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Old 30th Nov 2020, 6:41 pm   #11
dtvmcdonald
Pentode
 
Join Date: Mar 2016
Location: Champaign, Illinois, USA.
Posts: 227
Default Re: Racal RA17C12 AGC

Around here there are only three overload problems: 580 and 1400 kHz and 94.5 MHz.
The latter is so awful its even audible in the RA17 if every screw is not tight, and in the R390A (barely) even if they are. It appears due to mixer drive harmonics. But other than that no tube (valve) set is anywhere near bothered. My Airspy, however, direly needs really good prefilters, and on good propagation days there is one station at exactly 6MHz that is a severe problem. Those problems were solved
with a set of prefilters that cost more than the Airspy itself plus the Spyverter combined.

I love making mods ... tinkering has been my whole life. Its served me well as a grad student and professor. Especially fun is mixing electronics and liquid helium. Its took lots of tinkering to get a noise figure of -16 dB, and an input impedance of 1 megohm in parallel with 1 pF.

The mods I propose will have an effect on overload only in the range between when the overall AGC delay starts kicking in and when the current source RF stsge delay kicks in, and that change will reduce overload. It won't reduce useful sensitivity as the
overall AGC delay is in fact probably a bit too much.
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