[Collins] Collins 51S-1

[Dr. Gerald N. Johnson]

On Mon, 2007-09-03 at 17:22 -0400, Merle wrote:
> Hi Dr. Jerry..
> 
> I have heard you mention that before about the 51S-1 vs. the 75S-3B / C I have a couple of late model 51S-1 receivers and I love them ! I also have the 75S-3B and I don't seem to see any difference between either receiver, they both have about the same sensitivity using my old HP 606B  I am sure your test equipment is more modern than mine but I would not swap either of my 51S-1 radios for a 75S-3C on a bet ! Guess I am spoiled having easy access to all bands with the flick of the band switch ! Just my opinion.
> 
> Merle W1ZS

All I have is a URM-25D and a single HP8640B. I need another 8640B to do
good intermod tests. I have started doing sensitivity and blocking range
tests with a noise diode and the 8640B at VHF.

If the 51S-1 has the same MDS as the 75S-3B/C, I believe it will not
handle signals as strong as the 75S, e.g. will have a smaller dynamic
range simply due to the third mixer. My modified 75S-3B will do better
at the high end because I improved the second mixer drastically lowering
its noise and then lowered the front end gain to take advantage of that
lower noise leaving more room for strong signals.

And I've thought today that my boss may have been adding a bit of
fatherly advice (he was also an elder in the church I belonged to before
we moved to Texas from Iowa) knowing that the 75S-3B would cost me 3
weeks wages and the 51S-1 several times that much. One might have called
him frugal. When I had interviewed the preceding spring, he took me
around town in his '56 Chevy (that was the spring of 1963) that I recall
was spotless, just not new.

Still his statement that the 75S-3B was the better receiver is exactly
what he said and it has stuck with me.

I'm sure he was a father figure to me as he had been at Collins longer
than I had been alive.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer