Joe, (and other inexperienced sat operators). When I use the term 'you' in this post it is not to be taken personally. If the shoe fits...well, then yes, take it personally, otherwise just take it as a way to describe an operating guide.
1. Yes running too much EIRP aka Effective Radiated Power, (power plus antenna gain - feedline loss) ruins operations for other operators. It may also cause a malfunction of AO-7, to include FM'ing on SSB or shutting down the xponder entirely.
AO-7 is a particularly sensitive case. So, let's set it to the side for the moment.
On the other linear (SSB/CW) birds like CAS-4A, 4B, XW-2A, 2B, 2D (again), and 2F here are the issues:
The downlink power (the sat's transmitter) is shared. It is shared in proportion to the strength of the uplink signal from each individual station. So, if a station is running *excessive EIRP,* they capture the vast majority of the available downlink power and everyone else's signal is driven into the noise floor. This happens at a syllabic rate on voices (heard by others running proper power levels as a pumping up and down of their signal at the speech rate of the offending signal). On cw, it is even worse, with each keyed character driving all the other signals into the noise floor at the keying rate.
Saying, "I'm only running 5 watts" is NOT an acceptable answer. It also demonstrates that those saying it have no idea how to considerately operate on a satellite.
*There is one simple rule: You should never be louder on the downlink than the strength of the CW beacon, period.*
It is the ops responsibility to stay within this limit. No excuses, no explanations, just do it.
Unfortunately, this pumping/power robbing happens frequently on all birds, because operators either:
1. Have no idea what they are doing....or 2. Don't care that they are ruining the operation for others.
I have many hours of 15 minute pass MP4 recordings of these situations and have been tempted to publish them. I have resisted publishing them because so many of them seem to be the result of "innocent" mistakes.
So, what is excessive EIRP and how do we avoid it? For simplicity's sake, I'm going to refer to EIRP as power.
You should adjust your uplink power so that it *NEVER *exceeds the strength of the CW beacon you are hearing *AT THAT TIME*. Simply looking at the beacon once in an entire 15 minute pass does not reflect what is happening throughout the pass. The beacon reference needs to be repeatedly checked during the pass to see if you need to power down. It's a LOT easier to tell if you have enough power (you can hear yourself), but a lot harder to pay attention to the fact you are too loud.
I cannot tell you how many times I have witnessed a QSO where one op tells the other, "*You have a great signal*"....yeah, 8 dB above the beacon, stealing the downlink power from the considerate operators who have kept their uplink power low enough to stay no stronger than the beacon. Yes, they are loud. But on this shared resource we call a satellite downlink passband, being an Alligator (big mouth, poor ears) is not something to be proud of, nor should we be complimenting operators for this lack of either 1) awareness; or 2) consideration, for the other operators.
Also, you may sound weak because of poor receiver performance on your end, so you are tempted to turn up your transmit power to make up for your poor ears. *This is a constant problem on the birds as they are being used lately. *Many ops seem unaware of how poorly they are hearing and it has little or nothing to do with their bright and shiny new rig. :-)
Someone else mentioned, that if you can't hear the beacon, don't transmit. *Truer words were never spoken*. If your rx performance is so bad that you cannot hear a signal that is easily 15 to 25 dB above the noise, then don't transmit, all you are going to do is power rob others.
The truth is, all of the linear birds on mode B (2m downlink), have beacons that consistently run 15 to 25 dB above the noise floor. If you don't hear them that strong, fix your receiver setup. Add a preamp, use better coax, increase your receiver antenna gain. etc.
Another simple test: do you hear passband noise from the satellite? When it comes into view, you should be able to hear a marked increase in your receive noise. At the peak of the pass you should be able to hear it easily. If you don't, your rx performance is poor. 9700 and SDR users will see a marked 'hump' shape of the passband if they are set to a wide panoramic view.
Turning up your transmit power is not the solution and you will, indeed, ruin other people's qsos.
In another post, I mentioned a simple and dirty way to tell if you have adequate receiver performance. It requires no test equipment.
