[Amps] RF in Vehicles

[Mark Bitterlich]

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



----- Original Message ----- 
From: "Jim W7RY" <jimw7ry at gmail.com>
To: <jim at audiosystemsgroup.com>; <amps at contesting.com>
Sent: Thursday, April 20, 2017 12:30 PM
Subject: [Amps] RF in Vehicles


> Agree to all of what Jim, K9YC says here!
>
>
> 73
> Jim W7RY
>
>
>
> On Thu,4/20/2017 9:00 AM, Gary Smith via Amps wrote:
>> A few years back we had a 2011 Toyota Prius. When I decided to install a 
>> vhf/uhf rig, I contacted Toyota with concerns about the on-board 
>> computer.
>
> VHF/UHF in a vehicle is FAR less likely to cause problems with automotive 
> electronics that HF. Two very important reasons. First, power levels are 
> generally a LOT lower. Few rigs put out more than 50 W, and the largest 
> commonly available power amps put out about 160W on 2M and 100W on 440 
> MHz.
>
> Second, at HF, all the metal in the vehicle serves as the counterpoise for 
> the vertical part of the antenna, but connections between that metal is 
> often poorly bonded or not bonded at all, insulated by paint. The result 
> can be lots of RF current flowing in metal parts in close proximity to 
> vehicle wiring. That current can couple quite strongly into that wiring, 
> especially if it is not twisted pair. And, taking wavelength into account, 
> RF current maxima are much more likely to be confined to the reoof of the 
> vehicle, as compared to HF where they are next to sensitive wiring.
>>
>> What I received was a nice two page letter on where to run the power and 
>> control cabling. Their general instructions was to run the cabling in the 
>> trough to the right of the passenger footwell in the right side of the 
>> car so to keep the rf away from the ob computer/controller.
>
> 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.
>
> 73, Jim K9YC
>
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