AM Radio Transmission

Yes, buy an AM preselector. Car radios are far better built than home radios as they need to work far and near.

http://www.google.ca/search?hl=en&safe=off&q=AM+%2Bpreselector&btnG=Search

Now you know why they invented FM! AM sucks for distance, room on the spectrum, and it only gets worse at night. However, I too listen to AM and my favorite station is about 100 miles away from me. Here's what I did...

First, unless you want to get inside the radio, you need a radio that has connectors for an external AM antenna. Then go down to your local big-sized electronic store and buy a "twin ferrite coil" antenna. The first loop is about 10 inches in diameter. The second loop is at the bottom of the first and is about three inches wide; it also has a knob for fine tuning. You'll probably spend about $40.00 for the antenna, but it really sucks in the AM and helps if your channel is getting stepped on by another station. Keep in mind, however, that even with this antenna, there will always be a few nights where no matter what you do, AM will really suck.

vermin,

I like your tunable antenna.

Actually though, AM is far better for distance than FM, (which is only "line of sight"), although FM is far more resistant to interference.

Interestingly, analog TV broadcasts the picture on AM, and the sound on FM, so in fringe areas you may well get a weak/snowy picture but no sound.

Greg

It is not the modulation type that impacts distance in this regard. AM is a a low frequency and so experiences ground wave propagation in addition to the fact that the lower frequencies bounce off the ionosphere. At night the ionosphere is higher than daytime and the resultant angle of reflection causes longer range propagation. As a result, AM broadcast stations that are not clear channel stations must reduce their broadcast power at night to reduce interference with other stations occupying the same channel in distant cities. Depending on your location with respect to the station this could decrease the quality of your night time reception but you might also be able to hear stations much further away. The higher frequencies of FM and TV broadcast penetrate the ionosphere and do not bounce back to earth so are strictly line of sight.

Yeah! What he said!

Also, not to mention the guy in my general location that starts up some kind of machinery during the graveyard shift. My evening is toast, unless I want to listen to "Waaaaaaaaaaaaaaaaaaaaaaa." That's the other thing about AM... An awful lot of non-radios like to emit it.

Rcapper,

I understand that Am radio is allotted much lower frequency bands and the effect of the ionosphere plus the ground hugging tendencies of lower frequencies.

On TV though you've got me wondering. Channels 2-4 and 5-6 are all below the FM radio band at least in the U.S., but not by much (6 actually ends at the beginning of the FM radio band).

Back in my tube TV and antenna days, there were times when I could receive far off pictures, but not sound. Then I read about the AM picture, FM sound method of transmission and that very effect was attributed to it. (That the AM portion of the TV signal could carry further). Now I know my own experience is merely anecdotal and doesn't count for much if anything, and the written information that reinforced it could certainly have been in error, and/or the effect of picture carrying further than the sound is/was true but for entirely different reasons (such as the relative efficiency of the receiving circuitry).

I'm sure member Berniek would know but so must some other CR4 members and hopefully they will shed some insight into why the picture and sound might have different propagation characteristics, or that they do not.

Greg

AM is sort of a wide open thing. If it is there and above the noise level you can see or hear it but until it is at least 6dB above the noise it may not be very useful. FM is good at reducing noise because noise is primarily an amplitude event and is not rendered by the FM detector. Depending on the type and how well the FM detector (technically an FM discriminator) is designed, you need a certain signal level for it to work at all. Also, since the AM video and FM sound portions of a TV signal are transmitted at different power levels (the video signal requires a higher power level) in the fringe area you will loose the sound before you loose the video. Of course all this is going to change since analog TV is scheduled to be phased out soon.

That is scheduled for 2009, isn't it? How will the Phase out effect AM/FM radio stations? Are they going to make an adapter so we can use what we have to get the digital channel? I wonder why the government needs the skys free of signals anyway. They're probably flying something that it interferes with. Anyone else have any ideas?

