[TowerTalk] Groundscreen extraordinaire. Was: R-7000 & What is going on at Cushcraft?

[Guy Olinger, K2AV]

Just in case you weren't thinking about the effects of groundscreens/radials in
earlier threads...  Look between the lines in this story originally posted about
a service problem with antenna manufacturer.

1) High SWR does not indicate the performance of the antenna, if a) it can be
matched with a transmatch, b) the line loss is not large, c) the potential
overvoltage on antenna components doesn't fry it, d) it's a vertical and it's
over a good ground screen.

2) Is there anybody but me that suspects that most commercial multiband
verticals are designed ASSUMING a poor to mediocre ground without a ground
screen/radials (which is what most installations have),  JUST SO that when Joe
Averageham installs his Magic Wand multiband V10k, he will have the ALMIGHTY SWR
low. This would be instead of having a high SWR, & the factory telling him the
reason why the impedances don't match is because he has an awful ground under
it.

IT AIN'T TUNED for a GREAT groundscreen like a tin roof! If it was, it would
look terrible on the SWR meter at Joe Averageham's place

3) The reason why a lot of shortened antennas look broad is because SOD LOSSES
AREN'T FREQUENCY SENSITIVE. If half your power is lost in the sod (and the
factory boys have tuned it for the normal nasty ground losses), it will cut down
your swr hugely at the edges of the range, giving the appearance of a broader
antenna.

Put it back over the tin roof  and SWR goes up and bandwidth narrows (but it
plays better because no near field ground losses).

- - . . .   . . . - -     .   . . .     - - .   . - . .

73, Guy
k2av@contesting.com
Apex, NC, USA

----- Original Message -----
From: <WA4TUF@aol.com>
To: <towertalk@contesting.com>
Sent: Wednesday, October 27, 1999 7:32 PM
Subject: [TowerTalk] R-7000 & What is going on at Cushcraft?



I have an R-7000 and I am mighty unhappy with Cushcraft.

The antenna worked great - I was amazed at how well it worked even when the
SWR was high.  I busted pile ups and had a blast mounting it 25 feet up --
about two feet above a tin roof.   This puppy really gets out.  I regularly
got better reports than guys running beams.  I could never get it adjusted to
meet specs on all the lower bands so I just lived with the SWR.  It would be
resonate too low on one band and too high on another -- both of which were
controlled by the same dimension.  I am sure many on this list agree SWR
isn't the issue in getting out but it sure does become an issue when you run
power.




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