[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]

Its the Antenna

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]

DSAB maybe

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]

Servo DSAB

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]

Still can figure this out

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]

Solved I think

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]

Not fixed

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.

 

[Neal@F14]

Ferrite Beads?

You might try putting some ferrite beads/choke cores around your DSAB and other A/P wires at both ends and see if that helps. Those wires are probably picking up stray RF from the antenna and its coax when you transmit. Ferrite beads/choke cores sometimes do magic to kill stray RF that's getting induced into other wiring.

You can get snap-together ferrite choke cores from Radio Shack

http://www.radioshack.com/product/index.jsp?productId=2103222

 

[k5wiv]

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.

It sounds like you are dealing with radio frequency interference, so ground all shields at both ends, and if you use pigtails make them as short as possible. EMI backshells on the connectors which provide a 360 degree termination of the shield and bond to the device chassis are ideal, but very short pigtails will work.

Ferrite beads may help but, typically, will add more weight than shields on the wires.

 

[RVG8tor]

90 degree adapter

Well a Google search provided information about 90 degree adapters causing issues with RFI.

I had figured out that I am experiencing a massive RFI leak and so after the Google search I installed the two radio antennas cables without the adapters and no RFI, reinstalled the adapter RFI, took adapter off no RFI. I don't want to jinx myself but I am fairly certain I found my problem.

I think I can make the A210 work without a 90 degree adapter but the 430W is just too close to the baggage wall, I could force the fit for my test but this can not work in operation.

I bought the adapters from Radio Shack so that was my first mistake I guess. Any ideas on where to get 90 adapter, I know I could go though Stein but was thinking maybe a local source might move things along faster.

Thanks.

 

[RVG8tor]

Nope!!



Back to the drawing board. I hate it when something seems to fix then later on you find out you are wrong.

I am still getting drops in DSAB with COM 2 and my interior LED strips blink when I transmit with COM 1. Go figure.

Well a Google search provided information about 90 degree adapters causing issues with RFI.

I had figured out that I am experiencing a massive RFI leak and so after the Google search I installed the two radio antennas cables without the adapters and no RFI, reinstalled the adapter RFI, took adapter off no RFI. I don't want to jinx myself but I am fairly certain I found my problem.

I think I can make the A210 work without a 90 degree adapter but the 430W is just too close to the baggage wall, I could force the fit for my test but this can not work in operation.

I bought the adapters from Radio Shack so that was my first mistake I guess. Any ideas on where to get 90 adapter, I know I could go though Stein but was thinking maybe a local source might move things along faster.

Thanks.

 

[RVG8tor]

Saga Continues

Well I am getting closer but still not there. I realized I had two ground wires that come off the Dynon to be used for sensors, I don't have a use for them now so I just attached them to the instrument panel ground block. This seemed to help a great deal but now I am getting the DSAB drops with the other radio but in a narrower band of frequencies. Still don't have it up on the gear I am going to assume that will help when I can test it out of the garage, I certainly will not rivet on the top skin till I track all this down.

I took a handheld and while transmitting ran the antenna close to various wires and could not duplicate the DSAB drops.

Please any one running a Dynon 180 with HS34, AP74 please PM me and tell me what you did.

Frustrated!!

 

[Brantel]

The Dynon DSAB is a 3 wire 485 based system with their proprietary protocol running on it. This type network is used all of the industrial world to control automated equipment.

Take a look at all the Google info available on how a 3W-485 network works and it might help you figure out what is going wrong.

If you have access to a dual channel O'scope, you will be able to see what is happening to your network.

 

[RVG8tor]

2 DSAB wires

When you say "3 wire 485" system, does that include a ground wire? As you know the Dynon labels the DSAB just as two wires, "A" and "B".

Thanks for the idea I will see what I can learn about the 485 network today. Since attaching a couple of the ground wire (Pin 5 and 17 on D180 DB37) things improved greatly. But I am now getting network loss when transmitting on the 430W, before it was fine, but it seems to only happen on frequencies 129-134.00.

I have kind of ruled out the cables, I used a store bought section of RG58 between the radio and antenna and still have the issue.

My problem now might be just being in the garage. I have parts coming in that will allow me to put the plane up on the gear, this way I can wheel it outside and see what issues I still have.

The Dynon DSAB is a 3 wire 485 based system with their proprietary protocol running on it. This type network is used all of the industrial world to control automated equipment.

