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Cheap NAV Antennas?

RudiGreyling

Well Known Member
RVators,

I am upgrading my SL40 to a SL30 to be IFR legal and now need to run NAV antennas I did not have before. I am looking for a simple and easy way.

I have search Vans Airforce for the past hour and found prominent members had good success with the following.
1) Marker beacon: 37 to 40" Stripped Coax
2) Glide Slope: 16" Stripped Coax

Now I want to turn attention to VOR and LOC antenna: The SL30 uses one input for GS/LOC/VOR. The VOR operates 108.0 to 117.95 MHz and the localizer is 108.1 to 111.95 MHz. Therefore you can use the same antenna to receive both VOR and LOC but GS is on the third harmonic of LOC. 329.3 to 335.0 MHz

Now my Question What length does my stripped coax need to be to receive all 3 GS/LOC/VOR keeping in mind that Recieve antennas are not too picky about being tuned exactly to frequency?

See my idea is to run a simple piece of stripped coax in the right place of my airplane and connect it direct to the SL30 maybe around the rollbar or in the cowl.

Thanks in advance.
Rudi
 
Rudi,

A 1/2 wave long piece of wire would be somewhere in the neighborhood of 52" long. You need a real good ground plane for this to work very well. Finding a 52" long spot to mount this and keep a good symetrical ground plane will be difficult.

If it was me, I would put a cheap nav antenna on there and forget it. The SL30 has a built in diplexer so you only need one.

$125-$150

AV-12.jpg
 
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Van's is cheap

Rudi,
Van's sells a piece of 25" (63.5cm) long copper foil that is soldered to the nav coax. The instructions say to put horizontally in the wingtip as the VOR signal is horizontally polarized. That would make it difficult to mount on the roll bar. If you mount it in the cowling it would need to be disconnected every oil change. I have a SL30 and find the VOR reception adequate, actually better than the old radios I used to fly. The VOR signal is weak when the opposite wingtip is pointed at the VOR station. The glideslope and localizer works as it should.
 
Can't get much better for the price than an Archer VOR antenna. Does VOR, Loc & GS with one antenna. They work great and very reasonably prices. http://steinair.com/avionics.htm

It's a long shipment there but I'm sure with some research this antenna could easily be imitated with parts found locally.
 
Thanks guys, I should have been clearer, I want it even simpler than Cats wiskers or Bob Archer, I don't want to run the wire all the way to the tail or wingtip, since I will have to drill new holes in the ribs for new antenna cable routing...to much work to get in there now, so i am looking for something in cockpit or in cowl which is a simple firewall penetration.

I really would like a stripped coax route, along the rollbar or even in the cowl, but need to know the length and orientation required for a 3 way cable. It seems success have been achieved with the GS at 16" stripped Coax, but what about VOR & LOC combined?

Rudi,
Van's sells a piece of 25" (63.5cm) long copper foil that is soldered to the nav coax. The instructions say to put horizontally in the wingtip as the VOR signal is horizontally polarized. That would make it difficult to mount on the roll bar. If you mount it in the cowling it would need to be disconnected every oil change. I have a SL30 and find the VOR reception adequate, actually better than the old radios I used to fly. The VOR signal is weak when the opposite wingtip is pointed at the VOR station. The glideslope and localizer works as it should.

Dave I can't find info on Van's Site about that product. Do you have a link
 
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Rudi,

The GS @16" is basically a 1/2 wave dipole antenna where the airframe is the other half of the antenna.

For the equivelant for VOR/LOC, the wire would need to be around 52" long.

If you want to try 1/4 wave, just cut that in half.
 
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Rudi,

The GS @16" is basically a 1/2 wave dipole antenna where the airframe is the other half of the antenna.

For the equivelant for VOR/LOC, the wire would need to be around 52" long.

If you want to try 1/4 wave, just cut that in half.

Brantel Thanks,

So if 1/4 wave GS = 16"
and 1/2 wave VOR/LOC = 52" then 1/4 wave VOR/LOC = 26"
So midway between the 2 receiveing antennas would be (16+26)/2=20"

It would be a simple experiment to expose a piece of coax 20" long and run from a SL30 to somewhere in the cockpit and then see how good it is or not.

I am NOT looking for VOR at 100 of miles, primary nav over long distance will still be GPS until close proximity say 10 miles of VOR. But solid GS is a must. So one might even tune specifically for GS at 16" and live with the comprimised VOR receiption if it gets you 10 miles or so.

I can't wait for my SL30 goodies to get to SA so I can start to experiment.

I will continue research and see what the composite kit guys do, I hear they sometimes inbed antennas in their airframe during the build.

