Topband: Palomar R-X Noise Bridge

[Charlie Cunningham]

All generally true, I expect, but I also believe that dielectric constant
and dielectric losses also figure in and the lowest loss lines would be
filled with air, dry nitrogen or evacuated. I expect those would likely be
the lowest loss AND highest velocity factor cases.

73,
Charlie, K4OTV

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Jim Brown
Sent: Friday, February 14, 2014 9:42 PM
To: 'TopBand'
Subject: Re: Topband: Palomar R-X Noise Bridge

On 2/14/2014 2:17 PM, Carl wrote:
> Isnt that what "lowest loss" means? At least that was my intention. 

I must not have written clearly enough. I was not questioning the low 
loss, only that the high Vf was the way to get it.

You DO get the low loss by going to larger coax, (like the 7/8-in hard 
line), but it's the fact that it's LARGER and has lower RF resistance, 
NOT the higher Vf.

Think of it this way -- The higher Vf cable has less attenuation per ft 
because the higher Vf allows the center conductor to be larger.
But a stub made with foam coax with Vf = 0.84 must be 27% longer than 
one with with a solid dielectric and Vf =.66. If those coaxes are the 
same diameter and of comparable quality, the stub attenuation and Q will 
be nearly the same.

73, Jim K9YC
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