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Antenna Question

asw20c

Well Known Member
I figure there are folks on this forum that understand antenna voodoo and can explain something that makes no sense to me. When I started on my slow-build wings, I knew that I wanted ground-based navaids as a backup for satellite navigation and approaches; i.e I wanted to be able to navigate by VOR and make ILS approaches if I had to. Stein was happy to sell me a Bob Archer VOR antenna that fits in the wingtip (pick one) that they said would do VOR navigation and ILS approaches.
Fast forward and I'm now at the stage where it is time to install the antenna. I did a quick internet search and found that VOR frequencies are 108-118 MHz, and the instructions that came with the antenna say it covers that range and more (I think 108-136MHz) so I know it is good for both VOR navigation as well as localizers. However glide slope frequencies are 329-335 MHz which clearly this antenna was not designed to receive.
I called Stein today to ask them about this and they said that if you have a modern navigator, like a GTN650, that it is able to sort out the localizer and glide slope frequencies from this one antenna and that they said other people have been using these same antennas with no complaints.
Can anyone explain this? Is there a misunderstanding between me and Stein? Can anyone here vouch for the fact that they have one of these antennas and can make an ILS approach? i.e. a PRECISION approach?
 
I figure there are folks on this forum that understand antenna voodoo and can explain something that makes no sense to me. When I started on my slow-build wings, I knew that I wanted ground-based navaids as a backup for satellite navigation and approaches; i.e I wanted to be able to navigate by VOR and make ILS approaches if I had to. Stein was happy to sell me a Bob Archer VOR antenna that fits in the wingtip (pick one) that they said would do VOR navigation and ILS approaches.
Fast forward and I'm now at the stage where it is time to install the antenna. I did a quick internet search and found that VOR frequencies are 108-118 MHz, and the instructions that came with the antenna say it covers that range and more (I think 108-136MHz) so I know it is good for both VOR navigation as well as localizers. However glide slope frequencies are 329-335 MHz which clearly this antenna was not designed to receive.
I called Stein today to ask them about this and they said that if you have a modern navigator, like a GTN650, that it is able to sort out the localizer and glide slope frequencies from this one antenna and that they said other people have been using these same antennas with no complaints.
Can anyone explain this? Is there a misunderstanding between me and Stein? Can anyone here vouch for the fact that they have one of these antennas and can make an ILS approach? i.e. a PRECISION approach?

I have made countless approaches in my RV with said antenna in my left wingtip, works great.
 
The Glide slope frequency is near the third harmonic of the localizer frequency and antennas perform fairly well on odd harmonics, an antenna designed for 108 to 118 MHz will also be useful on 329.3 to 335.0 MHz.
The ground based Glide Slope antenna beams most of the 40 watt signal toward the aircraft which is only about 5 miles away so it does not take much of an antenna to receive the signal.
 
As Don said, antennas that are resonant at half-wavelength are also resonant at 3/2, 5/2, etc., wavelengths, so they work well at 330 MHz. The 50 ohm matching network may be off a bit, but, as Don said, the GS is relatively strong. There are 1000?s of flying airplanes with dipoles for 110 MHz up on their tails that also use the same antenna for 330 MHz GS. My SL30 doesn?t even have a separate GS antenna input - it expects to use the nav antenna. BTW, I have an Archer in my wingtip, it works fine - vor, loc, and GS.
 
I?m in the ?I can?t explain how it works, but it works? category. I have a GTN650 with the Archer antenna in the right wingtip. I have flown multiple ILS approaches, including one in a pretty good rain shower and it?s rock solid every time. Have not tested the localizer or GS receiver to see how far out I can get the signal but I have always been able to fly any published approach I attempted. I?m very happy (and confident) with this setup.
 
