[TowerTalk] Measuring DX Performance of Verticals
hwardsil at centurytel.net
Wed May 7 11:53:21 EDT 2003
> > The bottom line is that trying to make any kind of an A/B comparison
> > a
> > sky-wave path is pretty much an exercise in futility. Signal levels
> > wildly +/-20 dB in a matter of seconds, so comparisons would have to be
> > made
> > on a second-to-second basis.. You would need synchronized antenna
> > switching
> > systems and some fairly sophisticated test gear
> > //To judge multiple skywave paths simultaneously, this does seem to be
> > issue; however to get a pretty good feel for one or two well known
> > paths isn't so difficult. When I compare antennas, I use nearly
> > instantaneous switching (coax switch, local or remote) and "beacon" type
> > signals, such as those broadcast 5 days a week by W1AW in the form of
> > their code practice and bulletins. W1AW is almost precisely 3000 miles
> > from me, and it's obviously a skywave path, and although there is indeed
> > QSB over the path most of the time, taking dozens of readings over a
> > period of a few minutes and then averaging those to find the mean signal
> > strength (as well as standard deviation, if you wish) isn't a big chore
> > all, and I've done it many times. If you take a reading every ten
> > for five minutes, using two or three antennas in a comparison trial,
> > average all those readings for each antenna, you have a pretty good idea
> > which one is working better for that path. Maybe not for "all" paths,
> > certainly for that one.
> > Then, I switch to a different "beacon" type station...10m is full of
> > 24/7 of course, from many directions...but if 10m isn't open, there are
> > beacon-like stations on other bands, including CHU on 7335 kHz, etc. I
> > even use high-end-of-the-radio-dial AM BC stations to compare 160m
> > antennas -- pretty close.
> > -WB2WIK/6
Tongue-in-cheek, I reply, "Go ahead!"
You are no doubt obtaining fairly valid results, but only for your location
and installation. DXers in New England have grossly different launch angles
throughout an opening than for those of us on the Left Coast, for example.
Using a vertical for intra-US QSOs requires an entirely different set of
My supposition remains that the relative efficiencies of the verticals as
measured by our tests correlates well with how the verticals will perform in
a wide variety of useful settings over a wide range of useful launch angles.
Yes, it is possible that at very high or very low angles, there may be
slight variations, but these variations are likely to be greatly
overshadowed by the characteristics of your installation and environment.
The goal of the tests are to identify the broad characteristics of how the
antennas radiate a signal. You then need to evaluate these behaviors with
respect to your own particular requirements for use and installation.
Trying to push the test methodology into these highly variable areas adds
little value and creates data that is unlikely to be reproducible. This
violates two of the "Three-R's" - that the tests be Repeatable and
Reasonable. This is similar reasoning as to why we do not claim to measure
absolute gain of the yagi in the companion tests.
73, Ward N0AX
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