Cyril Gibb Posted June 7, 2016 Report Posted June 7, 2016 After 2 days of troubleshooting at our local avionics shop, there is still static in both com radios. No other radios affected, even nothing on the ADF which would ordinarily pick up static. When we give even the slightest tap on any part of the plane, the com radios crackle like static (when the squelch is broken). We've got it down to the most fundamental point possible after eliminating everything the guys at the shop could think of. Here's where it now stands. When we connect a handheld radio picking up the local ATIS through a known good coax connected to either com antenna with NO power to the aircraft (master off, ELT removed, fuse removed to the normally hot dome light), if we tap lightly ANYWHERE on the aircraft we get crackling for a few seconds before it dissipates. Not bouncing the fuselage; just a tap like you would knock on a door. We tried 2 different handheld radios, 2 different (tested) coaxes and installed a new antenna verifying correct bonding just to see if it made a difference. Nope. This is very good avionics shop and they've never seen anything like this. Anybody ever heard of something like this? Quote
ArtVandelay Posted June 7, 2016 Report Posted June 7, 2016 So you tried listening to the VORs and that works? I got think that the antenna is somehow electrically connected to the fuselage but you seem to verify it, the use of handheld eliminates every thing but the antenna? I'd imagine that you don't have to tap, just touching the fuselage lightly causes the problem, yes? Wish I could help... Quote
takair Posted June 7, 2016 Report Posted June 7, 2016 Odd, but not all is lost yet. Did this start suddenly? Have you tried disconnecting the main ships battery? Sounds like a ground loop somewhere in the ship. Imagine a solenoid or power wire partially shorting to ground. The tap on the airframe may cause it to behave different. All a long shot, but sounds like you've tried all of the common things. Do you have any memory hold up batteries? Any other batteries? Where are the antennas mounted? Are they on skin or a panel? Also, try the handheld with the antenna removed from the aircraft and be sure it is not misleading you. Does this happen in transmit and receive? Sorry for the million questions... Quote
Cyril Gibb Posted June 7, 2016 Author Report Posted June 7, 2016 Touching doesn't have an effect, you have to knock. We wasted time thinking it was engine related because it only happened when the engine was running. That was Friday, a calm day. When we shut down the engine the static went away. Today, it was windy. When we took the plane out of the hangar without the engine running, the radios were crackling just with the plane being moved slightly with the wind gusts. We moved it back to the hangar to continue troubleshooting without wind movement. We meticulously went over all the bonding points, measured resistance with a micro-ohmeter. Checked all points and found less than 2 micro-ohms resistance. Used jumpers with alligator clips on everything moveable including the control rods/yokes/pedals/flight surfaces/etc. to see if it made a difference. Nope. No memory hold anythings with batteries and removed the ELT just in case. Antennas on top. No static heard on VOR receivers, ADF or DME. Handheld not affected unless connected to ships antennas. Antennas were removed, bonding checked, new antennas tried (4 antennas tried in all). Static is also heard in the background on transmit if the plane has any movement. Both coms were removed and bench checked with no static. Not sure if it started suddenly or not. Last week the tower complained about background static. I don't know if I was just unaware of the static before and just accepted it as "normal" or if it's been getting worse. Quote
takair Posted June 7, 2016 Report Posted June 7, 2016 What about disconnecting the battery? The energy has to come from someplace and it seems unlikely to be a static build up when you have so much activity on the aircraft. If you remove the battery and it is still there then it gets really mysterious. I have seen similar situations a number of times. In one case we had a Beech 1900 that had an intermittent problem. When you walked down the aisle it would appear...you had to be at the right station and it turned out to be chaffing. The very slight flex or the airframe would trigger the situation. You have eliminated almost everything, but not everything... Quote
yvesg Posted June 7, 2016 Report Posted June 7, 2016 Have you tried putting a new temporary coax going between a ship antenna and the handheld? I would try this to eliminate any issue with the old coax going through the ship hull. Yves 2 Quote
