[TenTec] Century 21

[Bwana Bob]

That is correct.  The C22 PTO tunes 6  to 6.5 MHz, thus avoiding the 
second harmonic problem.

				73,

				Bob WB2VUF

Bill Miner wrote:
> Jerry,
> 
> 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" <geraldj at weather.net>
> To: <tentec at contesting.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:
>>> 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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> 
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