> > 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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