[Antennas] Dipole question

2002年3月22日 10:39:10 -0600

John, if you are already operating your 10 meter dipole on 20 using a tuner
and 300-ohm line, why not do the same but with the longer antenna. It will
work the same way, just have a different impedance at the driving point and
thus a different impedance for the tuner to deal with at the 300-ohm line
input. If you have trouble tuning the longer antenna, try changing the
feedline length a few feet one way or the other until you get something
your tuner can handle.
Offhand, I would suspect that your present antenna is as effective or more
so than would be a helically wound antenna, which you presumably would feed
with coax on 20 meters (?). If you still want multi-band operation, what
you have is probably better than the complexity of a PVC tube that long
helically wound.
That said, I suspect that you will find very little difference in the
performance of a 20 foot antenna vs a 16 foot antenna. Theoretically a mite
more gain, perhaps, on some bands, but not on 20 as it is still shorter
than a 33 foot dipole for that band.
Rotating the dipole is a great idea, and I would concentrate on that part
first. If you can also conveniently lengthen the radiator you can try it,
but I really doubt that you will see much change, one way or the other. 
73/72/oo, George W5YR - the Yellow Rose of Texas 
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe 
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
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John Pate wrote:
>> Ok, now that I got the address right, here is my question:
>> Currently running a dipole cut for 10 meters, up about 30 feet and fed with
> 300 ohm twin lead. The antenna is constructed of aluminum. Am using this
> for 10-15-20 meters.
>> I would like to construct a longer dipole, but I a huge canopy of maple
> trees, so about 20 feet total length is about all I can do. Could I wind
> wire cut for 20 meters helically around PVC or some other insulator. I read
> once in QST about a 20 meter dipole made this way, can't find the QST now.
> I would like to use this for 20, 15 and 10 meters. I would also like to add
> a antenna rotor to get some directivity. Would this help? Any advice or
> suggestions greatly appreciated