I figure there are folks on this forum that understand antenna voodoo and can explain something that makes no sense to me. When I started on my slow-build wings, I knew that I wanted ground-based navaids as a backup for satellite navigation and approaches; i.e I wanted to be able to navigate by VOR and make ILS approaches if I had to. Stein was happy to sell me a Bob Archer VOR antenna that fits in the wingtip (pick one) that they said would do VOR navigation and ILS approaches.
Fast forward and I'm now at the stage where it is time to install the antenna. I did a quick internet search and found that VOR frequencies are 108-118 MHz, and the instructions that came with the antenna say it covers that range and more (I think 108-136MHz) so I know it is good for both VOR navigation as well as localizers. However glide slope frequencies are 329-335 MHz which clearly this antenna was not designed to receive.
I called Stein today to ask them about this and they said that if you have a modern navigator, like a GTN650, that it is able to sort out the localizer and glide slope frequencies from this one antenna and that they said other people have been using these same antennas with no complaints.
Can anyone explain this? Is there a misunderstanding between me and Stein? Can anyone here vouch for the fact that they have one of these antennas and can make an ILS approach? i.e. a PRECISION approach?

Stein is correct. The Bob Archer hooked to the GTN 650 will sort out the higher frequency from the Archer antenna quite nicely. I have one under the fiberglass tip on my RV-10 and it works perfectly.

On my RV-8, I actually made the GS antenna with a tuned length of stripped coax and ran the GS antenna down the inside of my left gear leg fairing and it works perfectly on the Garmin 430 WAAS. The reason for the doing it that way was the 430 has a second B&C connector for the GS antenna input. Others have used splitters on the one antenna and that works too, but the signal strength may be less.
 
....On my RV-8, I actually made the GS antenna with a tuned length of stripped coax and ran the GS antenna down the inside of my left gear leg fairing and it works perfectly on the Garmin 430 WAAS....

I've been researching this for a while now and I'm going to do it for my VOR and GS this weekend but my plan was to install it in front of the canopy arc like in this thread

http://www.vansairforce.com/community/showthread.php?t=40633&page=3

For the last 3 weeks researching this my doubt has been, and I'm still trying to it figure out, why everyone is using 16" because 234/113 Mhz (middle of frequency range) = 2.07 feet not 16" !

What length did you strip on your RV-8 and why?
 
I've been researching this for a while now and I'm going to do it for my VOR and GS this weekend but my plan was to install it in front of the canopy arc like in this thread

http://www.vansairforce.com/community/showthread.php?t=40633&page=3

For the last 3 weeks researching this my doubt has been, and I'm still trying to it figure out, why everyone is using 16" because 234/113 Mhz (middle of frequency range) = 2.07 feet not 16" !

What length did you strip on your RV-8 and why?

First of all, the GS frequencies are 329 to 335 MHZ. If you used the listed 234/113, that's why your math is not working out.

Using the formula of WAVELENGTH X FREQUENCY = SPEED OF LIGHT (C) and run the numbers for the middle of the band for GS frequencies, the math works out as 35.55 inches for a full wave antenna. This makes the exact length of the stripped portion of a 1/2 wave antenna at 17.78 inches. The 16 to 17 inches of the stripped center conductor of a piece of coax stuffed down the gear leg of my 8 has worked perfectly for years.


Would do it again in a second:).

I had to get the calculator out and shake off a few cobwebs in the brain on that one:)....
 
This makes the exact length of the stripped portion of a 1/2 wave antenna at 17.78 inches. The 16 to 17 inches of the stripped center conductor of a piece of coax stuffed down the gear leg of my 8 has worked perfectly for years.
...

This just illustrates what Don said, above: with a 40 watt gs transmitter 5 miles away, almost anything, including a coat hangar, will work. A ?proper? half wave dipole for GS will have 9? of insulated center conductor (no shield) oriented left-right, and 9? of shield (no center conductor) running right-left, with the intact coax running away at 90 deg (usually up). 18? of center conductor running down a gear leg is a poor 50 ohm match, limited horizontal polarization, yet often works okay. Modern receivers are incredibly sensitive.
 
So, which wing is best to install the Archer antenna, Left or Right?

