

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#97
In reply to #87

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/11/2018 10:55 PM

"The carrier is there, and only changes amplitude transmitted to the extent of whatever portion of the energy spectrum is still in that center frequency."

I do understand that, if the sidebands exist, they contain energy, and that energy must come from the transmitter. Whether that energy must be subtracted from the energy of the unmodulated carrier is not at all clear.

Going back to Rixter's Post#44, "A carrier signal amplitude modulated in the time domain is mathematically equivalent to a carrier frequency and symmetrical sidebands in the frequency domain."

Since both sides of an equation can be interchanged, the above statement can be rephrased: A carrier frequency and symmetrical sidebands in the frequency domain is mathematically equivalent to a carrier signal amplitude modulated in the time domain.

I don't live in the frequency domain; I live in the time domain! In my world, those sidebands don't exist! It's just an 800kHz sine wave with amplitude changing according to the modulating signal.

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#100
In reply to #97

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/12/2018 5:43 AM

GA. As I keep trying to point out, I don't live in the frequency domain either. If you looked at Louis Armstrong and Kate Bush in the frequency domain you would easily be able to tell which was which, but, although your first WAG would almost certainly be correct you would not be able to tell who was singing "Wonderful World" and who was singing "Wuthering Heights".

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#110
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/12/2018 1:20 PM

Then your world is a 0th order approximation of reality.

I just felt obligated to throw that out there for you. This is not a simulation, and it is not a drill.

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#113
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/12/2018 2:10 PM

I guess I've got a thick skull! If this isn't a simulation, what is it? Since apparently no one can actually build a receiver with a 1Hz bandwidth at 800kHz, then it can't be tested (proven true or false), and we're both wasting our time.

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#121
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/15/2018 1:03 PM

Whether you can build a 1Hz bandwidth receiver is irrelevant. The point of the OP's puzzle is that to transmit information (i.e. music) over a radio channel requires bandwidth. For example, if your music has a bandwidth of 0-5KHz, you would need 10KHz bandwidth for Amplitude Modulation.

There are ways to reduce the bandwidth required, e.g., single sideband, or digital radio with sampling and compression, but some bandwidth will still be required.

https://en.wikipedia.org/wiki/Single-sideband_modulation

https://en.wikipedia.org/wiki/Digital_radio

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#122
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/15/2018 2:04 PM

I have been aware of sidebands since the late '50s or early '60s. My brother had an SSB amateur radio system in that time frame.

BUT!

1. Assume you have an 800kHz oscillator whose amplitude can be varied (modulated), connected to an antenna [transmitter].

2. Assume you have an extremely high-Q resonant circuit with a receiving antenna, tuned to exactly 800kHz, with some method of determining/measuring the current circulating in that tuned circuit [receiver].

3. Assume that there are no other significant 800kHz signals in the vicinity.

THEN:

A. If the transmitter is turned off, the tuned circuit will have no currents circulating, so the output will be zero.

B. If the transmitter is turned on, unmodulated, with an appropriate power level, the tuned circuit will have some current circulating, so the output of the receiver will be some fixed value.

C. If the power level of the transmitter is then increased to a higher power level, the circulating current in the resonant circuit will soon increase, so the output of the receiver will go to a higher value.

D. If the power level of the transmitter is then reduced to the Step B power level, the circulating current in the resonant circuit will soon return to the previous lower value (although the circuit has a high Q, it will not be lossless), and the output will return to the previous lower value.

ETC. Please! where is the flaw in the above reasoning?

I'm not saying that the output will precisely follow rapid changes in the power level of the transmitter. In other words, I'm not saying that the system will be capable of conveying high quality music, speech, etc.

But I AM saying that (at least slow) changes in the level of the transmitted signal will influence the output of the receiver, without responding to any frequency other than 800kHz. NO sidebands required!

