One detail:
When knowingly using coax with a high vswr, though
dB rf loss may not be too bad, watch out about the
possibiliy of voltage breakdown. This can be largely
avoided using "good" RG8 or 213 type coax which typically
have breakdown voltage ratings from 3500 to 5000 volts, rms.
Just be sure you know what it is you are using when
high vswr is a certainty on the line to the antenna from
the tuner.
On the other hand, RG8X coax has breakdown voltage
ratings of only 300 volts RMS or so!
RG58 usually is rated about 1400 volts rms.
The rms voltage on a transmission line with vswr present
is calculated as the square root of the product of the
power on the line, the line characteristic Z, and the SWR
of the signal on the line.
For example, 1500 watts of power, a 50 ohm coax line,
and a vswr of say, 10 (the coax connected to random
radiator with no other matching at the feedpoint after the ATU:
Product of 1500 X 50 X 10 = 750,000
And the rms voltage is the square root of 750,000, or 866 volts.
So, no voltage breakdown problem with good RG8 or 213 coax.
You certainly could not use RG8X, and I would not use RG58
either. As the peak voltage on the line is 1.414 times the
rms voltage, it pays to mindful about that number also, or
in this case, peak V is 1224 volts--or also do not use RG58
either!
If the SWR gets really high, look out! Similarly, if you go QRO
somehow to snag that really rare DX, hi.
73, Jim, KH7M
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