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Antenna(s)

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phd1993

Joined: 04 Apr 2006
Posts: 18
Location: Overland Park, KS

Posted: Wed Nov 01, 2006 7:19 am Post subject: Antenna(s)

I have just ordered NAV/COM (King KX-125) and  Transponder (Garmin GTX-327) - and am of the understanding that I will need  3 antennas.  One for COM, one for NAV, and one for  transponder.

  

 Any suggestions (both source and item numbers) for  what to purchase?  Which units seem to work better?  Which units seem  to always cause problems.

  

 Appreciate any feedback.

  

 Sam H.

   [quote][b]

Float Flyr

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

Posted: Wed Nov 01, 2006 9:38 am Post subject: Antenna(s)

although all three are in  approximately the same frequency range the Nav antenna is usually horizontally  polarized while the Com and the ELT are vertical.  In short you will need  three antennae.  the type of antennae will depend on the speed of your  plane.

  

  

 

Noel [quote]   

   --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Wed Nov 01, 2006 9:34 pm Post subject: Antenna(s)

The nav and com radios operate in the nearly the same frequency band but the transponder operates at a much higher frequency band. The transponder antenna is usually a short  (~1 1/2") spike antenna mounted on the belly of the airplane. You can pick one up for about $15 at Aircraft Spruce. 

The VOR signal used by the nav receiver is transmitted with a horizontal polarization because that results in less distortion of the signal. It requires a horizontally polarized antenna to recieve a decent signal. I built my own Nav antenna from a couple of FM whip antennas, a PVC pipe cap and some coax cable for about $15 in parts. I mounted it on top of the rudder and it works pretty well. You don't need to spend a lot of money to get good results.



For the com radio you should use a wide band antenna to get decent function across the entire com band. A simple wire whip is only good for a narrow band of frequencies. You could make a com antenna out of copper tape embedded in a fiberglass shell. It needs to be mounted vertically. Any commercially available antenna designed for the com band will work as long as it's installed properly.



Jim Weir has published some articles on how to make your own antennas in KitPlanes magazine. I the artcles are available on his website http://www.rst-engr.com/



A general rule of thumb is to mount any transmitter antennas at least three feet from any other antenna to reduce the chance of interference.



On Nov 1, 2006, at 12:36 PM, Noel Loveys wrote:

[quote]although all three are in approximately the same frequency range the Nav antenna is usually horizontally polarized while the Com and the ELT are vertical.  In short you will need three antennae.  the type of antennae will depend on the speed of your plane.

 

 



Noel[quote]

--

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

Float Flyr

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

Posted: Thu Nov 02, 2006 6:00 am Post subject: Antenna(s)

There are all sorts of methods  that can be used to increase band spread on a Com antenna.  I think the  most important of these is to have a good ground plane.  I've seen a few  .. OK more than a few antennas that were mounted to a corroded mess. and then  the operator was wondering why the radio doesn't work.  When installing a  Com antenna or a VOR antenna into a composite aircraft allowances should be made  for the installation of a good ground plane.  Allowances should also be  made for any metal ( hinges etc ) within three feet of the antenna that may act  as parasitic elements.

  

 A point that I didn't make on  the ELT is that there are two frequencies commonly in use for ELT.   121.5MHz VHF and double that frequency 243MHz UHF.  If your ELT has the UHF  transmitter then you will actually need another antenna..

  

 Starting to look like a forest  Eh.  

  

 I never mentioned the  transponder antenna but you make a valid point about it being on the bottom of  the plane so as not to shadow the earth station.  

  

  

 

Noel [quote]   

   --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

craig(at)craigandjean.com
Guest

Posted: Thu Nov 02, 2006 6:21 am Post subject: Antenna(s)

The latest ELTs also send on 406 MHz - my Artex ME406 came  with a triple-band antenna.

  

 -- Craig

  

   [quote][b]

SilentLight(at)verizon.ne
Guest

Posted: Thu Nov 02, 2006 11:04 am Post subject: Antenna(s)

Hi,



I am a newbie to the list and since you brought up the VOR antennas, I was 

hoping you folks can help me out with this.... My plans are to build an IFR 

601. My rudder kit is on order and hopefully will get here next week. Would 

it make sense to install 2 VOR antennas on the rudder the same way Cessna 

installs them on the 172 tail? Wouldn't the antenna coax wires get in the 

way of rudder's operation? From which direction should I route the wires 

out of the rudder (2 antenna, 1 tail light, 1 rotating beacon wire)?



