At 04:20 PM 6/2/97 -0500, Chad Kurszewski WE9V wrote:
>If you haven't already, you should check out the article Lew, K4VX, wrote
>about NOT breaking up the guys at all. It was in QST, early 90's.
>Maybe '91 or '92.
>He showed that the degredation was negligible or an acceptable comprimise.
>Also, I think Brian Beezley has a AO type program called GUY. Haven't
>used it, but it could be useful and save some money. I see that's it's
>included with AO and says:
>> The GUY.EXE utility makes it easy to investigate the
>> effect of guy wires on antenna systems with the AO Antenna
>> Optimizer or NEC/Wires.
>> GUY lets you specify guy-wire geometry in simple terms
>> like attachment height, anchor distance, insulated-section
>> length, etc. It then generates a file containing AO wire lines
>> for all guy-wire sections.
>No insulators can turn this:
>>EHS Cable = 3000 feet X $.19 = $570.00
>>Big grips = 96 total X $4.95 = $475.20
>>502 Insulators = 48 total X $5.50 = $264.00
>>TOTAL for EHS guyed 197 foot tower = $1309.20
>Into $748.20 MUCH better!
For whatever it's worth, I partially emulated K4VX in my 100-foot "baby"
tower installation. The top guys have fiberglass power pole insulators as
the first 21 feet (out from the tower), but are continuous the rest of the
way and grounded at their outer ends. The middle and bottom guys are
insulated from the tower right at the tower, and then are continuous and
grounded at their outer ends. I was urged to do this insulation bit to
preserve the ability to shunt-feed the tower
My modeling shows only a little current on the guys from the 10-40 meter
radiators on top of the tower, and an acceptably low amount from my
80-meter K3LR lazy-vee array, which is quite close to and fairly parallel
with the guys. Note, however, that they are not resonant lengths on 80. The
real-world antennas confirm the model, as far as I can tell. But here's
the bad news -- when I model a 2-high stack with the lower yagi inside the
top guys, the pattern goes almost omnidirectional, and the guy-wire
currents are pretty high. The modeling suggests that I better plan on
Phillystran for the top guys and probably move the power-pole insulators
down to the second set.
I think the moral is that K4VX's data, while persuasive for his single test
case, are risky to generalize. Modeling is certainly a good idea, with
your particular combination of tower, antennas and guys!
PS It's quite easy, with EZNEC, to place guys accurately by rotating
carefully in the horizontal and vertical planes, then "trimming" to length.
The GUY utility would have made life easier, though.
73, Pete Smith N4ZR
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