1. Disconnect your antenna. 2. Connect a 50 ohm dummy load (a simple 47 Ohm resistor works fine) to the antenna input of your radio. You will not be transmitting. 3. If you can turn the agc off in your rx, do so. If not, set it to Fast. 4. Noise Blanker or Noise Reduction OFF 5. Now....turn up the volume so the noise coming out of the speaker is quite obvious, but not ear splitting.
Remember how loud it sounds.
6. Quickly disconnect the resistor and replace it with your satellite antenna.
Did the noise jump up considerably compared to the noise caused by the 50 ohm resistor?
If not, your rx performance is poor. You need to fix it, as above.
If it did jump up, at least a bit, you are probably in a relatively quiet RF location for noise and that is really good...and the fact that you can hear environmental noise above your receiver's internally generated noise is very good.
If it jumped up a very large amount, then your locally generated environmental noise is high, which is NOT good, because you will end up turning up your transmit power (uplink) to the birds to overcome it...and of course, the rest of the people using the satellite will be driven down into the noise floor, or power modulated by your speech rate or cw keying.
So, what do we do about all of this?
1. Exercise some real care about your operating practices. Take time to learn how your station performance varies by the nature of a pass (shallow, moderate, very high) and during a pass ((current elevation and polarization fading).
Using linear birds considerately requires skill and operator attentiveness. This is completely different than FM birds and is much more demanding of operator intervention.
*Most importantly, during the pass itself check the beacon strength several times and adjust your uplink power such that your received signal does not exceed the strength of the CW beacon.*
Those with the nice shiny new Icom 9700 have no excuse for ever being stronger than the beacon. They can simultaneously monitor the beacon level and their own signal (as well as others in the passband) with the panadapter feature of the 9700. Set your rx width on the panadaptor to +/- 25 kHz and center it so the PSK beacon is at the left edge of the display and the right edge is above the op of the satellite passband (and you will see the CW beacon just above (to the right) of the PSK beacon and the normal passband just above (further to the right) of the CW beacon). This should be on your display all the time. Then you can always see if you are too strong. It will be obvious.
2. If you have access to an SDR dongle like the FunCube Pro +, run software like SDR Console v3 (free). You will be able to see every signal in the passband in real time from the PSKBeacon to the CW Beacon to your signal and all the others.
When you can see what poor operating practices do to the satellite passband and everyone trying use it, you will be amazed.
Since more and more of the serious satellite ops are getting 9700s and SDRs, I find that the first thing I tell someone when I'm working them is how strong their signal is (in relative dBm) and how strong the beacon is (in relative dBm) . If they are exceeding he beacon, I ask them to reduce power. It's that simple.
I'd really like to not have to:
1. Chase people all over the birds asking them to reduce their signal because they are 6 to 10 dB over the beacon and are "power modulating" every signal on the satellite.
2. Get on their freq and politely call them....only to have to chase them all over the passband because they can't hear themselves and they continue to transmit anyway.
As the popularity of satellites, especially the linear birds, has increased, we are coming under more and more pressure to clean up our operating habits. These are NOT FM birds. *Getting on one freq and capturing the downlink with one signal with all the juice you can put out is not an acceptable operating technique on the linear birds*.
It is inconsiderate and destructive.
Hopefully, the directness of these explanations will help and not offend new satellite ops. It has gotten bad enough, that something needed to be said. We want all of you on the birds, just play nicely.
73, N0AN Hasan
On Fri, Mar 6, 2020 at 3:19 PM Joe KD2NFC via AMSAT-BB [email protected] wrote:
I was just on AO-7 and was told to lower my power from more then one person. Sorry about that folks, just getting adjusted here, please be patient with a satellite beginner.
Now that we are here I was curious what a lot of power in does to the linear birds, does it ruin the passband for others? Also how much is a good amount of power to start with or one shouldn’t exceed?
FM birds probably have similar operating rules as well right. I’m here to learn :)
Joe KD2NFC
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