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Comm Antenna Plane - Size?

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darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Wed Jun 18, 2008 2:04 pm Post subject: Comm Antenna Plane - Size?

Here is a question for the masses.  I have my radio and antenna (ICOM A210 and Comant CI-121) installed and working wonderfully (transmission and reception is clear as a bell) except that when I am not receiving or transmitting, I have consistent static...remember transmission and reception is clear.  When I disconnect the coax to the antenna and it goes away.



So, I called and spoke with Comant tech department and they said I need a ground plane (metal plate) that is 3' x 3' to reduce RF static.  This seems huge to me what do you guys think?  I thought it might be an electrical ground issue but he said that the mounting screws to the metal airframe provide the electrical ground.  Any thoughts??  Has anyone put this large a grounding plane on their airframe?

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

peteohms

Joined: 31 Oct 2007
Posts: 224
Location: Leander, TX

Posted: Wed Jun 18, 2008 3:15 pm Post subject: Comm Antenna Plane - Size?

Sounds like a squelch problem.  Do you have a squelch adjustment on the 

radio?



Pete

Kitfox III 912

Hell Paso, TX



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_________________
Pete
Leander, TX
Kitfox III, 912ul, Grove

peteohms

Joined: 31 Oct 2007
Posts: 224
Location: Leander, TX

Posted: Wed Jun 18, 2008 3:17 pm Post subject: Comm Antenna Plane - Size?

Look an page 20 of your manual "squelch test"



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_________________
Pete
Leander, TX
Kitfox III, 912ul, Grove

darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Wed Jun 18, 2008 5:23 pm Post subject: Re: Comm Antenna Plane - Size?

Pete,



I hadn't thought of that...I will look into it tonight and let you know.

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Wed Jun 18, 2008 5:27 pm Post subject: Comm Antenna Plane - Size?

1/4 wave length of 125mHz is around 23.6 in.  That is the minimum radius a

ground plane should be.  However there is no where that it states that a

ground plane need be solid.  Many radio stations only use a flower pattern

of wires under the ground and connected together at the outer edge. 

 

Back to reality



Com radios operate a considerably higher frequencies so the ground plane,

like the radiator can be considerably smaller.  You could easily glue a

ground plane of tin foil to the inside of your fuselage.  That won't cost

you a big weight penalty or a ton of buck$ either.  



Personally, it sounds to me like you don't have your squelch set or you are

running a 582 without both resistor caps and plugs.  That engine is a bit of

an oddball for needing both resistances.



Noel



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_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

gary.algate(at)sandvik.co
Guest

Posted: Wed Jun 18, 2008 6:18 pm Post subject: Comm Antenna Plane - Size?

My Ground plane is made out of Fly wire screen - I don't know if it's doing a lot but I have no noise in my radio at all. (apart from me and the person at the other end!) - I would be looking at the squelch control also as it appears to be pointing that way. 

 

Noisy radios can be damn frustrating

 

 Gary Algate

 Classic 4 Jab2200

 Office Phone: +61 8 8276 7655

 

 

 This e-mail is confidential and it is intended only for the addressees. Any review, dissemination, distribution, or copying of this message by persons or entities other than the intended recipient is prohibited. If you have received this e-mail in error, kindly notify us immediately by telephone or e-mail and delete the message from your system. The sender does not accept liability for any errors or omissions in the contents of this message which may arise as a result of the e-mail transmission. 

 



 

 

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Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Wed Jun 18, 2008 9:52 pm Post subject: Comm Antenna Plane - Size?

At 03:04 PM 6/18/2008, you wrote:

 	  Quote: 	
		  This seems huge to me what do you guys think?  I thought it might be 

an electrical ground issue but he said that the mounting screws to 

the metal airframe provide the electrical ground.  Any 

thoughts??  Has anyone put this large a grounding plane on their airframe?


