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Archer NAV issues....

hlangebro

hlangebro

Well Known Member
I realize this have been brought up many times here on the forums, but I still havent found my smoking gun for my bad Glideslope reception. Everything is routed as per instructions. My ground is alu tape on the tip and on the wing, though nutplates. LOC works fine, but of course it is a different frequency.
First thing that comes to mind is if the alu tape provides enough ground? I could put in copper or add a separate ground strap....?

I also have strobes and HD led landing lights. Can there be an EMI issue?
All of you who had this problem, how did you solve it?
If the coax was bad, then I wouldnt have LOC and VOR reception either right?
It is not that I dont have glideslope reception, but I only get it very close to the airports, and I have tried a few airports and the result is the same. It is about 1-2 miles out at the most...
 
I think it depends on the receiver you are using. My Garmin GTN650 does not have a GS antenna connection. However I believe the 430W and SL30 require a separate connection and it requires a splitter.
My Archer in the wing tip works great for GS. I do however get a interference with the HID lights on with the LOC. With HID lights off I get 100 miles. On only 50.
 
I have the SL30, and it has a built in splitter.
Like I said, it is not that it doesnt work, it is just the distance out from the airport that is not too far. I have the autopilot coupler in my RV, and it would be really nice to have that work reliably. I have done coupled approaches and once the glideslope catches on, it works great.

Did you come up with some shielding for the HID's?
 
Two suggestions:
1. Temporarily run a piece of coax from the SL-30 up to the top of your windscreen; split it there into dipole (horizontal) for 330MHz (two arms, each should be about 9" long). Tape them temporarily to the windscreen, go fly. You won't get the localizer very well but the GS should work. If not, you have a problem with the radio. (The GS is a separate receiver from everything else).

2. I did not understand the part about the aluminum tape ground. The Archer design is predicated on having a vertical (electrically conducting) ground plane very close to the location of the ground side of the antenna. This is usually the outboard rib in our planes, and one usually rivets the ground side of the antenna to the nutplates which attach to the wing skin, which in turn is riveted to the rib which is only an inch or so away. IF you used aluminum tape to "extend" the ground further outboard in the wing tip, further away from the outboard rib, the antenna will not work properly, and the degradation will be worse at higher (GS) frequencies.

Some people think the antenna will work better if they get it further away from the rib and the wing, but RF antennas don't work that way.
 
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As far as the alu tape, it is the interface between the antenna and the wing, through the nutplates, just as you said. I need to take some pics. I will most probably go out there on Friday. The coax thing you mentioned sounds interesting!
 
Nav issues

I have a VAL 2000 NAV, Archer Antenna, and Trutrak EFIS. My glide slope and localizer reception is OK but VOR reception is poor. I think it's EMI from the EFIS but I've never been able to fix it. I wasted a lot of time on the antenna. Even installed a second Archer in the other wingtip.

What tipped me off to the interference issue was my Sporty's handheld. I noticed that when I tuned the VOR on the handheld the reception would come and go depending on whether the EFIS was turned on. If you have access to a Handheld with glide slope you might use it as a test device to see if you're getting interference on the glide slope frequency.

These problems are the worst to me. Nobody seems to have an easy answer.
 
Hakan,
I had mounted the HID power supply on the outboard rib. Very close to the Archer. After finding the interference I moved the power supply inboard as far as I could. This helped but did not eliminate. I still get great reception so I left as is.
 
To check for RF interference just try turning these things (strobe, HD lights, EFIS) off, while listening to a VOR; see if the signal to noise improves.
For the record, I have an HD landing light in the same tip as an Archer, and I hear increased noise but just during the first few seconds while the light warms up. I did mount the power supply behind the rib, inside the wing.
 
hlangebro said:
I realize this have been brought up many times here on the forums, but I still havent found my smoking gun for my bad Glideslope reception. Everything is routed as per instructions. My ground is alu tape on the tip and on the wing, though nutplates. LOC works fine, but of course it is a different frequency.
First thing that comes to mind is if the alu tape provides enough ground? I could put in copper or add a separate ground strap....?

I also have strobes and HD led landing lights. Can there be an EMI issue?
All of you who had this problem, how did you solve it?
If the coax was bad, then I wouldnt have LOC and VOR reception either right?
It is not that I dont have glideslope reception, but I only get it very close to the airports, and I have tried a few airports and the result is the same. It is about 1-2 miles out at the most...
Click to expand...


If your receiver has a separate input (for G/S), make up a glide-slope antenna by stripping the shield off of last 16 inches of one end of the coax (leave the insulator on the center conductor) and connect the other end to the BNC connector. This makes a 1/2 wave antenna for the frequency of the G/S. I have one of these to my Garmin 430W slid down the left gear leg fairing of my RV-8 and it works great. Just costs a connector and a few feet of RG-400. YMMV.
 
