Hi Martin,
Boy, those are surprising results! I too used a MFJ analyzer with good results.
Im assuming when you measured resonate frequency you mean that was the frequency
with the lowest SWR.
To start, verify that the frequency calibration of the MFJ is close. Attach a
dummy load (can be 3 150 ohm resistors in parallel or a simple dipole) and sweep
across the com frequencies while listening on a hand held or your comm radio.
There is no modulation on the MFJ but you should hear something.
If the MFJ calibration is close, as I expect it is, then you need to tune your
antennas.
For the whip on the belly, be sure you have a good ground plane. Bob Nuckolls
does a pretty good job explaining how a dipole works and what constitutes a
ground
plane. Have a look at page 13-11 of AeroElectric Connection book for details.
If you have something similar and there is no corrosion and the connection
to the coax is good (assuming you are using RG58 or RG400 coax and the connector
is properly attached), then you need to trim your whip. It should start
at about 22 inches long. Try just taking off " to 3/8 and see what difference
that makes. Fortunately your antenna is too long!
Im really surprised at the Bob Archer antenna. Did you test it installed or
just
sitting on a table? Remember any metal near it will affect it. This thread
---From VAF in post 7 has instructions on how to tune a Bob Archer antenna using
a MFJ 259!
http://www.vansairforce.com/community/showthread.php?t=142149&highlight=tuning+bob+archer
It is a bit more complicated since the length will determine the resonant
frequency
but the gamma matching circuit will determine the SWR. Although the antenna
is new, be sure there is no corrosion where the aluminum bits are riveted
together.
Finally, you can construct a simple dipole per AEC using solid copper house wire
(12-14 gauge) and solder RG58 or RG400 coax to it. Don't worry about a balun
or torrids, this is just for testing and education. Just tape the elements
to a piece of wood. Lead the coax at 90 deg to the elements. See what the MFJ
says about it and try trimming to see the effect. You might want to do this
first to get some confidence in what you are doing:)
I hope some of this helps. Probably whoever loaned you the MFJ can assist.
Jim Butcher
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http://forums.matronics.com/viewtopic.php?p=494497#494497
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