Topband: Drake R4C
Sun, 22 Jul 2001 21:30:50 -0400
> What is the serial number information on the Drake R4C that will allow the
> Sherwood up grade?
X-Sponsor: W4AN, KM3T, N5KO & AD1C
All Drake R4C's will accept the Sherwood mods.
I put new homebrew mixer, IF, and AGC circuits in my receivers as
well as change some voltages and injection levels.
The best Drake receivers are receivers after the mid-18,000 S/N.
The way you can tell is look for a CW 1.5, .5, and .25 position on
the MODE switch. At that point, Drake changed from a tube first IF
amp and dual-gate MOSFET second mixer (that mixer was one of
the worse mixers even put in any receiver) to a 6BE6 2nd mixer
with a JFET first IF amplifier.
In the early R4C with the MOSFET mixer, close-spaced IMD and
blocking dynamic range are perhaps 20 dB worse than tube 2nd
mixer receivers. Early R4C's are on par with the FT101 transceiver,
about at the bottom of the performance list.
Drake was aware of the problem and would modify MOSFET mixer
receivers to a tube mixer for a fee so there probably are some
upgraded receivers around.
Later Drake receivers still need the 600Hz Sherwood CW roofing
filter if you expect them to be on-par with modern transceivers. If
you use a wider roofing filter (there are wide aftermarket filters
available), strong signals in the passband of the roofing filter will
cause blocking or IMD problems. You will also hear bleed through
of signals outside the narrow filter passband.
By the way, don't expect good AGC. The IF filter group delay
(several milliseconds) in the R4C causes AGC overshoot, which
makes the receiver thump and click on strong CW signals...
especially on fast AGC.
73, Tom W8JI
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