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Dual Band Antenna Question

 
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markfw



Joined: 28 Feb 2019
Posts: 27
Location: Seattle, WA

PostPosted: Sat Oct 05, 2019 4:52 pm    Post subject: Dual Band Antenna Question Reply with quote

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


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user9253



Joined: 28 Mar 2008
Posts: 1907
Location: Riley TWP Michigan

PostPosted: Sat Oct 05, 2019 5:24 pm    Post subject: Re: Dual Band Antenna Question Reply with quote

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.

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markfw



Joined: 28 Feb 2019
Posts: 27
Location: Seattle, WA

PostPosted: Sat Oct 05, 2019 7:00 pm    Post subject: Re: Dual Band Antenna Question Reply with quote

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 ± 1 MHz

To me this implies that there might be more going on than just a wideband antenna.

Mark


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John M Tipton



Joined: 07 Aug 2018
Posts: 45
Location: Devon - England

PostPosted: Sat Oct 05, 2019 10:31 pm    Post subject: Dual Band Antenna Question Reply with quote

But I query, why then is the 1090Mhz, plus, minus 1Mhz

Sent from my iPad

----x--O--x----

Quote:
On 6 Oct 2019, at 2:24 am, user9253 <fransew(at)gmail.com> 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.

--------
Joe Gores




Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=491635#491635











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Kellym



Joined: 10 Jan 2006
Posts: 1700
Location: Sun Lakes AZ

PostPosted: Sun Oct 06, 2019 4:15 am    Post subject: Dual Band Antenna Question Reply with quote

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:
Quote:


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











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Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD
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user9253



Joined: 28 Mar 2008
Posts: 1907
Location: Riley TWP Michigan

PostPosted: Sun Oct 06, 2019 5:02 am    Post subject: Re: Dual Band Antenna Question Reply with quote

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.


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user9253



Joined: 28 Mar 2008
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PostPosted: Sun Oct 06, 2019 6:01 am    Post subject: Re: Dual Band Antenna Question Reply with quote

Quote:
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?


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speedy11



Joined: 29 Jun 2015
Posts: 61
Location: Port Orange, FL

PostPosted: Sun Oct 06, 2019 7:38 am    Post subject: Dual Band Antenna Question Reply with quote

Mark,
I am not familiar with that antenna, but I can tell you what I discovered.
I bought the Echo UAT unit to pair with my classic mode C transponder. I contacted Avionix (Echo manufacturer) and they told me to use two separate antennae separated by the recommended distance.
Stan Sutterfield

Quote:
Subject: Dual Band Antenna Question

From: "markfw" <markwheelermd(at)icloud.com (markwheelermd(at)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 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


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nuckolls.bob(at)aeroelect
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PostPosted: Sun Oct 06, 2019 6:40 pm    Post subject: Dual Band Antenna Question Reply with quote

At 10:00 PM 10/5/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: "markfw" <markwheelermd(at)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 ± 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.

[img]cid:.0[/img]

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

[img]cid:.0[/img]

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.

[img]cid:.1[/img]

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 . . .


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PostPosted: Sun Oct 06, 2019 6:47 pm    Post subject: Dual Band Antenna Question Reply with quote

At 08:24 PM 10/5/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>

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:

[img]cid:7.1.0.9.0.20191006214029.006c2400(at)aeroelectric.com.0[/img]

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 . . .


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PostPosted: Sun Oct 06, 2019 6:49 pm    Post subject: Dual Band Antenna Question Reply with quote

At 07:52 PM 10/5/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: "markfw" <markwheelermd(at)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?

As Joe noted and I demonstrated, it's a
simple antenna with sufficient bandwidth
to offer satisfactory performance on all
those services.


Quote:
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 . . .


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PostPosted: Sun Oct 06, 2019 6:51 pm    Post subject: Dual Band Antenna Question Reply with quote

At 01:29 AM 10/6/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: John Tipton <john(at)tiptonuk.eu>

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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