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[TenTec] Hissness

To: tentec@contesting.com
Subject: [TenTec] Hissness
From: Don Rasmussen <wb8yqj@yahoo.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 12 May 2005 09:26:09 -0700 (PDT)
List-post: <mailto:tentec@contesting.com>
One other thing you may notice when comparing Corsair
II to non Ten Tec radios is that although the guys
here
have done a pretty good job of analyzing where hiss
comes from inside the Corsair II, it can be limited
substantially by turning down the AF gain in actual
operation. The signal still comes through the speaker
well even at low AF gain settings.

I think this may be due to the AGC employed on the
Corsair II, although I also see this effect on the
later OMNI's that don't have the AGC employed in the
audio stage.

Try this. Hook a big speaker to the C2, V, or VI+.
Find
an S5 or better (cw/Fast agc) signal, then turn up the
AF gain until you get a loud satisfying CW note 
filling the room. 

Now switch the A/B switch to (example FT890AT with
500hz filter) and turn up the AF gain to maintain the
same volume level of the cw note. 

No matter how strong the signal is on my FT890 (or
other typical rigs), if you want to hear a nice loud
signal, there is this noise penalty. The backround
hash always increases noticably with increases in the
AF gain regardless of the signal level. Noisy bands
make it worse. 

At higher AF gain levels and no signal, even with the
hiss of the C2, it's very quiet in comparison to the
other radio with it's speaker rumbling away. Equalize
the AF gain of both radios in no signal conditions and
you'll find that when an S5 signal comes along it will
probably be at a satisfactory loudness in the C2, and
hard to hear at the other rig. 

The moral to this story is, if you own an IC756Pro and
you are proud and happy with it, don't buy and old
Corsair II or OMNI, and NEVER put it on an A/B switch
to compare 500hz operation. I did, sold the Icom and
bought a second Corsair. Now I am stuck with a shack
of old radios. And what could be worse? ;-)




                
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