Mark,
I just had a few conversations with Allen of VHS about this while trying to make the Howell DDRR antenna work, and while trying to rectify a bleed-over problem with a second whip antenna. I have an MT-8000FA as well. Here's a brief recap of what he told me. And I'll add a caveat...please don't take this as expert advice at all...just passing along my interpretation of our discussion...I'd certainly defer to Allen, Sam or Pete for more expert advice.
1. CW is more power, CCW is less.
2. The pot is very non-linear. All the adjustment is in the last 1/4 turn (or 25% of rotation) at the CW limit. Full CW is full power, and turning it CCW more than 1/4 turn is effectively turning the power off.
3. The most effective way to measure the output is with a wattmeter, while transmitting into a dummy load. I'm not smart enough to tell you how to do that!
4. Allen said you can also measure the voltage at the RF amp (also transmitting into a dummy load, and it must be measured with an analog meter...digital meters won't pick up the short burst well, per Allen). However, he did say it was like trying to set the power to your house by measuring how bright or dim your house lights are. He recommended 2-3 volts when measured there (on the black RF chip, at the third pin away from the antenna attachment, marked with a red line below):
One thing Allen did say is that the MT-8000FA could be turned to full power safely, whereas the older 8000 needed to be set a bit lower to keep from frying the amp, in that 2-3 volt range (tested at the RF module). I know your question is more about setting the power to not overwhelm the net and PO other HAMs, but we never really talked about that...not sure its a factor, and would definitely defer the braintrust for more on that.
During my tests, I tried backing off the power to stop the bleed-over, but my two antennas are just too close together, and lowering the power did not help. So now I'm just transmitting near full power to give acceptable performance with my j-pole antenna, and very good performance from the whip (noise notwithstanding). I say near full power, because I have not tested to see what the output is...I just turned it down about a mini-screwdriver width...just a "titch". (Pete called it 1/128th of a turn!
)
Given the relative complexity of measuring the tracker's watts or the RF amp's voltage, this may be the easiest method (just turn it down a titch, fly it and see how the coverage is).
Allen did say on the next version he may add some more controls, just to satisfy pilots' insatiable desire to fiddle with controls and tinker. I sent him this picture as a suggestion for tracker controls
:
Just some background info from an APRS noob knucklehead...hope it helps! And let's see what the really smart guys have to say!
Cheers,
Bob
