Hey gang...
Here's the follow-up on my dead AEA SWR-121 I reported a few weeks ago. This
unit was the original model sold by AEA about 15 years ago. Apparently it
reached its EOL (end-of-life). The repair charges were going to be excessive so
I traded this old unit in for their new VIA Analyst
http://www.aeatechnology.com/html/via_analyzer.htm
Here's a very quick review of my experiences using this analyzer during the
last few days.
The new 66-page user manual (on CD) is written for real-life amateur radio
"issues", i.e., tuning HF antennas, cutting 1/4 or 1/2 matching lines,
measuring coax attenuation, etc. I bought the full package which includes
software for the PC, the interface cable, traveling case, etc.
The manual cautions the user about taking readings in high RF environments.
Indeed, the unit was useless at the qth of Lou, AC0X. He lives about a mile
from 50 kW AM 1500 and has never been able to use any brand of analyzer on his
HF antennas. Fortunately, I live in the sticks and don't have this problem.
Here's the first task I put the unit to work on.
I wanted to tune my 160-meter inverted vee antenna to 1.830 MHz. The apex is at
70 feet with one leg dropping down to 40 feet and the other leg dropping down
to 15 feet. The wire is 14 ga hard drawn copper with a thick Teflon jacket.
From the formula I ended up with 255.74 feet. I added a couple of feet for good
measure so I started with 258 feet total.
I ran the analyzer and saw a VSWR minimum at 1.750 MHz. I did a little more
math and calculated that 10 feet would need to be trimmed to move the antenna
to 1.830 MHz. I dropped one end, trimmed 5 feet, pulled it back up, and decided
to see what effect this had. The Analyzer showed the VSWR minimum moved up 38
KHz to 1.788 MHz. Trimming 5 feet from the second leg moved the antenna to
1.830 MHz, right to the target frequency!
I have posted PDF's of the charts at http://chudek.aberon.net in the AEA VIA
Analyst Charts folder. Here you will find VSWR (long) for the first scan. All
the other charts were created after the final 5 foot trim. You will find charts
for VSWR, Impedance, Phase Angle, Reactance, Resistance, Return Loss, and a
Smith Chart.
Here's the question for the reflector.
My next challenge is to determine why the minimum VSWR isn't closer to 1.0:1.
It drops to 1.69:1 (RL= -11.8 dB) at best. Maybe someone with a little more
experience in antenna matching can "see" the problem when viewing the graphs. I
do see both the antenna reactance and phase angle make a sharp swing from
negative to positive at 1.800 MHz. Beyond this, I haven't worked with Smith
Charts in 20+ years!
My immediate method will be the shotgun approach... remove the balun and see
what changes... swap out the coax to see what changes... cut a 1/2 wavelength
of coax for 1.830 MHz to get a true feedpoint measurement...
Here's a little info on my purchase.
At $695 retail, the AEA VIA Analyst is a pricey piece of test equipment but
could be a good investment for a club or group of antenna enthusiasts.
I am not a representative, have no monetary interest, or make any financial
gain from AEA Technology. As a matter of fact, I will let you know the first
unit I received from them was DOA... But their customer support was great. All
I needed to do was provide a tracking number and they cross shipped a
replacement unit the next day. The second unit worked perfect when it arrived.
IMO, this would be a great product for a QST product review.
73 de Bob - K0RC
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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