[TowerTalk] Analyzers

[Richard (Rick) Karlquist]

Denis Coolican wrote:
> Autek Research handle the VA1 antenna analyzer which goes up to 30 Mhz.  It can measure the + or - j values and indicate such.   I use a 1.8Mhz high pass in front of it and in front of the MFJ 259B.  The VA1 sure is nice and compact.  The MFJ you can still send out to have repaired if you have to.
> 
> The AIM 4160 looks good and probably comes the closest to a real General Radio  RF impedance bridge from the past. 
> 
> Denis Ve6aq

Note that you can't simply attach a high pass filter in front
of a network analyzer and expect to get the right readings.
At best, if the filter is low loss, you can measure SWR only.
Not R + jX.  Unless the network analyzer has a way of calibrating
out the effect of the filter, which the VA1 and MFJ259 do not.

I have an AIM4170 and also a real General Radio impedance bridge.
The AIM4170 is useless on my 160 meter vertical due to BCB RFI
unless I precede it with a very sharp BCB reject filter.  The
vendor recently added software that is supposed to allow you to
calibrate out the effects of the filter.  This calibration sort-of
works, but the resulting accuracy isn't very good.

Rick N6RK