	


         The metal frame IS the ground-plane, at least in all 

Kitfoxes I know. It does mean you need a really good electrical 

connection between the antenna base and the metal frame; no paint, 

etc. However, I don't think that's your problem. When I've had ground 

plane problems I've lost signal, meaning I had trouble sending and 

receiving. I agree with Pete, it sounds like a squelch problem in the 

radio or intercom.

Guy Buchanan

San Diego, CA

K-IV 1200 / 582-C / Warp / 100% done, thanks mostly to Bob Ducar.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Wed Jun 18, 2008 10:57 pm Post subject: Re: Comm Antenna Plane - Size?

Well, you all hit it on the head.  It was a squelch issue with the radio.  This will show how much of a novice I am but I didn't even realize the radio had an internal squelch setting...I knew my intercom did but not the radio.  I busted out my manual and found the squelch setting menu - it was set at 0 so I turned it one increment at a time and by the time I hit 3 the static was only intermittent...by 5 it was completely gone.  Made a radio check and all is working great.



Guy, my thinking is that the airframe acts as a large ground plane also.



Well, problem fixed...on to the next one whatever it might be.  Thanks guys!

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

mikeperkins

Joined: 22 May 2007
Posts: 123

Posted: Thu Jun 19, 2008 6:57 am Post subject: Re: Comm Antenna Plane - Size?

Glad your problem was fixed with squelch. You folks are good. I've read some of the other posts and would like to I'll reply to the ground plane issue. I've done some RF design and antenna design in my professional life, and have also installed antennas on airplanes, including a couple of Kitfoxes.  



A ground plane is definitely necessary. It should be a metal plate where the diameter is at least as wide as the antenna is long. The antenna should be mounted very close to the center of the plate, no matter what size it is. 



The ground plane is the "RF signal ground reference." It's not like a DC power ground such as aircraft ground. Aircraft antennas are designed specifically to be fastened to a metal plate. So the frame tubing does not make a good ground. It's not because it's a "bad" ground, but because the antenna is simply not designed to work with it. 



With ground planes, size DOES matter, but for a Comm antenna, you can get away with a plate that's about a foot in diameter. Bigger is better, up to three feet in diameter, but mine is 10" and works fine. However, it should be as thick as practical, though, up to 1/8" thick. (Yes, thickness matters, too. Aluminum foil is too thin, but 1/16" thick sheet stock works fine. Aluminum or steel window screen isn't as good as 1/16" stock, but it will work if you need to get around corners, but it's not my first choice.) The ground plane can be square, but go ahead and trim the corners to somewhat of an octagon shape because the excess beyond a circle is just extra weight and none of us like sharp edges. 



It is not necessary to connect the ground plane to the aircraft ground. In fact don't even bother because it has a better chance of hurting signal strength rather than helping. The ground plane is connected to the radio through the antenna and the co-ax cable, so just let it "float." 



Between the antenna base and the mounting location, make sure there's no paint or primer. You might even do a little cleaning of both the antenna base and the sheet stock to get good metal-to-metal contact, not oxide to oxide. Don't put a gasket between the antenna base and the sheet - if you need weather-proofing, put sealant around the antenna base. They tell you also not to paint the antenna. That's because the RF signal doesn't get through many of the pigments (acts like shielding) and can also actually "short out" the RF signal to the airframe. 



I put my ELT antenna inside my Kitfox airframe, just hanging upside-down from a 6" diameter plate right behind the seat. It works quite well (it's been accidentally tested by satellites). My Comm antenna is mounted outside, hanging down from the fuselage with a 10" diameter plate for a ground plane. It works fine, too. I cut a hole in the fabric for the antennal base so it could directly contact the metal ground plane. 



As an aside, I've made my own transponder antenna for about $3 per Jim Weir's write-up. I've also made fiberglass-and-copper antennas for $5 according to his articles and they work great. Some don't require ground planes, either. His articles are a great do-it-yourself antenna resource. 



