4) The major issue with SWR at the transmitter is giving the transmitter
a load that it is "happy" with. "Happy" means that it supplies full rated
power, AND is CLEAN. Distortion rises when an amp is mismatched to its
load and if it's not carefully tuned. Distortion = SPLATTER. That's why
God made antenna tuners.
I think it's important to note that a tuner placed at the transmitter is
performing several functions: (1) Z transformation from one complex Z value
to another; and (2) creating a reflection mirror for the reflected wave that
allows for re-combination with the forward wave back to the load. At the
load, reflected voltage is 180 degrees out of phase with the forward voltage
and both the forward and reverse currents are in phase. The tuner at the
transmitter will again reverse the phase of the reflection voltage so that
voltage and current of the reflected wave are in phase with the forward
wave.
Before solid-state RF amp designs, our old VT amps cared little about line
SWR, at least below ca. 3:1. Early link-coupled tuners and later, the
classic Pi network performed functions 1 & 2 noted above. Once solid-state
transceivers began incorporating built-in tuners, they were once again on an
equal footing with the older VT/Pi designs. Until L. McCoy and M.C. Jones
authored articles on their respective Monimatch devices in the mid '50s, ops
were making efficient use of their antennas and transmitters for several
decades without SWR meters. With low loss, moderate Z lines, the SWR meter
was not needed. Low-loss lines in conjunction with their link or Pi
networks is all that was needed.
When I started as a novice in the early '70s, I was mentored by my OM,
W9EAC. Although he understood transmission line mechanics, we did not own
an SWR. One day, an 8th grade friend of mine brought his Midland Monimatch
to the house. We inserted the meter into the line. The SWR on my 15m Yagi
was 2:1, but fed with about 75 ft of low-loss coax. My friend stated
"You've got problems. Your SWR is way too high." From that day forward --
well at least until I understood transmission line mechanics, I was obsessed
with SWR, despite my OM's insistence that the 2:1 SWR was not nearly the
problem my "know-it-all" friend made it out to be. One day, I was happy
making 15m contacts. Then all of a sudden, I was spending more time looking
at the SWR meter than the S-meter.
I echo K9YC's comments about SimSmith. For those intimidated by the Smith
Chart, consider starting with either TLD or TLW software. Simulating line
and load conditions is easy. Then, move on up to Smith charting software.
Paul, W9AC
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