[TenTec] Dual frequency receive

[Dr. Gerald N. Johnson]

On Mon, 2006-12-25 at 18:10 -1000, Ken Brown wrote:
> >>
> >> 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 band switching 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 HEAT.

In the S-line the BFO were independent. But they were cabled to use the
receiver crystals for the HF mixers, and the transmitter selects between
using the receiver PTO or the transmitter PTO for transmitting. Mismatch
of BFO crystals did sometimes make them not perfect transceivers.

> 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.

There were significant differences avoiding Collins patents and
proprietary parts like the PTO and mechanical filters.

I only know of one Collins engineer going to Heath, but its true he
worked on S-Line at Collins. There are probably twenty times as many
engineers who used to work at Collins than ever worked there at any one
time. Maybe more. Turnover was fairly high. I lasted one project which
took 3 years. I think it had something to do with Art's micromanagement.
Though my boss lasted his entire life and had a badge number lower than
Art's.

A significant fraction of the new hires each year lasted less than one
year.

> 
> DE N6KB
-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer