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allan · 28th May 2020, 12:02 pm

Latest results are pretty good Guy
I'm using a few chip sm parts in the homebrew detector and with the output set to 0dBm on the meter I see +0,8dBm on the spectrum analyser, give or take over the whole frequency range.

I guess when the detector output was too low (when the coupling capacitor was 33pF) the ALC loop was bumping up the RF amplifier to compensate.. hence too much RF output. The capacitor is now two 10nF chips in parallel. I used these when I found a small discrete 15nF worked OK'ish except for 500MHz.
A different detector diode (better than the 1N5711) might nudge up the output of the detector because the RF level is only 10dBm which is only circa 0.7 volts.
The detector output pot is set at max output so a little more voltage might help.

I'll be looking at the modulation aspects next to see how those function.
cheers
Allan

28th May 2020, 12:02 pm	#125
allan Pentode Join Date: Oct 2005 Location: South coast near Ringwood/Christchurch, Dorset, UK. Posts: 230	Re: HP8640B Signal Generator Latest results are pretty good Guy I'm using a few chip sm parts in the homebrew detector and with the output set to 0dBm on the meter I see +0,8dBm on the spectrum analyser, give or take over the whole frequency range. I guess when the detector output was too low (when the coupling capacitor was 33pF) the ALC loop was bumping up the RF amplifier to compensate.. hence too much RF output. The capacitor is now two 10nF chips in parallel. I used these when I found a small discrete 15nF worked OK'ish except for 500MHz. A different detector diode (better than the 1N5711) might nudge up the output of the detector because the RF level is only 10dBm which is only circa 0.7 volts. The detector output pot is set at max output so a little more voltage might help. I'll be looking at the modulation aspects next to see how those function. cheers Allan