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
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