A BC notch filter that works on 160 has two issues, first that it has to
notch out an interfering station, and second, that at each160 frequency to
be measured, the residual reactance of the notch must be tuned out, one
frequency at a time. The MFJ design will do this, but if one is being
bothered by more than one station, a single notch will not work.
Some have used a BC rejection high pass filter. For accuracy, the readings
must be compensated by whatever reactance and impedance transformation is
produced by the filter.
Certain newer devices, the AIM4170 is one, work in concert with a PC. A
calibration data table is created by scanning precision devices and then the
table is used in converting the raw readings to accurate presentations of
values. More expensive devices contain the calculating device in the unit.
This allows "custom" calibrations to be created looking *through* cables and
devices to precision devices on the far side. These named and saved custom
tables can translate raw data to what would be seen on the "far" side. E.g.
one can calibrate looking through a BC filter and compensate for the
miscellaneous distortions closer to cutoff frequency.
73, Guy.
On Sat, Oct 3, 2009 at 9:31 AM, Glen <k4kv@mds-ham.com> wrote:
> Hello,
>
> I inquired about a filter for the MFJ to block broadcast AM interference.
> Thanks for
> the responses!
>
> I built a filter from a QEX article. The filter worked great from 3.5Mhz
> up. It did not
> work for 160M.
>
> Just a note for others looking at QEX articles.
>
> 73's
>
> Glen K4KV
>
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>
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