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Mistakes are great learning tools, probably one of the best! We can learn two
ways, from making mistakes ourselves, or from looking at other mistakes. Please
take this page only as an educational tool.
The Sterba Curtain for all bands on Ham Universe claims to be
an all band 160-10
meter Sterba
Curtain. Looking
at that antenna, we can see some very common mistakes and learn to avoid those
mistakes.
From eHam Towertalk:
I am hardly a Guru – but I did make this exact
antenna from the same link several years. It sounded soooo good on the
web page. Alas like most antenna hyperbole on the internet it did
not meet my expectations.
It was a real pain to construct and erect. I put the top wire at
about 55 ft. I tested it. I tested it against my 75 mtr loop, 40 mtr
vertical and 130′ dipole fed with 600 ohm feed line. The sterba did
not win any test. In fact it was even worse than the all band (hyperboled)
Mystery Antenna that it replaced. And the Mystery antenna was pretty
poor…..
I took it down after 2 weeks, I think it is still in my junk box along
with the Mystery Antenna, a good place for both.
Do yourself a favor and put up a 130′ doublet fed with 450 or 300 ohm
feed line. It will perform much better than this Sterba….
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That probably is an accurate assessment, but it doesn’t help us understand
how or why antennas might not work.
The H-U All Band Sterba Curtain
The
antenna below uses the exact
dimensions of the
HU article. It contains
a representation of actual window line
in the elements.
Height is 47 feet to
the upper element, which is probably a reasonably obtainable height. Before we
do anything, we should look at performance of a standard antenna, like a dipole.
We have to know how a basic simple antenna performs, or we have no reference to
any new system. A basic simple dipole is a good reference antenna, because it is
reliable and easy-to-build.
The plots below
are for a standard wire dipole 5/8th wavelength above normal earth. This should
be the basis of any antenna comparison:
 
We see a basic simple dipole over normal flat earth can have about 8.5 dBi gain.
This is because reasonably good earth, even without any counterpoise wires, adds
around 6 dB of ground reflection gain to horizontally polarized antennas.
Here are antenna models of the Ham Universe all band curtain:
28.5
MHz gain is 12.55
dBi, or +4 dBd. It is a good antenna for ten meters!
24.9
MHz gain is 12.43
dBi, or 4 dBd. It is still a good antenna for 12 meters, a little better than an
extended double Zepp.
21.1
MHz gain is 6.13
dBi, or
-2 dBd. This is weaker than a dipole
by 2 db. While this will still allow many contacts, a dipole would be better.
18.1
MHz gain is 6.71
dBi, or
-1.5 dBd.
Weaker than a dipole
by about 1.5 dB. This is weaker than a dipole.
14.2
MHz gain is -1.62
dBi, or
-9 dBd.
Weaker than a dipole
by 9 dB. This is where the antenna is noticeably poor. A 100-watt transmitter
becomes a 10 watt QRP rig! You will still work people, but a dipole is about 2 S
units stronger!
10.15
MHz gain is 6.13
dBi, or
-2 dBd.
Weaker than a dipole
by 2 db
7.15
MHz gain is 5.51
dBi, or
-3 dBd.
Weaker than a dipole
by 3 dB
3.6
MHz gain is 1.8 dBi,
or
-6.5 dBd.
Weaker than a dipole
by 6.5 dB
1.8
MHz gain is -11.6
dBi, or
-19 dBd.
Weaker than a dipole
by almost
20
dB. This is dummy load category
It’s pretty easy to see why “making contacts” should not be a criteria for
claiming something works properly. If we add feed line losses to the above
analysis, some bands are 5 dB or more worse! Even a few watts ERP will allow
many contacts, but that doesn’t mean every antenna is an all-band antenna.
The main problem in the above antenna is phase-shift in the elements, and
mismatched impedances in the elements. This was missed because the only
performance reference was if someone could hear the signal. This is why we
should always compare antennas to a basic reference antenna.
return to main
curtain array page
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