ELT whine
I'm flying 1 76' PA28-151 with 170B radios. I changed to Lightspeed Zulu's and now I'm hearing an ELT whine when I transmit. My FBO manager commented on it this afternoon when I got back from flying. He said he can distinctly hear the ELT whine, although suttle it is definitely in the signal. Are we hearing alternator noise or is something wacky in the ELT someplace? Ideas??
Comments
Mark
It's highly unlikely that your ELT is being patched into your 170B. More likely is that you're hearing a sound that is ELT-like. First thing to do is an ELT test (at 5 minutes before the hour) while listening on 121.5 on your 170B. You'll hear the a distinctive, whoop-whoop sound. Shut all of that down and compare what you just heard to the offending sound. I suspect you'll find a distinct difference.
Your battery is the primary filter for alternator, strobe, and any other electric induction noise. A weak battery will not filter as well. Try swapping out your battery with a known good battery.
Try switching OFF the strobes, and listen for the noise. If it stops, it is likely your strobe power supply dying. Replacing the PS is the likely solution.
A failed diode in the alternator can cause increased "ripple" in the charging voltage, making a whining noise. A low charging voltage may be a clue to this failure, otherwise alternator removal and bench testing will show a diode failure.
Another possibility is a "ground loop." Ground loops occur when various electronic and electric driven devices are grounded at different locations on the airframe. As our planes age, these ground connections become poorer and sometimes not sufficient for modern electronics. The solution is a common ground point for everything or improving the ground connections currently in use by cleaning and resealing the connections. Ground loops can be extremely difficult to isolate.
Good luck!
VFRs, without TFRs,
Dennis_ARR
1978 PA28-161
KARR Aurora, Illinois