In the Right wing you have an autopilot servo and in the left you have the controller for the pitot heat (Dynon in my case). I plan on installing mine in the left wing, thinking the pitot heat controller would give less interference than the AP servo.

Thoughts?
 
First of all, the GS frequencies are 329 to 335 MHZ. If you used the listed 234/113, that's why your math is not working out.

Using the formula of WAVELENGTH X FREQUENCY = SPEED OF LIGHT (C) and run the numbers for the middle of the band for GS frequencies, the math works out as 35.55 inches for a full wave antenna. This makes the exact length of the stripped portion of a 1/2 wave antenna at 17.78 inches. The 16 to 17 inches of the stripped center conductor of a piece of coax stuffed down the gear leg of my 8 has worked perfectly for years.


Would do it again in a second:).

I had to get the calculator out and shake off a few cobwebs in the brain on that one:)....

You misunderstood my post. At the beginning of my post I said I was making a VOR and GS antenna.

I wrote 234/113 Mhz (middle of frequency range) = 2.07 feet not 16" !

where the 113 Mhz is the center of the VOR range 108 - 117.95

SO

234 divided by 113 = 2.07 feet x 12 = 24.84 inches for a VOR ( radiating element ) dipole.


If I were going to make it for the GS only I'd use the shorter antenna :

234/332 Mhz (332 is the middle of 329 to 335 Mhz) = 0.70 feet x 12 = 8.45 inches for the radiating element of the 1/2 wave dipole.

So my numbers were correct for a VOR antenna where apparently the 16" is what some are using for the GS only antenna. At least that cleared up where they got the 16".
 
You misunderstood my post. At the beginning of my post I said I was making a VOR and GS antenna.

I wrote 234/113 Mhz (middle of frequency range) = 2.07 feet not 16" !

where the 113 Mhz is the center of the VOR range 108 - 117.95

SO

234 divided by 113 = 2.07 feet x 12 = 24.84 inches for a VOR ( radiating element ) dipole.


If I were going to make it for the GS only I'd use the shorter antenna :

234/332 Mhz (332 is the middle of 329 to 335 Mhz) = 0.70 feet x 12 = 8.45 inches for the radiating element of the 1/2 wave dipole.

So my numbers were correct for a VOR antenna where apparently the 16" is what some are using for the GS only antenna. At least that cleared up where they got the 16".

My bad !! Sorry. I assumed you were using the Bob Archer antenna, which works great for the VOR.
 
Just to be clear, a dipole for 113 MHz consists of two center fed radiating elements, each of which is 25”.

Technically the entire antenna is radiating but in this case I used the term to differentiate between the stripped part and the double shielded part. I didn't want to confuse anyone so I tried to keep it simple. When they strip the shield back and leave 24.85" clear (the part they'll show exposed ) then by default they'll have 24.85" of shield ( the other side of the dipole).

That's why in my post you see it says radiating element. The other side of the dipole (the shield in this case) is also 24.85" long.

234 divided by 113 = 2.07 feet x 12 = 24.84 inches for a VOR ( radiating element ) dipole.
 
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VOR/NAV Coax ??

I have weak reception on both VORs which like most planes, share a V antenna. I did not build my RV6A so as I begin to troubleshoot, I want to make sure the coax that is installed is correct. This is my question... what coax type(s) are acceptable for the VOR/GS antenna system? Tom
 
RG-58 and RG-400 are two popular choices, RG-58 was used in thousands of Cessna and Piper aircraft with many still flying 50 years later with the original coax.
Rg-400 is a higher quality, premium coax widely used in military, commercial, and amateur built aircraft.
RG-400 is more expensive but fortunately not much is required in our small aircraft so the cost to go first class is not significant.
 
