Question About RF Radiated Power Vs Bandwidth

Sounds like they increased the bandwidth without increasing the power...

Did they "retune" the receivers "IF" for the wider bandwidth?

I'm suspecting that they would be "softune" radio transceivers, so it should be "easy" to realign them with the correct settings.

If the receivers are still on a narrow band setting then you will have issues due to blocking. Digital RF is finicky it has to be 110% perfect or there'll be corruption issues.

Also check the orientation of the antennas to ensure correct alignment and polarity. Antennas and terminations do deteriorate over time and harshness of the environment.

Now just so you don't get too confused, radiated power and bandwidth are 2 separate things, though they are alloyed. It is important to have sufficient carrier signal between nodes, that's where radiated power comes in. That has a significant bearing on signal to noise. The stronger the carrier is received the less noise will be imposed on the signal.

Bandwidth is the signal that utilises the carrier to transport the packets of data. Think of it as an invisible pipe, which depending on diameter will only allow a certain amount data to flow, the carrier should be considered as the support structure that holds the pipe in the air, the more support the pipe has the bigger the pipe can be.

There are limits to the amount of carrier level that a receiver can deal with, as well as the bandwidth of the signal. Like I said they are alloyed, but separate things.

So ;

Check that ALL the transceivers are properly aligned with the the right bandwidth settings.

Have the Antenna systems checked. Make sure that they're pointing in the right direction. Note any damage to the coax is lethal to signals at the 2.4 Ghz, any moisture ingress to the coax is bad. Also check for loose connections because that can be a signal killer too.

Ommmmmmmmmmmmmmmmmmmmmmmm.

That's as much Zen as I can offer from the other side of the globe..

The equipment is dead simple wifi stuff. No adjustable IF stages, power is digitally adjustable but is set at max available of 350 mW.

The only adjustment is the bandwidth of 5, 10 or 20 MHz.

Antenna alignment and polarity are of prime importance. At these flea power levels, a change between the correct polarity and 90 degrees out means about a 20 dB drop in signal level. We peak the reception of each antenna when installing it.

So should there be a difference if the bandwidth is set larger or not? I'm not sure I understand Solar Eagle's comment...it seems to be suggesting that the wider bandwidth needs more power to maintain a competent signal.

Thanks,

Jon.

Correct, unless a weaker signal can provide the same transmission quality, which seems not to be the case here. An optical analogy:

• The transmitter is a hypothetical 100W monochrome red filament lamp. The bandwidth is increased by adding a hypothetical monochrome green filament lamp of the same wattage at the same place. If the power available is limited at only 100W total, then the power of the 100W red lamp needs to be reduced in order to get anything out of the 100W green lamp; balancing the lamps might mean only 50W comes out of each lamp and each lamp will be dimmer to the distant viewer, though the bandwidth has increased and the power consumed is the same.

You cannot get something for nothing. When you widen the transmission bandwidth, more total energy is required for the same signal to noise level using the identical receiving equipment. Now if your receiver can be optimised (directional antenna, low noise receiving amplifier, removal of in band interference, optimized filter design, etc.) to reduce your received noise level then the same transmitting power can be used with a wider bandwidth.

SE is right. Think of it this way, each bit of information requires a certain amount of power to transmit, more bits more power, until you bump up against the power limit of the transmitter. At that point if you increase the number of bits, the amount of power that is available to go into each one can no longer increase, and will decrease further for each incremental increase in the bandwidth. This seen at the receiver end as a decrease in the signal strength as it falls below the noise floor inherent in the receiver.

Your Wifi guy is probably not an HRO (Ham Radio Operator).

Lets see what happens. I've asked the wifi guy to reset the network back to 5MHz. Hopefully they will get to it today. I'll report back on the performance of the network.

J.

I didn't read all the other responses yet but my first thought is the aiming of the dishes. The wider bandwidth will be more sensitive to the aiming of the transmitter/receiver dishes as well as the obstructions in the line of sight. make sure you have an American football shaped free space between your antennas. The mid point between them should be free of obstructions or you will experience losses of signal strength.

Transverse wave forms have a very weird set of requirements that seem to defy conventional logic. What worked at a narrow band may fail at wider bandwidths. Keep in mind that the mid point of the football shape of the transmitted signal gets wider as the frequency increases and that the obstructions that seemed to be unimportant at lower frequencies can become opaque and load the transmitter at higher frequencies.

Re-align your antennas across the full spectrum of your band. Then, you may need to increase your transmitter power and pre-amplify your receivers to get the full use of the new wider band. One way to do this easily is to increase the diameter of the the receiving and transmitting dishes.

I have successfully used a Yagi as the receiving element on an 11db dish with very good broadband results...

Another note: That wide football shaped area between the antennas can be loaded by anything containing water at or near 2.4Ghz. That frequency cannot pass through water and that is how a microwave oven works. The "football" shape is important. Even if something is several degrees off line-of-sight it is a significant load on your transmitter. You may be able to see from the center of your transmitting dish to the center of your receiving dish just fine, but any load just outside that line of sight is still affecting your signal strength. You must account for the space between the antennas, not just what the line of sight is. The center point between them is very significant to the loading and the resulting received signal.

However, we wanted to up the data bandwidth from 2Mbps to 4Mbps and we understood that a wider RF bandwidth was necessary to achieve this. (Our radio system can accommodate 5, 10 and 20 MHz bandwidths)

Doubling the data rate doubles the RF bandwidth signal. With the same power output, the power is spread over twice the spectrum. Noise power is proportional to bandwidth, so your signal to noise ratio at the receiver would be reduced to half or -6dB. So I would expect that your maximum range would be reduced.

While all of the above comments are accurate, they all focus on the transmitter/antenna system to fix the problem. Another method may be to add a small LNA (low-noise amplifier) to the receiver side to boost the reception above the noise-floor of its' mixer system. A good LNA for each receiver may be a lower cost solution with better value, and at the frequency range you are talking about, may be an off-the-shelf purchase.

(Just an option I would look into.)

First of all, be aware,that the art of specmanship -writing specifications one only attempts to reach - is alive and well with the folks in marketing. So take the written spec. with 3 grains of salt.

Yes, there are equations establishing relationships between factors relevant to transmission of data:

1,. The higher the gain of (either or both) antennas, the longer is your reach in an inverse square relation to the distance: you 4x the gain, you gain 2x the distance. An upgrade along these lines might be desirable.

2,. Your transmitter power is fixed. Either by possibilities or by regulation. If you spread it, you have proportionally less of it for every segment of the bandwith.

3,. The noise is assumed to be distributed evenly over every segment of the bandwith.

4,. Hence, the power to noise ratio goes down for the widening the bandwith for both 2,. and 3,. It can get expensive, but that is life.

5,. When you switch data rate, you might switch modulation mode to a more sensitive one. Be aware.

6,. IF the noise factor of either end is 3dB or higher, a LNA (low noise preamplifier) with lower noise factor is a quick way to upgrade, if physically possible. In most cases there is no way to insert the box. Keep in mind, that the same path between the electronics and the antenna is normally used both for transmit and receive.

7,. One factor does need more explanation, because it was left out of the discussion entirely.

Unless you transmit from a hillside thru an unobstructed path to the other hillside, that is. Normal folks grapple with the problems of the topography, where the trees, weeds and buildings literally eat up the meager transmitted power underway.

Raising one or both antennas is usually the answer to your problem. Frequently it takes ingenious solutions. This one takes real work.

Good luck. Let's hear from the progress.