On 2/14/2014 7:00 PM, Charlie Cunningham wrote:
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.
If you run the equations, you find that below about 1 GHz, the losses
are all copper losses. Dielectric loss is a few percent of the total
loss in the 500 MHz range. The benefit of a foam dielectric at HF and
VHF is that it allows the center conductor to be larger for a given
shield diameter. But the improvement in loss of a foam dielectric coax
below 1 GHz is entirely due to the center conductor being larger.
BTW -- the relevant equation is on each Times data sheet.
73, Jim K9YC
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