Topband: Palomar R-X Noise Bridge

[Jim Brown]

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