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messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Fri Nov 11, 2011 10:44 am Post subject: antenna connections

I read through stuff Bob has written about making VHF antennas. Here's how I understand it.



Coaxial cable has a center conductor and outer shield. The connector at the end of the cable connects the shield to the shell of this female connector, which gets screwed onto the male threaded barrel of the antenna mount. This part of the antenna mount is connected to the metal skin, which forms the ground plane.



The inner conductor wire connects to the inner conductor of the antenna mount, which is isolated from the surrounding male threaded barrel and hex portion that mounts inside the aircraft. The inner conductor of the mount is electrically connected to the 3/8" male threaded stud, which is also connected to the adapter, bolt, and antenna whisker.



To install this ebay mount, it looks like I'd remove the 3/8" female threaded hex barrel adapter, star washer, and what looks like an insulating shoulder washer. From the inside of the aircraft, insert the 3/8" male stud through the doubler and skin, then slide the shoulder washer and star washer on from the outside. Tighten the hex barrel adapter over the stud, then the bolt/antenna whisker.



If I've understood it correctly, there wouldn't then be an issue with lock-washer centering, which I didn't understand in the first place.



Thanks,

Dan

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_________________
Dan

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Nov 11, 2011 5:55 pm Post subject: antenna connections

At 12:44 PM 11/11/2011, you wrote:

 	  Quote: 	
		  



To install this ebay mount, it looks like I'd remove the 3/8" female 

threaded hex barrel adapter, star washer, and what looks like an 

insulating shoulder washer. From the inside of the aircraft, insert 

the 3/8" male stud through the doubler and skin, then slide the 

shoulder washer and star washer on from the outside. Tighten the hex 

barrel adapter over the stud, then the bolt/antenna whisker.



If I've understood it correctly, there wouldn't then be an issue 

with lock-washer centering, which I didn't understand in the first place.


	


   There's an article on the materials and process at:



http://aeroelectric.com/articles/Antennas/DIY_Comm_Ant/DIY_Comm.html



   I modify the adapter in a lathe to provide

   a centering shoulder for the lock-washer.



   Bob . . .

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Fri Nov 11, 2011 6:32 pm Post subject: Re: antenna connections

Yes, thanks, Bob. I should have mentioned that's where I got most of my info. This ebay mount has a so239 to connect to, which would take a pl259 on the cable end. I'm thinking of getting that mount from ebay and the cable from you. Would you have a pl259 to go onto that? Depending on where I locate the antenna, I might need a 90 on one or both cable ends. If you don't have those, would I be able to send them to you?



Speaking of antenna location, I've heard it's not good to get the xpdr and com antennas closer together than 5', 3', or 22". Could you shed some light on this?



One last thing. The 1/8" SS piano wire (or welding rod?) can be soldered to the bolt with my Kester 44?



Thanks,

Dan

_________________
Dan

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Nov 11, 2011 9:21 pm Post subject: antenna connections

At 08:32 PM 11/11/2011, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "messydeer" <messydeer(at)yahoo.com>



 Yes, thanks, Bob. I should have mentioned that's where I got most of my info. 	


  Okay, good.



  	  Quote: 	
		   This ebay mount has a so239 to connect to, which would take a pl259 on the cable end. I'm thinking of getting that mount from ebay and the cable from you. Would you have a pl259 to go onto that? Depending on where I locate the antenna, I might need a 90 on one or both cable ends. If you don't have those, would I be able to send them to you? 	


   I have rt-angle BNC connectors. Suggest you put

   a UHF to BNC adapter on the antenna mount



 [img]cid:7.1.0.9.0.20111111231035.01dd8338(at)aeroelectric.com.0[/img] 



   and use right-angle BNC's to finish up the

   task. I can craft cables to your needs.

   



 

  	  Quote: 	
		  Speaking of antenna location, I've heard it's not good to get the xpdr and com antennas closer together than 5', 3', or 22". Could you shed some light on this? 	


   Most transponder antennas go on the belly and

   comm antennas on top. If both are on belly, then

   just get them as far apart as possible.



  	  Quote: 	
		  One last thing. The 1/8" SS piano wire (or welding rod?) can be soldered to the bolt with my Kester 44? 	


   No, silver solder. Tin lead is too weak and won't flow

   to stainless.



 

   Bob . . .

