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Archer Nav antenna proximity to other materials

jwyatt

Well Known Member
I'm experiencing some "wagging" on my VOR / LOC indication (GTN650Xi + AFS4500) an trying to track down potential causes.

My Archer Nav antenna is installed in the left wingtip using the same strategy others have shown here -- as far aft as practical, away from the tip lights. I do have foam ribs inside the wingtip, though. Will this cause a problem with reception? I presumed not when I intalled it, since the instructions say it can be laminated into a fiberglass structure.

PXL_20220630_012516683.jpg

Tonight I was able to pick up a VOR at ~30nm, 1700AGL, but the indication wags +/- 4 degrees on a 6-10sec period. AP is unusable to track the radial due to the swinging.

Wouldn't be as concerned, but I'm planning to start IFR training and would like things to work properly for that endeavor.

I could cut away the foam ribs. Also remount directly to the tip rib on a piece of angle, to bypass the hinge connection (the hinge did have the anodize sanded off where the antenna is riveted on).
 
I wouldn't think the foam would have any adverse affect on reception.

Bob has some VERY specific guidelines about how the antenna wires are routed, but I don't have his instructions in front of me right now. Is your RG400 cable run exactly as he describes? It may very well be within his parameters, but I seem to remember mine running differently.
 
The antenna base needs to be tied to the airframe ground to work properly and is a key requirement for this style of ant. Most do this by sandwiching it under the nut plates and this provides a good, low resistance connection. Yours is sandwiched under a hinge and I would speculate this is producing a lot of resistance (hinge eye to rod to hinge eye, all of which is loose). I suggest using a wire with connector to bring an airframe ground on to that ant base, then re-test. This would explain the wild variations on the needle, as the resistance is constantly changing due to vibration. A sloppy hinge is a bad way to get a low resistance electrical connection. If you waxed or greased the pin, this just makes it worse.

I get rock steady indications at 80-90 Nm with my archer.

Larry
 
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I'm not flying yet so I don'y have a baseline, but the instructions that came with it didn't reference having it as far aft as possible.

I remember because I thought it was odd, but they want all the wiring run in a specific way, with the wires to the lights routed along the leading edge of the antenna.

I'd start by trying it with all the wingtip light off (especially the strobes) and also make sure wire routing is per the installation instructions.

Fiberglass and foam has nothing to do with your issue.

FYI- here's cut and paste of part of teh installation instructions having to do with wire bundle routing.

"IMPORTANT NOTE / INFO!
The idea is that we want the antenna and the lights and wires to appear as one to the RF energy. That is why all the wires should go through the provided clamps and snuggle up to the lights etc. If the lights and wires are separate from the antenna they act as independent antennas and with the low impedance to ground short out a significant amount of signal to ground. I know this is counter-intuitive but that is how RF energy is sometimes. Maybe I should say usually. The bare metal of the antenna and any bare metal of light housings etc. should not be touching unless they are very well connected because if they touch intermittently from vibration it could cause noise on the system."
 
This is how I always install my DYI wingtip antenna. VOR range is consistently over 100nmi.

Carl
4-BCE022-A-02-A1-49-F6-914-F-7192-DAC90-C24.jpg
 
The coax is connected per the install guide. The position and strobe light wires are not run along the antenna, because I would have needed more length on the light wires than I had (this was a retrofit install). I researched here and found others who had installed like this with good claimed results.

Turning off all lights (nav, strobe, led taxi/landing) however, makes zero difference in the problem. I’ve also tried shutting down both alternators, ignition coils (one at time), transponder, and other electrical items.

I’ll try a grounding strap to bridge the hinge, and see if that improves things. If so, might remount it directly to the tip rib (like Carl shows above). I’m hoping it is the antenna installation, as that’s easy/cheap to address versus a problem with the radio.
 
The coax is connected per the install guide. The position and strobe light wires are not run along the antenna, because I would have needed more length on the light wires than I had (this was a retrofit install). I researched here and found others who had installed like this with good claimed results.

Turning off all lights (nav, strobe, led taxi/landing) however, makes zero difference in the problem. I’ve also tried shutting down both alternators, ignition coils (one at time), transponder, and other electrical items.

I’ll try a grounding strap to bridge the hinge, and see if that improves things. If so, might remount it directly to the tip rib (like Carl shows above). I’m hoping it is the antenna installation, as that’s easy/cheap to address versus a problem with the radio.

