intercom noise?

[tx_swordguy]

I have been working on radio issues for the past couple of months. Originally I would get some FM interference in certain areas overpowering all other radio traffic. I just replaced my antenna with a flexible dipole and solved that problem. I also replaced my headset mic with an electret high noise mic and solved the excessive ambient noise. Now I am hearing the impulse of the fuel pump coming through the headset. I have isolated it enough to know it is coming through the intercom (wired headset directly to handheld and bypassed the intercom= no noise). I just sleeved the fuel pump wires in SS braid and it had no effect. I also put a noise filter on the radio/intercom switch, still no effect. I have a couple of options was hoping to save a little work going from easiest to hardest/most time consuming. 1. ground fuel pump directly to battery and away from the common ground plate. 2 install ferrite beads on fuel pump wires close to pump.3 sleeve all intercom wires coming off intercom box in SS braid.
Should I be trying to shield the offending device or shielding intercom FROM the offending device?
Both the power and ground are on common bus connections and I am leaning toward it feeding through the power supply somewhere.
Mark
ps yaseu handheld with intercom system and headsets

[efwd]

I have no experience in any of this yet but it just so happens I was reading the "Aircraft Wiring Guide" last night that describes something like this. If I remember correctly it specifically notes that the Audio Lo from your headset should be grounded someplace other than the ground buss that all your other stuff is grounded to. What might happen if you ground your radio/intercom someplace other than the common ground as you describe it is currently?

[tx_swordguy]

Update, I have the flight com 2sx 2place intercom with a yaseu handheld radio. The fuel pump impulse noise is still there and definately coming through the intercom. I just tried the pilot isolation switch and with it on the sound is gone ( I cannot however hear myself talk through the headset like I normally can with the intercom open) I have never tried communicating with the isolation switch on so don't know if it even works properly. What I have done to try and fix the problem. 1. tried grounding fuel pump and radio/intercom on different grounds. 2 completely took fuel pump off airplane electrical and directly tied to the battery to try and seperate it as much as possible.3 shielded fuel pump wires with braided SS. 4. put noise filter on radio and also tried it on fuel pump wiring. 5. ferite bead on fuel pump pos wire. 6. wrapped fuel pump in aluminum foil as a last ditch effort. The only thing that did anything was switching on the pilot isolation switch and it cured sound (at least on pilot headset didn't try passenger side like that) I am doubting it will transmit that way since I cannot hear myself in the headset with the isolation switch on. The only thing I can think of that I have not tried is shielding the wires of the intercom (a real pain). Come to think about it the previous owner taped all the intercom wires together to make it cleaner. Would the power wire being taped next to the input/output wire cause bleed over maybe?

[jiott]

My intercom (PS Engr) installation instructions required all the wires to be shielded, with the shields daisy chained together at the intercom and then grounded.

[tx_swordguy]

I will look into that. I have found that the intercom will work fine on the 9volt portable power battery (designed for ultralights without power source) or on a completely separate 12v battery just sitting in the cabin. once it is plugged into the aircraft 12 volt system the trouble starts .

[TJay]

Wire one of these in the power source that feeds the radio, should take care of it, they work quite well,
http://www.ebay.com/itm/12V-NOISE-FILTER-HUM-KILLER-ENGINE-SUPRESSOR-POWER-WIRE-IN-CAR-STEREO-AUDIO-/260741326774?hash=item3cb564e7b6:g:9QIAAMXQS6pRrwo I&vxp=mtr

[jiott]

Apparently they, PS Engr, feel the wiring and shielding is so important that they imply they dont warranty the unit unless you buy a premade wiring harness from them. I made my own but followed their instructions exactly and no trouble for over 3 years now.

[tx_swordguy]

Tjay I already tried that with no luck. I don't know if I wired it wrong and fried it or not. I tried the blue wire as both going from battery and going from the intercom and vice versa with the red wire. It operated the same in both directions. I also after shielding the power wire to the intercom used a jumper to ground the shielding also with no luck. I did go flying this afternoon and was using only the 9volt on the intercom and airplane 12 v disconnected from intercom. On transmitting initially there was interference for the first 20 min of the flight and then it seemed to be transmitting "ok". That didn't make alot of sense. I guess I will keep trying. Any more ideas would be greatly appreciated.
Mark

[jrevens]

Mark,

This is probably a dumb question, but are you sure the noise is coming from the fuel pump? I once had a noise in my headsets that could be described as rhythmic, and it was very irritating. I finally discovered it was coming from my iPhone. It was intermittent, and only occurred when my headset cord or the passenger headset cord got close to the phone, and it was not created by the phone all the time (maybe just when the phone was "talking" to a cell tower or something). I thought it might be coming from my iPad for awhile. Anyway, just a thought.

[Norm]

Now I am hearing the impulse of the fuel pump coming through the headset. I have isolated it enough to know it is coming through the intercom (wired headset directly to handheld and bypassed the intercom= no noise).

Quick question? What kind of fuel pump, what kind of engine?
Is the noise there all the time or just when you transmit or recieve?

[tx_swordguy]

rotax 582 facet electric fuel pump. noise is only there when the fuel pump is turned on. if it is off the noise is gone. I can keep the radio/intercom switch on and turn other switches off and it is isolated to the intercom for some reason. I bypassed the intercom and went straight to the handheld with no problems. The same power wire powers both the intercom and the radio charging station. I am only assuming but I feel there is enough power absorbtion going through the radio charger into the radio battery and finally out the radio to filter out the noise that way but for some reason it is pulsing through the intercom. I just tried putting an 1800uf capacitor on the radio power and it did not work. I am thinking I may put a higher capacitor on the fuel pump to see if that may do something. Any ideas on what capacitor?

[Guy Buchanan]

I'll reply, since nobody else offered this suggestion. (Got to keep you busy!) I had noise problems from the 912 regulator I mounted behind the firewall. Talking to Bob Nuckols over at Aeroelectric he was adamant that my only problem was a ground loop. After shielding the entire world, I finally got serious about isolating ground loops, found one, and of course fixed the problem.

Problem was, I thought I had been very careful about single path grounds. It only took one. What I did was use a ohm-meter to check every ground path, disconnecting each ground wire from the ground bus one at a time. I finally found one that grounded with its ground wire disconnected. That was the loop I needed to isolate. This should offer you hours of enjoyment. (Kidding!)

One more thing. I think you asked about isolating power from signal wires. According to Nuckols, this is always a good idea. It's also a good idea to twist or braid power and ground wires to help eliminate any transmission, and to shield any signal wires, grounding the braid at only one end. (No ground loops!)

Good luck! And I highly recommend checking in with the Aeroelectric Connection on Matronics if you get really frustrated; Bob's still incredibly helpful. (Amazing since he's probably heard every question a hundred times in the last 20 years.)

[tx_swordguy]

Guy, Thanks for the info. Not being the smartest guy in regards to the testing of electrical equipment could you explain how you use an ohm meter for that? I understand checking voltage on a dc circuit. Just unsure how checking ohms will find a ground loop in this regard. I would assume you place one lead on the ground bus and one lead on the disconnected grnd wire and if you get a reading other than infinity you have a loop is this correct? Would it make a difference at what setting you put the ohm meter? I will also pull my pump wires out again and twist the whole strand and then put it in braid. I just ordered a 500mf capacitor to put at the pump thinking that may help. I will keep trying and if I can fix it I will give an update otherwise I may keep pestering you guys