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messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Fri Nov 11, 2011 11:09 pm Post subject: Re: antenna connections

Thanks 



I'll be mounting both xpdr and com antennas on the bottom. I could get 36" between them without a problem.



I looked over silver soldering. Had thought that was an old saying for 'soldering'. Another option would be to get a SS whip antenna, like this from Radio Shack: http://www.radioshack.com/product/index.jsp?productId=2102428&CAWELAID=107599032 It's 102" but has a 3/8-24 fitting. Cutting it down would be no problem, but putting a 45 bend could be. I assume this would be a tube that could kink. 



ACS has one for about $20, but I thought I read someone say it didn't have the standard fitting, which seems odd. I'll have to check with them.

_________________
Dan

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Nov 12, 2011 7:40 am Post subject: antenna connections

At 01:09 AM 11/12/2011, you wrote:

 	  Quote: 	
		  



Thanks 



I'll be mounting both xpdr and com antennas on the bottom. I could 

get 36" between them without a problem.


	


   That will be plenty . . .

 	  Quote: 	
		  I looked over silver soldering. Had thought that was an old saying 

for 'soldering'.


	


    Soldering is a generic term for joining two metals (which

    may be alloys) with a dissimilar third metal (which can

    also be an alloy).



    Welding is the jointing of the first two metals

    by melting a similar metal into the surface of the two.

    Soldering DISSOLVES a molecular layer of the two bases

    into a fluid third without actually melting the bases.



    Brazing is a form of soldering. We commonly

    think of "solder" as being that legacy tin/lead stuff

    for wiring, copper roofing and stained glass windows.

    There are in fact an infinite number of solders tailored

    by alloy and flux to achieve a useful melting point, ability

    to 'wet' the base metals and structural strength.



    Legacy tin/lead won't wet stainless and is too soft. Some

    common silver solders contain phosphorous (Sil-Fos)

    and I think should be limited to copper/brass fittings

    like in refrigerators. The other silver alloys are fine

    but can have widely different flow-temperatures. A local

    weld shop probably has some choices and data that

    gives the melting points.



 	  Quote: 	
		    Another option would be to get a SS whip antenna, like this from 

 Radio Shack: 

 http://www.radioshack.com/product/index.jsp?productId!02428&CAWELAID7599032 

 It's 102" but has a 3/8-24 fitting. Cutting it down would be no 

 problem, but putting a 45 bend could be. I assume this would be a 

 tube that could kink.


	


   No, it's a solid rod. Good idea actually. I may

   update my article to include this option. You can

   cut it to length by grinding a 'break notch' all

   the way around the rod . . . then round it off for

   safety. Save the remaining cut-off. That can be

   used to build more antennas where silver soldering

   is not a prohibition. In fact, the tip end of the

   antenna has the 'safety ball' on it . . . this would

   become prime antenna stock. Just tailor the hole in

   the base-bolt to be a few thousandths of an inch

   oversized to allow silver solder to flow into the

   hole and around the base of the antenna rod.



   To bend, heat the bend location with your torch

   to at least dull red and then pull around a radius

   held in your vise . . . a piece of pipe or some such.

   Don't bend too far. You can always bend more but it's

   a real bear to 'unbend'.



   The area heated will be tarnished after you finish

   the bend but it can be polished up again with some

   fine sandpaper.



 	  Quote: 	
		  ACS has one for about $20, but I thought I read someone say it 

didn't have the standard fitting, which seems odd. I'll have to 

check with them.


	


   Don't know what a 'standard' fitting would be but

   the Radio Shack part is about the same price

   and you can probably pick it up locally. Better

   yet, it provides enough material for at

   least 3 comm antennas.

   Bob . . .

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Mon Nov 14, 2011 7:23 am Post subject: Re: antenna connections

Thanks, Bob 



I'll prolly get that antenna from RS. I had read some about antennas being 'tuned', so any 22" long one would work?



Also heard something about different resistance in either the connectors or the antenna. Do I need to be concerned about that?

_________________
Dan

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Nov 14, 2011 7:54 am Post subject: antenna connections

At 09:23 AM 11/14/2011, you wrote:

 	  Quote: 	
		  



Thanks, Bob 



I'll prolly get that antenna from RS. I had read some about antennas 

being 'tuned', so any 22" long one would work?


	


   Yes, that's total length from top of mounting surface to

   tip of antenna . . . so that includes height of the mount.



 	  Quote: 	
		  Also heard something about different resistance in either the 

connectors or the antenna. Do I need to be concerned about that?


