ISO: Batwing Antenna Design Information
kd...@amsat.org
I'm in search of design and construction infomation for a Batwing
(Masters Superturnstile) antenna for 70-cm (430 MHz) Amateur Television
repeater system use. I've done extensive research, and have concluded
that a multi-bay Batwing antenna, with it's nice broad bandwidth, would
be ideal for this application. The Alford-Slot antenna we are currently
using is providing terrible performance.
I realize that most commercial Batwing antennas are used by Low-VHF
television broadcasters, but the design should work quite well in my
application simply by scaling the dimensions up to the 430 MHz range.
Most of my questions relate to the proper feeding of each batwing layer,
as well as suitable construction techniques. (This antenna will be
mounted on a commercial communications tower at 350 feet AGL, and
failure is NOT an option.)
I've created a short web page containing some ideas and drawings I've
come up with. The URL is as follows:
http://www.njin.net/~magliaco/batwing.html
I'm soliciting comments from anyone would might be able to provide
construction and design information details. None of the antenna
literature I have come across provides enough PRACTICAL information
to formally develop a set of plans for constructing such an antenna.
Any help and/or assistance that can be provided would be greatly
appreciated.
Thanks!
John <kd2bd at amsat dot org>
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Robert Casey
is different than say 56MHz and 6MHz BW. A scaled up batwing
would have excessive bandwidth for your application. Might not
hurt, but out of band strong signals could cause trouble.
Cbo...@earthlink.net
>
> Hi.
>
> I'm in search of design and construction infomation for a Batwing
> (Masters Superturnstile) antenna for 70-cm (430 MHz) Amateur Television
> repeater system use. I've done extensive research, and have concluded
> that a multi-bay Batwing antenna, with it's nice broad bandwidth, would
> be ideal for this application. The Alford-Slot antenna we are currently
> using is providing terrible performance.
>
> I realize that most commercial Batwing antennas are used by Low-VHF
> television broadcasters, but the design should work quite well in my
> application simply by scaling the dimensions up to the 430 MHz range.
A Batwing has a bandwidth of up to 20% which is why it is so popular
at lowband freqs...On TV2 this means about a 10 MHz bandwidth more
than enough for 6MHz TV signals. On UHF it will have much more than
enough bandwidth to work the entire 420-450 band likely!
> Most of my questions relate to the proper feeding of each batwing layer,
> as well as suitable construction techniques. (This antenna will be
> mounted on a commercial communications tower at 350 feet AGL, and
> failure is NOT an option.)
>
> I've created a short web page containing some ideas and drawings I've
> come up with. The URL is as follows:
>
> http://www.njin.net/~magliaco/batwing.html
Excellent info...You can look in the book "Antennas" by Kraus for
some detailed info on the Batwing. Also the "Antenna Handbook Volume
III" by Lo/Lee has some good info on it and other horizontal
antennas that would be great for use on 440 ATV.
> I'm soliciting comments from anyone would might be able to provide
> construction and design information details. None of the antenna
> literature I have come across provides enough PRACTICAL information
> to formally develop a set of plans for constructing such an antenna.
See above...btw to feed the batwing is like any other crossed dipole
antenna..you merely use power dividers or coax matching lines to
split the feed and then provide matching to the elements which are
50 ohm nominal....The wings themselves are attached to the mast at
the top and bottom....hence they are grounded already! I can send you
some pictures of commercial batwings and their matching/feed so
you can get an idea on how they do it...
Chris
WB5ITT
Chief Engineer
KDMX / KEGL
Clear Channel, Dallas
kd...@amsat.org
Robert Casey <wa2...@ix.netcom.com> wrote:
> The ratio of carrier frequency to bandwidth on 430MHz to 6MHz BW
> is different than say 56MHz and 6MHz BW. A scaled up batwing
> would have excessive bandwidth for your application. Might not
> hurt, but out of band strong signals could cause trouble.
It shouldn't be a problem in this case. The repeater's receiver
and transmitter are protected by two layers of bandpass filtering
(interdigital and combline), and the fact that the antenna is
horizontally polarized will further reduce pick-up from nearby
vertically polarized signals.
The broad bandwidth will also relax the construction tolerances
somewhat, and make the antenna less subject to the de-tuning effects
of rain and ice on the radiating elements.
I just need to be concerned with keeping the number of dissimilar metals
to a minimum to reduce the IMD that could be produced by a broadband
antenna in a high RF environment.
73, de John, KD2BD
kd...@amsat.org
> A Batwing has a bandwidth of up to 20% which is why it is so popular
> at lowband freqs...On TV2 this means about a 10 MHz bandwidth more
> than enough for 6MHz TV signals. On UHF it will have much more than
> enough bandwidth to work the entire 420-450 band likely!
No problem!
> Excellent info...You can look in the book "Antennas" by Kraus for
> some detailed info on the Batwing. Also the "Antenna Handbook Volume
> III" by Lo/Lee has some good info on it and other horizontal
> antennas that would be great for use on 440 ATV.
I have the Kraus book, which provides the physical dimensions of each
batwing. Someone suggested trying to find info on the Batwing from an
old issue of "RCA Review" around the time the Batwing was introduced by
RCA. That'll be a challenge. :-)
> See above...btw to feed the batwing is like any other crossed dipole
> antenna..you merely use power dividers or coax matching lines to
> split the feed and then provide matching to the elements which are
> 50 ohm nominal....
They ARE 50 ohms? I thought I read somewhere they were closer to 70
(might have been in an old First-Class Radiotelephone License manual).
If that's the case, I would make the entire array a 70 ohm antenna, and
use an alternate line transformer after all the power dividing and the
90 degree delay line to bring it down to 50 ohms.
> The wings themselves are attached to the mast at
> the top and bottom....hence they are grounded already! I can send you
> some pictures of commercial batwings and their matching/feed so
> you can get an idea on how they do it...
That would be ideal. A picture is worth a thousand words. :-)
Thanks!
> Chris
> WB5ITT
> Chief Engineer
> KDMX / KEGL
> Clear Channel, Dallas