When I turn down the RF gain on my Corsair II (if memory serves), the noise
almost vanishes. I get further reduction of hiss using the Autek QF-1A you
got for me at Dayton, Steve, thanks again.
Mike
----- Original Message -----
From: "n4lq" <n4lq@iglou.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Thursday, May 12, 2005 1:01 PM
Subject: Re: [TenTec] Hissness
Very good points Don. One thing I've noticed over the years; Most of the
rigs these days have way to much RF gain, especially on the lower bands.
On my TS-xxx, I turn off the pre-amp, kick in the attn and lower the
RFgain and have gain left over. Basically, we can lower the gain until
the noise just moves the S meter a tad. Signals stronger than that noise
wil sound fine. Signals weaker than the noise wouldn't be heard anyway
no matter how high the gain is cranked.
I have a really cool sound DB meter from Radio Shack that is great for
making test like you mention. Tonight I'll try to compare my OmniVI with
the TS-wood and see what happens.
The Corsairs bug me when using the 250hz filter and headphones. The IF
hiss is unbearable
Steve
-----Original Message-----
From: Don Rasmussen <wb8yqj@yahoo.com>
To: tentec@contesting.com
Date: Thu, 12 May 2005 09:26:09 -0700 (PDT)
Subject: [TenTec] Hissness
> 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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