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Belly Com Antenna Shadowing

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Daniel.Snow(at)wancdf.com
Guest

Posted: Mon Dec 04, 2006 5:15 am Post subject: Belly Com Antenna Shadowing

I'm getting ready to mount my bent-whip com antenna on the belly of my

RV-9A (tricycle gear).  I would like to mount it near the main landing

gear weldment forward of the spar where the bottom skin is thicker and

where I can easily reach the BNC connector during flight.  Can anyone

give me an idea how much shadowing will occur from the gear leg?



Thanks



Daniel Snow

RV-9A, Electrical

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N777TY

Joined: 09 Apr 2006
Posts: 69
Location: Charlotte, NC

Posted: Mon Dec 04, 2006 6:10 am Post subject: Re: Belly Com Antenna Shadowing

It works fine in that location.

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_________________
RV-7A
N777TY

aurbo(at)ak.net
Guest

Posted: Mon Dec 04, 2006 6:44 am Post subject: Belly Com Antenna Shadowing

Daniel,



I just ordered a bent whip antenna to mount on the belly of the RV-9 I am 

building. I am considering mounting it on the other side of the fuselage so 

that the co-pilot can reach it. Why? I thought that if I ever have a radio 

failure and have to switch to hand held then I will just ask the co-pilot to 

hook up the radio rather than me doing it while trying to fly and navigate. 

If I don't have a co-pilot at that moment then I guess I will get to 

practice my "lost comm." procedures. I remember during my initial flight 

training many years ago my instructor would yank the microphone out of my 

hand and tell me, "The Wright brothers invented the airplane not Marconi, 

FLY the Plane".



Mike Ice

RV-9, Electrical



---

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sportav8r(at)gmail.com
Guest

Posted: Mon Dec 04, 2006 10:12 am Post subject: Belly Com Antenna Shadowing

Why not run coax to a bulkhead jack on the panel so either one of you

can reach it with a patch cord from the handheld?



Regarding antenna location, I doubt you'll notice shadowing from the

gear legs.  I have done my RV-6A this way and it's not an operational

issue.  I abandoned wingtip antennas due to shadowing and a subsequent

turtledeck location due to severe RF in the cockpit (headphones) due

to _lack of_ shadowing.  I could not ameliorate that problem with

ferrites on the headset cabling, so I gave up and moved the comm whip

to the belly between the gear legs where it apparently belongs .



You will likely experience front-end overload when close to another

transmitter- signals will sound garbled- but that's not shadowing and

should not depend much on antenna location anyway.



Best,



-Stormy



On 12/4/06, Michael T. Ice <aurbo(at)ak.net> wrote:

[quote] 



 Daniel,



 I just ordered a bent whip antenna to mount on the belly of the RV-9 I am

 building. I am considering mounting it on the other side of the fuselage so

 that the co-pilot can reach it. Why? I thought that if I ever have a radio

 failure and have to switch to hand held then I will just ask the co-pilot to

 hook up the radio rather than me doing it while trying to fly and navigate.

 If I don't have a co-pilot at that moment then I guess I will get to

 practice my "lost comm." procedures. I remember during my initial flight

 training many years ago my instructor would yank the microphone out of my

 hand and tell me, "The Wright brothers invented the airplane not Marconi,

 FLY the Plane".



 Mike Ice

 RV-9, Electrical



 ---

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G-VANN

Joined: 08 Nov 2007
Posts: 1

Posted: Thu Nov 08, 2007 2:17 am Post subject: Re: Belly Com Antenna Shadowing

I have installed a bent whip antenna in my RV-7A located centrally about 20cm behind the main gear legs and I have had a lot of trouble with it.  I have had trouble with stations close to me and contacting FIS.  I am looking for suggestions.  I want to move it either forward or rearwards.  Rearwards will put it behind the steps which I think are interfering with the signal.  I am also going to mount a straight antenna on top of the aircraft fuselage and connect one to the main com and the other to a through panel 50 ohm bnc connector so that I can connect my handheld to it without fiddling about.  I look forward to hearing any suggestions on belly locations.

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nuckolls.bob(at)cox.net
Guest

Posted: Thu Nov 08, 2007 6:30 am Post subject: Belly Com Antenna Shadowing

At 02:17 AM 11/8/2007 -0800, you wrote:



 	  Quote: 	
		  

<donald.carnegie(at)bilsolutions.co.uk>



I have installed a bent whip antenna in my RV-7A located centrally about 

20cm behind the main gear legs and I have had a lot of trouble with it.  I 

have had trouble with stations close to me and contacting FIS.  I am 

looking for suggestions.  I want to move it either forward or 

rearwards.  Rearwards will put it behind the steps which I think are 

interfering with the signal.  I am also going to mount a straight antenna 

on top of the aircraft fuselage and connect one to the main com and the 

other to a through panel 50 ohm bnc connector so that I can connect my 

handheld to it without fiddling about.  I look forward to hearing any 

suggestions on belly locations.


	


   I would explore other reasons first. It is exceedingly

   difficult to "shadow" a VHF comm antenna so severely

   as to attenuate your signals that bad. Those steps

   will have some influence . . . but it would take

   a carefully controlled setup on the antenna range

   to quantify it.



   Make sure the SWR is good on the antenna as-installed

   and that the transmitter's power output and modulation

   are up to snuff. I've seen deeper "shadows" due to

   local surroundings. I presume you're only having trouble

   on the ground. Does the hand-held with rubber-duck antenna

   work good when the panel mounted radio and belly antenna

   does not?



   Bob . . .

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list(at)toddheffley.com
Guest

Posted: Sun Nov 11, 2007 6:53 pm Post subject: Belly Com Antenna Shadowing

donald



You might consider waiting before you drill another footprint in the  

bottom of the airplane.



My experince is that a Lower bent whip, near the middle of the  

wing/fuselage is an ideal location.



Is it possible that you are fighting a bad antenna/antenna ground, or  

(more likely) a bad coax/coax connector/Rack mount connector....



An interfence with the gear would seem reasonable for a whip mounted  

within an INCH of a gear leg.



I am picturing your installation is a foot from each gear leg...???...

Keep lookn', before you start drillin'.



todd

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