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Old 10th Nov 2018, 5:13 pm   #84
Ian - G4JQT
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Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,320
Default Re: Building the 'Minimod' AM modulator-questions!

Mike, I must have missed your question the first time - sorry.

The 10k was chosen in the fist instance because that's what similar 2N3819 circuits with an NPN buffer used in various books. When I changed the FET to the BF256, I did just what you did, I put a pot there to see what happened. On the three I tried this on I found about 2.4k seemed optimum, but there really wasn't much difference.

Your 400Hz/2 hour frequency drift is probably as good as I've ever had. The only time you'll notice it is if you've chosen a channel with a strongish signal on it already, which you wouldn't chose to do anyway.

Veroboard shouldn't make much difference at these frequencies, but it's important to cut/separate any stray strips.

After I worked on yours and compared it to mine, the video I sent you didn't show any significant difference between the two in modulation quality when both were received on an Ekco A23 or a Sony ICF-SW7600.

Regards,

Ian
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