Thanx...Eddie

Los Angeles, CA



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

Time:   09:34:01 PM PST US

From:   Bryan Martin

Subject:        Re: Antenna(s)



The nav and com radios operate in the nearly the same frequency band but 

the transponder operates at a much higher frequency band. The transponder 

antenna is usually a short (~1 1/2") spike antenna mounted on the belly of 

the airplane. You can pick one up for about $15 at Aircraft Spruce. The VOR 

signal used by the nav receiver is transmitted with a horizontal 

polarization because that results in less distortion of the signal. It 

requires a horizontally polarized antenna to recieve a decent signal. I 

built my own Nav antenna from a couple of FM whip antennas, a PVC pipe cap 

and some coax cable for about $15 in parts. I mounted it on top of the 

rudder and it works pretty well. You don't need to spend a lot of money to 

get good results. For the com radio you should use a wide band antenna to 

get decent function across the entire com band. A simple wire whip is only 

good for a narrow band of frequencies. You could make a com antenna out of 

copper tape embedded in a fiberglass shell. It needs to be mounted 

vertically. Any commercially available antenna designed for the com band 

will work as long as it's installed properly. Jim Weir has published some 

articles on how to make your own antennas in KitPlanes magazine. I the 

artcles are available on his website http://www.rst-engr.com/ A general 

rule of thumb is to mount any transmitter antennas at least three feet from 

any other antenna to reduce the chance of interference.

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Thu Nov 02, 2006 1:02 pm Post subject: Antenna(s)

The top of the vertical tail is a good place for the VOR antenna  

because it keeps it away from any large pieces of horizontal metal  

structures that might interfere with reception. That's why most  

manufacturers put it there. And since the antenna is omni- 

directional, the motion of the rudder on the 601 won't affect the  

reception. Those two metal whips actually form one antenna and you  

will have only one antenna cable feeding from them.



My wires come out of the rudder above the top hinge and are arranged  

so that a few inches of the wire bundle runs parallel to the hinge  

axis and twists as the rudder moves. This should put less strain on  

the wires than allowing a much shorter length of wire to bend at the  

hinge point. The wires are routed along the top of the rear fuselage  

where the horizontal stabilizer attaches and then through grommets in  

the bulkheads on the inside of the rear fuselage.



A rotating beacon is not necessary for IFR, a good set of wing tip  

strobes meets the anti-collision light requirement. I would consider  

a rotating beacon as just unecessary weight located far aft of the  

CG. If you really have a good reason for a flashing light on the  

tail, I would suggest using LEDs. Since these lights don't need to  

satisfy any regulations, you can use anything that meets your needs.



The reason that most certificated aircraft have a flashing beacon on  

the tail is that that beacon met the FAR anti-collision light  

requirement that was in effect when those aircraft were first  

certificated and it still meets the requirement for them. Those  

lights alone no longer meet the requirement for more recently  

certificated aircraft and aren't necessary under the current  

regulations.

On Nov 2, 2006, at 2:20 PM, Eddie G. wrote:



 	  Quote: 	
		   

 <SilentLight(at)verizon.net>



 Hi,



 I am a newbie to the list and since you brought up the VOR  

 antennas, I was hoping you folks can help me out with this.... My  

 plans are to build an IFR 601. My rudder kit is on order and  

 hopefully will get here next week. Would it make sense to install 2  

 VOR antennas on the rudder the same way Cessna installs them on the  

 172 tail? Wouldn't the antenna coax wires get in the way of  

 rudder's operation? From which direction should I route the wires  

 out of the rudder (2 antenna, 1 tail light, 1 rotating beacon wire)?



 Thanx...Eddie

 Los Angeles, CA



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




	


-- 

Bryan Martin

N61BM, CH 601 XL,

RAM Subaru, Stratus redrive.

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Thu Nov 02, 2006 2:48 pm Post subject: Re: Antenna(s)

That's a lot of stuff to put on the 601 Rudder. I'd go with the tail light and maybe an antenna but the Beacon isn't required as long as you have strobes but if you must have it put it somewhere else.



All that I'll have on mine is the tail light and the wires run straight from it forward to a hole in the front of the rudder.



Look on my web site under the "Tail" button for some pictures.

 	  SilentLight(at)verizon.ne wrote: 	
		  Hi,



I am a newbie to the list and since you brought up the VOR antennas, I was 

hoping you folks can help me out with this.... My plans are to build an IFR 

601. My rudder kit is on order and hopefully will get here next week. Would 

it make sense to install 2 VOR antennas on the rudder the same way Cessna 

installs them on the 172 tail? Wouldn't the antenna coax wires get in the 

way of rudder's operation? From which direction should I route the wires 

out of the rudder (2 antenna, 1 tail light, 1 rotating beacon wire)?



Thanx...Eddie

Los Angeles, CA

_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

Eddie G.

Joined: 03 Nov 2006
Posts: 15
Location: Los Angeles, CA

Posted: Sun Nov 05, 2006 2:24 pm Post subject: Re: Antenna(s)

Can a pair of whip antennas be mounted inside the horizontal stabilizer's tips, connected with a coax cable and tapped off in the center? Or is the distance between the two whips and the impedance of the coax connecting them just too much to work right?



