Strobe radio interference

Lawson Laslo

Lawson Laslo

Pre-takeoff checklist
Joined
Jan 18, 2019
Messages
403
Location
Sundance airport Oklahoma
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Display name:
N2005H
Hello,
My FS 4400 STROBE light make high pitched noise over the headsets. Is there any way to eliminate this issue? The strobes IS grounded directly to the airframe.
I might just replace with an led strobe but the current strobe is extremely bright and can be seen 25 mile out during the day, doubt an led can do that.

https://www.aircraftspruce.com/catalog/elpages/fs4400.php?clickkey=22408
 
Lawson Laslo said:
ongoing issue, just gets annoying on long cross countries
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Ok. Yes the noise can be reduced. But hard to t/shoot via the internet. Strobe/radio/intercom/headset grounding issues tend to be the leading cause of noise so ensuring all grounds, grounding planes, airframe grounding straps, etc. are correct and clean would be the 1st path to follow. A quick poor mans check is to rig a temp ground wire for the strobe power supply directly to the battery. If the noise goes away then need to find which ground path is at fault. Which in itself can be a daunting task. If the noise doesn't go away then look at the overall installation of the strobe/radio/intercom/headset jacks for any discrepancies. Usually one of these paths turns up the reason for the noise, but is not a guarantee.
 
Bell206 said:
Ok. Yes the noise can be reduced. But hard to t/shoot via the internet. Strobe/radio/intercom/headset grounding issues tend to be the leading cause of noise so ensuring all grounds, grounding planes, airframe grounding straps, etc. are correct and clean would be the 1st path to follow. A quick poor mans check is to rig a temp ground wire for the strobe power supply directly to the battery. If the noise goes away then need to find which ground path is at fault. Which in itself can be a daunting task. If the noise doesn't go away then look at the overall installation of the strobe/radio/intercom/headset jacks for any discrepancies. Usually one of these paths turns up the reason for the noise, but is not a guarantee.
Click to expand...
I will jump the ground directly to battery and see if it helps, there is no strobe circuit breaker and Im thinking it might be on the radio, or ICS circuit breaker, I'll test it out tomorrow and see.
 
How old is the airplane? Even mild corrosion in electrical connections can give these symptoms. I replaced the master switch, alternator breaker, and voltage regulator wiring in my RV-6 to correct this problem...
 
Lawson Laslo said:
there is no strobe circuit breaker
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FYI: some strobe installations use a circuit breaker switch which combines the two actions into one. These switches are readily different than a normal switch.
 
Bell206 said:
Ok. Yes the noise can be reduced. But hard to t/shoot via the internet. Strobe/radio/intercom/headset grounding issues tend to be the leading cause of noise so ensuring all grounds, grounding planes, airframe grounding straps, etc. are correct and clean would be the 1st path to follow. A quick poor mans check is to rig a temp ground wire for the strobe power supply directly to the battery. If the noise goes away then need to find which ground path is at fault. Which in itself can be a daunting task. If the noise doesn't go away then look at the overall installation of the strobe/radio/intercom/headset jacks for any discrepancies. Usually one of these paths turns up the reason for the noise, but is not a guarantee.
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Unhooked ground of strobe and ran directly to a known ground point, no change, the strobe worked with no ground at all so it must be grounded via the mount also
 
You can get some ferrite noise filters and snap them around your headset cable and see if that will resolve the problem. These are fairly cheap from Amazon or EBay. They come with different hole sizes so you would need to measure outside cable size to make sure it would work. I have used ground loop isolator filters on the XM input cable to my audio panel and those really work but are designed for 3.5mm jacks and not the 1/4" jacks on the headsets.
 
Lawson Laslo said:
Unhooked ground of strobe and ran directly to a known ground point, no change, the strobe worked with no ground at all so it must be grounded via the mount also
Click to expand...
FYI: Unless you ran the temp ground wire from the ground screw on the strobe case direct to the battery with the light removed and isolated from the airframe, you didn't really check much. The idea is to bypass/isolate the existing airframe electrical ground plane path which might be causing your noise.
Lawson Laslo said:
the strobe worked with no ground at all so it must be grounded via the mount also
Click to expand...
The 4400 is a case grounded unit so it could still work when installed on the airframe without the ground wire connected. One issue with some 4400 installs is there is a chance to create a ground loop when the existing ground wire from the strobe case to the airframe does not terminate in the same area (ground plane) as the strobe mount. So if your existing ground wire from the strobe case runs up to a ground point in the front of the aircraft and the strobe also picks up a case ground at the mount ring, then you can create situation where noise can be generated.

But as I mentioned earlier these problems are very difficult to t/shoot via the internet so I'm hesitant to send you on a red herring expedition. Sometimes it's best to start simple and check/clean all the power and ground connections for the battery/radio/intercom/strobe/headset. However, another attempt at the temp ground wire but done as noted above may get you a chance result.
 
