Re: Analog Alley: pos temp coefficient trimmer cap

 

Jerry,

Same work issues here, I am one week in town and the other at my coffee farm dreaming of the mods to try on Bitx40!

I did the same with MV209 ugly piggy backed and the coil tweaked with less turns to provide me with 7 - 7.2 range.

Change the BFO caps to C0g or NP0 and it helps. I put in a Murata trimmer and zero's in my BFO optimally.

Rahul had suggested that we put in a diode in series with the tuning pot to provide some temp. compensation.
I have not treed this mod as yet.

Raj


At 27-06-2017, you wrote:
Hi Raj,
Thanks. Yes, have a ten turn pot, and wanted wider tuning range so actually have 3 more MV209's parallel with the surface mount one already on the board! (It is not pretty) The USA 40 meter band is pretty wide but I can almost cover all of it including most of the CW portion. Those MV209's seem very stable. The tuning is so wide that I am considering adding a band spread pot to one side of the ten turn one. If I had it to do again I think I would just set it up to cover the SSB portion up to a bit above 7.2 and be done.... currently I think there is low enough drift that you could easily qso without worry but if you put a frequency counter on it, it seems to very very slowly consistently drift in one direction. I also changed the inductor to a larger type 7 but that is only marginally better than type 6. I have also considered switching in a polystyrene cap but have not tried it yet. I just have not gotten to the point of saying good enough. Plus I have to travel for work and onl
y get to attack it sporadically leaving plenty of time to consider more options.
jerry

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