takair Posted June 7, 2016 Report Posted June 7, 2016 One other long shot, what powers your clock? Also, you described a couple of different noises. Is the noise you hear in the handheld identical to that you hear in your on board radios? I recently fought my own crackling and it turned out to be the cheap USB power adaptor breaking squelch. A friend had similar issues and did all of the typical things...then unplugged the USB adaptor. It even surprised me that this low power gadget caused so much interference on a broad range of frequencies. The handheld my be something else. You are on a different ground plane than the handheld. I have seen a lot of people waste a lot of time (including me) when the troubleshooting aid introduced a similar....but ultimately different problem. I know you tried multiple coax, antennas and handhelds, but the environment..different ground reference remains ...common. It can cause a vicious cycle. Also, be sure your hangar has not introduced a new variable when you are using the handheld. You have different sources of interference and bounced signals. Wish I could help on site, sounds like an intriguing problem. Quote
Cyril Gibb Posted June 7, 2016 Author Report Posted June 7, 2016 19 minutes ago, yvesg said: Have you tried putting a new temporary coax going between a ship antenna and the handheld? I would try this to eliminate any issue with the old coax going through the ship hull. Yves Several TDR verified coaxes were used.... ships coax not used Quote
Cyril Gibb Posted June 7, 2016 Author Report Posted June 7, 2016 Just now, takair said: One other long shot, what powers your clock? Also, you described a couple of different noises. Is the noise you hear in the handheld identical to that you hear in your on board radios? I recently fought my own crackling and it turned out to be the cheap USB power adaptor breaking squelch. A friend had similar issues and did all of the typical things...then unplugged the USB adaptor. It even surprised me that this low power gadget caused so much interference on a broad range of frequencies. The handheld my be something else. You are on a different ground plane than the handheld. I have seen a lot of people waste a lot of time (including me) when the troubleshooting aid introduced a similar....but ultimately different problem. I know you tried multiple coax, antennas and handhelds, but the environment..different ground reference remains ...common. It can cause a vicious cycle. Also, be sure your hangar has not introduced a new variable when you are using the handheld. You have different sources of interference and bounced signals. Wish I could help on site, sounds like an intriguing problem. The scratchies aren't enough to break squelch. Static is only when squelch is already broken or on transmit. Handheld static sound identical to ships radios. USB adapter removed early on. Avionics shop lighting is not fluorescent to avoid interference problems. We were using ships radios, then bypassed ships coax with ships radios using a new (tested) coax jumper, then used the hand held on the bypass coax (master off) to the ships antenna(s). Tried with one com removed and then with the other com removed. All with no change. We didn't try removing the battery itself, but each connection to the battery and master solenoid was first tested (with no measured resistance) and then removed, cleaned and reinstalled anyway. Quote
Mooneymite Posted June 8, 2016 Report Posted June 8, 2016 At the airline, we had an aircraft that went nordo for static every time it went into a cloud. Maintenance would check it, try something, return it to service and it would be in service until it flew into a cloud. This went on for a couple of weeks. The final finding was a defective grounding wire on one of the nose wheel doors that would only break contact when the gear was up and locked. The maintenance man-hours and operational disruption caused by this must have been staggering. Good luck. Quote
orionflt Posted June 8, 2016 Report Posted June 8, 2016 I have seen issues like this when I was in the Navy, the short is the aircraft developed areas on the fuselage that became magnetized. we would identify the affected areas then run a degaussing tool over them. fixed several aircraft with the same problem. here is a good link to P static and some other possibilities that may be contributing to the issue. the degaussing was the last thing we did after confirming that the aircraft was properly bonded. http://www.smartcockpit.com/download.php?path=docs/&file=Precipitation_Static.pdf Brian Quote
LANCECASPER Posted June 8, 2016 Report Posted June 8, 2016 It's a longshot but I would pull every circuit breaker except the com radio and see if it does it. If it doesn't then add one item at a time to see if it can be narrowed down. Quote
Cyril Gibb Posted June 8, 2016 Author Report Posted June 8, 2016 Thanks for the suggestions.... headsets: tried lightspeeds, david clarks and an old telex from all 4 seat positions: identical grounding: i think we jumpered everything we could see that moved including the push-pull rods, flight surfaces and gear doors degaussing: i'll read the article and run a compass all over the plane breakers: did that before going to the avionics shop Quote
