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Author Topic: Problems with VHF Handheld during helo ops  (Read 620 times)
JASEMCKEE
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Posts: 3




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« on: February 28, 2002, 12:21:08 PM »

Hello all,

First time poster, great site.

I work as a Radio Operator Offshore and we have a slight problems with our two handhelds that the Helicopter landing office uses during helo ops.

Before the helo lands on the heli deck, we have perfect comms with the landing officer, as soon as the helicopter lands, the landing officers radios begin to break up and he becomes unreadable.

I think that it may have something to do with the headset microphone that he is using. Its a David clark amplified dynamic microphone. This has only started happening recently and it happens when we use either of the headsets. Would the wind turbulence from the helicopters rotors cause the distortion, we are totally stumped with this one and would appreciate any help.

Thanks in advance.
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KC0HBM
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Posts: 24




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« Reply #1 on: February 28, 2002, 12:30:05 PM »

"....landing officers radios begin to break up and he becomes unreadable. "

I know it may be hard to tell, but do you think the radio is transmitting but the audio is breaking up? (distorted)  Or is the audio okay but the transmitter is broken? (like someone randomly keying and un-keying the radio while talking)

You also mention that the interference begins when the helo is on the pad... does it actually have to be touching the pad or can it be just a few inches/feet above the pad for the interference to begin?  If the pad is conductive metal then prehaps there is a strange conducted RFI phenomenon going on here.  

Thats about all I can brainstorm for now, I hope it helps a bit.

Mark
KC0HBM
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JASEMCKEE
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Posts: 3




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« Reply #2 on: February 28, 2002, 12:54:57 PM »

Mark,

Thanks for your help, the problem gets worse as the helo gets closer to the rig.

Would the helicopter be transmitting something that could cause this interference? As I said, comms are fine until it begins to close in on the rig. You can hear the heli officers voice, but it is unreadable. And as soon as the helo takes off, the problem goes away. Whats stumping us is that this has only started to happen recently. We really are baffled by this.

Thanks

Jase.
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K0RFI
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Posts: 10




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« Reply #3 on: February 28, 2002, 04:11:17 PM »

Sounds like a similar problem I ran into in commercial radio-- as soon as the ambulance left the barn and called in mileage, they were unreadable, but several miles down the road, they had perfect copy.  The problem---front-end overload to the receiver. The repeater tower was about 150 feet away from the ambulance barn. We solved this particular problem by having the crew use their portables when calling in mileage rather than the high power mobiles.  
You might have the helo crew reduce transmitter power (if possible) while on the pad, or fit your receivers with attenuation pads, if front-end overload actually is your problem.
73, Mike k0rfi
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KE4SKY
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« Reply #4 on: March 11, 2002, 01:59:03 PM »

Yup! Overloading front end of Rx.
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N7INK
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« Reply #5 on: March 14, 2002, 01:54:23 PM »

While on active duty I went the Air Assault course at Ft Campbell. One of the training points was preparing to hook up for sling loading of various pieces of equipment to the hook underneath the helicopter. One person was always assigned to take a ground stake with cable and an insulated probe to immediately discharge the electrostatic charge between the aircraft and ground before the hook up man actually attached the load to the aircraft. If you screwed up and did not discharge that electrostatic load first, you would pick yourself up off the ground from the tremendous static charge that hit you.  I have been told the charge is enough to kill you.  There is probably enough electro static build up that it could also be affecting your HTs at that range.  Desense from proximity as previously mentioned by another responder is also a good explanation.
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