[AMRadio] LOG, LINEAR, and REV LOG


John Coleman jc at pctechref.com
Thu Sep 6 17:09:11 EDT 2007


So, with a normal log pot, if you wired it normal and started with it fully
CW then turned it CCW 10% from the top you would be 10DBV down (divided by
10)and CCW 20% from the top would be 20DBV down (divided by 100), etc.

But if the control was a reverse log and wired normal then turning it CCW
10% would only yield a 1 DBV drop and 20% down from the top would yield a 2
DBV drop, etc.  To get 1/2 voltage or 3.1DBV you would need to turn it down
30%. And at the other end to get a 10DBv change you only need to turn the
pot 1% from where it was (assuming it was not all the way at the CCW
position).

I hope I said all that right for it can be very confusing!

Perhaps if wired as an inverse feed back control it might seem mere useful?

Reverse log pots don't seem very useful to me but then I don't have a lot of
experience with store bought stuff.

In the case of HAM radio speech equipment, I prefer linear pots so if I need
to change the audio voltage by 10% then I turn the pot 10% regardless of its
current position.  Of course in stereo HIFI equipment, where there is an
acoustic listener, I use log pots. 

John, WA5BXO




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