[600MRG] More on accurate RF power measurements... ( again )

[Dave Riley]

Had some pretty good luck last night with several EU TA receipts of aa1a 
WSPT beacon @ 500 milliwatts eirp...

It seems that there is headroom enuf left to ease on down to 200 
milliwatts and see if any beacon messages get through tonight...

It gets tough to read these lower power levels or see what the real  
truth is on the 'guages' ( all reading very low ) so now the SDR-IQ is 
heated up, properly calibrated with the known reference of 50 watts, 1 
amp of RF current on a 50 ohm line sent in to a freshly tuned loop...

50 +/- J0

Keyed down on CW with known 50 watts of signal, increased coupling from 
receive antenna via step attenuator in to a 50 ohm load thence connected 
in to the SDR receiver input...

Set this 50W level to read -20dBm on the Spectra Vue log scale... Set 
Vertical sensitivity to 3db/vertical scale...

Eased down -3db on the power and it looked like 25 watts OK on the other 
guages, same procedure down to _2 watts_ and see scope and toroid 
current sensor all look like the RF is correct level for 200 milliwatts, 
since the TX loop gain is -10db...

Lucky duck so far!!

That's what is was on a cold day in Yankee land, de aa1a QRV WSPR 475.685

* bonus... The Dallas Lankford noise phaser was used with VO1NA CW 
beacon to affect a net 2db of signal to noise ratio... It's tough to 
deal with qrn and qsb but with only four controls and a switch I get to 
know where some noise went and where the best receive azimuth settings 
are...

Major changes in RX antenna are forth coming...  Like #1 phaser input to 
be a hot f.e.t., isolated e-probe WAY out in the woods and nulled out 
against the BOG...
Much noise here has to be dealt with...

Good luck, y'all doing a great job... Lots to keep up with...

Tinker DaveR @ aa1a sed that...






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