Regards
Rudi
 
Rudi,

The GS @ 16" is a ~ 1/2 wave for GS frequencies.

Optimize for the VOR/LOC frequencies and the GS will use the same antenna since it is a harmnonic of the VOR/LOC freqs.

If you use 26" for VOR/LOC (~1/4 wave) then that will be a ~3/4 wave for the GS.

All of this is not as critical since you are only using em to recieve. If you were transmitting, it would be more of an issue.

Sure won't hurt anything to test and see what you get for performance.
 
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Kent Paser, who raced a very fast Mustang II, wrote a book about it:
Speed With Economy
He tries and documents many speed mods, including the NAV antenna.
He made a Jim Rushing designed "V" dipole antenna from copper tape which he applied to the inside of the canopy, near the back. Jim was a Mustang II builder.
MMII's have a slider canopy, so you need a wire that is long enough to allow opening, yet Kent said this worked fine. He did say the reception ahead was better than astern, like 80 miles / 50 miles, but that was a zero drag, low cost antenna.
You can read about it on pages 93 - 95 in his book, which is cheap and full of great info that you might find useful. You can check the link to aircraft spruce:
http://www.aircraftspruce.com/catalog/bvpages/speed_econo.php
 
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VOR/GS ANTENNA

Rudi
Could you post pictures of your set up if you can..I'm really interested in ways to install them other than the traditional set up..

Thanks

Bruno
[email protected]
 
RVators,

OK so I finally got my goodies installed and started with my testing. I have 1 sample to report at this time...

I exposed 16" of coax and laid it flat on top of my panel dash. This was not satisfactory since I only got the VOR at 8-10 miles. I am thinking to change to location of the home made antenna to the roll bar, and increasing the exposed point to 20" this weekend and will report back.

Regards
Rudi
 
I am thinking to change to location of the home made antenna to the roll bar, and increasing the exposed point to 20" this weekend and will report back.

What ever happened Rudi?! I've been waiting 8 years for the results! :D

In all seriousness, has anyone else had luck with something this simple? I have a -4 with the wingtips glassed on (No Archer antenna...) and hanging a draggy antenna out in the breeze isn't really an option either.
 
Such confusion!
52? is the total length of a 1/2 wave dipole (26? attached to coax center conductor, another 26? attached to coax braid) tuned for 112 MHz. It is also a 3/2 wavelength dipole for 336 MHz (glide slope), and should work well. These half wave dipoles do not need or want a ground plane. They work okay if run left-right on a -10?s fiberglass roof. Most of their sensitivity in this orientation is forward and aft - great for GS and LOC, not so great for VORs 90 deg off the nose. If you run the wires like a V (ends aft of the middle) you can get better reception off to the side, at some loss in the forward direction.
A half wave dipole for GS will be 1/6 wave at vor and loc, and will perform poorly.
 
Scott had it right about the copper foil in the canopy, though it would be a little trickier to tune in a narrow RV-4 canopy. That was a very common technique back in the days of scratch-built everything, when VOR was all we had to navigate. Could work in the bottom cowl as well, though you'd have the disconnect issue as others mentioned.

The marker beacon is a non-issue. Remember, the only time it matters is when you're within a couple of miles of the transmitter, or directly over it. With an SL30, the VOR dipole takes care of all your needs. For models with a separate input for marker, the common 'wet noodle for an antenna' joke applies here. If you have fiberglass gear fairings, you can just drop a random length of lamp cord, romex, etc down the gear leg.

Charlie
 
Shoot fire - a lot of churn and some bad information. Some thoughts:
- A Marker Beacon antenna can be a simple piece of wire strung under the engine and ending in BNC bulkhead connector on the firewall. The wire would be 36? or so long (1/4 wavelength). Marker Beacons transmit energy is almost straight up so even a very poor antenna works just fine. I pick up Marker Beacons with this set up miles from airports when at altitude.
- You will find any dipole style VOR antenna mounted inside the cowl to not work. There is just way too much ignition noise when the antenna is only inches away from sparkplug wires.
- You will find any dipole style VOR antenna mounted to roll bars and such to not work. Too much coupling of the high impedance ends of the antenna to ground.
- I did try a temporary dipole VOR antenna run along the top of the fiberglass cabin top in the RV-10. It worked, but poorly. Even there the noise from all the panel switching power supplies was not acceptable.

