View Single Post
  #12   Report Post  
Old May 20th 08, 10:30 PM posted to rec.radio.amateur.antenna
Lumpy Lumpy is offline
external usenet poster
 
First recorded activity by RadioBanter: Feb 2008
Posts: 53
Default Why is my dipole low impedance?

Roy Lewallen wrote:
Something's seriously wrong there. A shorted quarter wavelength of
coax should read very high impedance when the far end is shorted and
very low when the far end is open. The only time it should read 50
ohms with the far end shorted or open is if it has many dB of loss.
And no even half decent coax should have anywhere near that much loss
in a quarter wavelength.


Maybe I'm not testing correctly.
100' length of new coax. Tests ok for no shorts or open.

MFJ set to 2.4MHz gives me a Z (on the advanced
menu) of 50 ohms with distal end of the coax
either open or shorted. Actually shorting the
end with a screwdriver shaft drops the Z from
50 to 49. I assume 1 ohm is within normal limits.

Same settings gives me an R (on the main menu)
of zero ohms either open or shorted.

I get exactly the same results on several
pieces of coax, old/new, RG8 or 58. Resistance
is zero, impedance is 50, shorted or open at
the resonant quarter freq.

Craig 'Lumpy' Lemke

www.n0eq.com