[TowerTalk] Best vs. Maxwell -- Again??( LONG !!)

[Tom Rauch]

Jay,

What Best forgot, and what you also neglect to mention, is 
amateur antennas with MODEST SWR VALUES work just fine with 
some mismatch even using regular coaxial cables. 

Loss is nowhere near the "match efficiency" or "reflected power" 
would indicate, IF the transmitter or receiver end is matched with a 
matching network.

If the transmission line has low matched loss, it will also have less 
mismatched loss. That why open wire lines can be operated with 
extreme SWR and still have excellent efficiency.

Best, despite openly flaunting his "experience and credentials", 
initially had that concept totally wrong! I'd respect him today if he 
had been able to utter the words "I made a mistake".

With lines under 1/4 wl, minimum line loss can (and usually does) 
occur with an INTENTIONAL mismatch! That's because an 
overwhelming amount of line loss is due to conductor resistance 
and NOT dielectric losses (as many people seem to think).

Air insulation in feedlines offers less loss mainly because  
impedance is higher for a given conductor size. There is less 
current and lower I^2 R losses because the line has higher 
impedance for a given conductor size, or the same impedance line 
uses a LARGER conductor.  

The change by matching at the load in TYPICAL installations when 
using feeders with very low loss is negligible, just as is the change 
when the line is short.

There are some exception. Situations can add significant loss...

1.) Lines with significant initial matched loss

2.) Line where VAR power in the line becomes extremely high 
(current becomes extremely high in areas of the line).

Your use of the plasma coupling as an example is about like telling 
us about losses when feeding an unloaded six foot mobile whip on 
3.5 MHz with a tuner at the rig.

When a person spews several pages of complex math based on an 
extreme examples (as Best did), or gives an example based on a 
SWR that would make most calculators overflow (as you did), it 
probably does more harm than good to the people who are trying to 
learn. 

The poor bloke trying to understand what it all means is left with a totally wrong impression.

Bottom line is.... if feedline loss is fairly low in a matched condition 
a system can tolerate a fairly high SWR with NO noticeable 
change in performance on receive or transmit if a matching network 
is placed somewhere in the feedline system.

Feeding a six meter dipole on 160 meters is more in line with your 
Plasma example. Feeding a dipole cut for 21MHz on 18 MHz is 
more in line with the real world.  


73, Tom W8JI
w8ji@contesting.com

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