The cheapest and most effective VOR antenna is a homebrew wingtip antenna. I?ve built many for my planes and others - perhaps $3 of parts. You can get the basic design out of the AeroElectric book. If you do not know how to tune an antenna or have the needed antenna analyzer then don?t build, just buy. You can improve performace by:
- Not running the nav/strobe wire on the antenna leg like Archer tells you to do. Just slide the antenna aft a few inches.
- Strive to change the dimensions to extend the antenna as far into the wingtip as it will go.
- Mount the antenna on a light piece of angle that is connected to the end rib, not glassed into the wingtip. The wingtip just slips over the antenna.

My wingtip VOR antenna works out to 100nmi and picks up the LOC/ILS at well beyond practicable range - both far more than I will ever need.

Carl
 
On wingtip mounted VOR antennas, if my wingtip is carbon fiber this is not a viable option yes? Or is it more of a "It won't be 100% but will work good 'nuff" situation?
 
On wingtip mounted VOR antennas, if my wingtip is carbon fiber this is not a viable option yes? Or is it more of a "It won't be 100% but will work good 'nuff" situation?

This is a problem. I?ve seen workarounds on Lancair IVs that cut out a section of the carbon fiber and replace with a fiberglass ?window? to get around this - but most just mount in the tail where it is all fiberglass.

What airplane uses carbon fiber for the wingtip? This is gross overkill.

Carl
 
Still have the Van's cheapo foil in the right wing. SL30 still picks up VOR signals good to 80 or so miles (always use GPS so don't pay attention). Still picks up LOC and GS too.
 
Shoot fire - a lot of churn and some bad information. Some thoughts:
- A Marker Beacon antenna can be a simple piece of wire strung under the engine and ending in BNC bulkhead connector on the firewall. The wire would be 36? or so long (1/4 wavelength). Marker Beacons transmit energy is almost straight up so even a very poor antenna works just fine. I pick up Marker Beacons with this set up miles from airports when at altitude.
- You will find any dipole style VOR antenna mounted inside the cowl to not work. There is just way too much ignition noise when the antenna is only inches away from sparkplug wires.
- You will find any dipole style VOR antenna mounted to roll bars and such to not work. Too much coupling of the high impedance ends of the antenna to ground.
- I did try a temporary dipole VOR antenna run along the top of the fiberglass cabin top in the RV-10. It worked, but poorly. Even there the noise from all the panel switching power supplies was not acceptable.

The cheapest and most effective VOR antenna is a homebrew wingtip antenna. I?ve built many for my planes and others - perhaps $3 of parts. You can get the basic design out of the AeroElectric book. If you do not know how to tune an antenna or have the needed antenna analyzer then don?t build, just buy. You can improve performace by:
- Not running the nav/strobe wire on the antenna leg like Archer tells you to do. Just slide the antenna aft a few inches.
- Strive to change the dimensions to extend the antenna as far into the wingtip as it will go.
- Mount the antenna on a light piece of angle that is connected to the end rib, not glassed into the wingtip. The wingtip just slips over the antenna.

My wingtip VOR antenna works out to 100nmi and picks up the LOC/ILS at well beyond practicable range - both far more than I will ever need.

Carl

Carl, do you have any pics of the vor antenna attached to the wing rib? I'm trying to visualize it but the antenna seems to flimsy to be mounted like that.
 
Antenna for legal IFR

Trying to make decisions about what equipment to install for a legally capable IFR capable RV-7A without taking out a mortgage to buy an expensive GPS navigator. I went through the FARs and relevent ACs and the conclusion I came to was that the Minimum Equipment List and cost would be a TSO?d VOR/ILS nav/com and associated installation. This requires a TSO?d antenna according to my read of the regulations. While a stripped coax may be made to work clearly it wouldn?t stand up to examination as meeting any objective requirments for a ?certified? antenna. Unbalanced, no isolation for vertical polarization, undefined VSWR, undefined beam pattern - to name just basic parameters. So if the basic idea is to have a VOR/ ILS capability for Flight under VMC conditions it is in persuit of our certification in the ?experimental? category but not suitable or legal for flight in IMC conditions. I am persuing purchasing a second hand certified antenna on Ebay for a fraction of the new price and doing my own recert process. This may turn out to be a wasted effort - will update as progress is made.
KT
 
I'm far from being an authority, but my understanding is that while GPS must be TSO for IFR even in homebuilts, VOR/ILS can be whatever 'meets the requirements'. Perhaps someone with more intimate knowledge will jump in.
 