N601RX Posted June 8, 2016 Report Posted June 8, 2016 Remove the com coaxes from the radios and place 50ohm termination caps over both radio side of the coax connections and see if it is still present. This should confirm if it is indeed coming in over the coax or if its coming in on the radio wiring. 1 Quote
Cyril Gibb Posted June 8, 2016 Author Report Posted June 8, 2016 23 minutes ago, N601RX said: Remove the com coaxes from the radios and place 50ohm termination caps over both radio side of the coax connections and see if it is still present. This should confirm if it is indeed coming in over the coax or if its coming in on the radio wiring. No ship radio wiring or coaxes were used or connected. Final test was tried using different handhelds connected by different (tested) coax jumpers directly to either of the newly cleaned/bonded/tested ships antennas. Both com radios and the ELT were removed from the plane. Master switch off. All CBs pulled. Fuse removed for normally hot dome light. No other sources of electrical power in or near plane. No fluorescent lights in hangar, but we tested again outside anyway, also with no difference. Quote
Piloto Posted June 8, 2016 Report Posted June 8, 2016 Cyril, you must be in a low humidity environment for this to happen. Does it happens in flight? Looks like your tires are not discharging your plane static charge build up, try washing them. The reason you do not notice it on your ADF is because the ADF antenna is a loop type (H field) vs an E field for the COMs. Airliners COMs antennas are DC grounded to overcome static noise and lightning strikes. But GA antennas are not DC grounded. José Quote
N601RX Posted June 8, 2016 Report Posted June 8, 2016 Just now, Cyril Gibb said: No ship radio wiring or coaxes were used or connected. Final test was tried using different handhelds connected by different (tested) coax jumpers directly to either of the newly cleaned/bonded/tested ships antennas. Both com radios and the ELT were removed from the plane. Master switch off. All CBs pulled. Fuse removed for normally hot dome light. No other sources of electrical power in or near plane. No fluorescent lights in hangar, but we tested again outside anyway, also with no difference. It may still be that their is a EMI/RFI event being generated by something on the plane which is then being picked up by the antenna and transmitted down the coax to the handeld or regular com radio. Based on the numerous coaxes and antenna's already tried it likely comes back to something being radiated by something else on the plane and then picked up by the antenna. Quote
mooniac15u Posted June 8, 2016 Report Posted June 8, 2016 Have you tried the handheld radio with its regular flexible antenna inside and in close proximity to the plane? That might tell you if there's a localized EMF associated with the airframe. Quote
Cyril Gibb Posted June 8, 2016 Author Report Posted June 8, 2016 5 hours ago, mooniac15u said: Have you tried the handheld radio with its regular flexible antenna inside and in close proximity to the plane? That might tell you if there's a localized EMF associated with the airframe. That's an obvious one I hadn't thought of. I'll try that tomorrow. And Jose, it happens in flight also, but I'll try grounding the whole aircraft. It's been damp any rainy here, not dry at all. Quote
yvesg Posted June 9, 2016 Report Posted June 9, 2016 I would also investigate outside elements: Cell phone in your pocket? Anything with a battery nearby the aircraft? A flashlight in the back of the aircraft? Yves Quote
Marauder Posted June 9, 2016 Report Posted June 9, 2016 Also take a look at anything you may have changed. My avionic noise was caused by the newly installed JPI. Sent from my iPad using Tapatalk Quote
Cyril Gibb Posted June 10, 2016 Author Report Posted June 10, 2016 O.K., I tried to sniff around the plane with the handheld and its antenna. No scratchies on the handheld, but still there on the ship coms. Then who should pull up at my hangar but Clarence (and Mo). I wanted to show him the issue, so I powered up the master, turned on the avionics and turned up the radio. I tapped the plane. No scratchies. ?#@!*&% I jumped up and down on the step. No scratchies. WTF ! To cut to the end of the next hours confusion, I had trimmed down to the limit to get the yokes out of the way to get the bikes and camping gear in. Turns out that the radio interference maxes on the middle third of the trim and is gone completely at full forward or aft trim. Clarence installed a bonding strap between the fuselage and the empenage. No change. Most peculiar! Quote
Mooneymite Posted June 10, 2016 Report Posted June 10, 2016 (edited) ! ??? That's a weird one. Edited June 10, 2016 by Mooneymite Quote
N201MKTurbo Posted June 10, 2016 Report Posted June 10, 2016 Have you tried pulling the radios and the audio panel and cleaning their contacts? Mine gets scratchy sometimes and if I violently shake the audio panel back and forth in the panel, the scratchy goes away. Quote
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