I recommend running a dedicated ground from your last rib (or anywhere you like) to the antenna as the piano hinges are not conductive, unless the coating on top is removed. Put your volt meter on two parts of the same piano hinge and do a continuity check, you will see the result.

As the foam goes, which is a different subject, I highly doubt that it has anything to do with the reception of your antenna, but foams generally are not a good material as they can collect moisture.

As a reference, I can pickup a steady signal 100 NM away from a VOR and my setup is similar to yours but I do have a extra ground wire connecting from the rib to the antenna body.

P.S. If you are up for redoing the antenna, I would move it even farther back. Three NAV antenna in the wing tips (installed as far back as I could) and have had zero issues.
 
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A few thoughts.
1. Like others, I don't think your foam/fiberglass is an issue (assuming it's not carbon fiber!)
2. If you follow up on others' suggestion with a direct wire connection from the antenna ground leg to the end rib, keep the wire as short as possible.
3. I don't like the coax running over the radiating end of the antenna.
This is where the highest RF current will be. Look at Carl's photo, he has the coax going away from the feed arm at 90 deg, then immediately up against the end rib then into the wing.
4. Have you tried an ILS? Just curious to see how that works. As you know, the way the signals are encoded is completely different.
5. Any chance the line of sight between the antenna and the VOR passed thru the prop arc? Sometimes the prop can 'strobe' the signal and produce strange effects like this. Next time try a small rpm change, see if that does anything.
 
I also have this wagging needle when tuned to a VOR with my IFD440. I can receive at more than 80 miles or be looking at the VOR station, doesn't matter, the needle wags.

If I've tuned a Localizer, it has a rock-solid indication

Let us know if you figure it out.

Travis
 
Bob and Carl are far more knowledgeable than I, but I suspect that your choice of fixation of the base leg to the end rib/airframe via the hinge material *is* the issue.

AN257, MS20001 hinge stock is anodized and is a lousy conductor at RF/AC and DC.

The radiator/driven element in the gamma match (the little stub of aluminum sandwiched with FR4) needs to "see" the reflector in the system -- with the mounting you've chosen, the reflector (the end rib/airframe) is not present.

The fix, as Mehrdad suggested, is to connect that base leg to the end rib via a ground strap -- I would use two, equal length connectors at each end. Or, as I, Carl, and others have done, directly mount the base leg to the end rib.
 
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Archer VOR Antenna

Joshua,

Let us know if you get anything worked out. Brian may have it pegged. "AN257, MS20001 hinge stock is anodized and is a lousy conductor at RF/AC and DC."

I have basically the same issue with my archer VOR antenna. Mounted as the pic you posted. Only I have never been able to pick up any signal.

Eulice Curington
RV-10 N104EW Flying
 
It is really important to sand the piano hinge where it contacts metal. If you didn’t remove the anodizing then the only ground plane that you have is running through the rivet holes (which is not good). That is your most likely reason.
 
Just for curiosity’s sake run a jumper grounding wire from the antenna shield/ground terminal to a #6 or #8 machine screw maybe add a couple of toothed washers as well into one of the tooling holds in the outboard rib to see if that clears up the intermittent signal that’s causing the “wagging needle”
 
Joshua,
I have basically the same issue with my archer VOR antenna. Mounted as the pic you posted. Only I have never been able to pick up any signal.

Eulice Curington
RV-10 N104EW Flying

Even with a horrible ground you should receive something. Something else is wrong.
 
I'm experiencing some "wagging" on my VOR / LOC indication (GTN650Xi + AFS4500) an trying to track down potential causes.

My Archer Nav antenna is installed in the left wingtip using the same strategy others have shown here -- as far aft as practical, away from the tip lights. I do have foam ribs inside the wingtip, though. Will this cause a problem with reception? I presumed not when I intalled it, since the instructions say it can be laminated into a fiberglass structure.

View attachment 36467

Tonight I was able to pick up a VOR at ~30nm, 1700AGL, but the indication wags +/- 4 degrees on a 6-10sec period. AP is unusable to track the radial due to the swinging.

Wouldn't be as concerned, but I'm planning to start IFR training and would like things to work properly for that endeavor.

