Gary:

This question is out of my league, suspect Roy will be able to answer with
no problem--probably a lot of the others too...

However, in my expermenting, I have adusted the match at an antenna fed with
300 twin lead (causing a high SWR) while watching Field Strength on a meter
which was positioned so it could only "see" a good section of the
feedline... you could watch radiation from the feedline go up with SWR--I
cringe when they say coax has even more "loss"--or perhaps this is not the
"loss" you mean...

Warmest regards,
John
--
Marbles can be used in models with excellent results! However, if forced
to keep using all of mine up... I may end up at a disadvantage... I seem
to have misplaced some!!!


"Gary" wrote in message
...
| I've read for years ( and never asked why ) that when you're operating
| into a high SWR that a high impedance feedline ( say 450 Ohm ladder
| line VS 52 Ohm coax ) provides much less loss. I think I recall
| someone in this group saying that its mostly current losses. Does the
| high impedance line have higher voltage points across its length and
| therefore less current flow for a give power level ( say 100 watts )
| than the 52 Ohm coax ?
|
| I guess an analogy if the above is true could be made about the 120Kv
| + power lines on tall steel towers that are about 500 feet behind my
| shack. ( Lucky me ! ) They have much less loss than trying to run say
| 120 volts and all the current flow that would entail for the same
| wattage delivered to homes, business etc ? I can imagine the size of
| the conductors required to deliver the same amount of wattage at 120V
| VS 120 Kv +/-.
|
| Thanks .... Gary

Thanks for the reply and example John. I was referring to the loss in
power when operating into a high SWR with coax VS a high impedance
line like twinlead / ladder line / open wire. Someone in a post here
mentioned it was mainly current losses and that piqued my interest.
Cecil answered my question and gave me the formula. In his example the
coax was carrying about 3 times the current of the 450 Ohm ladder
line, which explains it.

73 Gary

On Fri, 13 May 2005 21:47:40 -0700, "John Smith"
wrote:

Gary:

This question is out of my league, suspect Roy will be able to answer with
no problem--probably a lot of the others too...

However, in my expermenting, I have adusted the match at an antenna fed with
300 twin lead (causing a high SWR) while watching Field Strength on a meter
which was positioned so it could only "see" a good section of the
feedline... you could watch radiation from the feedline go up with SWR--I
cringe when they say coax has even more "loss"--or perhaps this is not the
"loss" you mean...

Warmest regards,
John

Gary wrote:
Thanks for the reply and example John. I was referring to the loss in
power when operating into a high SWR with coax VS a high impedance
line like twinlead / ladder line / open wire. Someone in a post here
mentioned it was mainly current losses and that piqued my interest.
Cecil answered my question and gave me the formula. In his example the
coax was carrying about 3 times the current of the 450 Ohm ladder
line, which explains it.

Remember, that is for the *SAME SWR*. When the SWRs are different,
as they will be for a fixed load, that loss ratio figure will vary
away from 3 to 1.
--
73, Cecil http://www.qsl.net/w5dxp

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