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#123
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/15/2018 4:00 PM

I agree pretty much with all of that, but I might add that the higher the Q (and narrower the passband) of your receiver, the slower the receiver will respond to changes in the 800 kHz transmitter power. If the Q of your receiver were infinite with zero bandwidth (if there were such a thing), it would take an infinite amount of time to respond to changes in signal level.

https://en.wikipedia.org/wiki/Q_factor

For the transmitter to put out a perfect 800 kHz signal (zero bandwidth), it would have to generate a perfect sine wave of constant amplitude for an infinite time. (Obviously, there is no such thing.) Anything done to the amplitude of this sinewave, including turning it on or off, widens the bandwidth. The more often you change the amplitude, the wider the bandwidth of the transmitted signal. (A 1 Hz amplitude modulation would result in a 2 Hz bandwidth).

So, you have a transmitter with a non-zero bandwidth signal, depending on how rapidly the output changes. You have a receiver with a non-zero bandwidth, depending on its Q. If the frequency plot of your transmitted signal fits inside the receiver's passband in the frequency plot, all is good. Otherwise, your receiver is filtering out part of your transmitted signal. It's just another way of saying that the receiver is tuned properly and can respond as rapidly as the transmitter signal changes.

I hope all of this is helpful.

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#124
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/15/2018 5:09 PM

All these is helpful, but it does not add to the answer to the question.

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#125
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/15/2018 5:50 PM

Yes it does answer the question!

"...Would you hear the music more clearly using such a radio receiver, "

The answer is NO! You would hear it less clearly, because of the lack of the higher frequencies, or you would hear nothing at all, if the cutoff frequency were lower than the listener can hear.

...and apparently the cutoff will indeed be below 20HZ, so you won't hear anything, although you might feel something with an appropriate transducer.

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#128
In reply to #125

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/16/2018 8:36 AM

You will hear nothing! Just a hummmm

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#136
In reply to #128

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/16/2018 3:01 PM

Since it is a "perfect receiver", there should be no hummmm! You should hear silence.

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#126
In reply to #123

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/15/2018 11:38 PM

Ok Thanks. I think we're pretty much on the same wavelength...

The one thing I think I picked up here is that to get zero bandwidth, you would need infinite Q, and that could could only be achieved if the circuit were indeed lossless (superconducting). Such a circuit, once set to oscillate, would (theoretically) continue to oscillate after the transmitter had shut down, so would be unable to detect any modulation of the transmitter signal.

Now on the other hand, as soon as you try to measure the current flowing in that circuit (detecting the signal), the act of measuring will gradually remove energy from it, so it no longer is lossless, and its Q would no longer be infinite. I gather that then its bandwidth would no longer be zero.

Thanks again for your patience!

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#127
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/16/2018 6:16 AM

"For the transmitter to put out a perfect 800 kHz signal (zero bandwidth), it would have to generate a perfect sine wave of constant amplitude for an infinite time."

Why on earth do you say that?

What's wrong with the picture I put in post 120 Where the modulator produces one full circle of the carrier at one amplitude followed by another at a slightly greater amplitude?

And of course once I get an answer to that question I'm going to start reducing the length of those DC steps.

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#129
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/16/2018 8:54 AM

Watching from the sidelines, I believe that most of the lack of agreement stems from a logical fallacy, namely that BECAUSE the transmitter spreads the transmitted information over carrier wave and sidebands, THEREFORE the receiver necessarily must process both carrier wave and sidebands in order to extract all the required information. My understanding is that the full information is carried in the modulated shape of the carrier wave, and can be detected by an envelope detector circuit. The fact that there are sidebands carrying the same information is irrelevant to that process, but it demonstrates one of the inefficiencies of AM modulation.

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#132
In reply to #129

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/16/2018 1:41 PM

What you said is only true for a single side-band transmitter, and that is clearly not what Randall and DK Warner are speaking of.

At this point, any further attempts to convince those on the "carrier only" side of this coin, will not be convincing no matter how correct they may be.

Final answer: this entire conversation is moot, since no one (in their right mind) would attempt to transmit or receive information in such a manner.

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#134
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/16/2018 1:46 PM

This is a theoretical question and a non-existing receiver. Don't forget this.

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#135
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/16/2018 2:24 PM

"At this point, any further attempts to convince those on the "carrier only" side of this coin, will not be convincing no matter how correct they may be."

You could start by answering my incredibly simple questions. I'm away for a few days so you've a while to think about them.

