Topband: VF drift in coax

[cris blak]

Hello Tom and all,

I don't believe for a moment long term VF drift in foam 
cable is any more of a concern in foam coax as it is in 
solid dielectric coax.
I can't even think of any reason that would be true!

Does anyone know why that would be possible or true?
There is something true on this legend!
One time I intended to use an hard line CATV 75Ohm Coax cable (about 1/2" in diameter) for phasing line on an TX/RX system. Bad choice. Why? Because the foam from such cables are not design to work on a high RF environment (1KW or more!). The results, the coaxial gets hot and detuning the system. This is because the foam instability. I replace that coax with a thicker one (about an RG58 size!) made for aviation TX system and everything were OK. The inner isolator of this new coax were Teflon...
For a receiving system this is not the case apart from the case you use that cable in a high temperature variation! If you want to use such coax for TX (>1KW) than I think is not a good choice.
Foam looks similar to an 50 Ohm hard line but...is not!

73 de YO3FFF
Cristi

 
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