Hi Wolf, Jim, Stewart and LF group,
mni tnx (also to Alberto!) for the enjoyable QSO and Jason tests. As I hadn't
read about the sched on this reflector before, I sort of stumbled in when I
heard Jim asking for lower power Jason.
Markus used his linear TX with an output power between 130 W down to
100 mW.
The first two steps of the power reduction were done in an improvised manner
by loosening the inductive coupling to the antenna variometer, which presents
a higher load impedance to the PA and preserves its efficiency. In the
beginning, I had some trouble with my automatic antenna tuner: Apparently,
the sharper antenna resonance produced more gain in the phase detector servo
loop, resulting in oscillation of the variometer and calling for a
(literally) hands-on solution. Stewart may possibly detect some low-level 3
Hz sidebands... The even lower powers were generated by additionally
modifying the PA's duty cycle, aided by a scope coupled to the antenna for
relative amplitude calibration. The step from 1 W to 0.1 W was in the middle
of the last Jason transmission.
I don't know what Markus' lowest ERP was when Jim had still fair copy - he
may explain himself.
The efficiency of the antenna is about 8*10^-4, so 1 W results in 0.8mW EMRP
or 1.5 mW EDRP.
it seems my old laptop is not suitable for this - Windoze asked me to
close
the application which occupied the soundcard, and a second PC was not
available during the test.
...same here. Without AC97, I guess we have to resort to a-posteriori
decoding.
Thanks for the test to everyone involved. Jim told us he will be putting
out
a Jason signal tomorrow, maybe something to listen for across the pond if
he
uses full power ?
Perhaps with a lot of luck, as condx seem a little unfavorable presently. Had
a spectrogram running last night and most of today, to evaluate what looks
like CFH's idle carrier on 137029. Nighttime levels were consistent at a very
moderate level around 4 dBuV/m (compared to good nights peaking in the 30 to
40 dBuV/m range), but then on the other hand it was visible all day, down at
-15...-10 dBuV/m.
Best 73
Markus, DF6NM
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