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Re: [TowerTalk] Analyzers

To: Denis Coolican <coolican@telus.net>
Subject: Re: [TowerTalk] Analyzers
From: "Richard (Rick) Karlquist" <richard@karlquist.com>
Date: Sun, 01 Jun 2008 15:03:49 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
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

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