I have read this thread with interest but was a little shy in commenting
because I did not want to start a P-----g contest. BUT ....
Many years ago there was a publication called ... ARP ..Amateur Radio
Profiles ...The goal of such was to test Amateur Equipment and publish the
results as true blue as possible ...The publication accepted no
advertisement so there were no favors owed..
The antenna testing was unique, at the suggestion of Sid Kittrell, at the
time the CEO of the former Hygain, ARP erected two crank up towers, 2 wl
apart .... three monobanders were built under the guidance of Jim Lawson and
were used as the control. Two stations one in London and the other in
Germany were the observers on transmit and receive, we naturally in Georgia
did the figures on receive....
When Sid put the word out, antenna started flying in the front door...
The procedure went like this...
The control antenna was taken to one wl above ground......the antenna under
test on the second tower was also at one wl.
Based on past practice we determined the opening..peak and closing of the
band.
With both the RX and TX station on the telephone, we fired up the control
antenna at 1500 watts and then sent out a CW constant tone... ..The
receiving station had a Wayne Overbeck calibrated VU meter, and a Rhode -
Swartz receiver with the AGC shut off .... the VU meter reading was
recorded, then we immediately switched over to the antenna under test and
repeated the exercise...Then switched back and forth 5 times .
Testing was exhausting... we would TX on alternating antennas they would
record the readings, then they would TX and we would flip back and forth for
the incoming readings on the Overbeck meter......
All test were done at one WL on 10/15/20 meters....The Overbeck meter could
pick out fractions of a dB on the 8 inch meter face. The dual towers were
identical the same and amount of co-ax, same grounding system.
So the tests were pretty much on spot....based on knowledge at/on hand 30
some years ago...
The first year we did tri band antenna's the second year we did
monobanders....
As the testing proceeded we felt we could throw all the antenna's into a
sack and use the one that fell out first, we wondered why anyone would want
more than a real honest 3 element monobanders antenna...
We waited with baited breath, for the system that would give us a honest 3
Db power point jump over the competition. It finally came from the West
Coast Folks..KLM
The surprising antenna was a 2 element all metal Quad by Hygain ....
Speaking of Quads they were fine but the eye opener were a set of the 4
element monobanders quads
which we built for a friend/supporter.
The biggest smiles came one Saturday when the "Brothers from New Jersey"
were finishing up on a big contest station in the neighborhood. Late in the
afternoon they were testing a big 5 element into VU land ...we rode along
with the 2 element Quad mentioned above .... They had to stop and drive over
just to check...and walked away shaking their heads..Of course the
difference was we had the propagation they were too high.
Also amazingly enough there are quite a few antennas that have stood the
test of time, still being sold after 30 some years!!!!
After all that I have often said ..If I were a young man starting all over
....what would I do....
I would built a 120 foot tower, with a side car trolley, to move a 4 element
stepperIR up and down to the proper propagation point. Or if I were really
industrious I would build 4 towers 2 wl high with trolley on 10-15-17-20
meters, then put a Lawson 4 element monobanders on each tower....
Bill Winkis .... KC4PE
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Ward
Silver
Sent: Wednesday, October 17, 2012 9:11 AM
To: Towertalk Reflector
Subject: [TowerTalk] Antenna Testing
As K9YC and others observe, this is a highly non-trivial exercise and takes
weeks. I just do not have the time for the undertaking. That's actually
part of why we published the detailed protocol...so that some other
motivated group could build on it. Another possibility is for one of the
big antenna or aerospace companies to make a test range available for a day
or two and have a large group do it like Field Day. But the write-up and
data-crunching will still take many, many hours.
K5GO's idea has merit - given the availability of sophisticated modeling,
much of the data could be generated computationally. However, that presumes
accurate models that aren't cherry-picked or biased...perhaps third-party
models could be developed. But any model would have to be validated...and
that requires testing. Furthermore, modeling would not have uncovered the
problems with the KT34XA trap rebuild kit or pointed out that there might be
feed line interaction on the PRO-57B. And neither do you get a feel for
whether the antenna is a mechanical nightmare or exceptionally robust or
came with missing or cheap hardware or whatever intangibles that models
don't include. So there is no free lunch when you get right down to it.
And there are political issues...I remember the neighbors got mighty nervous
when there were five big antennas assembled on sawhorses in the north
pasture :-) They were greatly relieved to hear that I was only planning a
test and some of them offered to help - no doubt to speed its completion and
get the antennas on their way.
More seriously, building up a set of data like Rob Sherwood NC0B has done
for receivers might be a good long-term project. Someone would need to make
a commitment to maintaining a decent test range in a consistent
configuration. A standard protocol would have to be developed and the
equipment to implement it maintained as well. Over a period of years, a set
of data could then be built up for comparison.
On the other hand, with antenna modeling so powerful and ubiquitous, claims
of extraordinary performance ("Flash! Just worked South America!") are much
harder to make (more than once) and so the need for third-party checks has
been reduced. I applaud companies that take great pains to publish
free-space dBd values with all the necessary supporting data such as
elevation angle. Don't be afraid to ask for that data - if it's not
available, take a closer look at the claimed performance and the antenna
itself.
73, Ward N0AX
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