Whoa Hoss! I think you are not following along here or mistaken about
receiver circuits Dave...or Im reading u wrong. Or maybe I have "cockpit
troubles"; anything is possible!
The ricebox uses diode switched filters BEFORE the RF stage. So any
preamp ahead of those filters will just magnify the problem. A high pass
filter that attenuates the BC band can be very helpful and should be the
first line of defense. From there you have to determine if it is an
outside or indoor problem.
The TS940, at least, uses relay switched resistor attenuators in the
front end. Some other rigs use variable biased PINS as attenuators and
can add even more crud. Under real strong QRN or pileup condx it can be
advantageous to kick in 10dB or so of attenuation and the added 10dB to
the RX noise figure is buried in the band noise anyway.
Sherwood and Rhode have both written articles on proper gain distribution
in a RX but the ham manufacturers do not pay attention.
With PIN's in the various stages you can afford to use a small preamp if
necessary but a proper Beverage xfmr design will usually not require a
preamp. I only use mine as a tuneable preselector 90% of the time and a
max of 10dB gain at any time. I cant fathom why a tube preamp would offer
any advantage (except maybe lightning survivability), modern solid state
devices have far superior signal handling capability when in a well
designed circuit.
Those Beverages with the Misek BFR core are particularly lossy and
usually need the help of a preamp; which is the wrong approach IMHO. I
dont know what the ZJ box uses. I use a minimum size of a FT114-61 and
some FT140-61's too. Loops, EWE's, Snakes and other real negative gain
antennas need 20-30DB or more of preamp.
I've heard many good comments about the Omni VI. I feel that the TS870
could be an outstanding performer if and when the IF overload and
filtering problem is fixed.
CU in the pileups............Carl
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