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#137
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/16/2018 3:10 PM

I believe you and I were asking the same questions, using different words. Look at the series of posts starting with Rixter's #121. I believe our questions have been answered, although not necessarily in the manner that we would have preferred.

The bottom line is that a zero bandwidth receiver can't be made, and a 1HZ bandwidth receiver, if it could be made, would not detect variations in amplitude of the incoming signal that had a modulation frequency above 0.5 Hz.

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#138
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/16/2018 3:25 PM

Yes, I agree with you.

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#139
In reply to #137

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/16/2018 5:12 PM

You will have to explain this to me then. It comes from electronicsnotes

_______________________________________________________________________

AM diode detection process

In rectifying the RF signal, the AM diode detector provides an output equivalent to the envelope of one half of the signal, i.e. it is an envelope detector.

In view of the operation of the diode detector, it may sometimes be referred to as an envelope detector.

The incoming amplitude modulated RF signal consists of a waveform of both positive and negative going voltages as shown. Any audio transducer would not respond to this.

AM diode envelope detection process.

The diode envelope detector rectifies the waveform leaving only the positive or negative half of the waveform.

The high frequency element of this is then filtered out, typically using a capacitor which forms the low pass filter and effectively ‘fills in’ the high frequency elements, leaving a waveform to which a transducer like a pair of earphones or a loudspeaker could respond to and convert into sound waves.

____________________________________________________________________

To me it seems that receiving music on an AM transmission is like buying a vinyl record from one of 3 branches of a chain of record shops. You can get it either from the lower sideband (amazon.com) or the carrier frequency (amazon.co.uk) or the upper sideband (amazon.com.au). You do not need to invoke 2 or 3 branches to buy 1 record.

The only way in which the perfect receiver would fail to receive a signal and deliver the music would be if the transmitter failed to deliver an exactly specified frequency. I'll go along with that, but the sidebands are irrelevant.

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#140
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/16/2018 10:43 PM

The flaw in that thinking only appears when (as in the original Post) they specify a receiver having a very narrow bandwidth ("...perfect radio receiver that can only tune exactly at 800 kHz, excluding all other frequencies.")

Now that statement is open to several possible interpretations. Strictly speaking, if the radio can only receive "exactly at 800 kHz", then it could not receive 799.9999kHz nor 800.0001kHz, In other words , the receiver has zero bandwidth. Another possible interpretation would be that it can receive signals with a frequency greater than 799.9995kHz and less than 800.0005kHz. (any value that rounds to 800,000 HZ).This is a bandwidth of 1Hz. Yet another possible interpretation would be that it can receive signals with a frequency greater than 799.5kHz and less than 800.5kHz.(any value that rounds to 800, with three digits of precision) This is a bandwidth of 1kHz.

Although the original statement says it is a "perfect" receiver, nothing is perfect, and a zero bandwidth is impossible, so I have been assuming the 1Hz bandwidth interpretation.

Now the key is: what is necessary to obtain a very narrow bandwidth? To receive a specific frequency requires a circuit resonant at that frequency. Resonant circuits have a property called "Q" (Quality). Low Q circuits respond weakly to a fairly wide range of frequencies, while high Q circuits respond more strongly to a signal, but over a narrower range of frequencies. To obtain a receiver that only receives a 1 Hz bandwidth would require an extremely high Q resonant circuit. A high Q also means very low losses. A low-loss resonant circuit will continue to oscillate (Ring) after the stimulating signal has been removed. A really high Q circuit will continue to oscillate for considerable time after the stimulus is removed.

This means that the very high-Q receiver will not be able to drop its output voltage quickly when the amplitude of the transmitted signal drops quickly.

So the very high-Q receiver can not follow rapid changes in the amplitude of the transmitted signal.

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#141
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/17/2018 4:54 AM

Ah, but my perfect receiver works with two high-Q filters, one each side of the carrier frequency, allowing the centre frequency to pass untroubled to the detector circuit.

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#143
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/17/2018 9:40 AM

The question is very clear: the receiver can ONLY tune to one frequency (800 kHz) and nothing else. You can't assume that the bandwidth is 1 Hz or 1 kHz, because, by doing so you are answering a different question, not the one posted.

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#144
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/17/2018 11:33 AM

No, that is NOT clear. Depending on the precision of the number 800...

