Topband: Good Receivers for Top Band

[Tom Rauch]

> >  Now the Sherwood first IF CF600 is a great filter for cw...but
> >  honestly,
> > with the GUF-1 that you have in there you will run rings around any
> > Collins receiver ever made...thats a fact.....Thats why Sherwood and
> > Sartori and many others will tell you right off that the R-4C is still
> > the finest competition grade receiver ever made..IF you replace the
> > first IF filter, which is a 4 pole one, with an 8 pole GUF-1...thats all
> > you need Phil and you have one....

I don't know what a GUF-1 is, but unless you use a roofing filter 
that cuts off the strong signals the Drake R4C will have IMD 
problems in the second mixer during CW contests. It will also have 
that problem on SSB if a strong guy parks inside the roofing filter 
passband.

I use a switchable LSB/USB 2.4 kHz filter in my SSB R4C's and 
always use a 600 Hz filter on CW, in the first IF.

The R4C has inadequate mixer injection, especially in the second 
mixer. The first mixer overloads almost 20 dB before the RF 
amplifier causes problems, and the second mixer is worse yet. The 
second mixer flaws are incurable without changing it to a carefully 
designed double-balanced low-noise mixer and adding gain after 
the narrow  filters following the second mixer.

If you are going to use a wide roofing filter, you will have bleed 
through on CW (out of the narrow filter passband) and multiple 
strong signals inside the passband of the first IF roofing filter will 
mix in the second mixer giving you "bloops and bleeps" that aren't 
really there.

Any R4C for serious CW use should have a narrow roofing filter 
installed, otherwise you will be at IC-751, FT-1000 and TenTec 
performance levels except you'll have more filter blowby. Without a 
narrow filter you'll hear a higher pitched tone for a few kHz up and 
down from strong signals.

For operation on uncrowded bands or 4 or 5 kHz away from strong 
signals you don't need a narrow first IF filter......but you also don't 
need the R4C. I have a half dozen R4C's, all of which have the 
Sherwood 600 Hz filters. I can very clearly hear the difference when 
the narrow filter is switched out.   

73, Tom W8JI
w8ji@contesting.com



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