RadioBanter - View Single Post

January 3rd 06, 10:47 PM posted to rec.radio.amateur.antenna

wrote:
I have a MFJ-269 and I measured a value of 65 and j16 for my 6-meter
dipole, the dipole is a little long so I assume that the j16 is
inductive and I need to add a cap of equal reactive value.
Also, The measurement was taken directly at the antenna feedpoint
without any coax.

How did you keep your body from affecting the measurement?
Why do you think an SWR of 1.5:1 is enough to worry about?

Once I back calculate the cap value ,should I place this cap across the
antenna input at the feed point or in series with the signal line of
the feed point to cancel out the j16 and leave me with 65 ohm
resistive?

The impedance displayed by the MFJ-269 is a series impedance.
If the feedpoint impedance is indeed 65+j16, two caps of -j8,
one to each side of the dipole on the antenna side of a 1:1
choke-balun will tend to keep the currents balanced.

But here's another approach for your consideration. A little
less than 1/2WL of 300 ohm or 450 ohm line will bring the antenna
to resonance, assuming a 65+j16 feedpoint impedance. That's about
8.5 feet on 6m. A series section of ladder-line is usually easier
to install than discrete components. And if you did make an error
in your measurement, trimming the ladder-line to resonance is a
pretty easy task.
--
73, Cecil http://www.qsl.net/w5dxp