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

[Barry N1EU]

Paul, the Omni 6 circuit is exactly as you describe, with a 270 ohm
charge capacitor and a 330K discharge capacitor.  It uses a 3.3uF
electrolytic capacitor in fast mode which is paralleled with a 10uF
capacitor in slow mode.

Tnx/73,
Barry N1EU

On Tue, Dec 13, 2011 at 8:58 AM, Paul Christensen <w9ac at arrl.net> wrote:
> 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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