[OZAPRS] HF APRS upsets the car's climate control

Ian Bennett ibennett at tpg.com.au
Fri Dec 19 11:23:16 EST 2008

	Just because you "know" does not mean everyone else does and conveying 
knowledge by belittling a person's attempt to do so does not work.
	Had you posted this information previously in a more constructive tone, you 
may have saved Tim some work.


On Fri, 19 Dec 2008 11:02:05 Ray Wells wrote:
> I'll say it again. You have an antenna radiating lots of RF and you're
> worried about radiation from the coax?
> You have vehicle wiring in the presence of a strong RF field from the
> antenna, not some piddling, insignificant leakage from the coax which,
> by the way, won't be affected by VSWR. Coax doesn't mysteriously become
> "leakier" just because the VSWR is high.
> Think about the nature of the situation, and when you have, dump any
> notion that radiation from the coax is likely to cause the problem.
> You need to prevent the RF on the wiring from getting into the
> controller by applying RF suppression techniques to the controller
> wiring. As somebody else commented, make sure the bonnet is bonded. Use
> DECENT bonding straps (the braid from RG213 coax should be considered an
> absolute minimum. Don't waste your time with RG58 braid) around the
> hinges (yes, both of them). Don't expect that to be a cure-all, because
> the front of the bonnet is a long way (in RF terms) from the grounding
> points, when the hinges are at the windscreen end. Is the problem any
> worse/better with the bonnet up/down. That will give an indication of
> the effectiveness of bonnet bonding. Fit ferrite "filters" around the
> wiring into the controller. RF bypass caps will likely have no effect
> because of the difficulty of providing a SHORT, DECENT ground point,
> which could also be alive with RF.
> Make yourself a field strength meter (a 1mA FSD moving coil meter,
> diode, bypass cap and a sensitivity control) in a metal enclosure with a
> coax socket for the input. Use a length of coax with just 25mm of the
> inner conductor protruding at the far end (away from the meter). Use
> that as a probe to assess the level of RF at various point on the car
> wiring. If you need more sensitivity, use a DC blocking cap (say 0.01uF)
> attached to the inner conductor of the coax and touch various points of
> the wiring with the capacitor. It's extremely simple and effective.
> Suppressing interference both to and from transceivers in a vehicle
> situation can be very time consuming and, sometimes, very ineffective.
> What works in one case won't work in another, and what you might think
> is "earthed" isn't necessarily so. A major trap with heavier 4WD
> vehicles is that the body is not necessarily bonded to the chassis, it
> sits on rubber mounts. Bonding around those mounts can return a huge
> improvement.
> Some years ago a neighbour's diesel Landcruiser produced S9+ noise on
> 27MHz. The source of the problem was a combination of the oil sender
> unit and the wiring to the instrument panel. I used a probe like the one
> described above, attached it  to the affected radio, and probed the
> engine compartment. The entire engine was alive with crud. I reduced
> that noise to absolutely nil by bonding around the two front rubber body
> mounts.
> Suppressing interference problems can take a lot of time, but that time
> can be reduced if you don't go chasing improbable causes.
> I had 25 years of installing two-way radios, and some of what I learned
> hasn't escaped via that sieve between my ears :-)
> Ray vk2tv
> Tim Ahpee wrote:
> > Hi Folks,
> >
> > I spent sometime last night re-routing the coax from the left side of the
> > car to the right side of the car. Now the coax is away from the fan. I
> > also checked the antenna match using a network analyser and it reports an
> > SWR of 1.1:1. I also added a clamp on ferrite torroid onto the coax near
> > the antenna end.
> >
> > So far, no change. At least it's only the fan that it seems to be
> > upsetting and nothing crucial like the cruise control :-)
> >
> > I'm going to have a play with grounding over the weekend and also get a
> > hold of a dummy load.
> >
> > If worst comes to worst I can mount the antenna up the back of the car
> > away from the over-sensitive electronics.
> >
> > Cheers,
> > Tim
> >
> > On Thu, Dec 18, 2008 at 11:40:13AM +1100, Damien Gardner Jnr wrote:
> >> Yeah ditto on my the VR Calais I had - ended up using all remote head
> >> gear in the boot, with antennas mounted off the boot...  Havent gotten
> >> around to looking at what this VHF radio i swapped a mate an MTR-8000
> >> for many moons ago is yet, so haven't put radios in the VT wagon and see
> >> if that has a problem... :)   The old '87 diesel luxie never had any
> >> issues at all. It's just a shame it was such a dog to drive ;)
> >>
> >> --DG
> >>
> >> On 17/12/2008, at 8:52 PM, Norm VK3XCI wrote:
> >>> I've been here with my old VN Calais. Make sure the bonnet is bonded
> >>> to the rest of the body!!! also the bullbar, tho I think you said the
> >>> spotlights are on it. Maybe bond the base of the antenna directly to
> >>> the rest of the body. Use double shielded coax?
> >>>
> >>> Worst possible case, put the antenna at the back of the vehicle. Good
> >>> luck, these things are usually simple or impossible.
> >>>
> >>> Norm VK3XCI
> >>>
> >>> Tim Ahpee wrote:
> >>>> G'day Folks,
> >>>> I've just got HF APRS running in preparation for my trip at the end
> >>>> of the
> >>>> year and have come across an interesting one. Each time the rig
> >>>> transmits the
> >>>> fan in the climate control goes to full power. Nothing else seems to
> >>>> be
> >>>> affected just the fan. It was a bit of a shock the first time it
> >>>> happened. I
> >>>> was driving along and heard the TX relays go click then I was
> >>>> blasted in the
> >>>> face with air. Details:
> >>>> Rig: Icom IC-7000
> >>>> Car: Toyota Prado 2008 Diesel
> >>>> Antenna: Diamond HF30FX mounted on the bull bar
> >>>> Any thoughts? I'm wondering if the RF is getting straight into the
> >>>> motor
> >>>> controller for the fan because if the fan is off nothing happens.
> >>>> Cheers,
> >>>> Tim
> >>>> VK3TZA
> >>>> _______________________________________________
> >>>> Ozaprs mailing list
> >>>> Ozaprs at aprs.net.au
> >>>> http://aprs.net.au/mailman/listinfo/ozaprs
> >>>
> >>> --
> >>> Regards de Norm, VK3XCI
> >>> Mildura on the Murray
> >>> QF15bt
> >>> _______________________________________________
> >>> Ozaprs mailing list
> >>> Ozaprs at aprs.net.au
> >>> http://aprs.net.au/mailman/listinfo/ozaprs
> >>
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