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Old May 21st 08, 01:55 AM posted to rec.radio.amateur.antenna
Jerry[_3_] Jerry[_3_] is offline
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First recorded activity by RadioBanter: Dec 2007
Posts: 25
Default Why is my dipole low impedance?


"Lumpy" wrote in message
...
Harry Lippitz wrote:

1 - Are you using a short test jumper cable or adapter connector
between the test instrument and the end of the coax? Could the test
lead or connector be at fault?


Nothing seems to make a difference. 12" coax
to the antenna, 50' RG8, 100' RG8, 50' RG58.


2 - Is there any possibility of a STRONG signal coming back down the
cable to stuff up your test instrument readings? Do you live near a
source of RF, such as local broadcast radio?


I don't think so. I'm receiving (I'm transmitting!)
just fine. No local signals clobber me.


3 - Is there any possibility both feeder cables are defective?
Perhaps you are using coaxial cable not meant for this purpose? TV
coax, or LAN cable?


Nope. Several 50 ohm 8/58 coax. Some from cablexperts.com.


4 - Have you wiped out your neighbours TV viewing or something?
Checked the cables for sabotage (pins or nails)?


No, nothing like that.


5 - Have you climbed the mast and checked the antenna directly at the
feed point, without a feeder cable?


I can't climb this mast but if I bring it down to 10' and
get up there with a ladder, same results.


You have probably thought of all these, but I had to ask.


Feel free to ask, no matter how seemingly stupid
the Q might be.


Craig 'Lumpy' Lemke

www.n0eq.com




Hi Lumpy

I really like your music. You do a terriffic job with that guitar.
I'd suggest that you'd do yourself a favor if you recognize that the input
impedance of your antenna is not being measured properly by your meter.
Instead, try to think of something that is causing the meter to read
improperly.
Could the error be introduced by a stray (off frequency) signal effecting
the meter movement? You know, the antenna picks up the signal and
introduces an error.
Remember how the impedance looking into a length of coax, that is either
opened or shorted, varies all over the place when the length is
uncontrolled.. The only time it's impedance is equal to it's Zo is when
it's length is 1/8th wave ( or odd multiples). And, then, the impedance is
very nearly purely reactancive.

Jerry KD6JDJ