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[RFI] Mobile amps and vehicle issues

To: rfi@contesting.com
Subject: [RFI] Mobile amps and vehicle issues
From: "FoMoCo EMC" <fomoco_emc@hotmail.com>
Date: Wed, 11 Jan 2006 13:08:07 -0500
List-post: <mailto:rfi@contesting.com>
It may be shameful but it is going to be the shape of things to come.

Susceptible circuitry is rampant in a vehicle. Almost every electric motor in a vehicle is speed controlled by a pulse width modulated signal. A little bit of RF into the circuit and the motor will exhibit undesired RPM variations. There are a dozen sensors on the engine and throughout the vehicle that put out low level signals that can be disrupted. Imagine what occurs when the vehicle can no longer tell if tire rotation is occuring (wheel speed sensors) or can't determine the postion of the camshaft, crankshaft, or throttle plate.

Many of these same circuits also create noise that would be objectionable to weak signals. Plus the spark ignition noise doesn't do anyone any favors.

Manufacturers routinely test their vehicles for radiated immunity to around 100 V/m. The main emphasis of these tests is for safety with warranty claims a close second. Standard methods of testing have been developed but can't cover every possibility of on board transmitter installation (or mis installation in many cases).

Vehicle radio emissions are a concern for frequency ranges used by most vehicle users. AM/FM/SDARS are obvious areas. Remote keyless entry is not so obvious. Fleet vehicles used by police etc get a lot of extra attention for radio installations, but none of them are operating HF.

Manufacturers are not eager to fix EMC issues caused by or to ham radio unless it has a direct safety or warranty impact. Installation of 3rd party equipment that causes malfunctions would not be a big concern for most manufacturers unless you have a fleet of vehicles and are looking to buy more.

Since the needs of the many outweigh the needs of the few manufacturers do not want to add even $5 of cost to every vehicle to make a few hams happy. By the way $5 is around $5 million dollars to most of the large manufacturers on a yearly basis in just part cost.

That said, how many hams would be willing to pay (and how much) for a radio noise package if it were available? I would guess that it would have to be under $50 before anyone would bite. Thats just not going to happen.

If you intend to operate mobile you are going to have to be ready to violate your vehicle's warranty with special mods and you will need to understand how your vehicle works on a level more than the manufacturer would even tell you in the service manual.

There is lots of good info on this forum. I think your best bet for getting good help would be to post pictures of your installation and give good descriptions of the installation. Knowing exactly how things are connected makes a huge difference in performance.

Jim makes good points in not assuming what is and isn't grounded. I would always measure rather than assume. In his case these points not being grounded well may be shameful but if the AM/FM reception is satisfactory and a cell phone or passing an overmodulated high power CBer semi truck doesn't cause an engine stumble then the manufacturer probably has met their design goals.

EMC guy

I like the idea of HP mobile, but I still hear concerns about RFI to the car's electronics. Has anyone had any experience with this lately?

YES! I just put a 100w HF transceiver in my 2006 Toyota Sequoia and drive to CA with it. Power straight from the battery, antenna a Hamstick on the luggage rack, shield of coax bonded to a big bolt holding the luggage rack to the roof. Antenna works great, and I had lots of fun on 17m CW and SSB. Had to turn off the car's climate control when I worked CW, because it was speeding up when I keyed the radio.

BUT -- the Toyota Sequoia is an EMC nightmare -- when I fired up on 20 SSB
and called a 15 sec CQ, the Toyota's main computer crashed, leaving me dead
in the water in the middle of the Nevada desert! No fun. I managed to get
rolling by pulling the power lead off the battery to reset the computer.

Prior to installing the rig, Ron, K9IKZ and I poked around with an ohmeter
to see what was bonded to what so that we could find a decent connection to
the body for the antenna and understand how the vehicle was shielded. What
we learned is a disgrace -- two bolts a few inches from each other holding
the luggage rack to the body read 60 ohms between them. Bolts at opposite
ends of the luggage rack and on opposite sides are 3-6 ohms apart. A copper
strap supposedly tying the battery negative terminal to the body reads >10
ohms to those bolts and to the body near the bond! In other words, almost
nothing is bonded together, all the bolts and washers have paint between
them and the body.

Because I'm in the middle of moving from Chicago to CA over the next few
months, I won't have time to dig into this and clean it up. I will, of
course, add ferrite chokes to power leads for the ham gear and to what
senstive electronics I can find. And I'll bond everything I can find,
including body parts, tailpipe, hinges, etc. But what a mess! This is
absolutely SHAMEFUL!

Jim Brown K9YC

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