How did they confirm the power losses in the conductors
were 0.17 dB? Did they put the entire antenna in an
infinitely large thermos bottle and measure the heat
gain? Or did they use a COMPUTER MODEL's estimate
of power losses in a particular material? There is
a world of difference between the two. As I said
in my post, I have no problem with the table of
modeled gains. I do doubt that they have measurements
showing the gain and F/B to the degree of accuracy
stated in the ad, 0.25dB to 0.50 dB, especially since
a real antenna range at HF would have to take into
account ground effects.
Terry Zivney, N4TZ/9
From: Joe Reisert [mailto:firstname.lastname@example.org]
Sent: Thursday, September 19, 2002 2:10 PM
To: Zivney, Terry L.; email@example.com
Subject: Re: [Towertalk] SteppIR Performance and misleading advertising
Terry and Steve (WB2WIK),
Why are you guys trying to trash Fluid Motion and putting our false data.
If you notice, Fluid Motion gains are published in QST. Although they are
in dBi (the typical numbers done with computer modeling), one only had to
subtract 2.1 for dBd. They aren't trying to pull some fancy testing or
ground gain etc, like some companies do! The truth of the matter, according
to Mike at Fluid Motion, is that they did send the antenna out to an
antenna range and had the gain measured. If they hadn't done this and
didn't have the proper modeling, ARRL would not have accepted their
advertisements with the gain included.
As for the Fluid Motion performance claims etc., it is easy to verity on
YO etc. using 22 Ohm feed impedance. I've done it. The chosen driven
element resonance impedance for their design is about 22 Ohms so they use a
Sevick type unbalanced to balanced toroid to get a 50 Ohm match. 15 meters
is near the optimum boom length (about 0.35 WL). However, the shorter boom
does penalize 20 meters by about .5-.7 dB, a small price to get good
performance from 10 meters through 20 meters on a 3 element Yagi.
Furthermore, if you don't like the settings they provide (several
frequencies for 10, 15 and 20 and one for 12 and 17 meters), you can set
you own and go for maximum gain with poorer F/B, not a bad choice for those
not needing high F/B like us on the coasts.
At 08:54 PM 9/18/2002 -0500, Zivney, Terry L. wrote:
>Page 154, October 2002 QST:
>"performs as predicted by YO and EZNEC within .25-.50 dB"
>is patently unverifiable. I have no problem with the ad
>included a chart based on computer modeling but they have
>no way of proving that their actual physical HF antenna
>is within .25-.50 dB of the computer models, especially
>since they give free space gains and I am quite certain
>the manufacturer does NOT have a free space antenna
>Similarly, I am quite sure they have no way to confirm
>that the actual conductor losses are .17 dB; rather the
>model predicts losses of .17dB
>Again, to summarize, the table is ok - but the
>claimed accuracy puts them in the Gotham category
>when it comes to accuracy in advertising.
>Terry Zivney, N4TZ/9
>Self Supporting Towers, Wireless Weather Stations, see web site:
>Call 888-333-9041 to place your order, mention you saw this ad and take an
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>any weather station price.
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