EMC (was RE: [aprssig] APRS in a Car)

Dave Baxter dave at emv.co.uk
Tue Jan 31 05:32:41 EST 2006

All cars (and just about all electrical/electronic products) now have to
pass stringent EMC tests before being allowed to market.  The Civy
levels for transport systems (cars and the like) is I think some 50V/m,
HF to VHF. Military tests are even higher...  MUCH higher!

For domestic stuff, 3V/m, Industrial, 10V/m.  Not that it helps much in

Emissions are usually a problem these days for the likes of us.  The
limits are to protect broadcast services, where signal levels are
usually in the range of several mV's, not the single figure uV's that we
often look for.

Many common rail diesel engines now emit more QRM than the spark
ignition system petrol(gas) engines they replace.  (The inverters that
generate the high voltage for the injector solenoids are often a source
I believe)  But, that level is still below the EN limits, even though
for us it's the equivalent of an S9+ signal, and usually broad band in
nature, so almost impossible to blank out.   Don't go messing with the
injectors, you'll mess up the engine's fuelling map if you add diodes
for example, and also run the serious risk of engine damage.

Susceptibility, is not usually a problem, you'd have to run silly power
levels (kW's) and have a very badly installed radio/antenna to cause any
real problems for the vehicle, but, you should still take care, and only
run the minimum power needed to keep the QSO/link running.

Many of the automotive test houses (EMC facilities) have CB, HAM and
Military radios and antenna's available to them, just to make sure.  But
those particular tests are not a requirement for the standards, just
that some manufacturers like to have them done.

If your car/truck/van/bike(?) starts to misbehave (misfire, odd
lights/warning, wipers starting/stopping etc) when you TX, stop TX'ing,
or at least reduce the RF levels, till you find out what and why.

Any accident so caused, and investigated etc, you could find yourself
with no insurance as a result, and maybe even no drivers licence after
the court case!

Take care, great care!..

Dave G0WBX.

(Take a look at our company web site, I may know more about this than I
care to admit!  www.emv.co.uk)


> -----Original Message-----
> From: Dale Blanchard [mailto:wa7ixk at earthlink.net] 
> Sent: Monday, January 30, 2006 1:26 AM
> To: AA3JY at Winlink.org; TAPR APRS Mailing List
> Subject: Re: [aprssig] APRS in a Car
> AA3JY at Winlink.org wrote:
> > Dave wrote:
> > 
> > A lot of modern cars do not have "Always on" power ports 
> any more.  It 
> > seems to depend on the philosophy of the individual maker.  
> The Honda 
> > Accord I have now does not.  Other cars I've had in the 
> last 5 years 
> > have..
> > ================
> > You think that is bad...
> > BMW's single-wire, CAN-bus electrical system, which greatly 
> reduces the number of wires used in the main harness and 
> dramatically reduces weight and complexity.  Part of the 
> CAN-bus is a new fully electronic instrument cluster 
> featuring Info-Flatscreen for additional system information 
> available at a glance.
> > 
> > One would wonder if RF will have any affect on this new system...
> > 
> > Regards,
> > 
> > Clay AA3JY
> > (via WL2K)
> >__________________________
> I have heard that BMW has tested some cars in a high RF 
> facility similar to what the military does.
> I have great faith in the CAN systen. But can not afford one.
> It has been used for over 10 years now. Some one should have 
> heard some rumers by now.
> It is not a new system.

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