I could cut away the foam ribs. Also remount directly to the tip rib on a piece of angle, to bypass the hinge connection (the hinge did have the anodize sanded off where the antenna is riveted on).

The grounding problem is the most likely issue. The hinge joint probably won't provide an adequate ground. The entire edge that you have riveted to the hinge has to be grounded extremely well. My wingtips are screwed on. I put 4 layers of aluminum foil under the inboard part of the antenna and wrapped it around on top of the wing tip where it screws on. I also made sure the aluminum skin was completely bare un the underside where it was going to serve as a ground. The VOR for my GTN650 works great. As well as the corporate jets I flew for a living.
 
The grounding problem is the most likely issue. The hinge joint probably won't provide an adequate ground. The entire edge that you have riveted to the hinge has to be grounded extremely well. My wingtips are screwed on. I put 4 layers of aluminum foil under the inboard part of the antenna and wrapped it around on top of the wing tip where it screws on. I also made sure the aluminum skin was completely bare un the underside where it was going to serve as a ground. The VOR for my GTN650 works great. As well as the corporate jets I flew for a living.

I suggest such extreme measured for “ground” are not required or desired. The antenna is looking for a counterpoise - not a DC ground like your battery. Bolt the base of the wingtip antenna to the end rib and you are done - even if it is primed. If you are installing antennas with a piece of sandpaper I recommend you reconsider.

Most antenna issues are not about “ground”.
Carl
 
I suggest such extreme measured for “ground” are not required or desired. The antenna is looking for a counterpoise - not a DC ground like your battery. Bolt the base of the wingtip antenna to the end rib and you are done - even if it is primed.

Lousy weather here has meant no ability to flight-test any mods until this afternoon. Running a wire from the antenna shield lug to an existing screw on the end rib seems to have improved performance but not a complete resolution (the wagging needle is less severe but still present particularly for distant stations, and range still seems limited compared to what others are reporting). I’m going to redo the mount directly to the end rib.
Carl, are you saying above that it’s not necessary to remove primer from the end rib where the (unprimed, I presume) mounting angle attaches?
 
It is really important to sand the piano hinge where it contacts metal. If you didn’t remove the anodizing then the only ground plane that you have is running through the rivet holes (which is not good). That is your most likely reason.
+1
Even with a horrible ground you should receive something. Something else is wrong.
Bob you'd be surprised. Major AD's on transport jets have involved anodized parts separating grounding. Not sure reason his VOR is wiggling but this could be it.
 
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SNIP
Carl, are you saying above that it’s not necessary to remove primer from the end rib where the (unprimed, I presume) mounting angle attaches?

To review:
- The wingtip NAV antenna is a simple, quarter wave antenna using a traditional gamma match to bring it to ~50 ohm impedance to match the coax.
- A quarter wave antenna can be considered a dipole where one leg of the dipole is replace by a ground plane or such. For this antenna the ground plane is the wing rib.
- While an electrical connection is required to the end rib, we need not get carried away. Mount it like I showed on my photo using two #8 screws, add a star washer if you like between the mounting angle and the rib.

For those of you mounting it to the hinge, be careful. The hinge material on the wingtip will provide the antenna “ground” that you need. I’m not sure about the effect of the wingtip hinge and hinge pin - as in if there is always a good RF connection then all will be good. If not, your could have transient issues.

Adding jumper wires and such to “ground” the antenna become elements of the antenna. Results are unknown pending analyzer check out.

I suggest two paths forward:
- Mount it like I did.
- The antenna installation is not done until you put an antenna analyzer on it to verify operation (just like you should do for all your antennas). Every EAA chapter should have one in their shared tool locker. Attach the analyzer at the connection to your radio to ring out the feed line and the antenna.

Side note - I modify my antennas to extend out the fill width of the wing tip. This gives a longer leg out before the “front to back” leg. For quarter wave antennas the base of the antenna (here the leg going out from the wingtip) is the high current point - and does the majority of the work. The “front to back” leg brings the antenna into resonance at the desired frequency.

Carl

C81172-AB-9-CD3-4467-BA9-C-14-FF4-BEAE617.jpg
 
I suggest two paths forward:
- Mount it like I did.
- The antenna installation is not done until you put an antenna analyzer on it to verify operation

Taking advantage of a little warmer weather, I remounted the antenna much as Carl depicted, directly to the end rib with a piece of angle and a couple screws.