As for the beacon, I like flying at night, but it's very annoying when a plane taxis opposite of me and makes me go blind with its high intesity strobes. So, to be nice to the other pilots I just hit my strobes when I take the runway and turn them off when I get off the active (my CFI who now works for Flight Safety pounded that into my head!!). I picked up a $6 lightweight cone type semi-truck decorative light which I think with a little digital flip-flop circuit I can turn it into a beacon to use as anti-collision light at night.

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Sun Nov 05, 2006 11:35 pm Post subject: Antenna(s)

I don't think this would work very well, not because of the distance  

between or the impedance of the coax but because of the radiation  

pattern of a whip antenna. A whip antenna has sharp nulls in its  

pattern directly off the ends of the whip. If you put the antennas  

inside the stabilizer tips, each antenna would only be able to pick  

up signals from one side of the plane due to the shielding effect of  

the aluminum stabilizer so one antenna wouldn't be able to fill in  

the gaps of the other's radiation pattern. The antennas would have to  

be mounted with the tip pointed either forward or aft, so you would  

have basically zero reception forward or aft. A whip antenna also  

requires a ground plane with a radius of about the same as the length  

of the whip.



To get decent omnidirectional reception of the horizontally polarized  

VOR signal you need a half-wave dipole mounted horizontally. This  is  

basically two quarter-wave elements mounted end to end with the feed  

line connected at the center. If the elements were mounted at 180  

degrees to each other they would have the same sharp nulls off the  

ends as the whip antenna. Mounting them at an angle of about 120  

degrees or so eliminates the nulls and you have a true  

omnidirectional pattern. Another thing to note is that a dipole  

antenna is a balanced load and a coax cable is an unbalanced feeder,  

so a balun is needed to match the coax to the antenna.



With a metal airframe, you are pretty much stuck with mounting your  

antennas externally.



On Nov 5, 2006, at 5:24 PM, Eddie G. wrote:



 	  Quote: 	
		   

 <silentlight(at)verizon.net>



 Can a pair of whip antennas be mounted inside the horizontal  

 stabilizer's tips, connected with a coax cable and tapped off in  

 the center? Or is the distance between the two whips and the  

 impedance of the coax connecting them just too much to work right?



 As for the beacon, I like flying at night, but it's very annoying  

 when a plane taxis opposite of me and makes me go blind with its  

 high intesity strobes. So, to be nice to the other pilots I just  

 hit my strobes when I take the runway and turn them off when I get  

 off the active (my CFI who now works for Flight Safety pounded that  

 into my head!!). I picked up a $6 lightweight cone type semi-truck  

 decorative light which I think with a little digital flip-flop  

 circuit I can turn it into a beacon to use as anti-collision light  

 at night.

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

Float Flyr

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

Posted: Tue Nov 07, 2006 5:48 am Post subject: Antenna(s)

I agree with you n the use of a balun... An unbalanced dipole will work,

especially on a receiver, but with reduced efficiency.  For the weight of a

modern balun ( a couple of ounces) its well worth the few dollars to

purchase.



For those out there that don't know balun comes form the two words

"balanced" and "Unbalanced"  All 300Ohm twin lead like they used to use on

television antennas is balanced line, all Coax is unbalanced....  Dipoles,

as Bryan said are balanced arrays.



There are some composite aircraft that have various antennas cast into the

flight surfaces.  Even in these aircraft they have to be very careful to

make sure there are no parasitic elements (Metal) close to the antenna that

could play havoc especially with transmitters.



Noel



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

N601RT

Joined: 25 Feb 2006
Posts: 31
Location: Hillsboro, Oregon

Posted: Tue Nov 07, 2006 9:33 am Post subject: Re: Antenna(s)

My plane has a Dipole VOR/GS/Localizer Antenna, probably a Comant CI-157P. This is mounted on the bottom of the fuselage just under where the rudder cables exit the fuselage. See attached photo. The signal from this antenna can be shared with multiple receivers by using an antenna coupler. The only wires going to my rudder are for the white, rear position light.



Many RV's have similarly mounted a Dipole VOR/GS/Localizer Antenna. 



(I also have a comm antenna and a GPS antenna on the turtle deck, a GPS antenna on the top forward skin, the belly of N601RT has a cheap bent whip comm antenna for my hand held, a marker beacon antenna, and my transponder antenna. My ELT antenna is from a handheld radio and is mounted on the baggage shelf, just behind the passenger seat. No flames please. Check the archives for discussions about ELT antenna locations. I should have put both GPS antenna's under the canopy, but didn't.)



Regards,



Roy



N601RT: CH601HDS, nose gear, Rotax 912ULS, All electric, IFR equipped, 651hrs, 750 landings

N601RT Nav Com 1 5.JPG

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Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Tue Nov 07, 2006 12:37 pm Post subject: Re: Antenna(s)

Roy, that is the spot all of the old-timers who come and inspect my plane have suggested I install mine as well. Between the lot of them they probably have over 300 years of tinkering with airplanes experience.

_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

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