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Re: [TenTec] Century 21

To: tentec@contesting.com
Subject: Re: [TenTec] Century 21
From: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Reply-to: geraldj@weather.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 03 Sep 2009 23:27:12 -0600
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
On Thu, 2009-09-03 at 19:30 -0800, Bill Miner wrote:
> George,
> Sorry but I do not think it would be possible to modify the C-21 for 30 
> meter operation.
> The PTO operates 5MHz to 5.5MHz with the second harmonic being on the 10.1 
> MHz band.   Also the I.F. frequency is 5 -5.5 MHz.   If Ten-Tec has used a 
> different I.F. frequency then it would be possible to use the Aux position 
> of the band switch for 30 Meters.

The IF is 9 MHz. The VFO gets mixed with a crystal to produce 19-19.5
then mixed with the 9 MHz VFO IF to produce 10-10.5. 9 will probably
leak through and the second harmonic of the VFO can leak through the VFO
mixer and the signal mixer. In the Corsair II, that crystal is on 13.99
MHz and is also the low 10 meter crystal. Also the injection is the
same, uses the same bandpass filter.

So adding 30meter means using the low 10m oscillator mixing and filter
and then adding a 10 MHz bandpass filter to the bandpass board. Can't be
a stretched 7 MHz filter because of the 9 MHz leak through.

If it works in the Corsair II and it does, it can work in the Century 21
if you can sacrifice another band or can add a switch to switch in the
10 MHz bandpass filter in place of the rest of the bandpass filters.
> If anyone else has some thoughts on this I would be interested.
> 73,
> Bill - K6WLM
73, Jerry, K0CQ

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