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Author Topic: RF Interference to climate control in Toyota  (Read 1687 times)
WI2Q
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Posts: 4




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« on: March 15, 2002, 10:02:21 AM »

So I tried 20Meters (only band w/problem) in my new 4Runner this morning and to my surprise, on voice peaks, the main fan in the climate control system of the truck goes to max.  I suspect I'm going to have to add some ferrite donuts somewhere but thought I'd put out the question hopine someone has been there, done that....  Thanks
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KC2RFQ
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« Reply #1 on: September 27, 2010, 01:34:17 AM »

I have virtually the same issue on my 2002 Chevy Trailblazer. Were you able to resolve your issue? How? I've choked the coax at the antenna, choked the motor leads for the screwdriver, bonded numerous places on the vehicle body to the frame, assured proper power wiring per GM guidelines, located radio appropriately, etc....all without success. Problem is only on 20M and output must be 30watts or better. Voice peaks send the temp setting up/down and affects the fan speed as well. If you've been able to resolve, PLEASE post your method.
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WX7G
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« Reply #2 on: September 27, 2010, 05:40:55 AM »

What I like to do for this type of troubleshooting is the "threshold" the level at which the problem appears. Run the radio in CW and increase the power until the problem occurs. Now as you try various fixes you threshold again to see if you are making progress.
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KC2RFQ
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« Reply #3 on: September 27, 2010, 08:31:53 AM »

Yes, I agree that this is a very rational approach. It's the methodology I have been employing; to no avail. So far I've been unable to identify/target the cause. I hope others experiencing similar issue will post their findings...all clues are useful.
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K0BG
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« Reply #4 on: September 27, 2010, 05:00:47 PM »

This is a classic example of common mode current. I don't know the antenna, and I don't know the mounting methodology. However....

If it is a short, stubby antenna like the Lil Tarheel, my first look would be at the motor lead choke. Yes, they supply a mix 31 bead, but 3 or 4 turns isn't any where near the impedance needed. The rule of thumb is, the impedance needs to be two magnitudes greater than the impedance of the antenna. That is 5 k Ω, and perhaps a lot more depending on how you mounted it.

If the mount is something like the K400 series, then in addition to the control leads, you need to choke the coax feed line. If you're using RG58, or RG8X, you can get 6 to 7 turns through a 3/4 inch, ID, mix 31 split bead. That makes a choke about 2 k Ω t 10 MHz, which should be adequate in most case, but not all!

If you want more data, visit my web site.
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KC2RFQ
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« Reply #5 on: October 02, 2010, 12:29:55 PM »

Thanks Alan,
Even with chokes wound as you describe on your website for both the sense and motor leads and a choke on the coax, the problem remains on my Chevy Trailblazer. And yes, it's a Little Tarheel II mounted on a K-400 to the rear hatch with significant attention to grounding of the mount and bonding.
If I remove the tarheel and place a dummy load at the mount I see full power output on the meter and no interference with the automatic climate control. I'm guessing this implies the climate control is picking up radiated RF? Any additional ideas appreciated.

UPDATE:
PROBLEM RESOLVED!!!!! (at least in the Chevy Trailblazer)
I can't believe how blind I was. Several years ago I installed a new high end radio/video monitor system in the Trailblazer. In order to retain the steering wheel controls for both the radio and the climate control, I had to add a small device which interfaces with the vehicle's Class 2 data bus. I had forgotten completely about this. Well, all that was needed was a a few turns through a ferrite on the data wire coming from that unit where it taps into the vehicle data line...a very simple fix and less than 5 minutes work. I have spent maybe 40 hours pouring over the car's wiring diagrams and was just at the point of installing caps on all of the leads going into the HVAC control module. An AhHa! moment at 3:00AM this morning led me to go back to basics; what else had I done to this car that could be susceptible to radiated RF? My first step was to disconnect the data wire from the device going to the car's data bus. (I had wisely installed  a quick connect here). Problem was immediately gone. Step two, would a ferrite on this lead solve the issue? Wound 4 or five turns thru a ferrite, reconnected and YIPPEE! Issue Resolved!
« Last Edit: October 04, 2010, 02:15:09 PM by Steven Fishman » Logged
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