christofire wrote:

"Roy Lewallen" wrote in message
...
Antonio Vernucci wrote:
. . .
Under the assumption that dielectric loss is negligible, a permittivity
2.26 time higher than that of air results in a lower inner conductor
diameter, for a given outer diameter cable and a given impedance. . .

Yes, and this is why foamed dielectric cable has lower loss than solid
dielectric cable. Not because of lower dielectric loss (at least below a
few GHz), but because it has a larger center conductor for the same
impedance and outside diameter.

Roy Lewallen, W7EL


You've got it ... spread the word to all those amateurs who are hung up on
(negligible) dielectric loss!

It isn't the amateurs so much as the advertising. Marketing departments
highlight the foam dielectric because it's more obvious, and pretty soon
even the manufacturers are believing their own publicity.

As for the 50-ohm impedance, the reasons why it became an industry
standard are interesting but purely historical. The reason for using it
now is almost exclusively because it *is* an industry standard.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek