[Amps] RF in Vehicles

Fri Apr 21 18:39:31 EDT 2017

 Carl, the transmitter ranges from 60 MHz, to 500 MHz.  David, the reason 
for
 that much power is that it is used for jamming.   Bob Moody, it is
 impossible to radiate this transmitter on the ground.  There are serious
 HERP and HERO issues.  Ron, same answer.  Can't transmit it on the ground.
 Further, the power source is a Ram Air Turbine.  The transmitter has been
 checked on a bench and operates normally.  The antenna and feedline have
 been checked with a VNA, but not under load, which of course makes them
 suspect.  They were replaced.  Same problem.  Jim, the electronics are
 pretty well designed.  Yes, I agree that the RF is coupling to the wiring
 (thus my point when I presented this true condition) but in a way that is
 not obvious and not easy to troubleshoot.  My comment was also intended to
 make the obvious connection that RF outside can easily become RF "inside"
 even with a properly designed antenna, ground plane and feedline. 
Amazingly
 enough, this problem occured at the exact same time as the "RF in vehicles"
 subject line appeared, so I thought I would mention it.

 Interestingly enough, at 1-10 GHz, at the same or higher power level, there
 are no issues with the generator.

 The length of the wiring from the transmitter enclosure to where it enters
 the aircraft is about 12 inches or less.  It is also extremely well
 shielded, and also has been replaced.  The grounds for these shields have
 not been extensively tested, only with a standard ohm meter.  Using a 
bridge
 to check it down to milliohms is being done.

I am not permitted to redesign the aircraft.

 Mark

> ----- Original Message ----- 
> From: "Carl" <km1h at jeremy.qozzy.com>
> To: <qrv at kd4e.com>; <amps at contesting.com>
> Sent: Thursday, April 20, 2017 9:07 PM
> Subject: Re: [Amps] RF in Vehicles
>
>
> 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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>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>
>>
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