Topband: Handheld Impedance Analyzer
Guy Olinger K2AV
k2av.guy at gmail.com
Mon Mar 28 03:29:02 EDT 2016
Grant has a good list of possibilities in his post. Some newer ones I
haven't tried yet.
SWR is an extremely limited measurement to analyze antennas. I have had
many correspondences with hams led off on a wild goose chase by SWR
measurements. With their MFJ 259's etc, I have them create graphs of X and
R by frequency so they can see what is happening. That's a lot of trouble,
and the MFJ doesn't tell you the sign of the X value. But the graphs
usually turn on the lights in Georgia.
The best tools for analyzing antenna issues are instruments that produces a
graph of R vs frequency overlaid by X vs frequency. Resonance is where the
X graph crosses zero. Capacitive reactance should be a negative value.
The other useful trick is many analyzers' ability to show impedance
presented at the far end of a transmission line. This is done in a software
or firmware program after saving characteristics of the transmission line
with a calibration procedure of one sort or other. The conversion is a math
There is a tendency to assume that the measurement in the shack is the same
as the measurement at the antenna. This is just about never true over
bandwidth and the effect of an unfortunate length of transmission line can
cause changes in SWR at the shack to apparently run backward from component
changes at the antenna creating enormous confusion and waste of time.
Having the instrument convert values based on it's calibration of a
feedline completely eliminates this kind of confusion.
And there are most excellent NON-resonant antennas that simply cannot be
setup properly with SWR readings.
Beyond that, the "transmission line" can contain a filter for highpass,
lowpass, or bandpass to remove unwanted signals from overloading an
instrument. The calibration of the transmission line is made with the
filter in line and that calibration data and the program math will correct
for the impedance changes caused by the filter as well as the coax. This is
extremely handy with BC stations nearby. My AIM 4170 has this feature and
has paid for the cost of the instrument many times over, being able to
obtain clean graphs regardless of any high level crap RF around.
Once you realize what you are seeing with graphs of R and X vs frequency,
you will realize that SWR tells you about the same as an oil pressure lamp
in your car. All you know is that it's changed from what you had before.
But to analyze and chase troubles, you will immediately go for the R and X
SWR is grotesquely over-valued as an indicator. It can be a flat liar for
some trouble shooting and can make an antenna gone really bad look good.
Just remember that the best dummy load has a really great SWR.
It will cost you some money, especially if you get to realizing how useful
TWO port devices really are. But those too are coming down in price, and if
you really want to know what is going on with wires and matching networks,
you will get the good stuff, and put away the toys.
73 and good luck
On Sun, Mar 27, 2016 at 8:45 PM, Grant Saviers <grants2 at pacbell.net> wrote:
> My 2c, having owned MFJ269, AIM4170, VNWA2.3 & 3, AA54, SARK110, old noise
> bridges, and used a friends FG-01 on a DXpedition.
> The MFJ is old, not all that accurate and really useless in the presence
> of other strong RF, eg BCB. Sold it. I'd call it obsolete vs current
> AIM4170 (old serial port) was next, still own it and use it, the separate
> DC power and PC is a pain for "handheld" but done that, nice graphics,
> accurate, PC output, full calibration capabilities, it's a full S11
> analyzer + TDR.
> VNWA 2.3 then upgraded to VNWA 3, full 2 port network analyzers, these are
> in a league of $$$ bench instruments, rarely used for antennas, but most
> heavily used of all.
> AA54 bought as real "handheld" for on tower or at antenna, no PC needed,
> funky menu system, simple B&W graphics, no auto find capability, but did
> what I needed in the yard and on DXpeditions, SO239 connector and rugged
> case make it pretty sturdy.
> SARK110 is the latest, fits in shirt pocket, much better color graphics
> and PC output than AA54, a real S11 analyzer, TDR, signal gen, etc. Most
> bang for the buck. Cal capabilities. Fragile connector. Several auto
> modes that are useful when tuning. Rechargable battery, decent life. The
> winner for me.
> You Kits FG-01 (now FG-011), smallest, does the swr measuring job, easy to
> navigate, cheapest
> Caution: Experience (bad) shows the SARK110 and FG-01 won't handle much
> RF, you can blow the front ends if tuning an antenna while another nearby
> is transmitting which can happen on DXpeditions. Probably true for all of
> the others, but so far avoided with the AA54. The others stayed home.
> Big antennas can sometimes hear enough RF to make these handheld units
> yield ambiguous results. There really aren't the bandpass filtering and
> bullet proof front end needed that you find in R&S, Agilent, etc. Learned
> that recently and needed to fall back to my K3 at 5w to be sure of the
> tuning. Or add your own bandpass filter.
> Grant KZ1W
> Redmond, WA
> n 3/27/2016 12:08 PM, dick.bingham wrote:
>> Greetings All
>> I am getting fed up with multiple trips between new antenna matching
>> stations and the
>> tx-source/VSWR and not converging on a good match in quick order !
>> Please send me - OFF LINE - your recommendation for a handheld impedance
>> measuring tool that covers 400KHz to at least 150MHz. I looked at the
>> RigExpert AA-220 in the latest QST and it looks like a decent tool.
>> I certainly do not want to restart this topic but new stuff is becoming
>> available and I don't want to settle for second best if 'best' is not 2X
>> more costly!
>> 73 Dick/w7wkr CN97uj
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