PXL_20230117_004108153.jpg

No performance details yet, as we're not scheduled to see anything but low clouds for the forseeable future, but I'll update the thread when I have a chance to give it a try.

Meanwhile, an antenna analyzer is on its way to me, so I'll occupy myself learning how to use it and checking out all my antennas.
 
I'll update the thread when I have a chance to give it a try.

A brief break in the 400 OVC we'e had for what feels like ages allowed for a quick hop this afternoon; sadly the VOR indication is still wagging with the antenna now firmly mounted to the wing end rib. Max receive range at 4k' was about 35nm to three local stations; anything outside that distance caused the CDI to flag.

Antenna analyzer (measuring at the radio end of the coax) indicates that it's tuned a fair bit high, with an SWR range of 1.7 to 2.8 across the VHF NAV range. This is a stock prebuilt Archer; I could try riveting on a few extra inches of aluminum strip to the trailing edge to tune it lower -- I'm not enough of an RF guy to know if this is bad enough to be impacting performance as much as I'm experiencing.

24.01.2023_19.59.58.png

I should also note that I've tried turning off most everything electrical, including both alternators, ignitions & fuel pumps (one at a time), all lighting, and other radios. The only electrics remaining are the things needed to stay airborne -- EFI/EI, one fuel pump, and my EFIS. None of that made a noticeable difference in either the indication, orany audible noise on the NAV receiver.

Next steps I suppose are
  • run new, freshly terminated coax (via a different route - eg. not in the same bundle as other wiring?);
  • find another GTN650Xi to temporarily swap in;
  • mount a cat-whiskers to the tail, again with new coax & connectors;
  • and/or take it to the avionics shop (where I assume there might be some sort of VOR test equipment available).
 
When I look at the photo in post #20 it appears there is something (resistor?) attached at the coax feed point. What am I looking at?
 
When I look at the photo in post #20 it appears there is something (resistor?) attached at the coax feed point. What am I looking at?

No resistor, the coax conductor and shield braid are crimped into standard AMP ring terminals. You may be seeing the orange self-fusing tape I wrapped around the cable to allow the supplied nylon clamp to get a firm grip on it and prevent vibrations. A crop from the full-size photo is attached.

37DE843E-3A7D-43EB-B1CB-6CAA4705F634.jpeg
 
Next steps I suppose are
  • run new, freshly terminated coax (via a different route - eg. not in the same bundle as other wiring?);
  • find another GTN650Xi to temporarily swap in;
  • mount a cat-whiskers to the tail, again with new coax & connectors;
  • and/or take it to the avionics shop (where I assume there might be some sort of VOR test equipment available).

A problem in the coax or it's crimped on terminals would be the next place that I was looking. I would bridge the center pin to the shell on one side and then measure resistance between center pin and shell on the other side. It should be close to 0.
 
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For grins and giggles, place a pieces or pieces of aluminum sheet or HVAC tape (the aluminum kind, not the mylar kind) over the lightening holes in the tip rib, between the rib and the antenna base leg.

This is a total wag, but if the driven element needs a “reflector” (counterpoise), the location of the gamma match relative to the giant hole may be the source of the issue…
 
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Considered VOR Class & expected Range ?

Max receive range at 4k' was about 35nm to three local stations; anything outside that distance caused the CDI to flag.

Have you considered Info in Airmens Information Manual (AIM) 1.1.8 NAVAID Service Volumes ?
RST = Rochester VOR-DME Altitude code: L (low) 40nm when 1000 above transmitter elevation (1380 msl)
AEL = Albert Lea VOR-DME Altitude code: T (terminal) 25nm when 1000 above transmitter elevation (1265 msl)
ODI = Nodine VOR H-VORTAC 40nm when 1000 above transmitter elevation but less than 10000 (1280 msl)
FOW = Halfway VOR T-VORW/DME 25nm when 1000 above transmitter elevation (1098 msl)
Actual measure performance MAY not be as lacking as you think.
 
You have a BNC male connector on the coax, close to the antenna. Is this going to a female bulkhead connector installed on your rib? If so, is the body of the bulkhead connector insulated or connected to the coax shield (both types are available).

