[Collins] Collins 62S-1 Transverter Downconversion Gain??

[Dr. Gerald N. Johnson]

On 9/21/2010 9:32 AM, Carl wrote:
> In 1965 I modified a 75A4 in the shop at National to a 6GM6 RF and 7360
> mixer but havent found the test data yet. The improvement however was
> substantial on 10-15M and so was the signal handling. My primary operating
> was DX and contests on CW and SSB. Before that I had a Drake 2B which would
> fold up on 40M almost nightly.

Mixers have always been the achilles tendon of receivers. Pentagrid 
mixers as used in the A4 were about the poorest possible, lots of 
inherent noise meant they needed plenty of RF stage gain for weak 
signals and poor strong signal handling was made worse by that high RF 
stage gain. The 7360 was so good a low noise and high dynamic range 
mixer that it sometimes was used connected directly to the antenna. In a 
class all by itself.
>
> In 1980 I used a 5722 NF device to tweak the A4 and wound up with a 8.6dB
> system NF on 10M.

The 5722 is nearly a primary standard of noise generation when the plate 
current is emission limited, but very dependent on the quality of the 
resistive termination at least below 400 MHz where capacitance and 
resonances within the tube affect the noise level.
>
> In 2002 I bought a surplused HP 4970A NF meter from work and attacked the A4
> again resulting in a 6.8dB NF on 10M. Swapping the front end tubes with NOS
> didnt improve it by more than .2dB so I left the oldies in place. Id always
> wondered about the 5722 accuracy.

How did you use the NF meter? most HP depend on a 30 or 140 MHz IF 
frequency, not an audio output meter. And they look at noise levels 
coming out of the stage under test to compute the gain. With gain in 
hand they compute the RF stage NF ignoring the effects of its finite 
gain and the generally higher NF of the following stages. So a stage 
could easily show 6.8 dB NF while the system had 8.6 dB NF.

> The A4 is still in use but primarily for 160/80M CW DX as its had numerous
> other changes dating back to 65 and is a better in the noise CW receiver
> than a loaded TS-940.
>
> For 6M these days I use a vintage HA-6 transverter with a SS RX path with a
> measured 1.25dB NF from antenna to 28 MHz IF ports. Devices are selected and
> biased for signal handling and gain made up in the post mixer IF amp. An old
> Ameco nuvistor converter measures 2.3dB NF but the signal handling is poor.
> The HA-6 feeds a slightly modified TS-830, the combination has negligible
> phase noise and hears well way down into the band noise.
>
> Getting back on track to the 62S1, it was a luxury item for the well heeled
> casual operator or when the bands were wide open.
>
> Carl
> KM1H
>
>
Art liked it that the gear was a luxury item. He was not pleased that 
the S-line was affordable though it sold well. He wanted ham gear to 
again be like the gold dust twins, affordable only by the elite. In 
early 1964 before my job moved to Richardson, I knew of a new 
transceiver design with a 5894 PA, but it didn't get beyond drawings. I 
don't think a prototype was built. The concept Art was pushing was a 
closet radio controlled through a remote cable, he'd have liked Ethernet 
remote controlled radios on the market today. And he wanted it to cost 
ten times the price of a 75S-3B. I don't know that concept got beyond 
working papers, because the next ham gear to appear was the KWM-380 
several years later.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.