At 10:25 PM 4/5/1999 EDT, Steve wrote:
>
>Greetings, TowerTalkians --
>
> The common wisdom is that steel guy wires in the radiation field of an
>antenna causes (interaction?) problems. I have to admit that I haven't seen
>any studies or articles on this topic. In broadcast circles they talk about
>RF absorption. How real are these problems?
>
> The only thing I've seen in the amateur literature is Lew Gordon,
>K4VX's article that showed steel guys actually made his wire antennas
radiate
>better so I'll have to admit that I'm a little confused. I've got my own
>anecdotal information that leads me to believe that there is interaction but
>don't have anything more substantial.
Well, W3LPL's towers all have fibreglass guys.
Unless we totally dismiss the validity of antenna modeling software, I
think the issue isn't in doubt. I have a model of my entire station,
including guys. While I wouldn't swear to its absolute fidelity, the model
shows significant currents on certain guys with certain antennas on certain
frequencies -- if you believe that wires with RF current on them radiate,
then the fields of these guy-wire "antennas" will interact in complex and
not necessarily helpful ways with the fields from the intended antennas.
In my case, I have 21-foot insulators separating the tower ends of my top
radials from the tower. From there on down, the top guys are grounded at
the anchor end. My second and third sets are insulated from the tower and
grounded at the anchors.
On 40-10 meters, the model shows negligible currents flowing in the guys as
a result of interaction with the yagis at the top of the tower. When I
model my 4-element W9LT/K3LR-style 80-meter array, however, the current in
the guys is considerable. The array works really well, so I haven't
changed anything, but I just count myself lucky.
A final datum. When I modeled a second tribander below the first, inside
the top guys, the pattern and gain were a mess. The top guys then showed
considerable current, even though they are at a 45 degree angle from the
yagi elements. So if I build that stack, I'll be replacing the top guys
with Phillystran and moving the ones with the long insulators down to the
middle station. Whereupon, Murphy dictates, it'll screw up the 80-meter array!
73, Pete N4ZR
Loud is good
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