Topband: VF drift in coax

[Bill Tippett]

W8JI:

 >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!

<SNIP>

 >So where does the idea come from?

It came from this comment by W5UC:

 >While researching the topic of receiving arrays it seems that I read
 >in ON4UN a rather ominous recommendation that foam dielectric be
 >avoided for use as phasing lines, the reason being that the VF does
 >not remain constant with time & temperature. He recommended using
 >only solid dielectric coax for that purpose.  I know this isn't what
 >you wanted to hear, but it may save you a lot of grief down the
 >road.  I will try to find the exact paragraph in the latest ON4UN book.

         With nothing better to do than listening for
DU9/N0NM through the QRN this morning, I used the .pdf
search function on the CD-ROM and searched "foam" and
"drift" separately in the following chapters in ON4UN's
4th edition:

Ch. 3  - RX and TX Equipment
Ch. 5  - Antennas, General, Terms, Definitions
Ch. 6  - The Feedline and the Antenna
Ch. 7  - RX Antennas
Ch. 11 - Phased Arrays

There is no mention of any effect such as Mike described
above in those chapters.  I did not search the entire book
since each chapter must be done separately but I would
think any comments about VF drift would appear in the above.
Perhaps Mike saw it somewhere else but I don't think it came
from John's latest book.

                                 73,  Bill  W4ZV