Options for noiseless tuning in reflexed regeneratice receiver?
Even with this voltage controlled regeneration and frequency tuning I can still hear noise when I tune the frequency and regeneration.
I have tried pull-out alps potentiometers as well as new high quality spectroll ones. Did I have a bad luck with humitity in these or is this the case?
I have also tried these plastic tuning capacitors from old radios, which gave lower noise, but there was still a bit of noise when tuning quickly.
Other simple options for noiseless tuning?
A digital pot worked fine, but I am thinking in more simple discrete components terms.
Any ideas are welcome.
You need to find a reason for the tuning noise. It could be nothing more than natural variation in track resistance as the control is turned or it could be some kind of 'mode hopping' in the resonator. Remember that resonators are not designed to be used that way and as part of an oscillator circuit they experience many times the amplitude they would normally be expected to handle.
If it is just track noise, add a capacitor (~47uF) between the wiper and ground to filter out sudden voltage changes.
Brian.
I have tried it. It did not change anything. I have also tried an electrolytic from vcc to gnd, nothing again. I thought the LDR-LED would limit the potentiometer wiper noise, but not. I thought then that the LED being fast, could respond to sudden voltage variations due to potentiometer noise, so I replaced this with a small 12v incadescent lamp and removing the 470R, but nothing again. Then I thought that the noise could be induced to the circuit not from the LDR-LED but from the VCC side of the pot (the circuit is battery operated), so I tried isolating the regen pot by not feeding it directly to the VCC but through an 78L08, just to provide isolation from the VCC. But again nothing.
Now I am really thinking of building a custom potentiometer, by having a light source constantly to maximum light (no potentiometer) and control the amount of light by a transparent film, painted with black permanent marker, in a heliax-like pattern, so that as I turn the "wiper" light onto the LDR is faded out.
This would be the completely isolated potentiometer, but I would like to see if I can fix this with more standard parts instead of custom potentiometers.
Brian, will this also rectify RF as effectively as the BJT in my circuit?
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