Topband: TopBand Receivers

[Tom Rauch]

My first R4C post didn't make it to the reflector. I wonder why?

> I used the R4C with Sherwood mods (+ some others) for 25 years, and just
> very recently upgraded to a FT-1000D.  After doing extensive comparisons,
> I can say that neither receiver is better than the other. 

On the test bench, that is true Riki. The later R4C with Sherwood 
first IF filter, Omni 6 plus, and a slightly modified FT1000 all test 
reasonably close to the same blocking dynamic range.

The FT1000's, including the MP's, have significant phase noise that 
limits receiver performance. Of my receivers, the R4C has the best 
VFO system (low phase noise) by a large margin, Ten-Tec second, 
ICOM 751A third, and Yeasu's are last by a large margin.      

> thought one might be a hair better, but then at other times the other one
> was better.  The problem that I had with my R4C was that evidently, over
> the years, tuned circuits had deteriorated, and even with new tubes it was
> getting more and more difficult to keep its performance up. 

R4C's can be modified, by increasing mixer injection and adding 
the Sherwood first IF filter, to a world-class blocking dynamic range 
that is more than 30 dB more than any of the receivers mentioned 
earlier. On a congested band with strong signals it is very important
to have low phase noise and a wide blocking dynamic range.

Early R4C's had extremely poor second mixers and bad shielding, 
and should not be considered for high performance unless gutted 
and rebuilt to a better design near the first and second mixers and 
IF amplifiers.  

Most of the other R4C mods don't do anything, and some actually 
hurt.

BTW, the reason an R4C seems to work better through QRN is 
because the AGC responds very fast.

Hope this post makes it through!
73, Tom W8JI
w8ji@contesting.com

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