SL-30 has an internal splitter. So if localizer works okay, GS does not, and you have NOT installed any external splitters, the only thing left is the radio.
 
I was wondering if there would be a difference if the antenna was on the lower surface of the tip instead of the upper?
Just pondering that maybe the strobe and landing lights are shading the ILS beam more if it is on the upper. Maybe having it on the lower gives a better reception??
 
hlangebro said:
I was wondering if there would be a difference if the antenna was on the lower surface of the tip instead of the upper?
Just pondering that maybe the strobe and landing lights are shading the ILS beam more if it is on the upper. Maybe having it on the lower gives a better reception??
Click to expand...

I have had mine on the upper surface for 17-years. Never any issue. I also have an SL30. Can typically pick up a VOR signal before I can hear the ID. VOR Range is typically more than the FAA says it should be. GS and LOC both work very well. I also have a wingtip Landing Light, Nav Light, and Strobe light inside the wingtip.

As Bob Turner suggested, I would try a swap of your SL30 with a friend and see if his does the same and how yours works in his airplane.
 
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I am goin to change and redo my grounding this weekend. I thought it was good, but I will also add ground straps...
Currently I dont know of anyone nearby who has a SL30, so I have to do what I can do in the meantime...
 
I just read on a different post that you did not do the wiring yourself.
Get under the panel with a flashlight and look at the nav coax, from the radio outward as far as you can trace. Make certain that a GS splitter was not inadvertently installed (you're looking for a small square box).

At 6 miles out the localizer and GS signals follow very nearly the same path, so I doubt antenna placement is the issue. It's true the GS is off to the side of the runway; you could yaw the plane toward it, see if it makes a difference (I would be very surprised of it did).
 
BobTurner said:
SL-30 has an internal splitter. So if localizer works okay, GS does not, and you have NOT installed any external splitters, the only thing left is the radio.
Click to expand...

Not necessarily. Localizer frequencies are much higher than VOR frequencies. If the antenna is not properly coupled to the airframe it will have different capacitive and inductive reactance and may be usable at VOR freqs but not at the localizer freqs.

If the antenna does not have a solid low impedance ground to the airframe then it probably won't work well.
 
rocketbob said:
Not necessarily. Localizer frequencies are much higher than VOR frequencies. If the antenna is not properly coupled to the airframe it will have different capacitive and inductive reactance and may be usable at VOR freqs but not at the localizer freqs.

If the antenna does not have a solid low impedance ground to the airframe then it probably won't work well.
Click to expand...

Bob J, I think what you meant was "GS frequencies are much higher than localizer frequencies".
Not sure I'd say "much"; they are 3 times higher.
We all agree (see earlier posts) that he needs a good proper connection to the end rib. But is *sounds* like he has that covered.
 
If you can get your hands on an antenna analyzer or a network analyzer that would be your best bet. Most ham radio guys have one. I've solved a lot of antenna problems with mine.
 
BobTurner said:
SL-30 has an internal splitter. So if localizer works okay, GS does not, and you have NOT installed any external splitters, the only thing left is the radio.
Click to expand...

I agree with Bob. It sounds like the radio is the culprit.
However, I looked at a pic on your build log and it looks as though the antenna pigtail is tie wrapped in an odd manner. Review the Archer installation instructions for how to position wires as an improper installation can cause "issues".
Also by adding a coax connector at the wingtip antenna you have introduced a small amount of signal loss. I doubt that is the issue, however. The path of the coax across the antenna is an easy fix to try before you send the radio out for test/evaluation.

Don
 
hlangebro said:
I do believe the SL30 has a built in splitter, so that wouldn't change anything... unfortunately
Click to expand...

It would produce exactly the symptoms you see. A GS-VOR splitter is not a simple one-into-two box. It preferentially sends 330 MHz signals to the GS output, and 110 MHz signals to the VOR/Localizer output. So if your installer put an external one in by mistake (and just left the GS output open since there is no where to connect it with the SL-30) then the GS signal has been mostly removed before it gets to the SL-30.
 
pictures!

Pictures!
Does your installation look like the second photo, with the coax looped over the high current part of the antenna?
It should look like the first photo, with the coax going toward the ground leg, and then into the wing.
Remember that at 330 MHz a half wavelength is only about 18" (less in the coax) so that loop might do something strange.

I'm at KLVK (east of SFO), not exactly close, but if you want to fly up I'd be willing to swap SL-30's. My GS works fine.
 
Are you referring to the old pics in the build log?
I have changed it since then and routed it per Bob's instructions, but it didn't do much difference.
I will try to take some pics this weekend and hopefully we can see if something is wrong. I am also curious about EMI from the strobe, nav and landing light in the vicinity of the wires and antenna....
 
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