Take a look at all the Google info available on how a 3W-485 network works and it might help you figure out what is going wrong.

If you have access to a dual channel O'scope, you will be able to see what is happening to your network.

 

[Brantel]

There is really no such thing as a 2 wire RS-485 network. It is either 3 wire or 4 wire. Dynon uses 3 wire. The 3rd wire is the common ground between all the devices. If this ground is not common between devices and it floats around or is affected by noise sources, it can cause issues.

The perfect 3 wire RS-485 network would have one twisted pair bus that daisy chains between all the devices and has no stubs at all and the very ends of this bus on both ends would be terminated with 120 ohm resistors.

Having stubs, star connections to the buss and not having resistors can reduce the noise immunity of a RS485 network.

 

[RVG8tor]

Bad Multi RS485 network

I was just composing this post when you posted yours so here goes.

I was reading up on RS485 and came across this, it is considered a bad way to connect RS485 multi drop network. To me it looks like one of the ways Dynon says you can hook things up The daisy chain method would mean a failure in one component would fail down line units.

Multiple Cables
There are multiple problems with the layout in Figure 12. The RS-485 drivers are designed to drive only a single, properly terminated twisted pair. Here, the transmitters are each driving four twisted pairs in parallel. This means that the required minimum logic levels cannot be guaranteed. In addition to the heavy loading, there is an impedance mismatch at the point where multiple cables are connected. Impedance mismatches again mean reflections and, therefore, signal distortions.

Figure 12. An RS-485 network that uses multiple twisted pairs incorrectly.

I have my DSAB master and all other components going into a DB25 connector. The opposite side has the top pins connected with a piece of wire soldered to each pin cup, the same with the bottom.

NOTE: DSAB wires are mixed up in the photo, I caught and corrected this before testing equipment.

This is how I connect all DSAB "A" and "B" wires. Is this considered parallel setup as in the figure above? I read about terminating resistors, I kind of think that is built into the Dynon units, but my DSAB connection scheme might be my problem. I thought my setup made the connection that Dynon wanted "each wire electrically connected". When you say star, is this kind of the same thing as what I am doing. How did you connect the DSAB. All of my Dynon units except the servos ground at the instrument panel ground bus, this bus grounds at the forest of tabs via 5 wires that run from the instrument ground bus to the forest of tabs, you can see the ground bus below the DSAB hub in the picture below.

My servo DSAB wires are joined together under the floor and one set of DSAB runs to the DSAB DB25 Hub, all other wires from the servos are also joined here. Do you think this might be the issue? Maybe running each servo DSAB to the hub would be the answer. Did you run your servo DSAB together like I did, the instructions said this would be OK, that the wires could be joined anywhere along the way. I don't think my issue is with the servos though because the drops I get are with the AP74 first then HS34 if transmission is long enough. The HS34 DSAB wire is shielded, not sure where the shield terminates, the main panel harness was done for me by John Stark, I did the AP74 wires myself.

I have some shielded 2 wire on the way thinking this might help, but where do you attach the pigtail from the shield?

You can direct email me at rvg8tor "@" comcast dot net if you would like

There is really no such thing as a 2 wire RS-485 network. It is either 3 wire or 4 wire. Dynon uses 3 wire. The 3rd wire is the common ground between all the devices. If this ground is not common between devices and it floats around or is affected by noise sources, it can cause issues.

The perfect 3 wire RS-485 network would have one twisted pair bus that daisy chains between all the devices and has no stubs at all and the very ends of this bus on both ends would be terminated with 120 ohm resistors.

Having stubs, star connections to the buss and not having resistors can reduce the noise immunity of a RS485 network.

 

[Brantel]

I was just composing this post when you posted yours so here goes.

I was reading up on RS485 and came across this, it is considered a bad way to connect RS485 multi drop network. To me it looks like one of the ways Dynon says you can hook things up

Yes, Dynon says it will work anyway you can connect the wires and it will, but it will be less noise immune....(as you know)


The daisy chain method would mean a failure in one component would fail down line units.

No...The buss can be daisy chained and connected to the terminals of each device without actually passing thru the device so if that device fails, it will have no effect on the buss. Think of it as a really short stub connection to the buss which is OK.


I have my DSAB master and all other components going into a DB25 connector. The opposite side has the top pins connected with a piece of wire soldered to each pin cup, the same with the bottom.

