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  #1  
Old 01-01-2018, 12:15 PM
RandyAB RandyAB is offline
 
Join Date: May 2016
Location: St Albert, Alberta, Canada
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Default A couple of antenna questions.

I've searched and haven't found a definitive satisfactory answer for a few questions.

#1] I'm going to be using the Garmin GTX345R as a transponder. Is there a single blade antenna that will allow both ADS-B in and out combined? I believe there is but I can't seem to find which one would be best suited.

#2] Is there any difference at all between the Comant CI 122 and the Rami AV 17 other than price? Are they otherwise identical?

#3] For a cat whisker dipole antenna I'm understanding that a separate ground plane is not needed. Could somebody confirm this?

Thanks and happy new year to all on the board.
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  #2  
Old 01-01-2018, 12:39 PM
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Mike S Mike S is offline
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You might want to check out http://www.deltapopaviation.com/Home.html
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  #3  
Old 01-01-2018, 12:44 PM
BobTurner BobTurner is offline
 
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#3 is correct. If you look at a dipole, you see that it is symmetric with respect to a plane right thru the insulator between the arms. If you put a conducting surface in that plane, it can ‘replace’ one of the dipole arms. That’s why a vertical whip over a ground plane is 1/4 wavelength long, while a dipole is 1/2 wavelength.
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  #4  
Old 01-01-2018, 12:48 PM
BobTurner BobTurner is offline
 
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#1. If an antenna is good for transmitting on some frequency, it will also be good for receiving. But, you need your electronics to provide some sort of switch between the two. No sensitive receivers like having a 200 watt transmitter connected to them.
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  #5  
Old 01-01-2018, 12:58 PM
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Carl Froehlich Carl Froehlich is offline
 
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Quote:
Originally Posted by RandyAB View Post
I've searched and haven't found a definitive satisfactory answer for a few questions.

#1] I'm going to be using the Garmin GTX345R as a transponder. Is there a single blade antenna that will allow both ADS-B in and out combined? I believe there is but I can't seem to find which one would be best suited.

#2] Is there any difference at all between the Comant CI 122 and the Rami AV 17 other than price? Are they otherwise identical?

#3] For a cat whisker dipole antenna I'm understanding that a separate ground plane is not needed. Could somebody confirm this?

Thanks and happy new year to all on the board.
#1, No. You need both a transponder (& ADS-B out) antenna and an ADS-B in antennas.
#2, depends on your form factor preference. All bent whip antennas work the same.
#3, “Cat Whisker” antennas are a half wave dipole. They need not be grounded (but a few might be depending on matching networks). I would recommend you consider instead a wingtip VOR antenna. A well matched antenna will yield reception ranges out to 100nmi and pick up ILS signals way before the approach. Considering the limited (and declining) use of VORs for actual navigation, having a VOR antenna out in the breeze is perhaps not justified.

Carl
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  #6  
Old 01-01-2018, 01:07 PM
RandyAB RandyAB is offline
 
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Location: St Albert, Alberta, Canada
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Quote:
Originally Posted by Carl Froehlich View Post
#1, No. You need both a transponder (& ADS-B out) antenna and an ADS-B in antennas.
#2, depends on your form factor preference. All bent whip antennas work the same.
#3, “Cat Whisker” antennas are a half wave dipole. They need not be grounded (but a few might be depending on matching networks). I would recommend you consider instead a wingtip VOR antenna. A well matched antenna will yield reception ranges out to 100nmi and pick up ILS signals way before the approach. Considering the limited (and declining) use of VORs for actual navigation, having a VOR antenna out in the breeze is perhaps not justified.

Carl
Thanks Car for your answers to my questions. I will look at installing the extra antenna for ADSB. I have the cat whiskers already installed on the VS however so that is a done deal. I just wasn't sure if I needed to worry so much about potential ground plane.
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Last edited by RandyAB : 01-01-2018 at 01:16 PM.
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  #7  
Old 01-01-2018, 01:12 PM
RandyAB RandyAB is offline
 
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Quote:
Originally Posted by Mike S View Post
You might want to check out http://www.deltapopaviation.com/Home.html
Thanks Mike. I did consider them and their product looks nice and is certainly well spoken of here on VAF.

The price is less than the Rami but I can get free shipping from ACS here in Canada which I cannot get from Delta Pop. That mitigates the cost difference somewhat. Also, I'm going to be mounting under the rear seats so the Comant and Ravi antennas which screw in from below will be easier to service with this install. The DP antenna has studs which fasten from the inside as far as I can tell.
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  #8  
Old 01-01-2018, 01:13 PM
RandyAB RandyAB is offline
 
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Quote:
Originally Posted by BobTurner View Post
#3 is correct. If you look at a dipole, you see that it is symmetric with respect to a plane right thru the insulator between the arms. If you put a conducting surface in that plane, it can ‘replace’ one of the dipole arms. That’s why a vertical whip over a ground plane is 1/4 wavelength long, while a dipole is 1/2 wavelength.
Thanks for confirming that Bob. That was what I thought.
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  #9  
Old 01-01-2018, 01:14 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by RandyAB View Post
Thanks Carl. I have the cat whiskers already installed on the VS however so that is a done deal. I just wasn't sure if I needed to worry so much about potential ground plane.
The vertical stabilizer IS a ‘ground plane’ for your set up (assuming it’s aluminum). But if you took it away the antenna would still work the same.
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  #10  
Old 01-01-2018, 02:02 PM
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bkervaski bkervaski is offline
 
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I'm pretty sure the GTX345R only needs 1 antenna, it only has one antenna port.

The units you see with two ports are GPS equipped and that other port is for your GPS antenna.
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