Topband: Sherwood R4C vs. Orion on 160m

[Tom Rauch]

Ed,

I measured 160 meters on these receivers and have it on my
site. http://www.w8ji.com/receiver%20IM3%20sorted.htm gives
the data sorted by IM3DR.

The Orion main receiver is in the 90dB IM3 dynamic range
area at very close spacing, the stock R4C is very bad with
close spacing.

I wouldn't use an R4C as a standard. The second mixer is
very weak even if it is the vacuum tube mixer. Some Internet
sites carry misinformation claiming no difference between
the MOSFET 2nd mixer R4C and the 6BE6 2nd mixer, but they
are absolutely wrong. Any R4C lacking CW 1.5,CW .5, and CW
.25 MODE positions is a terrible receiver, unless someone
does major work on the second mixer.

Adding the 600Hz Sherwood Engineering filter roofs the R4C
receiver at 600Hz BW. This takes the second mixer out of the
equation for signals falling outside the filter bandwidth,
meaning performance wider than 600Hz spacing is fairly good.
It also cures most of the filter blowby problems inherent in
the R4C.

Keep in mind even with an aftermarket roofing filter any R4C
receiver suffers the same mixer problems and filter blowby
problems for signals inside the bandwidth of the roofing
filter. If you use a wide aftermarket roofing filter (like
the filters that allow you to still use the noise blanker
and receive SSB without switching out the first narrow
filter), the R4C remains a VERY poor CW receiver. The second
mixer is so poor, you should consider the modest-to-strong
signal bandwidth of the R4C to be the bandwidth of the first
IF filter.

73 Tom