You are connected in a Star configuration. This will work if the arms of the Star are not very long. I assume that the longest arms of the Star are for the Roll and Pitch servos and if so, I would install 120ohm resistors at the ends where the servos connect to the buss. One on each of the long arms of the Star. Do not put more than two resistors on the buss.


This is how I connect all DSAB "A" and "B" wires. Is this considered parallel setup as in the figure above? I read about terminating resistors, I kind of think that is built into the Dynon units, but my DSAB connection scheme might be my problem.

Most likley the Dynon devices do not have resistors built into them. There should only be two resistors at the ends of the buss line. If Dynon had one on each device, the impedance of the network would be too low and dependant on the number of devices connected.

I thought my setup made the connection that Dynon wanted "each wire electrically connected". When you say star, is this kind of the same thing as what I am doing.

Dynon's advice does not agree with the industry standard RS-485 specification used by thousands of devices in the automation world. Dynon did not invent the RS-485 buss, they just used it....

How did you connect the DSAB.

I used a Hybrid method and did not use terminating resistors but I can tell you that I have seen problems with noise as well. Not the ones you are having but others. I have used my DSAB bus as a way of finding the noise sources and fixing them at the source in my plane. I plan to rework my DSAB wires to fully follow the RS-485 specification and standards. This will ensure the best chance of noise immunity.

All of my Dynon units except the servos ground at the instrument panel ground bus, this bus grounds at the forest of tabs via 5 wires that run from the instrument ground bus to the forest of tabs, you can see the ground bus below the DSAB hub in the picture below.

If all of your DSAB devices do not share a common ground, it can lead to issues with the RS-485 differential signal. This third wire must be common to all the devices on the buss. There could be a significant difference in potential from the airframe ground at the servo to the ground at the forrest of tabs. When you transmit, there most likely is also many ground loop currents flowing around in the airframe as well. All of this could be changing your 3rd wire ground reference on your devices.

My servo DSAB wires are joined together under the floor and one set of DSAB runs to the DSAB DB25 Hub, all other wires from the servos are also joined here. Do you think this might be the issue?

You are branching arms of your Star which is also not recommended.

Maybe running each servo DSAB to the hub would be the answer. Did you run your servo DSAB together like I did, the instructions said this would be OK, that the wires could be joined anywhere along the way.

Again, Dynon's advice does not follow the spec. I used the Stein bundle which twist all the wires into a single cable. This seems to work OK. Both of my servo DSAB wires come all the way to behind the panel where they become the long arms of my buss.

I don't think my issue is with the servos though because the drops I get are with the AP74 first then HS34 if transmission is long enough.

You really can't tell where the issue is by what device drops first. The software may be more error tolerant in one device vs the other. The RS-485 interface chip in the device might be different in one vs the other ect.

The HS34 DSAB wire is shielded, not sure where the shield terminates, the main panel harness was done for me by John Stark, I did the AP74 wires myself.

There is no real reason to shield RS-485 wires since this type of network operates on a differential type signal. If shielded cable is used, make sure it has an impedance of somewhere around 120ohms to help prevent issues. Ground the shields at one end only.

I have some shielded 2 wire on the way thinking this might help, but where do you attach the pigtail from the shield?

One end only, does not matter which in this case but I would recommend the forest of tabs.

You can direct email me at rvg8tor "@" comcast dot net if you would like

If you were designing the perfect buss for the DSAB, I would recommend something like this:

Start the twisted pair buss with the pitch servo connected to the buss with a 120ohm resistor as close as possible to the servo.

Bring this buss up to behind the instrument panel and connect it to one set of the DSAB wires comming out of the D180 connector (twist the Dynon wires).

The other set of DSAB wires on the D180 (twist the Dynon wires) would then go to the HS34 and the AP74 where one would tap those devices into the buss with as short of a stub as possible.

Then extend those wires using twisted pair all the way out to the Roll servo with a 120ohm resistor as close as possible to the servo.

This would create the ideal RS-485 buss. It would have only two ends, two terminating resistors and no significant long stubs/arms that would cause any harm.

The order you did above does not really matter, just only have two ends, two resistors on the ends and do not make any long stubs or arms on the buss......

 

[RVG8tor]

Only one pair

The D180 only has one pair of DSAB wires that come off the DB25 EFIS connector the DB37 pin which carries the EMS functions and sensor but be internally connected to the DSAB. Oddly the harness came with Blue/Green wires out of the DB37 that are labeled "no used" maybe some future use. I removed the pins and wires for anything that was no getting used.