I originally had a similar setup with a grounded bulkhead connector, and it created an unusable condition similar to what you're seeing. Once I replaced that with an isolated bulkhead connector, all was well.

https://www.l-com.com/coaxial-coaxial-adapter-bnc-bulkhead-insulated-ground


If you're not using a bulkhead connector, ensure that the connectors are insulated and unable to touch other metal.
 
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Really appreciate all the suggestions!

I'm going to go after inspecting and testing the cable next, that's the easiest remaining thing to do before running new cable. It was installed running bac to the tailcone with the original build 12-ish years ago, and lay dormant until I installed this antenna, when I re-routed it to the wingtip.

place a pieces or pieces of aluminum sheet or HVAC tape (the aluminum kind, not the mylar kind) over the lightening holes in the tip rib, between the rib and the antenna base leg.
Ths would be easy to try ... added to the list.

Have you considered Info in Airmens Information Manual (AIM) 1.1.8 NAVAID Service Volumes ?
RST = Rochester VOR-DME Altitude code: L (low) 40nm when 1000 above transmitter elevation (1380 msl)
AEL = Albert Lea VOR-DME Altitude code: T (terminal) 25nm when 1000 above transmitter elevation (1265 msl)
ODI = Nodine VOR H-VORTAC 40nm when 1000 above transmitter elevation but less than 10000 (1280 msl)
FOW = Halfway VOR T-VORW/DME 25nm when 1000 above transmitter elevation (1098 msl)
Actual measure performance MAY not be as lacking as you think.
Good info Steve -- that's the exact list of sites I'm testing in flight. RST is just several miles from the airport, and I've been well inside 20 miles at 4k' when seeing the needle wag.


You have a BNC male connector on the coax, close to the antenna. Is this going to a female bulkhead connector installed on your rib? If so, is the body of the bulkhead connector insulated or connected to the coax shield (both types are available).

I originally had a similar setup with a grounded bulkhead connector, and it created an unusable condition similar to what you're seeing. Once I replaced that with an isolated bulkhead connector, all was well.
In the initial installation, I did have it as you described, with a grounded bulkhead jack on the rib. When I moved it to mount on the wingtip, I removed that bulkhead jack from the rib, and covered the mated connectors with shrink tube to isolate them, before securing them to the (plastic) wing conduit. So unless the insulation has been breached elsewhere in the cable run, it shouldn't be grounded other than via the antenna; I will recheck that with a meter, though.
 
Archer VOR Antenna Ground

Hinge mounted wingtip w/Archer VOR antenna mounted exactly as the original poster. Did not have signal. Installed a grounding strap from the leg of the Archer antenna to the wing rib as suggested. I now have signal.

Eulice Curington
RV-10 N104EW Flying
 
60 miles

With the antenna analyzer, I tested and added a length of aluminum strip to lengthen the antenna -- brought the SWR down to average 1.6 across the nav band:
29.01.2023_21.27.45.png
(red trace current, pink trace from before lengthening) I coud probably trim it just a bit still.

Some test flying indicated an improvement in performance, but interestingly I'm now noticing radio noise when I unsquelch the nav receiver. The GTN must be doing some significant automatic gain adjustments, because I can hear the noise floor change compared to the morse ID audio -- from very high noise at a distance to the station, down to a "normal" level when closer. I was able to isolate the major noise source to be my lighting -- nav lights, strobes, and taxi/landing lights are all contributing.

With lights off for testing, I can now pull in a station beyond 40 miles, and the needle is generally steady. Turning on any lighting will cause the indicator to flag unless much closer to the station. Flip-flopping from a near station to a far one, you can hear the gain ramp up. The strobes and wigwag lights create cyclic noise, the nav lights steady noise; all are LED units. I don't hear the same noise in my Comm with the squelch open.

I'm going to talk with the manufacturer of the nav/strobes, but they are installed as outlined in the instructions. My taxi/landing lights aren't the finest product -- just PAR36 replacements off Amazon -- but I'm surprised that there is so much noise in the nav band that's not in the comm band, unless the nav receiver is adding THAT MUCH more gain. I listened for radio noise in earlier testing, before tweaking the antenna, and didn't hear anything like this.

So, some progress, but still problems to deal with, as running lights-out isn't a solution. I still have the original halogen reflectors/bulbs that I could go back to on the PAR36 lights, but no replacement for the nav/strobes.
 
