[TenTec] Corsair II tuning

[Steve Hunt]

Using a 9 MHz IF conveniently gives you 80m and 20m coverage from a 5MHz 
VFO without the need for heterodyne crystals; however it does _not_ 
produce a sideband inversion. What happens is that the tuning direction 
reverses - on 80m the RF frequency gets _lower _as the VFO increases, 
and on 20m the RF frequency gets _higher _as the VFO increases.

If the 9MHz IF filter is, say, upper sideband, you'll get USB on both 
80m and 20m. It's one of those old "ham myths" that you get a sideband 
inversion with that mixing arrangement.

I have two Corsair 2s. In the CW or SB-N modes the sideband in operation is:

1.8 MHz LSB
3.5 MHz LSB
7.0 MHz LSB
10.0 MHz LSB
14.0 MHz USB
18.0 MHz LSB
21.0 MHz USB
24.5 MHz USB
28.0 MHz USB
28.5 MHz USB
29.0 MHz USB
29.5 MHz USB

Note the 18.0 MHz anomaly!

Changing the mode switch to SB-R reverses everything.

Steve G3TXQ


On 27/08/2018 04:14, MadScientist wrote:
> I forgot to add, the reason why 9m MHz IF radios “automatically select” LSB on bands below 9 MHz and USB above 9 MHz is that, back in the 1960’s, 9 MHz was a very popular IF because the manufacturer could save the cost of heterodyne crystals on 80 and 20 meters by adding the VFO to the IF on 20 meters and subtracting the VFO from the IF to get 80 meters.
>
> Thus LSB on low bands and USB on the upper bands became the de-facto standard for all SSB operators (Drake, in the TR-3 and TR-4, for example).
>
> Of course, Collins made no such preference since they used a conversion scheme that did not use the convenient 9 MHz IF.
>
> However, several manufacturers followed Central Electronics with this standard, and the use of 9 MHz IF. Together they sold far more radios than did Collins so the tradition took hold.
>
> Gary
>
>
>>
>> The Corsair II automatically selects the most popular sideband for a given band. Thus, one automatically gets USB on the higher bands and LSB on the lower bands when you are set to the “SB-N” position.
>>
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