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Dual Band Antenna Question

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markfw

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

Posted: Sat Oct 05, 2019 4:52 pm Post subject: Dual Band Antenna Question

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

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Sat Oct 05, 2019 5:24 pm Post subject: Re: Dual Band Antenna Question

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

markfw

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

Posted: Sat Oct 05, 2019 7:00 pm Post subject: Re: Dual Band Antenna Question

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

John M Tipton

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

Posted: Sat Oct 05, 2019 10:31 pm Post subject: Dual Band Antenna Question

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

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Sun Oct 06, 2019 4:15 am Post subject: 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:

 	  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

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

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Sun Oct 06, 2019 5:02 am Post 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

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Sun Oct 06, 2019 6:01 am Post subject: Re: Dual Band Antenna Question

 	  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?

_________________
Joe Gores

speedy11

Joined: 29 Jun 2015
Posts: 62
Location: Port Orange, FL

Posted: Sun Oct 06, 2019 7:38 am Post subject: Dual Band Antenna Question

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

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Oct 06, 2019 6:40 pm Post subject: Dual Band Antenna Question

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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nuckolls.bob(at)aeroelect
Guest

Posted: Sun Oct 06, 2019 6:47 pm Post subject: Dual Band Antenna Question

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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nuckolls.bob(at)aeroelect
Guest

Posted: Sun Oct 06, 2019 6:49 pm Post subject: Dual Band Antenna Question

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 . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Oct 06, 2019 6:51 pm Post subject: Dual Band Antenna Question

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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