- Mike Perkins

Kitfox N175KF

Havana, Illinois

n85ae

Joined: 14 Mar 2007
Posts: 403

Posted: Thu Jun 19, 2008 9:24 am Post subject: Re: Comm Antenna Plane - Size?

Providing you do a good installation, with good grounds, etc. the airframe

is plenty good all by itself as a ground plane. I had a friendly controller at 

our airport who I did a series of radio checks with and he was still reading 

me loud and clear at 100 miles out. I have a KX-155 with a RA Miller

comm antenna (I think it's a 529)



Jeff

michaega(at)verizon.net
Guest

Posted: Thu Jun 19, 2008 10:16 am Post subject: Comm Antenna Plane - Size?

Darin, 

  

Did you use the standard antenna mounting plate that Kitfox welded on your model 7. I have the exact combo as you describe. So you just mounted directly to the rectangular antenna mount and made adjustments to the A210??   

  

George 

  



 ---

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Thu Jun 19, 2008 11:27 am Post subject: Comm Antenna Plane - Size?

Right on Mike:  

   

I did the calculation  (300/Center Freq)/4 = the normal length of the antenna (23 in convert from meters)  

   

Optimal minimum size of the ground plane should be around 46in.  Which I'm the first to admit is overkill.  Com antennas are vertically polarized which gives good Omni directional coverage.  Having a good ground plane will help you get the best possible signal, Rx and TX.    

   

My advice has always been to use foil under the skin as a ground plane but one poster here mentioned fly screen which is a lot more durable just make sure you don't use nylon screen .  

   

As I'm sure you know most problems with Com radios can be traced back to corrosion if the antenna installation...  A word to the wise, keep it clean.  

   

   

[img]cid:image003.jpg(at)01C8D22D.24509040[/img]  

   

Noel Loveys  

Campbellton, NL, Canada  

CDN AME intern, PP-Rec  

C-FINB, Kitfox III-A  

582 B box, Ivo IFA, Aerocet 1100 floats  

[url=noelloveys(at)yahoo.ca]noelloveys(at)yahoo.ca[/url]  

   

   

   

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_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

n85ae

Joined: 14 Mar 2007
Posts: 403

Posted: Thu Jun 19, 2008 12:17 pm Post subject: Re: Comm Antenna Plane - Size?

The ground plane does not need to be a plate, the tubing itself works fine.

Think about a simple dipole antenna, which could be made from splitting

the coax and point the center conductor ~21" in one direction and the 

shield in the other. This is a really basic antenna, but it would work

plenty fine for Comm. If you attach to the airframe and aren't getting

good reception - 99.99% of the time it can be traced back to a poor 

connection OR a piece of bad equipment. Seriously you'll simply not 

find a case where the airframe ALONE as a ground plane  causes any

problems.



Regards,

Jeff

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Thu Jun 19, 2008 5:03 pm Post subject: Comm Antenna Plane - Size?

First of all what you say will work...  I’ve done it many times on many different bands...BUT Coax is unbalanced line so to get the most out of it you should use a balun (Balanced-unbalanced) which is similar to a transformer.  One thing you have missed is on the dipole the two radiators are 180deg to each other.  With the vertical antenna the ground plane is 90 degrees to the radiator.  The better the ground plane the better the signal.  This is not to say that you can’t get reasonable use out of the frame of the plane but at a hundred miles out you will probably find the reception better in one direction than the other.  The ground plane will help ensure optimal operation in all directions.  

   

I agree with you that over 90% of the time com problems are easily traced to corrosion (bad grounds)  unfortunately these problems can compound themselves and end up over heating the final RF amplifiers in the transmitter section of your radio.  Except for that I’d say close to 100% of problems can be traced to corrosion somewhere in the antenna circuit.  0.01%of the time faults can be caused by vibration and faulty power supply.  

