[TenTec] Omni6/Omni6+ AGC pop on cw leading edge

[Paul Christensen]

Barry,

Possibly leakage with age.  I heard the recording, but it sounds like the 
AGC attack time is a bit too long.  Most conventional AGC circuits sample 
the I.F. with a small signal diode followed by a series resistor to charge a 
parallel cap.  The attack time is set by the time constant of the R and C 
components.  What about the release time?  A second resistor is added in 
parallel with C, producing a value that decays the discharge but does not 
alter the charge time.  It's the diode that prevents discharge through the 
attack time resistor.

It's been a long time since I've seen the Omni Six AGC, but look for 
components around the 3.3 uF cap that show this charge/discharge 
relationship.  My guess is that if C replacement doesn't do the trick, then 
you will be able to find a value of series R to shorten the attack time.

Paul, W9AC

----- Original Message ----- 
From: "Barry N1EU" <barry.n1eu at gmail.com>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Tuesday, December 13, 2011 8:35 AM
Subject: Re: [TenTec] Omni6/Omni6+ AGC pop on cw leading edge


> Is it possible that I'm seeing AGC popping because the capacitors are 
> aging?
>
> I'm thinking of replacing the 14-year old 3.3uF electrolytic AGC
> timing capacitor with a new tantalum capacitor of equal or slightly
> smaller value.  Comments?
>
> Tnx/73, Barry N1EU
>
> On Sun, Dec 11, 2011 at 4:00 PM, Barry N1EU <barry.n1eu at gmail.com> wrote:
>> I notice up to a +10dB pop on the leading edge of cw elements with my
>> Omni 6+. Please see a recorded waveform at
>>
>> http://n1eu.com/omni6agc.gif
>>
>> and the accompanying 20sec recording is at
>>
>> http://n1eu.com/omni6agc.wav
>>
>> It's clear that when there's been no signal for a second or so, the
>> big 10dB pop is much more likely. Otherwise there's a "little" pop of
>> 3-5dB. I'm not seeing much in the archives but has anyone tried to
>> tame the "pop" via AGC time constants etc? Can anyone contribute a
>> little technical analysis?
>>
>> I see little difference in the popping with fast vs slow AGC.
>>
>> Thanks & 73,
>> Barry N1EU
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