At 01:39 PM 4/5/2007, W5LT wrote:
>Jake:
>You might consider the AIM-4170 Antenna Analyzer from Array Solutions.
>It is (to my knowledge) the only reasonably priced antenna analyzer that
>provides correctly signed reactance (X) in an impedance measurement
>(R+/-jX). This is a very important difference when it comes to needing to
>tune or match something.
>The software that comes with it can turn the X into Capacitance or
>Inductance values as appropriate. More importantly, it directly measures
>IMPEDANCE of the circuit under test, as opposed to other "antenna analyzers"
>that only measure VSWR or reflection coefficient.
Instruments that measure things by measuring reflection coefficient
aren't inherently bad. After all, that's what Agilent Vector Network
Analyzers do. The major distinction among all the various schemes
for this is whether or not you're making measurements that incorporate phase.
There's a sort of hierarchy:
Systems that measure only magnitude
Systems that measure magnitude and angle
Phase measurement with coherent detector (e.g. AIM4170, HP8510, etc.)
Phase measurement with amplitude only detectors
Those that can resolve 4 quadrants (e.g. "six-port
network" based analyzers)
Those that can't (e.g. MFJ-259B)
And then, there's a distinction between using broadband or tuned detectors.
So, when it comes right down to it, the AIM4170 is no different than
any other bridge type analyzer using a tuned detector.
>Once the impedance of the
>shunt feed (or trap or other circuit) is known, you to easily calculate an
>appropriate matching network, or whatever.
>It was designed by W5BIG, and the article describing it and how to make one
>is in the Nov, 2006 QST. Links to that article and more are at the AS
>webpage:
>http://www.arraysolutions.com/Products/AIM4170.htm#top%20of%20page
>
> >From the circuit shown, you can see there is a lot more to it than a simple
>bridge or directional coupler device.
Actually, the AIM just IS a simple bridge, but with a narrow band
tuned detector that can measure phase.
It basically compares the difference in phase and magnitude of the
test signal with a resistive load (the reference arm) and the unknown
load (the antenna arm).
The simplicity is why it's a nice design.
Using narrow band detection is nice because it rejects interfering
signals (always a problem with antennas)..
And, another significant difference between modern measurement tools
(AIM, N2PK VNA, TAPR VNA, HP, Anritsu, and R+S VNA,PNAs, etc.) is
that they can be calibrated with a relatively small set of
standards. That's what having a computer connected does for you.. it
can take the raw measurements and turn them into calibrated
measurements that account for all the imperfections of the
measurement system.
>Bob, W5LT
>
>
>-----Original Message-----
>From: jacobsen_5@msn.com [mailto:jacobsen_5@msn.com]
>Sent: Thursday, April 05, 2007 2:57 PM
>To: towertalk
>Subject: [TowerTalk] Cap/Inductance meter
>
>Has anyone any info on capacitance/inductance meters? A google search turned
>up a PROTEK CL200. I can't seem to find any reviews on it or any others.
>Would seem that it would greatly speed up antenna set up for home brewers.
>You could use a variable broadcast type cap to set up a shunt feed for a
>tower or trap, read it with meter, and then substitute fixed doorknobs. The
>same with coils. Just a thought. (Few and far between at my age)
>
>73
>K9WN Jake
>
>
>_______________________________________________
>
>
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk@contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|