Fwd: Re: [TowerTalk] 75 ohm line

[i4jmy@iol.it]

Often, mismatches and impedance transformations along lines are partly 
masked by inherent losses.
The SWR BW is then only apparently wider than aspected, and this is 
expecially noticeable when lines are long and losses not any more 
neglectable.
All the story perfectly apply where several 1/4 1/2 WL are involved in 
a line with losses, that's very possible when longer.
Althought measured SWR is low, the losses are still present likewise 
the increased mismatch.
Since the stub topic is still alive, it's worth to point out that last 
consideration roughly explain why a stub BW and attenuation is a direct 
function of used line loss. As much as the line is lossy, the shorted 
quarter wave stub doesn't reverse it's load into a real open circuit 
and it's attenuation is lower and smoother.
To eventually verify the above statements, several meters of lossy 50 
(or 75) Ohm (i.e. RG174 or RG58) already at 430 Mhz show a low SWR.
So low that SWR doesn't rise much when termination is removed or 
shorted.

73,
Mauri I4JMY


> ---------- Initial message -----------
> 
> From    : owner-towertalk@contesting.com
> To      : towertalk@contesting.com
> Cc      : 
> Date    : Wed, 27 Sep 2000 06:30:28 -0400
> Subject : [TowerTalk] 75 ohm line
> 

> Sometimes you'll notice that change, and sometimes you won't. It 
> depends on how long the line is and how narrow the antenna is in 
> the first place.
> 73, Tom W8JI
> w8ji@contesting.com
> 




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