Thanks Don

Thanks Don, my guess is I have 58 then. I can look in the back of the vertical stabilizer and see the BNC connector on the antenna. The outside looks corroded. For some reason there are over 20 rivets holding the top vertical stabilizer fiberglass cover on, which will need to be removed to obtain access to the connector to check it out. Tom
 
Thanks Don, my guess is I have 58 then. I can look in the back of the vertical stabilizer and see the BNC connector on the antenna. The outside looks corroded. For some reason there are over 20 rivets holding the top vertical stabilizer fiberglass cover on, which will need to be removed to obtain access to the connector to check it out. Tom

RG-58 is going to have a black outer cover, RG-400 is going to have a "rose-gold" outer cover.

In my experience, the failure of antenna systems is almost always at the termination -- bad crimps, broken wires, corrosion, etc. Occasionally a piece of coax will be "kinked" below the minimum bend radius or crushed or cut in half :) Generally speaking, if it did work at one time and has since gone bad, then it's likely at the terminations...
 
I don’t want to hijack this thread, but it seems the right people are participating, so: I have an Archer antenna installed in my right wing-tip and, while it works, the reception range is too limited to be useful. I receive a VOR only within about 5-7 miles from the station. That tells me the G650 is correctly wired, but even though I believe I wired the antenna according to the Archer instructions, there is clearly something wrong. I have RG400 coax with connectors installed at both the wing-root and wing-tip for ease of installing the wing and tip. How should I go about trouble-shooting? Suggestions would be appreciated. :eek:
 
I don’t want to hijack this thread, but it seems the right people are participating, so: I have an Archer antenna installed in my right wing-tip and, while it works, the reception range is too limited to be useful. I receive a VOR only within about 5-7 miles from the station. That tells me the G650 is correctly wired, but even though I believe I wired the antenna according to the Archer instructions, there is clearly something wrong. I have RG400 coax with connectors installed at both the wing-root and wing-tip for ease of installing the wing and tip. How should I go about trouble-shooting? Suggestions would be appreciated. :eek:

You likely have problem in the bnc crimp or the ring terminals. I wouldn't be surprised if the 650 could pick up a VOR at 5 miles with no antenna or at least a dummy load.

Did you ensure that the Archer is grounding to the wing structure? This is pretty critical.

Larry
 
Mark,

I agree - something is wrong. On my homebrew wingtip antenna I get 100+nm VOR reception at altitude.

I suspect you did not install the antenna correctly, or you have a bad connection. I note one GTN-650 install had a similar problem. Ringing out the coax identified the tray coax connection made was just a little proud on the solder joint - it shorted the center pin to ground.

As I have mentioned in other posts, troubles shooting and tuning of wingtip antennas requires an Antenna Analyzer. Find a local ham that has one and have him ring out the antenna and feed line. Better yet have your local EAA chapter get one for the shared tool bin. Here is the one I’ve been using for years:
https://www.dxengineering.com/searc...autoview=SKU&sortby=Default&sortorder=Default

Carl
 
Grounding

I don’t want to hijack this thread, but it seems the right people are participating, so: I have an Archer antenna installed in my right wing-tip and, while it works, the reception range is too limited to be useful. I receive a VOR only within about 5-7 miles from the station. That tells me the G650 is correctly wired, but even though I believe I wired the antenna according to the Archer instructions, there is clearly something wrong. I have RG400 coax with connectors installed at both the wing-root and wing-tip for ease of installing the wing and tip. How should I go about trouble-shooting? Suggestions would be appreciated. :eek:

I was fortunate to get about 90 minutes with Mr. Archer about a year before he passed. His background was fascinating and his willingness to pass on that knowledge free of charge was humbling.

The two things he stressed is that the antenna itself is only a part of reception. He is actually using the wiring within the aircraft as an extended antenna. For his design to work you need two things: (1) a very good ground to the airframe. If you are using a piano hinge to attach the wing tip, like me, be sure to sand off the anodizing. Anodize is an insulator. If using the standard screws, make certain you have a very good ground to the wing. (2) make certain the coax has a very good connection to the antenna, remember you are using the wiring harness as much as the actual antenna.

Conversing with Mr. Archer was a high point in my build.
 