- but I'm surprised that there is so much noise in the nav band that's not in the comm band, unless the nav receiver is adding THAT MUCH more gain.

Remember the wingtip Archer is something like 10 times closer to the nav/strobe lights than your com antenna. That’s 100x power difference.

If you’re looking to change nav/strobe lights, or landing lights, consider FlyLeds, either direct from Australia or from Flyboys in the US. They use dropping resistors instead of pulse width modulation to keep the leds from burning up, which means they draw more current than the PWM designs, but also means no RF generated.
 
I'm experiencing some "wagging" on my VOR / LOC indication (GTN650Xi + AFS4500) an trying to track down potential causes.

My Archer Nav antenna is installed in the left wingtip using the same strategy others have shown here -- as far aft as practical, away from the tip lights. I do have foam ribs inside the wingtip, though. Will this cause a problem with reception? I presumed not when I intalled it, since the instructions say it can be laminated into a fiberglass structure.

View attachment 36467

Tonight I was able to pick up a VOR at ~30nm, 1700AGL, but the indication wags +/- 4 degrees on a 6-10sec period. AP is unusable to track the radial due to the swinging.

Wouldn't be as concerned, but I'm planning to start IFR training and would like things to work properly for that endeavor.

I could cut away the foam ribs. Also remount directly to the tip rib on a piece of angle, to bypass the hinge connection (the hinge did have the anodize sanded off where the antenna is riveted on).


I thought that the Bob Archer antenna is VOR only?

Can it also be used as a LOC and G/S antenna?

In order to do both did you use a diplexer?
 
The GTN650 has only a single nav antenna connector, if there’s a diplexer involved, it’s internal to the radio.
 
I thought that the Bob Archer antenna is VOR only?

Can it also be used as a LOC and G/S antenna?

In order to do both did you use a diplexer?

The LOC and VOR frequencies are interspersed, so yes the antenna works for both. The GS frequencies are 3 times higher frequency than the localizer; the basic antenna works well at half-odd harmonics (1/2 wave, 3/2 wave, 5/2….) so it’s good at GS frequencies. The matching network won’t be perfect, but mine certainly works well enough (e.g., I alway get solid gs and loc signals at nominal intercept range).

No diplexer is need between loc and vor signals, the nav radio will automatically direct them to the proper de-coder circuit. If your nav radio has a separate gs input, then yes, you’ll want a diplexer. Many nav radios have one built in these days.
 
No diplexer is need between loc and vor signals, the nav radio will automatically direct them to the proper de-coder circuit. If your nav radio has a separate gs input, then yes, you’ll want a diplexer. Many nav radios have one built in these days.

Caution thread drift- It is interesting to note that glideslope originally required a separate blind box as a receiver. It was wired to the nav receiver for channeling, and used an independent glideslope antenna. Then it was determined that glideslope could use the nav antenna and people in GA started using a diplexer to split the signal and feed it to the glideslope receiver. As electronics got smaller, glideslope receivers were incorporated into the Nav receiver box, but still used a separate coax input. That gave folks the option of keeping a discrete GS antenna if they had one. As electronics has gotten smaller, now many nav receiver units include the diplexer internally as they don’t expect a GS antenna on the aircraft. Can’t remember the last time I saw a dedicated GS antenna except on some transport airplanes where they are mounted under the nose radome.
 
Caution thread drift- It is interesting to note that glideslope originally required a separate blind box as a receiver. It was wired to the nav receiver for channeling, and used an independent glideslope antenna. Then it was determined that glideslope could use the nav antenna and people in GA started using a diplexer to split the signal and feed it to the glideslope receiver. As electronics got smaller, glideslope receivers were incorporated into the Nav receiver box, but still used a separate coax input. That gave folks the option of keeping a discrete GS antenna if they had one. As electronics has gotten smaller, now many nav receiver units include the diplexer internally as they don’t expect a GS antenna on the aircraft. Can’t remember the last time I saw a dedicated GS antenna except on some transport airplanes where they are mounted under the nose radome.

Ha! Brings back memories. I once was a partner in a 1976 182 with original nav/GS. Nav rabbit ears high on vertical stabilizer fed coax to nav receiver in the panel. Small GS dipole on top of windscreen, coax ran back to tailcone where GS receiver was. Lots of wires connecting the two boxes and the CDI.
 
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