AP74 lost when Tx

[RVG8tor]

Hopefully someone has had this and knows how to fix it. This may or may not be a problem since I am transmitting in my garage.

My system is D180 EFIS, HS34, AP74 Garmin 430W and Garmin 240 intercom, radio 2 is ICOM A210.

When I transmit on the A210 my AP74 Lights come on and flash and I get AP74 lost alert if the transmission is long enough. I can get the AP74 back. It does not seem to effect the HS34 DSAB connection.

When I transmit with the 430W the AP74 is fine, the antenna for the 430 I the one farthest from the AP74 but don't know why only the AP74 is effected.

Anyone seen this happen, not really sure how to trouble shoot this.

Maybe this is all due to being in a basement level garage.

The other thing, using a handheld the A210 transmission comes through much clearer than the 430W if you can believe that.

[RVG8tor]

I swapped the antenna cable and the issue follows the Antenna. So now the question for you smart guys and gals is will this be an issue outside. I guess I need to get her on the gear and roll her outside! I have my VHF antenna like most RV8s, they are just behind the main spar on either side of the belly. I am guessing I will have good coverage since I can hear SEA Center even in the garage.

[rvmills]

Nemo,

I've seen this when testing some alternative in-wingtip antennas (j-pole, bazooka, bent whip). When transmitting, I saw all the AP-74 lights light up, then go dark, and the AP-74 had dropped off line. I would also see the needles on my Van's fuel gauges drop to zero, sometimes quickly, sometimes slowly. On some antennas, changing the frequency would change the intensity of the interference, so it was a variable SWR thing (I believe).

Your bent whip should be more broadband, and as long as its well grounded, should (may) not show the variability between freqs.

When you say it followed the antenna, do you mean only one antenna exhibited the behavior, or only one radio? If its the former (which I'm pretty sure you were saying), you may want to check out the ground plane connection.

Much of the testing where I saw this phenomenon was in a hangar, with the wingtip in close proximity to a big steel beam. Moving it outside decreased the intensity, but the problem remained. Pete Howell helped me figure that one out.

If I switched to the belly mount antenna and ran the test, the issue went away, so for me, it was the antenna...I'm pretty sure at least.

Another issue for me perhaps is that the BNC to the cable to my wingtip antenna is in the same bay under my seat as my roll servo, so the DSAB wires are somewhat nearby. If I switch to the belly whip, the BNC connection is a bay over. I'm not sure if its RF from the too-close BNC, or just SWR from my experimental wingtip antennas, but I think its the SWR.

On yours, if its only one antenna doing it, I'd check grounding, then SWR, then leaky BNCs (if they are close to the DSAB wiring at any point). Moving the plane outside may help a bit too, but may not eliminate it (from what I saw).

If it stays with the radio, and does it via both antennas, I'm not sure what to do. Perhaps Stein or Brantel will have some thoughts on that.

Just some ideas to get you tracking!

Cheers,
Bob

[flyvans.com]

this sounds very much like the interference issues that can affect trutrak autopilots. (pitch change while transmitting)

the solution there is to put a filter dongle between the unit and the corresponding wiring harness, which so far seems to work in practically all cases.

we've had it from our bent whip com antenna below the fuselage aligned with the same direction as the autopilot wiring. after the filter, no problems whatsoever.

your case may very well be similar in nature!

http://trutrakap.com/forum/showthread.php?t=43
http://www.l-com.com/productfamily.aspx?id=902

rgds, bernie

[RVG8tor]

Bob,

You maybe on to something, the problem is with the antenna, whatever radio is hooked to the antenna on the left side of the belly causes the AP74 issues.

My wires back to the pitch servo run up the left side and are anchored right next to the antenna doubler. I bought the twisted pair autopilot wire set from Stein when the Dynon autopilot first came out (no shields). I wonder if that is the cause. But the issue is with the communication to the AP74 I don't lose the Servos, I even engaged the autopilot to see if something weird would happen with the servo and it just goes clickity click like it does without an Tx.

Is there anyway to simulate shielding these wires like wrapping them if foil or something. I really don't know how I can run the wires from the pitch servo without getting close to the antenna. The other issue might be is I tied the roll and pitch servo wires to a terminal block under the front seat left side so I would only have to run one set forward of the firewall. I really need to figure this out while I can still get at the wires. As it is this will be a pain. I think I will try to unhook the DSAB wires to the servos and see what happens.

[RVG8tor]

Well now I don't know what to think. I removed the DSAB wires from the servos and tried several transmission with each radios and not problems. I put the DSAB wires back but in a different pin location (I am using a DB25 connector as a DSAB Hub). After putting the pins back I tried several transmissions with only once did a get a bit of a flicker in the AP74 lights. I think I will wait till I get the bird on the gear so I can roll it out of the garage and see what I come up with then. Here is a shot of my DSAB hub, the opposite side of the connector has all the pins on top soldered together, same with the bottom pins, seems to work great other than this issue. The hub does make isolating a unit easy.

