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Antenna(s)

 
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phd1993



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

PostPosted: Wed Nov 01, 2006 7:19 am    Post subject: Antenna(s) Reply with quote

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]


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Float Flyr



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

PostPosted: Wed Nov 01, 2006 9:38 am    Post subject: Antenna(s) Reply with 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]
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bryanmmartin



Joined: 10 Jan 2006
Posts: 1018

PostPosted: Wed Nov 01, 2006 9:34 pm    Post subject: Antenna(s) Reply with quote

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]
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Float Flyr



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

PostPosted: Thu Nov 02, 2006 6:00 am    Post subject: Antenna(s) Reply with quote

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]
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craig(at)craigandjean.com
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PostPosted: Thu Nov 02, 2006 6:21 am    Post subject: Antenna(s) Reply with quote

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

-- Craig

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SilentLight(at)verizon.ne
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PostPosted: Thu Nov 02, 2006 11:04 am    Post subject: Antenna(s) Reply with quote

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.


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bryanmmartin



Joined: 10 Jan 2006
Posts: 1018

PostPosted: Thu Nov 02, 2006 1:02 pm    Post subject: Antenna(s) Reply with quote

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

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


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N61BM, CH 601 XL,
RAM Subaru, Stratus redrive.


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Gig Giacona



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

PostPosted: Thu Nov 02, 2006 2:48 pm    Post subject: Re: Antenna(s) Reply with quote

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



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Eddie G.



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

PostPosted: Sun Nov 05, 2006 2:24 pm    Post subject: Re: Antenna(s) Reply with quote

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.


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bryanmmartin



Joined: 10 Jan 2006
Posts: 1018

PostPosted: Sun Nov 05, 2006 11:35 pm    Post subject: Antenna(s) Reply with quote

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.



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Float Flyr



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

PostPosted: Tue Nov 07, 2006 5:48 am    Post subject: Antenna(s) Reply with quote

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] --


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N601RT



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

PostPosted: Tue Nov 07, 2006 9:33 am    Post subject: Re: Antenna(s) Reply with quote

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


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Gig Giacona



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

PostPosted: Tue Nov 07, 2006 12:37 pm    Post subject: Re: Antenna(s) Reply with quote

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.

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