Here's a practical & realistic consideration I haven't seen mentioned -- but It
probably ought to be taken into account when worrying about gain & F/B across
the 40m (or 80/75m) band:
IMHO not much is gained by worrying about optimizing gain & F/B on CW. CW has
three advantages: very narrow transmit and receive bandwidths - roughly 1/8 to
1/10 as wide as SSB - and the human ear/brain's discrimination ability. Not
only that, but it's typically easier to know when and where to drop in your
call. I think most will agree that it's nearly always a lot easier to get
through even severe expedition and contest pileups on CW than it is on SSB. The
last few dB of signal strength and F/B simply aren't as crucial on CW as on
sideband. And your receiver really doesn't much care about VSWR or line loss -
at least not on the lower bands.
So my approach on any band is to optimize gain & F/B in the part of the phone
segment used most for DX...and remotely tweak matching of the DE to make the
amplifier happy & minimize xmit line loss. If the coax is good and not much
over 100' it may be quite satisfactory just to use a simple "L" network at the
amplifier output to make it happy wherever you're transmitting.
At W0AIH's contest superstation, Paul has successfully used the latter approach
for decades. He inserts simple L networks housed in shiny new little paint cans
at the input of each feedline, using mostly receiving-sized air caps. Since my
antennas and feedlines are vastly fewer than Paul's (aren't everyone's?) I
house multiple (reversible) little band-by-band L nets in a box right at the
operating position and choose feedline & L network with 5 - or 6-way relay
boxes. TopTen, DX Engineering, Drake and homebrew boxes in the shack with ALPHA
77Dx and ALPHA 87A amps have never been a reliability problem. Note that
feedline and/or antenna feedpoint input impedance may and often do change
enough across a given band to require reversing an '"L" matching network for
wide excursions in xmit freq..
For long coax runs and/or purists, remote tweaking of antenna VSWR is easy &
inexpensive to accomplish - except maybe in extreme environments like coastal
or marine where a vacuum variable cap may make weatherproofing easier. But a
housing of inexpensive 4" PVC or ABS pipe & end caps (Home Depot or Lowes) will
take almost any small ~1 rpm gearhead reversible d-c motor (Grainger) & small
"breadslicer" air variable cap (surplus, EFJ or Cardwell) and keep them (and
relays, if necessary) quite dry & clean for many years. It's crucial to use
only stainless hardware through the plastic.
Good luck!
Dick W4ETO/W0ID
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