Trying to make decisions about what equipment to install for a legally capable IFR capable RV-7A without taking out a mortgage to buy an expensive GPS navigator. I went through the FARs and relevent ACs and the conclusion I came to was that the Minimum Equipment List and cost would be a TSO?d VOR/ILS nav/com and associated installation. This requires a TSO?d antenna according to my read of the regulations. While a stripped coax may be made to work clearly it wouldn?t stand up to examination as meeting any objective requirments for a ?certified? antenna. Unbalanced, no isolation for vertical polarization, undefined VSWR, undefined beam pattern - to name just basic parameters. So if the basic idea is to have a VOR/ ILS capability for Flight under VMC conditions it is in persuit of our certification in the ?experimental? category but not suitable or legal for flight in IMC conditions. I am persuing purchasing a second hand certified antenna on Ebay for a fraction of the new price and doing my own recert process. This may turn out to be a wasted effort - will update as progress is made.
KT

Sorry - your assumptions are wrong. Only the IFR GPS navigator needs this certification.

Antennas are not rocket science. For me, my homebrew VOR/LOC/ILS wingtip antenna is first choice over any ?TSO? product, especially one purchased on eBay. I do however measure and tune each antenna for optimal performace. If you buy commercial, this step is typically not done.

Carl
 
Carl,
Thanks for the reply. I think the ebay antenna is a long shot for a number of reasons ( Dorne & Mangolin DMN-42 towel rail type) but we shall see.
I looked at the Bob Archer design for the wingtip and had the following concerns. The design looks optimized for the VHF band for VOR and Localizer with a gamma match. The gamma match will be way off at the 300 Mhz glideslope band so performance is problematic for glideslope. I also looked at the ?whisker?
type antenna that have a balun and matching network and work quite well across the two bands. I haven?t seen any beam pattern data for the Archer antenna but would suspect that it would have a R cos theta shape off of the wingtip with a null off the other wingtip. I would also be concerned that the rejection of the vertically polarized wave component is not adequate for either VOR or localizer.
I thought about designing a center fed microstrip phantom slot but the dimensions are quite large and placement would be a big issue. Another big issue is not having access to all the test equipment any more so I feel the need to go with a tested design. The Archer design is appealing - cheap to build, hidden in the wingtip and seems to have a lot of success but the glideslope performance is a question in my mind. If you have data on VSWR and polar signal strength plots for the Archer I would be very interested. Smith chart plots are OK.
Maybe I am just over thinking this issue but better now that after committing to a bad installation.

KT
 
KT,

Sorry again, but your concerns are an order of magitude below practical antenna performace. For example:
- Polarization. Take your VHF comm handheld radio and listen to any tower or aircraft communications. Rotate the handheld 90 degrees. Still hear the station, right? I routinely communicate with a vertical antenna to a horizontal antenna receiving station. VHF is not just line of sight. Consider the same handheld radio works inside your closed hangar. Why? Does it work better outside, sure. Performance is a mission driven objective, not an antenna test range measurement.
- Beam pattern. Sure, some effect but remember that the objective is adequate signal to noise ratio. My wingtip picks up VORs around the compass rose and out to 100nmi at altitude, and LOC/ILS beyond practical range.
- Gamma match. Resonance is resonance. A third harmonic and the same a gamma match L/C ratio that brings the antenna input impedance to match the coax will be the same.
- Gamma match eliminates the use of a balun. I’ve been using gamma match antennas with coax feed for close to 50 years.

Now a word of caution, any antenna is only as good as the installer tuning it for the application and mounting conditions. I put an antenna analyzer on every antenna I install (verifies the antenna and feed line). For the wingtip antenna I modify the dimension to use the full wing rib to wingtip outer edge length to enhance performance. From there I tune the antenna to resonance and then adjust the gamma match to achive the best match to the 50 ohm RG-400 coax - perhaps a 15 minute evolution. If you don’t know how to do this, buy the Archer product and follow the installation instructions.

Carl
 
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Carl,
I agree that performance is a mission driven objective. If the mission is ham radio communicating with someone through a repeater from the comfort of your shack that is a far different situation than the airborne navigation mission. Link margins and isolation from noise and interference take on a whole different meaning. If my life is on the line and dependant on objective expectations that I can tune in an ILS and fly the approach without loss of signal at the critical moment the only way I know how to do that is to know the theoretical link margins based on the specified performance compared with actual measurement of the ground based and aircraft based system components. The subjective ?lick it and taste? approach is perfectly good enough for the ham radio environment but shouldnt become standard operating procedure for VOR and ILS in the airborne environment. I have always considered the gamma match approach to impedence matching to be a brute force approach due to the impact on the beam pattern and yes I do know how to tune and match an antenna even though I only have my trusty MFJ 259 that I mostly use to tune my ham radio equipment.
KT AF7GP
 
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