	


   No. There ARE connectors designed for minimizing

   "impedance bumps" at the joints for the popular

   feed line impedances . . . but that's of no

   significance to our task.



   Bob . . .

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Mon Nov 14, 2011 8:19 am Post subject: Re: antenna connections

Goodie 



I know suggested I get a UHF-BNC adapter and that you have BNC right angle connectors. I just noticed the seller of these mounts also has a UHF right angle adapter. Would you have a straight UHF connector for the cable, or should I stick with plan A and get a straight UHF-BNC adapter?

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_________________
Dan

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Nov 14, 2011 11:06 am Post subject: antenna connections

At 10:19 AM 11/14/2011, you wrote:

 	  Quote: 	
		  



Goodie 



I know suggested I get a UHF-BNC adapter and that you have BNC right 

angle connectors. I just noticed the seller of these mounts also has 

a UHF right angle adapter. Would you have a straight UHF connector 

for the cable, or should I stick with plan A and get a straight 

UHF-BNC adapter?


	


   UHF to BNC



   Bob. . .

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Mon Nov 14, 2011 9:08 pm Post subject: Re: antenna connections

K.



Got the RS antenna. My only initial anal concern was the weight at .20" diameter at the 22" mark. It tapered down to less than 1/8", but that was near the end of the original 120". I've seen some com antennas listed as 0.15" thick, so I gained 1.5 oz. 



I bent it at ~8" to about 40 degrees after heating it with a propane/air torch. Used a little $10 HF tubing bender. It wanted to also put another bend real close to the base, but the bender config would have made that real tough, so I increased the bend to 68 degrees at the original location. 



I ran a scotchbrite roloc over it to get the discoloration out, which was fairly easy to do. Will this area be as stain resistant as the other areas? When I got my EGT probes, the bayonets were welded to hose clamps. Around the welded area there was rust.



Clearance under my Sonex  TD is ~19" at the planned location of the antenna. Vertical for the antenna is ~13", giving me 6" ground clearance. I also just bought that base connector off eBay. 



This has been the type of project I really like. Doing something simple and saving money. $22 for the antenna, $5 for the mount, $2 for the BNC-UHF adapter at Frys. That compares to over $65 just for the antenna at ACS, which still needs more bending to go on the belly. Thanks, Bob!

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_________________
Dan

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Nov 15, 2011 8:36 am Post subject: antenna connections

At 11:08 PM 11/14/2011, you wrote:

 	  Quote: 	
		  



K.



Got the RS antenna. My only initial anal concern was the weight at 

.20" diameter at the 22" mark. It tapered down to less than 1/8", 

but that was near the end of the original 120". I've seen some com 

antennas listed as 0.15" thick, so I gained 1.5 oz.


	


   Yup, that's called sifting through the options and

   evaluating the trade-offs. But it IS a robust antenna.

   This brings up another point. That antenna is not

   very compliant . . . I.e. it's stiff. Make sure you've

   got a robust doubler on the belly surface.



 	  Quote: 	
		  I bent it at ~8" to about 40 degrees after heating it with a 

propane/air torch. Used a little $10 HF tubing bender. It wanted to 

also put another bend real close to the base, but the bender config 

would have made that real tough, so I increased the bend to 68 

degrees at the original location.


	


   Sounds like a reasonable trade off . . .

 	  Quote: 	
		  I ran a scotchbrite roloc over it to get the discoloration out, 

which was fairly easy to do. Will this area be as stain resistant as 

the other areas? When I got my EGT probes, the bayonets were welded 

to hose clamps. Around the welded area there was rust.


	


   Heating a material to a ductile state does not change

   it's alloy. If it was 'stainless' to begin with, it's

   still stainless.

 	  Quote: 	
		  Clearance under my Sonex  TD is ~19" at the planned location of the 

antenna. Vertical for the antenna is ~13", giving me 6" ground 

clearance. I also just bought that base connector off eBay.



This has been the type of project I really like. Doing something 

simple and saving money. $22 for the antenna, $5 for the mount, $2 

for the BNC-UHF adapter at Frys. That compares to over $65 just for 

the antenna at ACS, which still needs more bending to go on the 

belly. Thanks, Bob!


	


   Pleased that you've been able to adapt the simple-ideas

   for one recipe and craft one of your own. You could

   take the scraps of antenna left over and craft two

   more to offer to others here on the list. By the time

   you've made the third one, you'll be way down on the

   learning curve and more of an authority on that idea

   than I am, I've only made the one you see in the article.