Old airplanes are fun. Aluminum sheets, riveted together, develop oxides between them that cause resistance, forcing electrons to find other paths. Sometimes those paths lead through radios or intercoms and any noise in the flow is carried into the audio. It can get weird, with alternator noise being heard by other pilots when you transmit, but you don't hear it yourself.

Ferrite cores work OK for RF, not so much for audio.

Now, how is your intercom set up? Is it a portable box you plugged into the airplane's jacks, or do you plug your headsets directly into panel jacks? If it's a portable, do not screw that thing to the airframe. Isolate it. It's one of those ground-loop paths we're looking for if it's grounded. If the jacks are in the panel, look and see if they are insulated from the panel. If not, you might have a problem there. I have fixed strobe and alternator noise by getting some insulators from an avionics shop and installing them, and running the jack's ground wire all the way to the radio or audio panel ground to eliminate any voltage potential between the jack grounds and avionics grounds.

upload_2021-2-4_16-55-32.jpeg
 
Dan Thomas said:
Old airplanes are fun. Aluminum sheets, riveted together, develop oxides between them that cause resistance, forcing electrons to find other paths. Sometimes those paths lead through radios or intercoms and any noise in the flow is carried into the audio. It can get weird, with alternator noise being heard by other pilots when you transmit, but you don't hear it yourself.

Ferrite cores work OK for RF, not so much for audio.

Now, how is your intercom set up? Is it a portable box you plugged into the airplane's jacks, or do you plug your headsets directly into panel jacks? If it's a portable, do not screw that thing to the airframe. Isolate it. It's one of those ground-loop paths we're looking for if it's grounded. If the jacks are in the panel, look and see if they are insulated from the panel. If not, you might have a problem there. I have fixed strobe and alternator noise by getting some insulators from an avionics shop and installing them, and running the jack's ground wire all the way to the radio or audio panel ground to eliminate any voltage potential between the jack grounds and avionics grounds.

View attachment 93821
Click to expand...
Panel mounted jacks
There’s no insulation
Will try that out
 
Dan Thomas said:
Old airplanes are fun. Aluminum sheets, riveted together, develop oxides between them that cause resistance, forcing electrons to find other paths. Sometimes those paths lead through radios or intercoms and any noise in the flow is carried into the audio. It can get weird, with alternator noise being heard by other pilots when you transmit, but you don't hear it yourself.

Ferrite cores work OK for RF, not so much for audio.

Now, how is your intercom set up? Is it a portable box you plugged into the airplane's jacks, or do you plug your headsets directly into panel jacks? If it's a portable, do not screw that thing to the airframe. Isolate it. It's one of those ground-loop paths we're looking for if it's grounded. If the jacks are in the panel, look and see if they are insulated from the panel. If not, you might have a problem there. I have fixed strobe and alternator noise by getting some insulators from an avionics shop and installing them, and running the jack's ground wire all the way to the radio or audio panel ground to eliminate any voltage potential between the jack grounds and avionics grounds.

View attachment 93821
Click to expand...
If I removed just the headphone jack from the pane would that let me know if it’s the issue?
 
Lawson Laslo said:
If I removed just the headphone jack from the pane would that let me know if it’s the issue?
Click to expand...
It might as long as the installer ran a ground wire back to the avionics and didn't rely on the panel for grounding.
 
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Installing a new stereo audio panel (replacing a mixing audio panel and a separate intercom). Replacing all audio wiring so I've gotten a really good look at how things were wired (at least 1990 style) and seeing what modern standards are.

As mentioned before, isolating the jacks from the airplane ground is critical. The airframe ground should never be used for any audio line. If only one jack goes to airframe ground they all are. All audio grounds need to run back to the intercom/audio panel and properly connected as there is usually a high pass filter on that ground line which eliminates noise.

With my old wiring, the shield was used as the audio low line. New audio panel wiring diagram shows a 3 conductor shielded line used for all connections (R, L, Lo /mic Hi, mic Lo, key). Shields are not used as an audio line and are grounded separately (daisy chained then attached to audio panel tray). Instructions indicate this is to reduce stray signals which I assume is necessary with modern high fidelity audio panels.

I have a strobe like you, and with my old setup I get the "strobe squeal" when it's on. Excited to see if new wiring and audio panel will eliminate it.

One other thing I noticed. The power line to the strobe was run in the same bundle as my COM and NAV antenna coax. The strobe draws a fair amount of current and the interference may be coming via the radio. I don't like having high powered lines next to antenna lines so the strobe power line is going to be relocated.

Just some things to think about.
 
Papa Pilot said:
One other thing I noticed. The power line to the strobe was run in the same bundle as my COM and NAV antenna coax. The strobe draws a fair amount of current and the interference may be coming via the radio. I don't like having high powered lines next to antenna lines so the strobe power line is going to be relocated.

Just some things to think about.
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Have your coaxial cables been upgraded to RG-400 yet? RG-400 has two layers of shielding.
 
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