AboutChris Bushman Expertise I have been an amateur radio operator for about 36 years.
Experience In real life I manage a small motion picture film lab in Hollywood. I've been a fireman, a teacher of English in Okinawa, a personal computer tutor.
I am an Advanced Class Ham radio operator using my originally issued callsign WB6EEQ. I have operated for extended periods of time from Okinawa (KR6FX & KR6OP), Texas (K5VXG), and Mississippi (K5TYP).
While in the Air Force, I was a Manual Morse Radio Intercept Operator.
BS Zoology, UC Davis
Member, Society of Motion Picture/Television Engineers http://www.smpte.org/ - Member, American Radio Relay League http://www.arrl.org/ - Member, Quarter Century Wireless Assn. http://www.lockport-ny.com/radio.htm - President, Zen Nippon Airinkai, So Cal Chapter http://ourworld.compuserve.com/homepages/Chris_Bushman/ - Member, Maltose Falcons Homebrewing Society http://www.westval.com/mfalcons/ - Alumni, American Brewers' Guild http://www.abgbrew.com/
Expert: Chris Bushman Date: 4/23/2008 Subject: Two way radio problem
Question Hello Chris. I am a race engineer for a Formula 3 team in the UK and i have a problem with the two way radio system in my car. The actual radios we use are vertex standard Vx 427e. Now the problem is when the driver keys on to talk to me there is an awful high/low pitch screeching in his ear plugs. Its fine when i talk to him but he cannot bear the sound when i talk to him. You can here the pitch of the noise change when you touch the areal or even wave your hand in the area around the co-ax. The problem goes way with a different set of ear plugs but the problem is the ear plugs he uses are special molded ones to the shape of his ear.
Im really stuck with this problem and i have a pretty reasonable idea of how radio comms work.
Any help you can give me would be great and please feel free to ask me a question so i can give you some more specific details.
Best regards
Matt Ogle
Carlin Motorsport
www.carlin.co.uk
Answer Well, Matt, it would seem that since you tried alternate ear plugs and the problem went away, and it only occurs when in transmit mode, that the problem is RF getting directly into the earplugs or the cable.
There are several things I would try.
First off, I'd make sure everything is snugged down really well. Make sure there is a solid ground for the radio and make sure all connections are clean and tight. Check to be sure solder connections in the audio connectors are good.
Are the cable lengths identical with the good and bad earplugs? If not, it may be that the bad one is resonant at a harmonic of the transmit frequency. That is, it may be the right length to be a good antenna.
Can you easily swap the cable on the good earplugs? If so, I'd try a shielded cable, not coax, but twisted pair with a shield. Grounding the shield would be good.
I'd also try a few ferrite beads on the cable, they're good for hindering RF.
If the RF happens to be getting directly into the ear plugs, then maybe a little mumetal foil might help.
That's all I can think of right now Matt, hope one of those works.
Chris Bushman
WB6EEQ
North Hollywood, California, USA