   Bob . . .

raymondj(at)frontiernet.n
Guest

Posted: Thu Nov 17, 2011 12:53 am Post subject: antenna connections

SNIP

 >

 > Heating a material to a ductile state does not change

 > it's alloy. If it was 'stainless' to begin with, it's

 > still stainless.

 >

SNIP



Greetings Bob,



While you are correct that heating a stainless alloy doesn't change the 

alloy, there are other issues associated with stainless that are worth 

considering when it has been heated.  The 2 that come to mind are 

passivating and changes in the structure at the ends of the heated 

section (in welding it is referred to as the heat affected zone). 

Without knowing the the alloy or the manufacturing process it is hard to 

predict, but if something unexpected occurs, it may be attributable to 

the bending process.



Raymond Julian

Kettle River, MN



"And you know that I could have me a million more friends,

and all I'd have to lose is my point of view." - John Prine

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Thu Nov 17, 2011 7:22 am Post subject: Re: antenna connections

Just for kicks, I started looking for some silver solder. RS has some for $7 http://www.radioshack.com/product/index.jsp?productId=2062717 It has 2% Ag, no P. Most of the other ones I found were in the 2-4% range. Rosin core seems like it would be easier. Will this solder work?

_________________
Dan

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Nov 17, 2011 2:23 pm Post subject: antenna connections

At 09:22 AM 11/17/2011, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "messydeer" <messydeer(at)yahoo.com>



 Just for kicks, I started looking for some silver solder. RS has some for $7  http://www.radioshack.com/product/index.jsp?productId 62717 It has 2% Ag, no P. Most of the other ones I found were in the 2-4% range. Rosin core seems like it would be easier. Will this solder work?

 	


    I should have been a bit more specific. "Solder" comes

    in a LOT of flavors and not all sliver bearing solders

    are intended to be structural.



    The solders used for electronics are not intended to

    make up highly stressed joints. Silver is included in

    these solders to make them more friendly to the task.

    We know, for example, that solder makes a joint by

    DISSOLVING some portion of the metals to be joined

    into the melt.



    WAAAAAyyyy back when, some premium electronics device

    like Tektronix scopes used terminal strips that were

    ceramic moldings with a sliver alloy bonded into

    the notches like this:



 [img]cid:.0[/img]



    These were popular with other high-end product of the

    vacuum tube era. One was well advised to use a silver

    bearing solder to make up joints on these terminals

    to avoid "washing" the sliver off the ceramic and

    breaking the bond. Many a 'scope I've opened from

    that era had a small quantity of suitable solder

    stashed somewhere inside by the factory.



    This sort of solder would be useful in making up

    joints on any silver-plated terminal.



    But when you're sticking things together that

    are highly stressed, it's a different kind of

    sliver solder that has more like 40% or more silver

    and melts at temperatures far above that produced

    by your soldering iron. Avoid "refrigeration" solder

    with phosphorous in it (sil-fos) as it is specific

    to joining of high pressure copper plumbing.



    The durn stuff is not cheap and you only need

    a gram or so. It might be that you'd want to

    drop by a weld shop and get it brassed (or

    silver soldered if they have it in stock).

    Here's an example of a 'hard' solder

 

  http://tinyurl.com/7t7ypah 



    If it's a process you want to be able to do

    in the future, then investing in a small chunk

    of solder will give you a joining process that

    can be accomplished with hardware store torches.

    You'll also need flux. A borax based paste that

    melts and looks water clear as the joint flows

    and cools to look like a layer of glass. Chips

    away easily.



 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Nov 17, 2011 2:32 pm Post subject: antenna connections

While you are correct that heating a stainless alloy doesn't change 

the alloy, there are other issues associated with stainless that are 

worth considering when it has been heated.  The 2 that come to mind 

are passivating and changes in the structure at the ends of the 

heated section (in welding it is referred to as the heat affected 

zone). Without knowing the the alloy or the manufacturing process it 

is hard to predict, but if something unexpected occurs, it may be 

attributable to the bending process.



    Absolutely. Heating and bending any structural piece gives

    rise to potential changes in the metal's performance.

    I've heard of brazed pieces failing outside the joint

    because the nature of the material changed due

    to heating for joining.



