Strobe bleed thru radio

AlphaPilotFlyer

AlphaPilotFlyer

Line Up and Wait
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Dec 15, 2020
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AlphaPilotFlyer
Still having issues with strobe interference over radios on certain frequencies. Issue was much worst when I got this 1970 c172. Over the years there was a lot of stuff installed and removed, leaving a lot of dead wires and ground wires grounded throughout chassis. Cleaned up most, and ran an avionics ground bus from battery ground strap in tail. Found one of the wing wire shielding grounded on both ends as well and corrected….both fixes Made a big difference. But still get pulse interference on some VHF freqs…. these are old radios, a narco 12d and original ARC so age not helping but they work well. Strobe is standard wheelen . I got low resistance in all leads annd connectors and solid clean cable shields grounded close to battery ground strap (my batteries re in aft baggage area), and tried other locations without effect. Otherwise strobes work normal. This is a normal issues with old planes I know, but bothered I can’t figure a solution…. Short of running all grounds to common peg rather than chassis, figure someone out there perhaps found different things to try.

Sort of out of ideas and considering disconnecting each bulb to find most offending circuit and adding a ferrite ring somewhere on power lead or try grounding shield at strobe end. Anyways, open to suggestions.
 
Strobe off in the daylight? I had a 66 Cherokee where the strobe effected some avionics, if I needed those avionics, I turned the strobe off.

Don’t fret about the possibility of an inadequately lighted Cherokee flying around. It wasn’t long after I sold it the new owner had a mishap, off to the salvage yard it went.
 
Bell206 said:
Get a 2nd coax and run it between the the radio and antenna. One radio at a time.
Is the inference heard on the ground or flight or both?
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humm, didn't think of that. What would the benefit be of additional coax per radio/ant? both radio chassis are commonly grounded at rack with shield, and running 2 radio/ant lines would certainly decrease resistance but I don't see how it would better isolate from common ground. I don't think it would effect SWR as length would be mostly same so no harm in trying. will check to see how difficult it would be

EE thinks it's mostly due to all the components being chassis grounded and creating different return paths as well as the energy, which I agree but don't have time to rewire everything and upgrading to led easier but costly. Old radios and original 1969 wiring and terminals don't help.

was thinking of using larger shielded wires to bulbs which may help path of least resistance back to common ground at battery, or maybe add a small resistor but it would likely blow considering the strength of pulse.

aircraft has beacon so don't use the strobes on ground much...will check next time.
 
AlphaPilotFlyer said:
What would the benefit be of additional coax per radio/ant
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You're not "adding" a coax, you're substituting a coax for troubleshooting. You need to determine if your interference is conducted or radiated. So if you take a 2nd coax, connect it at the radio and antenna, run it through the cabin or whatever, see if the interference changes or disappears. Given its frequency specific my 1st guess is radiated which points to a coax issue or shielding issue vs a physical wire connection.
 
It would be difficult to rewire everything correctly, but you might try at least running a dedicated ground wire for each strobe lamp rather than grounding to chassis.

The airframe serves as the ground plane for your antennas, and your strobes are injecting electrical noise directly into that ground plane.
 
I dont want to write a whole dissertation on radio design or stages, but the audible interference is not likely coming thru the RF segment(118-136Mhz way outside audio range). Aviation radios us Amplitude Modulation in the audio(third) stage for us humans to hear. AM is commonly affected by age with leaky caps in the amp stage, poor solder joints, bad elec ground plane(not airplane) or resistance at the plug/receptacle interface. You can have the caps in the radios replaced, resolder joints, clean the plug and receptacle with DeOxIt, but might just be chasing smoke. If you can try a different strobe, might be fastest and cheapest solution.
 
Barrett50 said:
I dont want to write a whole dissertation on radio design or stages, but the audible interference is not likely coming thru the RF segment(118-136Mhz way outside audio range). Aviation radios us Amplitude Modulation in the audio(third) stage for us humans to hear. AM is commonly affected by age with leaky caps in the amp stage, poor solder joints, bad elec ground plane(not airplane) or resistance at the plug/receptacle interface. You can have the caps in the radios replaced, resolder joints, clean the plug and receptacle with DeOxIt, but might just be chasing smoke. If you can try a different strobe, might be fastest and cheapest solution.
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Ever hear static from a lightning crash over an AM radio? RF noise rides atop the AM carrier and gets demodulated into the audio range.
 
Half Fast said:
Ever hear static from a lightning crash over an AM radio? RF noise rides atop the AM carrier and gets demodulated into the audio range.
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The enegy from lightning is not RF bleedthru to the audio stage. If there is crackling in the audio from a lightning strike nearby mostly it is due to the massive voltage potential entering behind the RF notch cut filter. Far different than a low level buzz created by the oscillator inthe strobe. Go on without me from here. Ive offered my piece of info, ignore it for all I care.
 
Barrett50 said:
I dont want to write a whole dissertation on radio design or stages, but the audible interference is not likely coming thru the RF segment(118-136Mhz way outside audio range). Aviation radios us Amplitude Modulation in the audio(third) stage for us humans to hear. AM is commonly affected by age with leaky caps in the amp stage, poor solder joints, bad elec ground plane(not airplane) or resistance at the plug/receptacle interface. You can have the caps in the radios replaced, resolder joints, clean the plug and receptacle with DeOxIt, but might just be chasing smoke. If you can try a different strobe, might be fastest and cheapest solution.
Click to expand...
agree that new unit likely quickest resolution... wanted to try any other suggestions prior to spending more $ to upgrade to LED strobes ... do you think grounding wire shields at wing tips rather than box worth trying?
 
AlphaPilotFlyer said:
agree that new unit likely quickest resolution... wanted to try any other suggestions prior to spending more $ to upgrade to LED strobes
Click to expand...

LED upgrade is the best AMU you'll ever spend. Saves weight, more reliable, less current draw, simpler installation, no interference. A total no brainer.
 
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