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@contesting.com] On Behalf Of Scott
Shepard
Sent: Friday, January 31, 2014 11:27 PM
To: tentec@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
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|