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VHF antenna mounting

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wgill10(at)comcast.net
Guest

Posted: Mon Jul 24, 2006 6:20 pm Post subject: VHF antenna mounting

Hello All,  

   

I’m mounting two VHF bent whip antennas on the belly of an RV-7. Where can I find information pertaining to doubler requirement? Also, a cork gasket/seal is installed between the Comant antenna base and the fuselage skin – is the antenna base grounded to the fuselage via the mounting screws since the cork seal insulates the antenna base? Thanks.  

   

Bill Gill  

RV-7 wiring  

Lee’s Summit, MO

jmoreau2(at)cox.net
Guest

Posted: Mon Jul 24, 2006 6:58 pm Post subject: VHF antenna mounting

What position are you mounting them in.  I am getting ready for bent whips on the belly of my RV8A.  I was wondering how close together you are mounting them.Are they side=by side, or in line with the centerline of the fuselage.  Any info would be appreciated.

Jeff Moreau

Virginia Beach, VA

On Jul 24, 2006, at 10:15 PM, William Gill wrote:

 	  Quote: 	
		  

Hello All,

 

I’m mounting two VHF bent whip antennas on the belly of an RV-7. Where can I find information pertaining to doubler requirement? Also, a cork gasket/seal is installed between the Comant antenna base and the fuselage skin – is the antenna base grounded to the fuselage via the mounting screws since the cork seal insulates the antenna base? Thanks.

 

Bill Gill

RV-7 wiring

Lee’s Summit, MO

wgill10(at)comcast.net
Guest

Posted: Mon Jul 24, 2006 7:14 pm Post subject: VHF antenna mounting

Hello Jeff,  

   

I’m mounting them side by side…they are about 32” apart.  

   

Bill  

   

--

FLYaDIVE(at)aol.com
Guest

Posted: Tue Jul 25, 2006 1:21 am Post subject: VHF antenna mounting

In a message dated 7/24/06 10:23:27 PM Eastern Daylight Time, 

wgill10(at)comcast.net writes:



 	  Quote: 	
		   Hello All,

   

  I'm mounting two VHF bent whip antennas on the belly of an RV-7. Where

  can I find information pertaining to doubler requirement? Also, a cork

  gasket/seal is installed between the Comant antenna base and the

  fuselage skin - is the antenna base grounded to the fuselage via the

  mounting screws since the cork seal insulates the antenna base? Thanks.

   

  Bill Gill

  RV-7 wiring

  Lee's Summit, MO

==================================
	


Bill:



It is just good practice to reinforce an antenna mounting with a doubler.  In 

most if not all antenna packages a doubler is supplied.

Considering the design of an antenna you have a lot of unsupported material 

just dangling out in the breeze, better to support it than to take the chance 

of metal fatigue due to concentrated vibration points.



As for the electrical grounding ... YES ... You are correct, the grounding is 

accomplished through the screws.  So you can imagine that a doubler installed 

against the unpainted aluminum, followed up with good screws and lock washers 

will do much to improve everything associated with the ground and function of 

the antenna.



One small trick with the cork seal, put a light smear of RTV on both sides of 

the cork.  This is not a major trick but it will keep out moisture and 

improve the seal.



Barry

"Chop'd Liver"



"Show them the first time, correct them the second time, kick them the third 

time." 

Yamashiada

FLYaDIVE(at)aol.com
Guest

Posted: Tue Jul 25, 2006 2:52 am Post subject: VHF antenna mounting

In a message dated 7/24/06 11:01:15 PM Eastern Daylight Time, 

jmoreau2(at)cox.net writes:



 	  Quote: 	
		   What position are you mounting them in.  I am getting ready for bent  

  whips on the belly of my RV8A.  I was wondering how close together  

  you are mounting them.

  Are they side=by side, or in line with the centerline of the  

  fuselage.  Any info would be appreciated.

  Jeff Moreau

  Virginia Beach, VA

=============================
	


Jeff:



By definition bent whips are belly mounted.  

Keeping antennas as far apart as possible is always a good thing.  If I 

recall the minimum distance recommended is 36" .  Yet that is very hard to 

maintain.  I have two mounted on the belly under the leg area of an RV-6 only about 

20" apart.  I do not have any front end overload or directivity to the pattern.  

