[Amps] RF in Vehicles

[Carl]

RF can flow on both sides of the aircrafts skin and it appears you have a 
typical common mode issue. If you would be a bit more specific about the 
frequency, since VHF/UHF covers from 30 mHz to 3 gHz, a solution can be 
suggested.

Carl


----- Original Message ----- 
From: <qrv at kd4e.com>
To: <amps at contesting.com>
Sent: Thursday, April 20, 2017 7:14 PM
Subject: Re: [Amps] RF in Vehicles


> He was speaking in shorthand.
>
> Of course the radio is the "source" of the RF.
>
> Presuming that the coax is properly connected to the radio, the
> radio is properly grounded, and the antenna is resonant then the
> problem would seem to be that something is coupling the RF from
> the antenna into the wiring to the Supervisory Control Panel ...
> or, the RF is somehow getting back though the power supply line.
>
> If the antenna is non-resonant, for some reason, then the coax
> can unintentionally become part of the antenna system ...
>
> 1KW at VHF/UHF is a ton of RF anywhere - but in the closed system
> of an aluminum container - wow. You don't have to misplace much
> of that power to cause mischief.
>
> Given your altitude I wonder about the need for so much RF power,
> but that's your business.
>
> Just one non-engineer Ham's thoughts ...
>
> 73, DavidC KD4E
>
>> So I have this airplane.  Not a Cessna 150, but not a B-52 either.  Jet 
>> with with about 30 KW available as the power source.  The transmitter 
>> consists of a phased combiner with four PA stages adding up to well over 
>> a KW in the VHF/UHF range.  The antenna is a basic monopole that uses the 
>> complete mounting base as a ground plane.  This arrangement is mounted on 
>> the aircraft centerline.  The aircraft itself makes a fairly good Faraday 
>> Shield in that it has a solid surface of aluminum that is overlapped and 
>> bonded to the internal structure.  Never-the-less, there are several 
>> wiring bundles that connect to this transmitter assembly for command and 
>> control that are fed inside of the aircraft and thus by-pass the "Faraday 
>> Shield".
>>
>> When the transmitter is turned on, one of the internal generators in the 
>> aircraft immediately turns off.  The generator is a 3 phase 115 VAC 400 
>> Hz model that uses an internal permanant magnetic generator at 40 volts 
>> AC 800 Hz, that is in turn regulated to control the field of the 
>> generator.  This is controlled by a Supervisory Control Panel that 
>> controls the field and also monitors for over/under voltage and 
>> frequency.
>>
>> Clearly the Supervisory Control Panel is being impacted by RFI thus 
>> shutting the generator down.
>>
>> The comment was:  "This makes no sense. Unless something is very wrong 
>> with the radio,  there should be no RF on power or control wiring. From 
>> an EMC point of  view, the ANTENNA and it's counterpoise (metallic parts 
>> of the vehicle)  are the source of RF, NOT the radio. Clearly, whoever at 
>> Toyota wrote this doesn't have a clue."
>>
>> Ok, so what's wrong with this airplane?
>>
>> Mark Bitterlich
>> WA3JPY
>
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