That is correct. The C22 PTO tunes 6 to 6.5 MHz, thus avoiding the
second harmonic problem.
Bill Miner wrote:
> The C-21 is nothing like the Corsair II. Ten-Tec calls the C-21 a "double
> direct conversion" receiver.
> The input stage has a diode ring mixer that has an antenna RF input and a
> second input from the crystal Mixer board. The resulting IF output is a
> broadband 5.0 to 5.5 Mhz (NOT 9 Mhz) signal. The detector board has
> another diode ring mixer with the broadband IF as one input and the 5.0 to
> 5.5 Mhz PTO signal as the second input with resulting DSB audio output going
> to an audio filter. There is NO AGC!
> I have been told that some people have done a 30 meter conversion to the
> C-21 but I would not try this.
> The Century 22 does include the 30 Mhz band but I believe it uses a
> different PTO frequency.
> 73, Bill - K6WLM
> ----- Original Message -----
> From: "Dr. Gerald N. Johnson" <firstname.lastname@example.org>
> To: <email@example.com>
> Sent: Thursday, September 03, 2009 9:27 PM
> Subject: Re: [TenTec] Century 21
>> On Thu, 2009-09-03 at 19:30 -0800, Bill Miner wrote:
>>> 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
>>> MHz band. Also the I.F. frequency is 5 -5.5 MHz. If Ten-Tec has used
>>> different I.F. frequency then it would be possible to use the Aux
>>> 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.
>>> Bill - K6WLM
>> 73, Jerry, K0CQ
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