If I was building the plane and had access to the tail easier I would install 

them in line on the center line (rivets permitting) and the recommended 36+" 

apart.



You might also want to take note that COM #2 is usually mounted on top of the 

plane.  This is to aid in better ground communication while on the ground.  

While Com #1 is used in the air.  Once airborne Com 1 & 2 do work very well in 

the air.

Barry

"Chop'd Liver"



"Show them the first time, correct them the second time, kick them the third 

time." 

Yamashiada

Hopperdhh(at)aol.com
Guest

Posted: Tue Jul 25, 2006 5:22 am Post subject: VHF antenna mounting

 

 Bill,

  

 I riveted 2 short pieces of leftover stiffener material from the  fuselage across between the seat ribs that the antenna screws go up through (for  one antenna).  The antenna feels pretty solid with very little weight  gain.

  

 Dan Hopper

 RV-7A

  

  

 In a message dated 7/24/2006 10:23:27 P.M. Eastern Daylight Time,  wgill10(at)comcast.net writes:

  	  Quote: 	
		        

Hello    All,   

    

Iâ€™m mounting two VHF bent whip    antennas on the belly of an RV-7. Where can I find information pertaining to    doubler requirement? Also, a cork gasket/seal is installed between the Comant    antenna base and the fuselage skin â€“ is the antenna base grounded to the    fuselage via the mounting screws since the cork seal insulates the antenna    base? Thanks.   

    

Bill    Gill   

RV-7    wiring   

Leeâ€™s    Summit, MO

gmcjetpilot(at)yahoo.com
Guest

Posted: Tue Jul 25, 2006 6:22 am Post subject: VHF antenna mounting

Bill:

   

  Yes the ground is thru the screws so make sure there is no 

primer and the nut plates are grounded to the airframe, 

assuming you will use nut plates which is highly recommend. 

   

  The primary load is air drag load, which is very small. You 

can go crazy and make very large structural doubler's. Back 

in the old days with huge ADF and VOR flying wing antenna's 

structural doubler's where important. Your light weight bent 

com antenna is tiny compared to those lead sails.

   

   

  The belly on the RV is very thick. If you are in the area fwd of 

the main spar, not much doubling is needed. You do want local 

stability to keep it from flexing.

   

  Old FAA best practices AC 43 12-2A (chap 1)

structures, shows antenna doubler's. 

   

  Here are some ideas from the FAA AC source:

    

   

  If you place the antenna near a stiffener or rib, a good idea, 

you can bend an angle into the doubler to joggle or butt 

against the rib or angle and rivet to that. It's standard. to 

fill the whole BAY from stiffener to stiffener laterally wide. Your 

doubler will be square/rectangle from stiffener to stiffener and 

the width, fwd/aft, will be long enough to extend past the 

antenna foot print by 1.5" min on each end or to a frame.

The above is ideal an very strong but not needed for a 

small COM antenna on a thick skin belly. If you put the 

antenna near a stiffiner the doubler may not be needed, 

at least on the RV forward belly. 

   

  

A traditional doubler, lets say just plop it right in the middle 

of a skin bay, has the same foot print but twice as large and 

one gage up from the basic material.  

   

  So with a COM antenna  you would have a tear drop airfoil 

shape about 8.5" long x 5.25 wide (approx give or take). Min 

edge width or edge margin should be 1.5" from edge of 

antenna foot print.  You don't necessarily need to attach to 

a nearby stiffener or frame but depends on the skin thickness 

and size of antenna.

   

  What some do is make a local doubler with the nut plates 

and than attach the doubler to the skin with just a few rivets. 

That way you are not putting a bunch of small 3/32 rivets 

for the nut plates into the structural skin. Just make sure 

the screws have a ground path to the airframe with bare 

metal or ground straps.   

   

  I suggest you put the COM antenna on the pilot side, just 

forward of the spar. You can make access to the coax while 

fairly well protected and out of the way. If you ever want to 

attach a portable radio to it you just reach down and  

remove the coax and attach a coax jumper from the antenna 

to the handheld radio (emergency only). Just a suggestion or 

idea. You can get fancy with panel splitters and so on but 

this is simple and works. Just don't TX with the main radio 

if the antenna is not connected of course.

   

  Bottom line you want the whip part of the antenna to 

bend or brake before wrinkling the skin. 

