Topband: Antenna analysers in close proximity to BC station.

[Guy Olinger K2AV]

The AIM 4170 (and probably some others) allows you to calibrate THROUGH
filters and coax, etc, to the far side. That way a high pass filter in
front of the unit is completely transparent, and you can see stuff on the
other side with the filter's impedance, passband ripple, etc taken out.
 All done in software.

That feature has been very useful on 160m for eliminating BC interference.
 Beyond BC band there are a lot of uses for remote calibration besides
making filters transparent.  Just one is calibrating to the end of a
feedline, and then using it as a reference to detect problems in the
feedline.  Terminate at the far end and any variation since it was new
shows up as departures from flat readings from the termination.

It DID cost me some money to purchase, it's not the cheep solution, but
I've never looked back.

Having good test equipment that does the job is really worth it.

73, Guy.

On Fri, Nov 2, 2012 at 6:31 PM, Greg - ZL3IX <zl3ix at inet.net.nz> wrote:

> 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<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.
>>
>>
>> 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.
>>
>>
>> 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.
>>
>>
>> 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.
>>
>>
>> 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?
>>
>>
>> 73
>>
>> Tom G3OLB
>> ______________________________**_________________
>> Topband reflector - topband at contesting.com
>>
>>
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