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Tuning Potentiometer

Vaughn
 

Hi all, read up on some of the mods for my BITX40 and one I have made is on the tuning pot. I have replaced the said single turn pot, with a 10 turn pot, to aid tuning accuracy.

My problem is, I have used the wrong value. I should have used a 100k pot, but I replaced the original with a 10 turn of the same value. this makes the frequency gallop at each end of travel.

My question is, can I use a 10 turn wire wound pot? These are quite cheep and easy to obtain and as it is only changing the frequency of the arduino, I think, they should not matter if not carbon made.

Thoughts please and if I need a carbon any links to obtaining these in UK in less than 100s parts please.

thanks Vaughn

Vic WA4THR
 

Actually, the value of the pot is not that important and a 10K will work as well as a 100K. The pot is between 5v and ground and you are just adjusting the voltage when "tuning" and that doesn't depend on the pot value.

The "jumping" is part of the original design. Since the ability to tune (especially with a single turn pot) gets very hard with the small adjustment available, the program is design to start jumping at either end (voltage close to zero or 5v) to step to a new tuning range. There are some fixes for that if you don't like it. One is to add resistors and shorting push buttons so it never reaches the end of rotation range, but you can step up or down with the buttons. Another is to modify the code to change the range you want to tune and even eliminate the jumping. I suggest loading Allard Munter's sketch for the BitX40 as it allows you to easily change the range you are tuning from the menu and offers a better tuning resolution through the technique of quickly averaging a bunch of readings for more accuracy. It really makes a fine improvement on the BitX40 and his illustrated instructions for some simple hardware mods (not required) add even more flexibility.

=Vic=

Allard PE1NWL
 

Hi Vaughn

try https://github.com/amunters/bitx40
and set the required tuning range in the SETTINGS menu

73 Allard PE1NWL