Re: Array Solutions AIM 4170 Antenna Analyzer
I was forwarded a link to a Towertalk post archived at
http://lists.contesting.com/archives//html/Towertalk/2008-06/msg00022.html
<http://lists.contesting.com/archives/html/Towertalk/2008-06/msg00022.html>
from someone who, in light of his experience, found N6RK's comments
puzzling.
The situation was a large 160m antenna with strong BC RF on the antenna, and
how to make that measurement with the AIM 4170 and a BCB high pass filter
and the custom calibration tool.
When using the proper procedure, one obtains much different results from
those N6RK obtained. Using the procedure contained in the documentation,
the result is the ability to make measurements with no loss of accuracy
through an AM broadcast band filter. The procedure has been available for
months now. It is called "custom calibration." It is not the result of a
recent software update. Those wishing to explore this powerful calibration
tool can download a copy of the software and run it as a demo on a PC. The
help files and manual embedded in the help file are very detailed. There
are also additional software tools to process the data including "Averaging,
smoothing, and trend". Correct application of this these should allow the
measurements even with significant RF on the antenna.
It is specifically designed for cases of high BCB RF existing on a large
160m antenna. It works extremely well, completely canceling out the effect
of a BCB filter, or any filter for that matter. In fact, the filter used
does not even have to be a symmetrical filter. The procedure requires
taking enough data points in a limited frequency range to completely cancel
out any filter transfer function no matter the loss of the filter with the
short, open, load technique used in VNA's. The calibration function has
been verified by the several broadcast engineers and is well documented as
very accurate. Since we have not heard from N6RK, we can suspect he did not
use the tool correctly or his analyzer was malfunctioning. I invite him to
call us, or send in the unit for testing if he feels it is malfunctioning.
As an example of performance to expect when the correct procedure is
followed in conjunction with a suitable BCB filter, I will relate my
experience with my 160 meter vertical. I have strong AM BCB signals,
especially from KRLD (50 kW) on 1080 kHz, as well as a station in the area
with 25 kW on 1700 kHz! I have approximately 32V peak RF on the antenna from
BC transmitters. Running the calibration per the documentation generated
very accurate curves, confirmed by comparison to our PowerAim 120 and a OIB
hot bridge. The PowerAim 120 has no problem blowing through antenna
measurements on AM broadcast stations that have more then 50 V peak-to-peak
RF on them. The correlation between the AIM 4170 and the PowerAim 120 was
perfect. I think my GR 1606 would probably burn up attached to this antenna.
Once a custom calibration is accomplished through a filter, one can verify
its accuracy by using a known load, purely resistive, purely reactive or
complex. A 100 ohm resistor for instance should be shown as 100 ohms of R
and X of 0 (zero ohms) and plotted as a straight line in the AIM's frequency
plot over the range the custom calibration was done.
With as powerful a device as the AIM 4170, it is more important than with
simpler analyzers to delve into the documentation in order to use the device
to its potential. Array Solutions welcomes inquiries, especially when a user
is unable to get the desired results. We are also interested in test cases
to explore other strenuous measurements. We invite users to send in
suggestions for additional software enhancements. Please also join the AIM
user group - go to <http://aim4150.proboards24.com/index.cgi?board=analyzer>
http://aim4150.proboards24.com/index.cgi?board=analyzer
Finally, K7LXC mentioned in a post his practice of making antenna
measurements while sitting in the yard or up the tower, which he thinks can
be duplicated with an AIM only by hauling it and a laptop out to the yard or
up the tower. The former is not too hard, the latter is definitely too
hard, but neither is at all necessary. Once the feedline is "characterized"
using the AIM 4170, the measurements data is the same as if the analyzer
were connected at the antenna terminals. The data it generates is much more
detailed than that provided by simple analyzers. The graphs can be saved
and overlaid for comparison. This is helpful not only while tuning an
antenna but when later determining if there has been a change. The
distance-to-fault cable test as well as cable loss measurements for cable is
also quite helpful when one encounters antenna system problems. There are
many more practical uses of this instrument and those are set forth at the
Array Solutions website.
Regards to the group,
Jay Terleski
Array Solutions
Jay Terleski
Array Solutions
972 203 2008
Military Communications Systems, Phased Arrays, RF Switches, Antennas &
Towers
<http://www.arraysolutions.com> http://www.arraysolutions.com
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