The current analogue TV band was designed for the transmission of relatively low definition video signals and while the system has been squashed and things like PALD 625 line squeezed in the bandwidth available is at it limits. If you wished to use HDTV with high quality sound it needs a greater bandwidth and that means it will not fit within the current band. The result is that there are two bands one for analogue and another for digital HTDTV and this is somewhat wasteful.

Since the HDTV is here and it is a better system I believe what has happened is that the governments around the world have decided to only use the higher frequency digital HFTV band and free up the old analogue TV band for other use. I believe a big chunk of the old analogue TV band has been promised to emergency services but I have not been able to confirm this.

The upshot is that we only have a limited spectrum of radio frequencies and to double up is wasteful so considering the need ever increasing need one of them had to go.

No, the phasing out of analog TV does not affect the AM and FM bands. By comparison these are rather small chunks relative to what had originally been allocated to TV. You will be able to buy converter boxes to continue to use analog TV's and there will be a brief market opportunity for that while all the legacy equipment dies. Also, cable and satellite will probably continue to offer analog on their boxes for quite some time. For a while it looked like VCR's were going to become hard to get but all they did was to start combining them with DVD's since it has gotten so cheap. Times are changing indeed, pretty soon incandescent light bulbs will be a thing of the past for home lighting. I happen to have a couple of old UHF converters if you need one of those, just kidding. Originally TV's only had a VHF tuner. When sets started showing up with UHF then there was a box you could get to allow your VHF only set to tune in the "new" UHF channels. Sort of analogous to what is happening now with the HD.

I have used this for many years down here in Australia to listen to distant AM stations- take 23 metres of insulated copper wire(enamel or other), gauge can be about 30, not important, & wind in a continuous coil over a frame, can be round or square, about 12 to 18 " in diameter- across the ends of the coil solder a tuning capacitor as used in AM radios to tune in stations- the radio is placed in or near the coil for best effect by experiment- the loopstick booster is aimed in line with the station, & the tuning cap tuned for best reception- this works by boosting the signal available to the inbuilt ferrite antenna in the radio- if a recent radio with an external loop antenna, place the loop in the booster for best effect. Another boosting effect is by placing the radio on a sheet of metal- this invokes a "ground-plane" effect.

We built a ant. quite similiar in College for Field Theory. I still wish i had it.

Thing would pick up anything, including early cell and baby monitors. I don't think it was really part of the design, probally a fortunate mistake that allowed it.

Have a great day

Interesting use of a re-transmitter. The only danger is if there is a HF transmitter in your area. Your retransmitter could retransmit the HF signal also. HF radiation is dangerous to your health.

Since we are talking about AM (Amplitude Modulation) radio transmission you may find it interesting to know that the VHF radios in aircraft use AM.

As for the distance that the transmissions go at night, I was once driving in Sydney Australia on a dark, still and cold night. and listening to an AM station on the car radio. When they gave the time check I thought that they gave the wrong time so I listened more intently to the next time check. The next time checked that they certainly were giving the wrong time so I continued to listen even more intently. I eventually realized that the time was actually correct for the location of the station. The station I was listening to was actually in Auckland New Zealand which is around 3,000 Km away and two hours ahead of Sydney.

You, obviously, have never experienced the pleasure of "South of the Border" radio in the US. They crank out so much power you can pick it up at night on your toaster!

• What is "South of the Border" Radio?
• Where does the border start?

I am at the southwest tip of INDIANA on the Ohio river. The city is in a valley so all I usually here on AM is static across the whole bar. With the exception of the "Coast to coast with George Norry" at Night and "the Dave Ramsey show" in the morning and afternoon thats all I can ever pick up. I love both shows and it seems like every time there is something interesting on there, I get bombarded with static. It bugs the hell out of you when you go across the station and you stop and backup, thinking what was that?, was that it? Then you start moving the stupid antenna. Those cheap radio companies should just not bother with putting a crappy tuner in. I'm 27yrs old but luckily, I got my hands on one of those 70's huge cabinet stereos with the 8 track and record player, thing had an awesome tuner in it, but it finally gave out.

neon signs, fluorescent lights and dimmers creat a lot of static. A car radio froma wrecker. Make sure it is a Ford or chevy of chrysler OEM radio, not a jap after market radio.

