Topband: Antenna analysers in close proximity to BC station.

[Greg - ZL3IX]

Hi Tom,

I used to have the same problem with my N2PK VNA, but then I put a 
switchable high pass filter in before the detector - after the 
reflection bridge that is.  Provided that the VNA calibration is done 
with the filter switch in the same state as you intend to do the 
measurement, it has no effect on the readings at all.

Don't know how easy it is to mess with the insides of the either the MFJ 
or Palstar, but if you can get at the detector the same solution should 
work.

73, Greg, ZL3IX


On 2012-11-03 10:21 a.m., Tom Boucher wrote:
>
> A ham friend asked me to design a matching network for his 160 metre end fed quarter wave, so I asked him to provide an impedance reading using his MFJ-259B. I would then use the Berkley site (http://bwrc.eecs.berkeley.edu/Research/RF/projects/60GHz/matching/ImpMatch.html ) to provide the necessary values for an 'L' network, as I have done many times at my own station.
>
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> The readings he provided were total nonsense and quite erratic, so we concluded his MFJ-259B was dead. He assured me that he always does a static discharge before connecting the MFJ.
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> So I paid him a visit, taking along my Palstar Antenna analyser thing, which has always performed well at home, and what-do-you-know, the readings on that were also erratic, total nonsense and it behaved in a way I have never seen before.
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> Than someone suggested the problem may be due to a 50Kw BC station on 909 KHz, situated less than 5 miles away, causing both antenna analysers to misbehave.
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> We ended up with a good old-fashioned link coupled parallel tuned circuit with the antenna tapped a few turns up from the ground end. This works fine but he is power limited due to arcing across the tuning capacitor. So we would ideally like to revert to the 'L' network plan, but how to use the antenna analyser in the presence of a high BC station field. Anyone any ideas?
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> 73
>
> Tom G3OLB
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>