    In this case, we were discussing the appearance of

    a lightly stressed part . . . buffing off the corrosion

    products from heating and the risks are low. But your

    point is well taken! Thanks!

   Bob . . .

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Thu Nov 17, 2011 6:27 pm Post subject: Re: antenna connections

Thanks for the silver solder info, Bob. 



What would be wrong with using a 3/16 or 1/4" rod of aluminum instead of SS and cut threads on the end? It's much easier to bend and a 2' piece of it from ACS is cheaper than a cup of coffee. It wouldn't fit into the 3/8-24 mount, but an adapter from a short piece of 3/4" rod aluminum could be made. Drill and tap one end for 3/8-24 and the other to fit the rod. You could even taper the adapter into a cone shape.

_________________
Dan

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Nov 18, 2011 6:53 am Post subject: antenna connections

At 08:27 PM 11/17/2011, you wrote:




Thanks for the silver solder info, Bob.



What would be wrong with using a 3/16 or 1/4" rod of aluminum instead 

of SS and cut threads on the end? It's much easier to bend and a 2' 

piece of it from ACS is cheaper than a cup of coffee. It wouldn't fit 

into the 3/8-24 mount, but an adapter from a short piece of 3/4" rod 

aluminum could be made. Drill and tap one end for 3/8-24 and the 

other to fit the rod. You could even taper the adapter into a cone shape.



   Excellent question!



   Unlike steel, aluminum has a 'service life' at

   any stress level. Non-ferrous (no iron) materials

   have a stress-to-cycles curve that goes all the

   way down to zero stress. This means that the thing

   is going to break sometime at what ever stress

   level you choose to operate it.



   Wings and things on aluminum airplanes are very

   lightly stressed so that their service lives are

   many times greater than the expected lifetime of

   the machine. Yet, pieces of aluminum routinely

   crack and fail. Sometimes it blows big holes out

   of the cabin walls of airliners!



   Steels are pretty cool in this regard. Once you

   drop below a certain stress level for that particular

   alloy, the service life becomes unlimited. I used

   to wonder at the legacy policy of allowing an engine

   to be 'certified' with only 75 or so hours on the

   test stand. But 75 hours at 2400 rpm is over ten

   million stress cycles on parts. If something doesn't

   break in that period of time, probability of breaking

   beyond this test interval is low.



   Getting back to our antenna, you'll find that the

   little whisker of metal 'hums' in the breeze of aero-

   dynamic turbulence around the fuselage. Unless it's

   a very robust aluminum part, you'll probably find that

   the comm system performance becomes severely degraded

   when the antenna departs the airplane.



   For that reason, "whisker" style antennas have always

   been made from steels . . . although from a radio

   frequency performance perspective, we'd like to have

   better conducting materials. This is why the 'shark fin'

   antennas can offer incrementally better performance.

   Their less robust, high performance materials are

   enclosed in an RF transparent housing to protect them

   from effects of air flow.

   Bob . . .

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Fri Nov 18, 2011 7:11 am Post subject: Re: antenna connections

Yeah, that sounds familiar about aluminum. On the other hand, I've found some antennas made out of aluminum. 



The DM C63-Series antennas are VHF communication antennas designed for high mechanical strength with machine tapered aluminum alloy radiating elements.



http://www.aircraftspruce.com/catalog/avpages/c63_2.php



Is there anything different about this type of antenna compared to the one I'd suggested, outside of a streamlined base?

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_________________
Dan

LynnCole(at)foxvalley.net
Guest

Posted: Fri Nov 18, 2011 8:24 am Post subject: antenna connections

 	  Quote: 	
		   Getting back to our antenna, you'll find that the

   little whisker of metal 'hums' in the breeze of aero-

   dynamic turbulence around the fuselage. Unless it's

   a very robust aluminum part, you'll probably find that

   the comm system performance becomes severely degraded

   when the antenna departs the airplane.


	


The humming that you refer to is due to vortex shedding (the most  

famous example of vortex shedding is the failure of the Tacoma  

Narrows Bridge).  The antenna on my car (steel) has a spiral wrap  

around it.  That trips the boundary layer so that only very short  

stiff lengths of the antenna can vibrate.  The vibrations where the  

wrap is on one side of the antenna cancel the vibrations where the  

wrap is on the other side.  Without the wrap the entire antenna,  

which is very limber, vibrates as a unit, and it can achieve some  

large amplitudes.



Lynn Cole

LynnCole(at)foxvalley.net

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