They are made for mobile and have good front end selectivity. A pair of computer speakers and a 12V 1 amp power supply = cheap solution

South of the Border Radio is radio coming from any number of Latino countries: Mexico, Central America, South America... Since it's all in Spanish, and I don't speak the language, I can't really tell the countries of origin. But at night, especially in the West, it stomps on almost everything! Not only that, I assume these guy are unregulated, because their transmitters broadcast harmonics up and down the band.

Yeah, Coast to Coast is a real hoot! That's why I listen to AM. I like getting it from a station that's 100 miles away because this particular station rebroadcasts the earlier show later at night. Hence why I got the twin ferrite antenna.

Your primary problem is that cheap portable stereos and home stereos have small ferrite antennas that are much times less efficient than the antenna of a car (even the loop on a windshield). Most home stereos have a connection for an external 300 ohm or 75 ohm antenna. If you are able to pick-up the signal in your car at home, then mount the antenna that came with the stereo or buy an aftermarket one.

Here's an interesting explanation from Wikipedia. A couple of local stations I like to listen to, during the winter (EST), cut their signal power from 4:30 PM to 7:30 AM. They're tough to pick up, even in a car. I'm in Philadelphia and I get better reception of a Montreal sports talk station.

"During the day, AM signals travel by groundwave, diffracting around the curve of the earth over a distance up to a few hundred miles (or kilometers) from the signal transmitter. However, after sunset, changes in the ionosphere cause AM signals to travel by skywave, enabling AM radio stations to be heard much farther from their point of origin than is normal during the day. This phenomenon can be easily observed by scanning an AM radio dial at night. As a result, many broadcast stations are required as a condition of license to reduce their broadcasting power significantly (or use directional antennas) after sunset, or even to suspend broadcasting entirely during nighttime hours. Such stations are commonly referred to as daytimers." (Wikipedia, "AM Broadcasting").

With all this talk about AM "skip," It deserves mentioning that FM and high frequency (line-of-sight) signals can span great distances as well, though the process is different. Under certain odd weather conditions, high frequency signal can get trapped between atmospheric layers. These layers can act as waveguides, steering the HF signals for considerable distances. They eventually come out of the tunnel at some other part on the Earth where they're received.

Just so ya know.

You get the ground wave during the day and at night; during the day, the ionosphere absorbs the signal but at night depending on the frequency the signal will refract and travel back to earth via the sky wave as well. That's why they make the stations cut power at night. The ionosphere varies daily but also works on a cycle of about eleven years - at the high end of the cycle, the Maximum Usable Frequency (MUF) during the day will usually allow 20 meter and sometime even some 40 meter, while in the low end of the cycle 10 meter is rough.

google AM antenna, there are numerous sites which will explain various homeade designs and the basic theories behind AM reception. I have built a few tuneable loop antennas with a pick up loop connected to the external antenna connections of the reciever.

I usually build these to pick up distant transmitted signals that are squashed by adjacent frequency higher power and closer transmitters. Hopefully the nearer transmitter is not directly inbetween the farther and lowerpower transmitter and the location of your receiver.

These antennas can be built with various radius and number of windings to better isolate and re-radiate the desired frequency to the pick up loop and then to the receiver.

There are some online calculators that will tell you the radius and number of windings to use based on your desired frequency. fine tune with caps.

I usually use PVC pipe to fashion a cross with perpindicular legs off each corner, drill small holes through each perpindicular piece and wrap your windings. I attach a PVC access box to the mounting end of the antenna, then thread each end of the windings back through the PVC to this box. Connect the ends of winding to tuneable caps. for the pick up loop i drill another set of holes one in each perpindicular arm and run cable through attach that to F-connector threaded inside the pvc, Then run coax to receiver. I found that putting another cross on the other ends of the perpindicular pieces promotes stability and reduces the sagging caused by the tension of the windings. Mount antenna tune and point to best suit your needs then secure. Always use lightining protection if antennas are roof mounted or outdoors.

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