If you were designing the perfect buss for the DSAB, I would recommend something like this:

Start the twisted pair buss with the pitch servo connected to the buss with a 120ohm resistor as close as possible to the servo.

Bring this buss up to behind the instrument panel and connect it to one set of the DSAB wires comming out of the D180 connector (twist the Dynon wires).

The other set of DSAB wires on the D180 (twist the Dynon wires) would then go to the HS34 and the AP74 where one would tap those devices into the buss with as short of a stub as possible.

Then extend those wires using twisted pair all the way out to the Roll servo with a 120ohm resistor as close as possible to the servo.

This would create the ideal RS-485 buss. It would have only two ends, two terminating resistors and no significant long stubs/arms that would cause any harm.

The order you did above does not really matter, just only have two ends, two resistors on the ends and do not make any long stubs or arms on the buss......

 

[Brantel]

I was going off memory and thinking of the D120 that has two sets of DSAB wires comming out of it. They are internally connected.

Either way, it does not matter. Just insert the D180 onto the buss with as short of a stub as possible and it will be OK.

The D180 only has one pair of DSAB wires that come off the DB25 EFIS connector the DB37 pin which carries the EMS functions and sensor but be internally connected to the DSAB. Oddly the harness came with Blue/Green wires out of the DB37 that are labeled "no used" maybe some future use. I removed the pins and wires for anything that was no getting used.

 

[RVG8tor]

RFI solved, I think, again!

I did not make any changes to the network. I decided I needed to change or move the DSAB wires from the AP-74. In order to do that I had to get to the main bundle it was tied to which meant removing the entire panel. This is what I will have to do to have easy access for riveting the top skin so it was a good test.

I had used a set of wires not used on the D180 pre-made harness for the AP74 DSAB since they were the same color. Instead of cutting them shorter I just ties a loop to the main bundle, well this loop was right behind my radio stack. Not sure this was the cause of my problems but I cut the wire short so it made a more direct route to the DSAB hub.

While untying the bundle to get to the DSAB wires I saw a wire capped off with some shrink tubing, I had a pre-made harness that came with the Safety trim, this wire also ran behind the radio stack. This wire was a power source for the trim indicators which I had decided not to use since the Dynon has trim indicators. I pulled this wire all the way back to the DB25 connector and removed this pin. Not sure if this was causing my RFI.

I then put everything back together and tested the radios transmissions on a range of ffrequencies and did not get any drops in the DSAB. I need to do more testing I did not have the time to methodically check the entire band of requencies because I had to leave on a trip.

Now the mystery is what was the cause because several things changed, removing the panel obviously reseated all the radios and intercom, then there was the removal of the trim indicator power wire, and lastly the shortening of the AP74 DSAB wires.

Just thought I would share what at least at this point is working.

Tentatively happy until I can do more testing to confirm.

 

[RVG8tor]

Problem is back

I don't know what the heck changed. I transmitted on every major frequency when I last posted and no problems. I do my pitot static lines and clean up some electrical stuff and my problems is back.

It is definetly frequency dependent, tends to make things drop in the lower band and it is doing it on both radios.

@Brantel

I sent you an email via VAF "send email link" I would like to send you some drawings of some proposals I have.

Cheers

 

[RVG8tor]

Wire length

I realized I never did follow up on this thread. I had my DSAB wires long thinking future changes. I decided to just them and remove all the loops. Reinstalled. Now that I am at the airport and it is all back together I have not seen the AP74 drop off. So DSAB wire length seems to have fixed my issue.

Cheers

 

[Neal@F14]

Anytime you take serial data wires (like the DSAB, or RS-232, RS-422, AIRINC429, whatever) and roll up excess cable into a loop, you can inadvertently form a very nice antenna for picking up stray RF interference to become induced into the data wiring and do all kinds of goofy things to the data signals.

Always a good idea to keep unshielded, twisted pair data cables as short as possible, and to never coil them up into a loop. Sometimes clamping a ferrite bead around one or both ends of the data cable can help eliminate RF interference being induced into the wire too.

 

[Norman CYYJ]

Don't rely on anything to work properly if you are in a building and transmitting. The RF will be bouncing all over the place. At least do your checks with the aircraft outside.