Topband: BCB Filter (related to Antenna Analyzer question)

[Rick Karlquist]

Mike & Coreen Smith wrote:
> Thanks for all the great replies both on and off thread WRT my MFJ-259
> (not
> B model)
> and some suggestions for a new analyzer.
>
> I think I have it narrowed down, but have a question.
>
> Will a simple filter like this be sufficient to allow (for example) an
> AA-200, AIM-4170 or a MFJ-269 to work on 160m
> or is there more to it? http://www.iceradioproducts.com/filtersrf.html#bcb
>
> I am presuming I could buy some kind of small "receive only" filter and
> the
> analyzer would not be enough to overpower the
> components???  Anyone have a suggestion of a CHEAP filter?  If I am
> shelling
> out $500++ for an analyzer, I don't want
> to spring another $100-$200 for a 160m filter.
>
> TNX 73 de VE9AA Mike

I purchased one of the ICE filters and the performance does NOT
meet the published curve.  Many dB off.  It does provide some
filtering.  The performance is OK considering the price.

However, whether a filter works or not depends on local radio stations,
what your antenna is, and which analyzer you are using.  So it is
impossible to say apriori.  The ICE filter might work in some
situations.

If you put a filter in front of almost any ham analyzer other than
the AIM-4170, the analyzer will not read correctly, even if
there is no AM interference.  This is because the input impedance
of the filter will not in general be equal to the load impedance
on the filter, especially when it comes to phase.

At my request, the AIM-4170 software has been upgraded to be able to
"calibrate out" the filter.  I also requested this feature of some other
analyzer vendors and they blew me off.  Perhaps by now they
have seen the light.  I believe the N2PK software can also do
a calibration.  But you have to build the hardware yourself
and you have to have a parallel port to control it.

For me, I needed a $100-200 filter and an AIM-4170, since the ICE filter
was insufficient.  I have a 50 kW station 6 miles away on 1140 kHz and
many other ones at somewhat greater distances.  (The filter was actually a
homebrew filter of equivalent performance to a purchased $100-200 filter. 
After building this filter, I can see why they aren't cheap to buy).  This
is not an ideal solution, but it is the only one I have.

But again, this is one of those "YMMV" situations.  You have to
try it.

Rick N6RK