On Thu, 29 Jun 2006, Chuck Harris wrote:

straydog wrote:
A bunch of stuff about Art Maxwell...

His name is Walter Maxwell and I did use his name correctly. I also wrote
a number of sentences about my experiences and I related all this to
Craig's questions.

Art, W4PON



Art, consider it this way, if you have high SWR, you are driving
a load that is the wrong impedance for your transmitter.

If you read Walter Maxwell's articles, you would see that by his
explanations the sentence you just wrote is wrong.

Suppose
we were talking about an audio amplifier that was designed to drive
an 8 ohm speaker.

I have measured the DC resistance of many 8 ohn speakers and they always
show less than one ohm of DC resistance.

If we drove a 1 ohm speaker, would you not expect
the audio amplifier to be over loaded?

Would you care to specify what you are driving that "1 ohm speaker" with?
DC, AC (complex waveform, sine waveform, square waveform)? Duty cycle? How
much voltage? Would you care to specify whether that speaker is heavily
coupled to the atmosphere or lightly coupled? If the speaker were in outer
space, what "X ohms" would you expect it to be?

Perhaps a little hot around
the collar? If we drove a 1000 ohm speaker, the amplifier would have
trouble generating enough voltage to get any significant power out to
the load.

Art Maxwell

I don't know any Art Maxwell, but the author that I talked about was
Walter Maxwell.

wanted to drive a low VSWR load because he was using
coaxial cable, and as the VSWR increases, the cable sees higher
voltages and currents inside of it than it will see at a 1:1 VSWR.

Walter Maxwell included a substantial amount of historical information
regarding the fact that amateurs used open wire feeders for decades before
coax came out and that all these guys didn't know anything about SWR but
when SWR was discovered, it was also discovered that all of these guys
were very effectively communicating under conditions of very high SWR and
the reason it didn't mean anything is tht open wire feeders have very low
losses, generally even much lower than good coax. I have seen attenuation
figures in the older editions of the Radio Handbook. Its true.

These higher voltages and currents will cause cable heating, and
a loss of power to the antenna.

I once ran a 100 watt output 440 mhz brick amplifier to a 440 mhz beam
with 1.2-1.1 SWR through a 50 foot length of RG-8/U on FM and the cable,
during the course of a 30 minute two way QSO became a good 20 degrees
warmer.

If one was using a high impedance ladder line type of transmission line,
it wouldn't much matter what the VSWR was, but not so for coax.

According to Walter Maxwell, it does not have to be high impedance
ladder/open wire. And, what does matter is that the transmission line,
regardless of its characteristic impedance, be low loss. I think he is
right.

-Chuck Harris