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Old July 7th 06, 05:39 AM posted to rec.radio.amateur.antenna
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Default Voltage feeding a VHF yagi


Jeff wrote:

I guess I'm missing it, but what problem is there
running the feedline to the normal center fed yagi?
No matter if against a mast, or mounted on a mast
with the center of the boom attached to the mast, I
don't see a problem. I do it all the time.
No matter what polarization, I tape the coax to
the mast, and then tape it to the boom to the feedpoint.
I'd much rather run the yagi in the normal manner.


This is a problem that is particular to vertically polarized yagis that are
mounted with a pole going between the elements. The pole has to come up
parallel to the elements to the boom. Some people overcome this by using
non-conductive pole, BUT what do you do with the feeder, if you tape it to
the pole you might just as well have used a metal pole!!!

However, as I said in my previous post, my simulations seem to show that
with careful positioning the effects can to quite small

73
Jeff


I think normally the effect is fairly small. But I suppose it can vary
per the position, and mast length, etc.. I guess it's all how picky
you are about the gain/pattern. For moonbounce, etc, it might be worth
worrying about. But for just a general purpose FM beam, I probably
wouldn't worry too much. Unless the mast was a certain length
to become resonant, it should pretty much be ignored by the antenna
for the most part. Seems to me, right in the middle of the two
midpoint elements would be about best, but I've never modeled
other positions. I have seen quite a few people run vertical yagis
with the midpoint mast mount with no serious problems.
I think any small loss of performance would be less than trying to
voltage
feed thats for sure. You'll see lots of antenna ad's with pictures of
vertical beams mounted on masts in that manner, so it shouldn't be
too bad. I agree. There should be little difference in using a metal
mast, or plastic, if the feedline shield is in place on both. I'd just
as
soon use the metal mast I think. It would look fatter with the extra
metal mast, but I don't know if that would be a plus or a minus...
MK

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