Now if you interpret the "exactly" in the literal sense, then the 800 has infinite precision, and of course that is impossible, just as an infinite Q resonant circuit is impossible, and I see no reason to waste time thinking about impossible situations.

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#145
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/17/2018 11:38 AM

It is EXACTLY 800 kHz. Period! This is a theoretical exercise!

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#146
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/17/2018 12:01 PM

Then I just lost interest in the thread. Bye!

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#147
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/17/2018 4:02 PM

First the theoretical perfect receiver. It is perfect because, using some as yet undiscovered principle, it acquires only the desired single frequency. Note that I leave the phrase "tuned to" out of that sentence, to avoid getting bogged down in high-Q discussion. That single frequency, in all its amplitude-modulated glory, gets passed in full to a simple diode detector.

Second, a receiver more akin to the real world. This has a wide-band RF amplifier stage, followed by 2 closely spaced notch filters. It does not have a stage tuned between the notch filter limits, so there is no problem with ringing in a high-Q circuit, but nevertheless the frequency which gets past the notch filters is what you want. And that single frequency, in all its amplitude-modulated glory, gets passed in full to a simple diode detector.

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#148
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/17/2018 4:09 PM

Built it, and let's see what is what. I do not believe you, it is a mathematical impossibility. Electronics is very simply put, math. No math, no electronics.

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#149
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/17/2018 4:28 PM

What a diode detector will do when encounters a pure sine wave of 800 kHz?! There is no envelop in this theoretical signal, so the diode detector is useless in this case.

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#150
In reply to #149

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/18/2018 5:36 AM

I think you are confusing purity of frequency with constancy of amplitude. And the point is that the diode detector will detect as soon as the amplitude of the 800kHz signal is modulated. It does not depend on the presence of sidebands. It need not know they exist. Or are you arguing that all the modulation information disappears into sidebands?

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#151
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/18/2018 11:38 AM

Here you are arguing a dead horse up out of the ground, even after burial. You could not be more wrong if you were deliberate about it, but it is fun to watch you make a pompous fool of yourself over it.

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#163
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/20/2018 2:51 PM

Erm, no. The horse is not dead but neglected. We already know that a detector can detect the presence or absence of a carrier wave. It follows that Morse transmission and reception is possible. It only remains to discuss the maximum frequency of such transmission, bearing in mind that the Q of any part of the perfect receiver circuitry is irrelevant.

After you have come to the conclusion that the maximum frequency of the Morse transmission is not limited by the design of the receiver, then you can consider the possibility that the detector may be able to register different amplitudes, as well as mere presence and absence.

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#152
In reply to #150

Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/18/2018 1:33 PM

Yes! All the modulation information disappears into sidebands!

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#153
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/19/2018 11:04 AM

Please look at my picture in post #120 where I have changed the modulating signal to a series of DC components.

Each full cycle of the carrier is a pure sine wave at 800 KHz and will be received by a perfect 800KHz filter.

Each subsequent full cycle of the carrier is a slightly different amplitude.

If I printed two full cycles of the modulating signal it would be indistinguishable from the first picture in post #119.

When you half wave rectify that you recover the original signal.

In what way does this have anything to do with the sidebands?

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#156
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/19/2018 4:28 PM

Interesting that something of what we are talking about applies to GIS.

Take two identical single frequency waveforms, offset one by the detection delay between the transmitter (possibly moving), and the two set (fixed) receivers.

If one performs the mathematical convolution of these two signals, one gets the same thing out (the same frequency wave) with a phase offset so the peak of the convoluted wave is at the time delay. Two pulses convoluted will produce a pulse with its peak at the delay of detection of the two original pulses.

All modulation techniques are essentially a subset of mathematical convolution. It is very interesting, and even plays into cryptography.

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#154
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Re: Fuddled Frequencies: Newsletter Challenge (January 2018)

01/19/2018 11:18 AM

When I can persuade people to answer my questions about how a perfect filter would react to a carrier modulated by increasingly smaller sections of DC signal, I am moving on to an incredibly simple (conceptually) filter which will react at the required speed and it will be obvious that as you decrease the bandwidth to zero will still work as desired.

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