The lowest loss cable I have here is 75 Ohm 1" General Cable Fused Disc; its
under a differnt name these days. Mostly air with poly discs and used for
the 200' runs for 10M, 2M, and 222 MHz.
For the 160/80 inverted vee it is 450' of regular foamed 3/4" 75 Ohm CATV
hardline with a RG-11 jumper and plenty of ferrite to the feed point. Ive
been using ferrite sleeve baluns since the mid 70's; I was introduced to
them by the company I worked for who was building equipment for the joint
CIA/DOD Tempest program.
Carl
KM1H
----- Original Message -----
From: "Charlie Cunningham" <[email protected]>
To: <[email protected]>; "'TopBand'" <[email protected]>
Sent: Friday, February 14, 2014 10:00 PM
Subject: Re: Topband: Palomar R-X Noise Bridge
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:[email protected]] 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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