Thanks for the quick responses! The grounding comments may be my problem. I did use hinges to attach the wing-tips and did not remove any anodizing. I have also contacted “a ham guy” to see if he is equipped to help “ring out” the antenna. This forum is truly a wonderful resource! :)
 
So how is the grounded leg of the antenna electrically connected to the hinges?
My money is on one of the connectors/connections. You can check them out with an ohmmeter.
 
So how is the grounded leg of the antenna electrically connected to the hinges?
My money is on one of the connectors/connections. You can check them out with an ohmmeter.

It is connected to the wing-tip side of the hinge, but only makes a ground connection to the wing through the hinge pin and whatever other contact between the two hinge halves. I had considered running a ground wire from the antenna to the outboard wing rib, but decided it would be awkward during wing-tip installation. I may end up doing that now to be sure.
 
Or - just mount it to the rib and skip the ground issue. The wingtip just slides over the antenna.
Carl
1-B560-D3-B-C2-D0-4-B89-B19-A-5883062-DDC2-C.jpg
 
Resolved Weak VOR Reception

In the air, 4-5 miles from the RQZ VOR, I could barely hear the VOR ID above the noise. Today, 12 miles from the VOR, one the ground in the hangar, very clear. The issue was the coax coming from the BNC connector on the bottom of the antenna puck was pressing hard against a rid on the top of the vertical stabilizer (see photo). Re-installed the connector and added a right angle connector. I guess 17 years of flying finally took its toll.
 

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Coaxial cables have a specified minimum bend radius (amount depends on cable), for reasons that are all too clear now. I guess the original guy didn't quite get that. Over 17 years the copper center conductor can actually migrate thru the poly dielectric at a bend like that.
 
To close the loop on my Archer antenna problem, I had a ham radio friend check the antenna from the 650 end and the SWR was about 9 vs the recommended <2. So, we pulled the wingtip to disconnect the antenna and install a standard to check the wiring, and discovered the center coax wire was broken at the antenna. Not sure if it was the result of vibration or wing tip removal in the paint shop. Anyway, the SWR is now about 1.8 and I have confirmed reception of multiple VORs and the ILS at my home field. No modification of the routing of the light wiring or the piano hinge is apparently going to be necessary. Thanks, again, for the suggestions and advice! 😎
 
Whats wrong with GPS approaches?

Mins are typically 300 AGL. Is that not low enough? Why add the weight and complexity of for and ILS. GPS is more reliable than LOC or VOR.
GPS is more accurate than LOC.
 
It is part of the 650 I have installed and it only took an antenna to have it as an option/redundancy. There are still a lot of airports that offer ILS first, although I often ask for the gps instead. ;)
 
Mins are typically 300 AGL. Is that not low enough? Why add the weight and complexity of for and ILS. GPS is more reliable than LOC or VOR.
GPS is more accurate than LOC.

But when there's a GPS outage it blankets a large area while one inop VOR only usually affects an approach into 1 airport, so you just fly the the next one.
 
Mins are typically 300 AGL. Is that not low enough? Why add the weight and complexity of for and ILS. GPS is more reliable than LOC or VOR.
GPS is more accurate than LOC.

No, no, and no.
1. My last instrument student and I encountered slightly worse than forecast wx on his ifr x/c. We had planned to use the 300’ DA LPV approach from the south, but ended up using the ILS from the north. Actual ceiling was 220’ agl.
2. A nav-com weighs an insignificant amount more than a com. There is the antenna, though.
3. I have never had an ILS fail while I was using it. But a year and a half ago I watched an ifr student under the hood start squirming, and finally admitting, that he didn’t think the LPV glide slope was working. I pointed out that the GS was in fact showing a flag, and that the green ‘LPV’ on the 650 had gone to a yellow ‘LNAV’. Ten seconds later everything went away, and a big red x appeared. We were about 800’ agl and, fortunately, in vmc. I’ve never had an ILS fail like that. We never did find the reason for the outage.
4. GPS is less, not more, accurate than an ILS. Technically an ils is a precision approach, but gps-lpv’s don’t quite meet the technical standards.
 
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