[Fwd: [RFI] MOBILE RFI KILLS ENGINE of 1998 Rodeo]

Blackburn Blackburn <blackburn@qnet.com>
Wed, 07 Jul 1999 20:25:42 -0700

For some reason, this didn't get posted.  Lets try again...

> Hi,
> Got a couple things that might help.  I haven't operated HF mobile in a number
> of years, but have some experience with RFI problems with HF radios on aircraft.
> First, remember that the vehicle body & frame is the antenna counterpoise, so
> there will be RF currents flowing in the body and structure equal to the RF
> current flowing in the antenna, regardless of what you do to the antenna.  The
> trick here is to make the current flow in such a way that it doesn't upset the
> automobile electronics.
> First, make sure all the body & frame sections are well bonded at RF, and the
> feedline shield termination at the antenna feed point is well bonded to the
> body.  This means low-impedance connections, i.e. wide flat straps at multiple
> locations across any joints that aren't welded together.  The idea is to make
> the RF impedance of the automobile structure lower than the RF impedance of the
> automobile wiring.  RF currents will distribute among the various paths, with
> the largest current in the lowest impedance path.  If  the lowest impdance
> happens to be engine controller wiring (or wiring routed with the engine
> controller wiring) because the body is not well bonded, you'll have lots of
> problems.
> Fiberglass bodies are problematic.  I once had a mostly fiberglass pop-up camper
> on a Toyota chassis, and in order to get the mobile to work at all I ended up
> having to run a loop of large guage wire all the way around the perimeter of the
> bottom of the camper, & bond it to the frame at a number of points.
> If you can get to the engine controller wiring, you might also try a common-mode
> choke.  A number of snap-on ferrite cores in series (they don't necessarily have
> to be adjacent) will increase the common-mode impedance of the wire bundle and
> encourage the RF to flow elsewhere.  You'll need some number of cores...one or
> two don't do much at HF.  Start with six or eight cores or whatever fits & see
> if that helps...you may need to add more depending on the characteristics of the
> cores.  If you can physically get to the wiring, you should be able to add the
> cores without violating the vehicle warrantee.  If the antenna control cable is
> an RF path, you might also try adding a common-mode choke near where the control
> cable exits the antenna.  Either a number of snap-on cores in series, or a
> number of turns through a single large core should help.
> Finally, make sure the wiring associated with the radio and antenna is dressed
> as close to metallic body panels as possible. This will help reduce coupling
> between the wiring and RF fields.
> Hope this helps...let me know if you're successful.
> 73,
> Keith  KB6B
> K3AIR@aol.com wrote:
> > In a message dated 7/2/99 11:07:24 PM EST, wa3gin@erols.com writes:
> >
> > >
> > >  Even though the antenna is matched and resonated it appears there is
> > >  significant RF on the control cable. Tomorrow I will install an RF
> > >  isolator on the coax feed to the FT-900 transceiver.
> > >  I will also install a brute force line filter on the power leads in an
> > >  effort to reduce RF from entering
> > >  the control cable.  Third I will re-route the control cable as I've
> > >  discovered the cable runs very close
> > >  to the main engine computer which may be the reason the engine stalls.
> > >
> > >  Suggestions welcome,
> > >  dave
> > >  WA3GIN
> > >
> > Hi Dave,
> >
> > I had a similar problem with my FT900 and Ford Taurus wagon.  I had the
> > transceiver in the cargo area and the control head up front and finally gave
> > up
> > that idea and mounted the whole radio on the hump.  Problem I still have is
> > I can't tune my screwdriver on 10m because RF gets into the 12VDC power
> > leads that go to the antenna.  Drives the thing crazy, gives me all kinds of
> > wierd SWR readings (flat when I'm powering the antenna but infinite when I
> > stop!), etc.  Still trying to find a cure for that, but still works great on
> > the other
> > bands.
> >
> > 73, Mike K3AIR
> >
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