Today's Message Index:
----------------------
1. 05:15 AM - Re: Dual Band Antenna Question (Kelly McMullen)
2. 06:03 AM - Re: Dual Band Antenna Question (user9253)
3. 07:02 AM - Re: Dual Band Antenna Question (user9253)
4. 08:38 AM - Re: Dual Band Antenna Question (speedy11@aol.com)
5. 07:40 PM - Re: Re: Dual Band Antenna Question (Robert L. Nuckolls, III)
6. 07:47 PM - Re: Re: Dual Band Antenna Question (Robert L. Nuckolls, III)
7. 07:49 PM - Re: Dual Band Antenna Question (Robert L. Nuckolls, III)
8. 07:51 PM - Re: Re: Dual Band Antenna Question (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Dual Band Antenna Question |
What can be shared or will be shared depends on the actual ADS-B UAT out
unit you install. Some do share the antenna, some like the uAvionics
wingtip and tail units have their own built in antenna.
To receive ADS-B In you will need a separate antenna, which is usually
built-in for the portables and usually needs separate external for
installed units.
In other words, need to know which unit(s) you are considering to advise
on antennas.
On 10/5/2019 5:52 PM, markfw wrote:
>
> Can anybody explain to me how a dual band antenna like this one:
>
> https://www.dallasavionics.com/comant/ci105-17l.pdf
>
> actually works?
>
> Does it have multiple antennae inside and use bandpass filters to route signals
to the correct antenna?
>
> I am trying to determine if I can share an antenna between my UAT ADS-B unit
and my Mode S transponder.
>
> Thanks.
>
> Mark
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=491634#491634
>
>
>
>
>
>
>
>
>
Message 2
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| Subject: | Re: Dual Band Antenna Question |
The ad says, "capable of both IN and OUT processing"
Notice that it does not say "simultaneous processing". I assume it can only do
one thing at a time. I agree with Kelly. Avionics equipment determines the
antenna requirements. How could two transmitters and a receiver all be connected
to one BNC connector without interfering with each other?
Follow the avionics manufacturer's instructions. Consider "TED" antennas.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=491645#491645
Message 3
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| Subject: | Re: Dual Band Antenna Question |
> But I query, why then is the 1090Mhz, plus, minus 1Mhz
Good question. The antenna is good for any frequency between 960 MHz TO 1220 MHz.
Why would they pick the center frequency within that range and specify plus
or minus one Mhz?
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=491646#491646
Message 4
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| Subject: | Re: Dual Band Antenna Question |
Mark,I am not familiar with that antenna, but I can tell you what I discove
red.I bought the Echo UAT unit to pair with my classic mode C transponder.
=C2- I contacted Avionix (Echo manufacturer) and they told me to use two
separate antennae separated by the recommended distance.Stan Sutterfield
Subject: AeroElectric-List: Dual Band Antenna Question
From: "markfw" <markwheelermd@icloud.com>
Can anybody explain to me how a dual band antenna like this one:
https://www.dallasavionics.com/comant/ci105-17l.pdf
actually works?
Does it have multiple antennae inside and use bandpass filters to route sig
nals
to the correct antenna?
I am trying to determine if I can share an antenna between my UAT ADS-B uni
t and
my Mode S transponder.
Thanks.
Mark
Message 5
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| Subject: | Re: Dual Band Antenna Question |
At 10:00 PM 10/5/2019, you wrote:
<markwheelermd@icloud.com>
>
>Joe,
>
>That certainly is a possibility, but when you
>look at the web site info, the vendor lists this:
>
>Frequencies Covered
>960-1220 MHz
>1030-1020 MHz
>978 MHz
>1090 =C2=B1 1 MHz
>
>To me this implies that there might be more
>going on than just a wideband antenna.
>
>Mark
Probably not . . .
One of the really neat things about antenna measurement
and design is that most characteristics SCALE very
nicely. So if you're wanting to fiddle around with
a 10MHz antenna (rather big) in the lab, you can
scale down to say 100MHz to do the studies and when
your happy with results, you can multiply by 10 and
be very close to the same qualities on the upscaled
antenna.
So borrowing from those knowledge nuggets, let's
take a look at this antenna. It's a simple, 1/4 wave
antenna I built for a telemetry receiver project
about 20 years ago.
Emacs!
That little red box underneath is a vector
network analyzer.
When you plot it's numbers on a vector network
analyzer, you get something like this
Emacs!
Okay, minimum SWR at about 495 Mhz. The
2:1 SWR 'box' extends from 445 to 660
Mhz. So we can say that this antenna
operated at 775 Mhz has a bandwidth
of 214 MHz for an SWR of 2:1 or better.
Okay, let's 'tighten' the box.
Emacs!
If we wanted to stay below 1.5 to 1
SWR, the operating bandwidth would have
to be bounded at 480 to 527 Mhz for
a total bandwidth of 107 Mhz or about
half of the 2:1 boundaries.
Okay, the advertised 960 to 1220 coverage
has a center frequency of (960+1220)/2 or
1090 Mhz. (1220-960)/1090 gives us a 23% total
published service bandwidth. The bench test
antenna has a 21% bandwidth for 1.5:1 SWR . . .
same church and only one pew further forward.
So I think we can assume that the antenna
you've cited is nothing special . . .
a simple 1/4 wave has a very satisfactory
SWR characteristic over that frequency
range. Those 'bands' are simply
citations of the spectrum used by
the various services ALL of which
fall inside the advertised operating
range for the device.
The bench test antenna was a very
slim wire . . . increasing the diameter
or changing the form factor to a 'blade'
would INCREASE bandwidth. The 'shark
fin' antennas will be better at
transferring signals . . . but not
so much better than you'd see any
difference in your airplane.
Bob . . .
Message 6
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| Subject: | Re: Dual Band Antenna Question |
At 08:24 PM 10/5/2019, you wrote:
>
>I think that it not a dual band antenna. It is a wide band antenna
>that operates at both 978 and 1090 Mhz. Those frequencies are close
>enough together that most transponder antennas will work
>satisfactorily at either frequency. Someone please correct me if wrong.
Correct . . .
Stealing from the spec sheet:
Emacs!
There are 4 frequency ranges cited, 4
SWR limits and 4 Return loss limits
for each of the four frequency ranges.
They appear to have given themselves some
headroom for the total bandwidth and
call out 2.0:1 max . . . I'm betting it's
lower than that.
Return loss is just a another way of
stating SWR measured with a directional
coupler as opposed to an impedance
bridge.
Bob . . .
Message 7
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| Subject: | Re: Dual Band Antenna Question |
At 07:52 PM 10/5/2019, you wrote:
>
>Can anybody explain to me how a dual band antenna like this one:
>
>https://www.dallasavionics.com/comant/ci105-17l.pdf
>
>actually works?
As Joe noted and I demonstrated, it's a
simple antenna with sufficient bandwidth
to offer satisfactory performance on all
those services.
>Does it have multiple antennae inside and use bandpass filters to
>route signals to the correct antenna?
>
>I am trying to determine if I can share an antenna between my UAT
>ADS-B unit and my Mode S transponder.
No, one antenna for EACH system please . . .
Bob . . .
Message 8
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| Subject: | Re: Dual Band Antenna Question |
At 01:29 AM 10/6/2019, you wrote:
>
>But I query, why then is the 1090Mhz, plus, minus 1Mhz
That just MIGHT be the spec-writer's
attempt to speak to a tolerance on the
antenna's center frequency . . . a
relatively insignificant fact.
Bob . . .
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