[TenTec] Omni D a gc popping

Barry N1EU barry.n1eu at gmail.com
Sat Feb 1 06:39:01 EST 2014

FWIW, the Corsairs also used audio derived AGC

(the key is turning down RF Gain as someone already suggested,
although you lose s-meter action)

73, Barry N1EU

On Sat, Feb 1, 2014 at 5:04 AM, Rick - DJ0IP / NJ0IP <Rick at dj0ip.de> wrote:
> The early series of Triton and Omni (analog) radios used audio-derived AGC,
> which did not have as much dynamic range as the typical IF-derived AGCs
> have.  They had popping at the beginning of the transmission of very strong
> signals.  The only way to stop the popping was to turn down the RF gain.
> So why did Ten-Tec use AF-derived AGC?
> Simple; to obtain good selectivity at a low cost.
> I think we're all familiar with the affects of using an add-on external
> audio filter with any radio.  It will remove adjacent channel audio, but it
> doesn't stop the adjacent channel signals from acting on the radio's AGC
> loop - regardless of whether the AGC is IF- or AF- derived, because it is
> filtering AFTER the AGC loop's tap.
> By using AF-derived AGC AND inserting a narrow AF filter inside the AGC loop
> (before the tap), the AF filter works similar to a Xtal filter, and not only
> removes adjacent channel audio, it also removes the adjacent channel signal,
> thus preventing it from causing the receiver to pump.  Though you still get
> that one short pop.
> Results:  whereas most JA transceivers of the day had a single 2.8 kHz SSB
> filter and a single 500 Hz Xtal filter for CW, the Ten-Tec radios had
> multiple switchable bandwidths and their selectivity was very good for the
> day.  Add in the advantage of their tunable (elevator) preselector on the
> front end and you had a darn good radio that performed better than most of
> the earlier radios with broadband front ends (like our radios today have).
> Why did Ten-Tec change to IF-derived?
> Two reasons:
> 1) it's better (higher dynamic range) and
> 2) the cost of Xtal filters came down.
> In those days, the radios cost about $1200 to $1500 and a Xtal filter cost
> over $100.  $100 was a lot of money in those days.
> (for some of us it still is)
> I think in the meantime most of us Ten-Tec users have learned to use the RF
> Gain more than the AF Gain anyway, so it really isn't a big issue for us.
> It's just an issue for the guy who still thinks the RF Gain is just there
> for looks and never touches it - i.e. "Yaecomwood user"  ;-)
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Scott
> Shepard
> Sent: Friday, January 31, 2014 11:27 PM
> To: tentec at contesting.com
> Subject: [TenTec] Omni D a gc popping
> The omni c did not seem to have much of a difference as I recall...still a
> great rig (I have owned all of them and still have another D I am working
> on)...seems the best method when having that pop from a loud station was to
> turn down the rf gain...I have tried some of the mods without much luck. If
> you search the net you will find it to be a much discussed issue...
> Regards
> Scott va3ied
> Sent from my iPad
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