   

   

[img]cid:image001.jpg(at)01C8D25B.A8AE20E0[/img]  

   

Noel Loveys  

Campbellton, NL, Canada  

CDN AME intern, PP-Rec  

C-FINB, Kitfox III-A  

582 B box, Ivo IFA, Aerocet 1100 floats  

[url=noelloveys(at)yahoo.ca]noelloveys(at)yahoo.ca[/url]  

   

   

   

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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

n85ae

Joined: 14 Mar 2007
Posts: 403

Posted: Fri Jun 20, 2008 5:56 am Post subject: Re: Comm Antenna Plane - Size?

Noel -



Well I'm just making the point that reality is that if you simply do a nice clean

installation it will work,well. If you screw it up it will not work well. If you 

install a nice big ground plane, and fine tune the antenna length, consult

the RF gods, etc, and do a bunch of incantations, it might possibly make

a slightly noticeable difference, or not ....



Radio choice makes a big difference as well. I have a Garmin GNC-250XL 

and a Bendix King KX-155 in mine. The KX-155 definetly is the better

radio for Comm. Both my antenna's are the same type, and even if I

switch antenna's the King simply out perform's the Garmin.



The Garmin is a very GOOD Gps/Comm and I would not get rid of it,

but the KX-155 is a better workhorse radio. 



A friend of mine spent half of last decade trying to get his Microair 760 

to get good range, but never got where he was happy with it.



Best Regards,

Jeff

darinh

Joined: 20 Apr 2006
Posts: 327
Location: Utah

Posted: Fri Jun 20, 2008 7:11 am Post subject: Re: Comm Antenna Plane - Size?

 	  michaega(at)verizon.net wrote: 	
		  Darin, 

  

Did you use the standard antenna mounting plate that Kitfox welded on your model 7. I have the exact combo as you describe. So you just mounted directly to the rectangular antenna mount and made adjustments to the A210??   

  

George 

  



 --- 	




George,



Yes, sort of.  My antenna came with a cork gasket and I didn't want to cut the fabric off the plate if I didn't need to.  According to Comant (maker of my antenna), the mounting bolts provide the required ground to the airframe.  Mine is working great right now and even inside my hangar (steel building) I get great reception and transmission so it appears to be working.  I have yet to fly the airplane so I don't know if I will how far I can receive from, although I can pick up KSLC tower and it is a good 25 miles away (this is also inside my hangar).  If you have any issues with your setup, I may be able to help seeing how I have spent the last 2 weeks looking at mine.

_________________
Darin Hawkes
Series 7
914 Turbo
Kaysville, Utah

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Jun 20, 2008 9:36 am Post subject: Comm Antenna Plane - Size?

I don't know about consulting the RF gods but Amen to what you said  LOL!



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

n85ae

Joined: 14 Mar 2007
Posts: 403

Posted: Fri Jun 20, 2008 10:18 am Post subject: Re: Comm Antenna Plane - Size?

Noel -



Ok, so we agree - The main things would be good clean installation, and

muttered incantations (very important)? 



Consulting the RF gods, and ground plane mods - Can be considered

optional?



Regards,

Jeff

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sat Jun 21, 2008 5:20 am Post subject: Comm Antenna Plane - Size?

As a ham radio operator I am, in theory at least, always trying to get the ultimate out on my radios.  This is not necessary in small planes.  That is the reason I totally agree with you on the necessity of a ground plane.  I’ve even used handhelds inside the ‘Fox on a duck with decent results.  

   

As an AME (Aircraft Maintenance Engineer) intern (Canada) I really appreciate a nice clean installation and a nice clean interconnect diagram for the scarce occasion that things go west J.  Of course with only an antenna connection there isn’t a diagram needed.  

   

   

[img]cid:image003.jpg(at)01C8D38C.593A3C10[/img]  

   

Noel Loveys  

Campbellton, NL, Canada  

CDN AME intern, PP-Rec  

C-FINB, Kitfox III-A  

582 B box, Ivo IFA, Aerocet 1100 floats  

[url=noelloveys(at)yahoo.ca]noelloveys(at)yahoo.ca[/url]  

   

   

   

   

   

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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

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