[TenTec] Dual frequency receive

[Ken Brown]

>>
>> If you truly have two VFOs, as was common with separate matching 
>> transmitters and receivers (such as the Drake 4 line, Heath SB series 
>> and Collins S-line) and some older transceivers with external accessory 
>> VFOs, then it is possible to have both VFOs combined into the LO port of 
>> the mixer and receive two frequencies (on the same band) simultaneously.
>>     
>
> I don't remember that the Collins, Drake, or Heathkit allowed
> simultaneous reception without user mods.
>   
>   
They do not. They do have two VFOs, really, not just virtually by memory 
switching. With user mods the Heathkit SB-301 and SB-401 can have dual 
simultaneous receive (and transmit too, though no doubt illegal and not 
a good idea even if it weren't illegal) for certain, because I have done 
it. It is only my guess that Drake and Collins could also be similarly 
modified.

The oscillator switching/sharing scheme of the Drake is somewhat 
different than the Heathkit. With the  Heathkit twins, when operating in 
transceive mode using a single VFO for both the transmitter and 
receiver, they also both used the same bandswitching oscillator and BFO 
(I don't recall whether it was the ones in the receiver or in the 
transmitter) , so your transmit and receive frequencies were definitely 
the same. There were three cables between the rigs for VFO, BFO and I 
think they called the other one HET. In the Drake twins I believe that 
there was a "netting" adjustment of the BFO , which if not done properly 
resulted in your transmit and receive frequencies not being exactly 
identical, even when transceiving using only one VFO. The Drake had only 
one cable called INJECTION. The BFOs in the transmitter and receiver 
continued to operate independently when in transceive mode, thus the 
need to "net" them.

The details of Collins S Line I do not know for certain, although I was 
often told that my SB-301/401 was a green S line, designed by former 
Collins engineers. Don't know if that is true.

DE N6KB