Topband: Receivers

[Tom Rauch]

> The r4c is a terrific receiver IF it has the sherwood 600
hz roofing
> filter(still available from Bob Sherwood I think), and/or
the GUF-1 filter
> (still available from International radio) and certain
other mods dependant
> on serial number.

The GUF1 won't help the R4C a bit for CW. It is too wide. It
barely makes a difference on SSB.
IMO the GUF1 is not worth bothering with.

The problem is the horrible 2nd mixer in the R4C. You can
consider the effective BW of the receiver the width of the
roofing filter.

The original Drake Filter is 8kHz. Within that 8kHz
bandwidth, two or more modest level signals will easily mix
and generate a new signal that really isn't there. Replacing
that 8kHz filter with another 6 or 8kHz filter with better
skirts just ever so slightly improves the receiver on SSB,
and really not anything that you would ever notice on CW.

What you can do is fit Drake transmit LSB and USB filters
into the receiver, and add a Sherwood 600 Hz CW filter. Then
you have a very good SSB and CW receiver, except AGC is a
little poor. The AGC problem comes from group delay time
through the filters. The signal takes so long to get through
the filters the receiver overloads in the early stages
before the AGC can rise. When it finally does rise, it rises
too much and then the gain goes through a period of being
too low. This is why the fast AGC on the Drake won't work on
CW without "motorboating".

I think the Drake R4C is a good receiver, but it is nowhere
near as good as an Orion (if you can stand the AGC in the
Orion) or my FT1000D.

Look at:

http://www.w8ji.com/receivers.htm

and follow the link to Sherwood also.

73 Tom