Minto, LF,
Maybe interesting for other homebrewers in the QRO region as well...
Actually the only thing that caused all the faults was a damaged WIMA
FKP-1-2 kV cap. I never have had problems with these caps before. Never
expected that. They are even suitable as a shunt cap for a 10 MHz 300W
class E PA or as the shunt cap in a 1 kW 137 kHz class E... But now one
looks quiet big here. I even heard it dying but thought the sound is
coming from the FETs, making some noise when switching, you know. Thus
the C was much lower and i didn't come on resonance. Probably the
undefined C (sometimes even an inner shortcut?) caused strong mismatch
and lastly destroyed the FETs.
That was the weakest link of the chain. QRO optimisations... The C was
0.33 nF + 1 nF + 2.2 nF in parallel, this in series to the small
variometer part in the shack. It allows resonating within the entire
band.
Now replaced, all works well again...
73, Stefan/DK7FC
Am 13.08.2011 00:17, schrieb Stefan Schäfer:
Hi Minto.
The signal must have been about 6 dB lower than yesterday. Still have
to go back to the old system, unfortunately. Difficult to do good
measurements here in the "shack" where all the stuff is floating either
on mains voltage or on 137 kHz or a mixture of that. Have a battery
supplied oscilloscope but anyway.
I didn't got more than that what you saw, no higher power was possible
even when running the SMPS at 320 VDC. Unfortunately now i saw what the
reason was/is: Some of the turns of the loading coil moved a bit and so
i was outside the resonance. Since the Q of the TX antenna is very
high, the power goes down quickly when beeing outside the resonance. I
haven't had the tuning-meter (U,I, phase) in line, and just tuned the
shack-internal variometer for a maximum signal.
After the unwanted fault and replacing the FET i had to find other
problems like a non conducting shunt resistor (current sensing). This
wasn't visible. For some reason the current limiting didn't work then.
A second loud BAAAAAAANG caused me to let it be for this week!
Now two mains fuses here at QRL are OFF and i don't have the key to put
them in again.
Anyway, i'm in holiday for the next 2 weeks and they will be back in
when i am back and no one will remember that, hopefully, hi.
Actually all that stuff should be exchanges in a QSO :-) BTW how about
YOUR PA? :-)
73, Stefan/DK7FC
Now trying to bring the coil back to its previous L...
Am 12.08.2011 23:07, schrieb Minto Witteveen:
Hi Stefan.
I see your CQ on my grabber at this moment.
How does your ERP now compare with yesterday (during your QSO with Mal)?
It looks like S/N is now worse here then yesterday. Reason
might
be the loop versus the miniwhip (with the miniwhip the winner). But on
the other hand there seems to be a lot of QRN (because of lightning at
this moment.
73’s Minto pa3bca
--------------------------------------------------------------------------
Ceterum censeo Carthaginem delendam esse
Sent: Friday, August 12, 2011 20:02
Subject: Re: LF: PA3BCA
Hi
Minto,
Am 12.08.2011 19:42, schrieb Minto Witteveen:
How much
power were you generating?
73’s,
Minto
pa3bca
It changes all the time. Not even sure since i just have an E field
probe to decouple some power from my TX antenna and feed it to a 50 uA
amperemeter, shunted by a potentiometer. This poti was adjusted to show
100% full scale when using 120 W RF before some weeks. Now reduced the
parallel R on the poti so it shows just 25 uA then. Got 50 uA anyway by
QRO and more (not sure). So it should be arround 500W. This is -6 dBfs
:-)
But the antenna, i.e. the coil and its cover is very lossy it seems.
When there was rain, i have up to twice the losses :-( Need to search
for an alternative cover (mustn't burn, so a water barrel is no
alternative...).
73, Stefan/DK7FC
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