[Elecraft] MP-1 and antenna analyzer

Mon Nov 25 00:53:01 2002

Tim:
  I'm sure others with deeper knowledge of these matters than mine will 
chime in in due course, but let me venture a few thoughts.  First, your 
body capacitance can and will have a major effect on the SWR of the antenna 
system.  There is no way you can remove this effect.  When any part of your 
body moves close to any part of the antenna system, you will change the 
tuning from what it was.

  The fact that you are also seeing change depending on whether you hold 
the MFJ or not indicates that it and the coax connected to the antenna are 
also acting as part of the antenna system.  So, when you touch the MFJ, the 
tuning will be different from when you are not touching it.  I suspect you 
can minimize this effect, however.  You need to isolate the MFJ from the 
antenna system.  First, you must be sure that the base of the MP-1 is 
properly grounded for RF.  Use a counterpoise wire  attached to the base 
that is 1/4 wavelength of the frequency at which you are making your 
measurements.  Either that, or use a tuned artificial ground to achieve the 
same end.  If that doesn't do the trick, try also making a choke of the 
coax feed.  Others will, no doubt, be able to provide good ways of doing 
this, but if you have a good sized toroid, try looping your coax through it 
a half-a-dozen or so times.  Or, if you have some clip-on ferrite blocks, 
use a few of them in a row.

best wishes,

dave belsley, w1euy

--On Sunday, November 24, 2002 9:26 PM -0700 [email protected] wrote:

> Hi folks -
> I'm starting to fool around with antenna measurements on my MP-1 using the
> MFJ analyzer. I'm surprized out how sensitive the analyzer is to almost
> anything! If I bring my hand close to the antenna it will change the SWR.
> If I put the meter on the floor, rather than holding it, the SWR can
> change. As soon as I touch the coil sleeve to move it readings will
> change also (not surprized by that though). It's pretty
> fascinating....but I'm wondering if anyone has hints on how to get a more
> stable reaction for an accurate reliable measurement. I'd like to model
> the antenna and coil with NecWIn Plus as an experiment and be able to
> take accurate readings from the MFJ meter....any thoughts on stabilizing
> the meter a bit more would be most appreciated. 73/tim NZ7C
>
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----------------------------------
David A. Belsley
Professor of Economics