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Re: [TenTec] Corsair II sidetone revisited

To: <tentec@contesting.com>
Subject: Re: [TenTec] Corsair II sidetone revisited
From: "Tommy" <aldermant@alltel.net>
Reply-to: tentec@contesting.com
Date: Tue, 9 Nov 2004 12:57:26 -0500
List-post: <mailto:tentec@contesting.com>
Yep. Lotta fixes for the 'buzzsaw'!!

Check N1EU (may have that call incorrect) website for several C II mods, including a replacement audio sine wave generator designed by N4LQ. Filters work, the SCAF on the C II's audio output will clean up the square wave harmonics. What I did on the TT units that had the UJT square wave 'buzzsaw' sidetone was get an old TT active filter (think it was a model 250 or 205) physically mount it on the side of the chassis, with it hanging out over the audio board. Then removed one of the series resistors in the sidetone circuit and connected the active audio filter (op amp filter) is series with the sidetone, feeding the audio amp. Worked excellent. Since the UJT generates a square wave, you have the fundamental and ALL of the harmonics, so what you are trying to do is just get rid of the harmonics (of course). The mods are relatively simple to do.

If you can't find the web site, let me know and I'll look it up and send you the URL. My half-asleep brain cell says its something like www.qth.net/n1eu

Tom - W4BQF

----- Original Message ----- From: <k7gt@charter.net>
To: <tentec@contesting.com>
Sent: Tuesday, November 09, 2004 12:09 PM
Subject: [TenTec] Corsair II sidetone revisited

I just did a thorough search of the TT archives re a
solid fix to the buzz saw Corsair II sidetone. G3JXS
had suggested and implemented an active filter solution
with which he was pleased. Others said that such would
lead to enough delay to affect QSK. It would seem that
a simple one- or two-stage passive filter might have less
delay and thus suffice as the 2nd harmonic is at about
1300-1500Hz (my sidetone is set at about 700 Hz, I was
trying to match the 750 Hz CW offset but couldn't go
quite that high). Before I dive into the books in an
attempt to design such, has anyone on the reflector already
done so?

BTW: I used one of my Corsair IIs in SS this past weekend.
(I am not quite through with the permanent station
setup with the OmniVIs after our recent move and am using
the C-II in a temp setup). I had a ball. The biggest
problem I had in a contest setting was quickly and
accurately zero-beating the CQing station. The SPOT
button give a fairly soft and deep (!!) pitch to center
on 0 Hz and the sidetone, as mentioned above, is neither
matched to the offset nor harmonic free for a pitch
matching method of zeroing ala OmniV and OmniVI.

73 K7GT

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