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

Ray Wells vk2tv at exemail.com.au
Sun Dec 21 06:59:30 EST 2008

That's great news, Tim.

Don't overlook the exhaust system, much of which is supported by rubber 
mounts so it makes an effective antenna under the car that's connected 
to the engine. A bond near the "open" (rear) end can be effective in 
some cases.

I worked with a guy many years ago who had a Swan mono-bander (40m) in a 
Mazda ute. He had no noise problems. Then, because the ute was getting a 
little old he replaced it with another Mazda ute and until the day he 
retired he never killed the noise from that vehicle. He bonded 
everything, used shielded spark plug wiring, "wrapped " the engine in 
gauze, etc. If it was suggested to him he tried it. There will always be 
a vehicle like that.

I bought an MQ Patrol in 1981. They were 24v and it had a mechanical 
voltage regulator. I ran every lead to the regulator through coaxial 
capacitors, fitted ferrite chokes, and bypass caps to ground, but 
nothing reduced the S9 noise on 2m. I replaced the regulator with a 
(homebrew) solid state unit and the noise went away forever.

Perseverance is the answer.

Cheers, Ray

Tim Ahpee wrote:
> Hi Ray,
> We (VK3BZQ and I) spent the day messing around with the radio and the car.
> The good news is that we seem to have eliminated the problem of the RD getting
> into the heater fan. 
> We added 3 bonding straps and probably should add some. So far we have put one
> between the body and the bonnet, one between the bull bar and the body and one
> between the body and the chassis at the rear of the car. It was the last one
> that seemed to do the trick. I think to complete the job I would add a second
> one on the bonnet, a second between the body and the bull bar and I'd also
> look for some more body-to-chassis points under the car.
> Heading off soon for a bit of a holiday so we'll see how the APRS performs
> both in terms of controlling the heater fan and getting into the HF i-gates.
> Thanks for the advice, it's worked :-)
> Cheers,
> Tim
> On Fri, Dec 19, 2008 at 11:02:05AM +1100, 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
>>>>> _______________________________________________
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>>>>> Ozaprs at aprs.net.au
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