   

   

  Cheers George M, RV-4, RV-7

   

   

  >From: "William Gill" <wgill10(at)comcast.net (wgill10(at)comcast.net)>

 	  Quote: 	
		  I'm mounting two VHF bent whip antennas on the belly of an 

RV-7. Where can I find information pertaining to doubler 

requirement? Also, a cork gasket/seal is installed between the 

Comant antenna base and the fuselage skin - is the antenna 

base grounded to the fuselage via themounting screws  since 

the cork seal insulates the antenna base? Thanks.

  
	


 

   

   



  	 	 Get on board. [url=http://us.rd.yahoo.com/evt=42298/*http://advision.webevents.yahoo.com/handraisers]You're invited[/url] to try the new Yahoo! Mail Beta.

jmoreau2(at)cox.net
Guest

Posted: Tue Jul 25, 2006 8:21 am Post subject: VHF antenna mounting

Thanks Bill

On Jul 24, 2006, at 11:11 PM, William Gill wrote:

[quote]

Hello Jeff,

 

I’m mounting them side by side…they are about 32” apart.

 

Bill

 

--

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Tue Jul 25, 2006 2:24 pm Post subject: VHF antenna mounting

On Jul 25, 2006, at 9:15 AM, Hopperdhh(at)aol.com wrote:



 	  Quote: 	
		  

 Bill,



 I riveted 2 short pieces of leftover stiffener material from the  

 fuselage across between the seat ribs that the antenna screws go up  

 through (for one antenna).  The antenna feels pretty solid with  

 very little weight gain.


	


Good. When I worked at a radio shop many, many years ago I was taught  

how to install antennas. The long and short of it was:



1. Always put in a doubler. Make it at least 4" (10cm) square if  

possible but bigger is better. Rivet it in and liberally use zinc  

chromate. (Remember, this was back in the early 1970's and we weren't  

using two-part epoxy primers then.)



2. Don't use the cork gasket that comes with the antenna. They never  

really seal well but they do a good job of keeping the moisture in  

once it gets in and this tends to corrode things. Use a good sealant  

instead.  If the bushings are long enough that it creates a  

significant gap use an aluminum spacer.



3. Where the antenna's mounting bushings contact the aircraft skin,  

make sure the paint is removed to ensure a good electrical contact.



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

wgill10(at)comcast.net
Guest

Posted: Tue Jul 25, 2006 5:55 pm Post subject: VHF antenna mounting

Thank you ALL for the great info. Maybe I'll have a com radio going by

this weekend.



Bill

--

nuckollsr(at)cox.net
Guest

Posted: Tue Jul 25, 2006 7:44 pm Post subject: VHF antenna mounting

At 08:52 PM 7/25/2006 -0500, you wrote:



[quote]



Thank you ALL for the great info. Maybe I'll have a com radio going by

this weekend.



Bill

--

rd2(at)evenlink.com
Guest

Posted: Wed Jul 26, 2006 4:43 am Post subject: VHF antenna mounting

_____________________Original message __________________________

                  (received from Robert L. Nuckolls, III; Date: 10:36 PM

7/25/2006 -0500)

________________________________________________________________



----other inserts snipped-----



   I published a mate-up sketch to the website a few months ago:



http://www.aeroelectric.com/Pictures/Antenna/Antenna_Installation.gif



   The emphasis for "grounding" the base of the antenna to structure

   needs to concentrate on the areas around fasteners where mate-up

   pressures assure the "gas tight" condition. Removal of paint or

   material surface protection any place else is a waste of time and

   only exposes those surfaces to the ravages of atmosphere. All the

   magic happens right around the screws and no place else.



   Bob . . .



----------------------------



Bob,

Speaking of the magic (grounding the base) - looking at the

Antenna_Installation.gif ,

I have seen toothed lock washers used between the doubler plate and skin.

This was on a Cessna. The doubler plate was not riveted to the skin (it

came with with the antenna replacement kit). The lock washer assured better

el contact (grounding). They used externally toothed lock washers, as per

attached. Maybe a better idea would be to use the external-internal toothed

type washers (also attached). Opinions?