Oh you observant ones will see that I had crossed up some of the wires, I caught this just when reviewing this picture. Even had the nice orange labels there to tell me! The picture was taken when I first installed things, thankfully I caught it before power up.

[rvmills]

Mike,

As Pete Howell has said to me many times, RF is black magic, and strange things happen. Could be the signals bouncing around the basement, could be the DSAB wires, could be proximity between them, or the fact that some of the wires run parallel to each other for part of the run.

I have some extra shield material that I can send you if you'd like to try it. It's metal mesh, and can expand big enough to cover a BNC fitting. Its a little heavy and bulky, but if you only need a short run of it, maybe it won't be too bad (I have a bunch you can use though).

My father in law (a HAM) gave it to me, which I tried on my antenna coax. I had two whips on the belly, and Comm 2 (a SAR radio) kept blitzkrieging my Comm 1 when transmitting. In my case, the shield didn't stop the bleed over...the two antennas were just two close to each other (28"), since I had to put them in the next-to-outer bay due to the roll servo location in a six. APRS transmissions via that antenna were also noisy on Comm 1. I now have 1 belly whip on the centerline (Comm 1), and one jpole the right wingtip for Comm 2 and APRS. (150.025 MHz and 144.39 MHz).

Now I'm trying to figure out how to put a Comm 3 antenna in the other wingtip, so I can add a second VHF comm (for formation lead). That's where I run into the AP-74 issue. The coax comes in from the wing, goes right by the roll servo and the DSAB wires. Its still pretty close when I use the belly whip, but SWR on the whip is so much lower than the homebrew wingtip antenna, that I think its the antenna doing the EMI.

Hey, here's another troubleshooting thought. Swap the antennas between locations on the belly, and see if it all stays the same, or moves to the other antenna location. If so, something's amiss with that antenna (ground plane or internal). I think!

Hope that wasn't too much rubbish!

Cheers,
Bob

[RVG8tor]

I am fairly certain the issue is with the proximity of the servo wire to the left antenna. When I remove the servo wires from the DSAB hub I can't get anything to drop but with them on I get the AP74 fail, and once or twice have gotten the HS34 to drop off the circuit.

I was messing with the lighting and had the light in the garage turned down and realized that my LED indicator light blinks when I transmit the radio without the issue with the AP74, also the strip LED lights on both sides flicker, but the strips in the rear seat side and the one that goes over the instrument panel don't blink. All of the LED strip lights run from identical dimmers.

I think I will get it up on the gear and see what happens when outside. If I still have the issue I will try to run shielded cable from the servos all the way to the DSAB hub.

Short of this I am out of ideas short of going to a wingtip antenna.

Keep the ideas coming please.

[RVG8tor]

Now I know why I keep putting off taking this thing to the airport, it is nice to just run down to the garage at 10:30 at night. This issue with the AP74 dropping was gnawing at me so I went downstairs to try some stuff. I knew that if I removed the servo DSAB wire this seemingly fixed the issue but the AP74 really does not do anything without it.

Well I went downstairs and tried to transmit though the left side antenna, I guess hopping somehow it was magically fixed but of course not.

I then proceeded to untie the wires where the servos join that is near the antenna connection. I was trying to see if I could move the wires further away. As I unhooked things I realized that for the set of wires going forward I had overlapped them on the on the other wires to make a service loop. It dawned on me that this might be the problem so I pulled them away and tried a few transmissions an no AP74 dropping. I pulled the wire forward and repeated my test on a range of frequencies and I did not get any drop in the AP74

The photo is shot looking down, forward is up in the picture. The roll servo wires come in from the right of the photo, and the pitch from the aft they come together just forward of trim servo tray and loop to the left at attach to a terminal block that is mounted vertically. The run forward ties to the other side of the block. The run forward had looped over the loop of the other two bundle (red line in the photo) You can see now it is straight out. I will have to figure out what to do with the loop in the wire.

I may not be out of the woods, as you can see the two servo bundles over lap, when I did my test I had the roll servo disconnected and the DSAB set up without it in the system. I will have to try that later.

[RVG8tor]

Well this morning I hooked up the roll servo and now when I transmit with the radio that uses the right antenna it make the AP74 drop. I am thinking I need to run the DSAB in shielded wire. My setup is not ideal I guess now Dynon says the DSAB should run separate from the rest of the servo wires as a twisted pair, the autopilot wire set I bought from Stein has the DSAB wires twisted with the other 5 wires.

At any rate I want to install shielded wire while I have easy access to the panel, the question is what to do with the shield, ground it at the servo or ground it where the DSAB Hub is located. I guess I will direct a query to Dynon but if anyone has done this successfully please post here.

Thanks.