EMRFD Message Archive 10477

Message Date From Subject
10477 2014-11-15 19:16:33 cqk1jeb IC-765 Total Gain Pot R414

Hi all,

I have an IC-765 which I did a total alignment on the receiver as the BFO was off such that the SSB audio did not sound right.

After alignment of the receiver the last step is adjusting the 'Total Gain' trim pot R414.

It said that the receiver should have the audio adjusted for 2.5Vrms of noise at the speaker output. then adjust R414 so that the noise is reduced 30dB.

I have an Inrad Roofing Filter added so I only get 1.5 Vrms of noise max at the speaker output not 2.5 Vrms or 2.2dB lower.

So how do I adjust this trim pot to? Do I adjust it to -27.8dB instead?

I did this and the receiver is now exhibiting S-9 out of the back ground noise when I plug the antenna in.

Which indicates the receiver is too sensitive.

I have an IC-718 radio. When I add the same antenna to the 718 the background noise is displayed as S-0.

Switch antenna back to the 765 I get an S-9 from the back ground noise.

Also once the total gain is set then the the S-meter is calibrated next. Which was done.

Need some help on this. Why is there a total gain adjustment?



10478 2014-11-16 07:28:08 Chris Howard w0ep Re: IC-765 Total Gain Pot R414
How about this:

Take out the Inrad Roofing filter, adjust the thing, put the filter back in.
10479 2014-11-16 07:44:57 Chris Howard w0ep Re: IC-765 Total Gain Pot R414
Sorry, kind of a snarky reply.

It looks to me like you are supposed to have the signal generator
running when you run the AF gain up to the 2.5 V rms and then
disconnect the signal generator from the antenna and
put R414 so as to make the noise level 30 db down from the 2.5 rms setting.

Is that the way you are doing it?

(I'm not sure this conversation is really the kind of thing for the emrfd list)