Rumen

External-Type-Lock-Washers.jpg

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nuckollsr(at)cox.net
Guest

Posted: Wed Jul 26, 2006 8:35 am Post subject: VHF antenna mounting

At 08:18 AM 7/26/2006 -0400, you wrote:



 	  Quote: 	
		  _____________________Original message __________________________

                   (received from Robert L. Nuckolls, III; Date: 10:36 PM

7/25/2006 -0500)

________________________________________________________________



----other inserts snipped-----



    I published a mate-up sketch to the website a few months ago:



http://www.aeroelectric.com/Pictures/Antenna/Antenna_Installation.gif



    The emphasis for "grounding" the base of the antenna to structure

    needs to concentrate on the areas around fasteners where mate-up

    pressures assure the "gas tight" condition. Removal of paint or

    material surface protection any place else is a waste of time and

    only exposes those surfaces to the ravages of atmosphere. All the

    magic happens right around the screws and no place else.



    Bob . . .



----------------------------



Bob,

Speaking of the magic (grounding the base) - looking at the

Antenna_Installation.gif ,

I have seen toothed lock washers used between the doubler plate and skin.

This was on a Cessna. The doubler plate was not riveted to the skin (it

came with with the antenna replacement kit). The lock washer assured better

el contact (grounding). They used externally toothed lock washers, as per

attached. Maybe a better idea would be to use the external-internal toothed

type washers (also attached). Opinions?


	


    We're really slice'n and dice'n mouse hairs here. Obviously

    the goal is to get a low ohms connection between the antenna

    base and the skin that is as good 10 years from now as it is

    the day we bolt it on.  This comes down to a few simple-ideas:

    (1) pressure high enough to bring two clean surfaces into intimate

    gas tight contact with each other and (2) exclusion of environmental

    effects that include (a) contaminants and (b) loosening that work

    against condition (1).



    Some designers embrace the idea that the toothed lockwashers

    provide a multitude of very high pressure points . . . even to

    the point of upsetting metal at the points of contact to achieve

    (1). My concerns are that a toothed washer is a spacer between

    the two surfaces that may contribute to initial joint quality (1)

    but leaves the gap "open" for ingress of (a).



    In all of our bonding specs at RAC, the use of lockwashers is

    never suggested. Self locking all metal nuts are the preferred

    anti-loosening technology. In the sketch I published, 99% of the

    magic needs to happen in the area just around the screw hole and

    between skin and antenna base. All other "prepared" areas add

    only marginally to the quality of the joint.



    Obviously, the "99% conductivity area" is of very small gap and

    the only thing one might add is sealant or anti-moisture guckum (Like

    silocone grease) to fill the tiny void around the periphery

    of the 99% area to prevent entry of oxidizing agents. Beyond

    that, maintainance of pressure over time is enhanced by use

    of largest practical hardware torqued to upper limits and

    secured with some form of locking technology . . . all metal

    locknuts being the technology of choice.



    When we were selling contactors with treaded studs for fat wires,

    the split-ring, steel washers supplied were discarded and replaced with

    internal tooth, phosphor bronze lockwashers. The supplied steel

    nuts were replaced with brass. Again, the lion's share of conductive

    magic happens were the terminal comes down against the bottom nut.

    The lockwasher and nut on top contributes to conductivity but

    only a tiny fraction of the total.



    Bob. . .

FLYaDIVE(at)aol.com
Guest

Posted: Wed Jul 26, 2006 8:37 am Post subject: VHF antenna mounting

In a message dated 7/26/06 8:48:44 AM Eastern Daylight Time, rd2(at)evenlink.com 

writes:



 	  Quote: 	
		   I have seen toothed lock washers used between the doubler plate and skin.

  This was on a Cessna. The doubler plate was not riveted to the skin (it

  came with with the antenna replacement kit). The lock washer assured better

  el contact (grounding). They used externally toothed lock washers, as per

  attached. Maybe a better idea would be to use the external-internal toothed

  type washers (also attached). Opinions?

  

  Rumen

=====================
	


Rumen:



By putting washers between the skin and the doubler you do not create a 

doubler, the would-be doubler now becomes a spring and you also create individual 

stress points at each screw.  Their may also be some crazy RF issues; better to 

do it like the book/manufactur says.  

The idea of improving the ground contact is good but that can be done with a 

clean surface, snug screw holes and star washers under the nuts.

The type of star washer you suggest is perfectly acceptable.  Just not 

between the skin and doubler.

Barry

"Chop'd Liver"



"Show them the first time, correct them the second time, kick them the third 

time." 

Yamashiada

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