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Author Topic: ATAS 120 activating door locks  (Read 6157 times)
KE5QEO
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Posts: 8




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« on: September 16, 2012, 06:11:28 PM »

I have a yausu 857 installed in a 2001 Isuzu Rodeo running to a ATAS 120 antenna mounted on the metal plate welded to the back bumper.  I also have a ground wire running directly to the frame.  Transmitting 100 watts.

When I transmit sometimes the door locks will activate.  Sometimes they will lock and unlock all the time I am transmitting. 

I have run a ground wire from the rig back to the negative on the battery.  The power for the radio is run directly from the battery with an inline fuse.

Any suggestions on how to stop the locks from activating.

Thanks

Mark
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W9MMS
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Posts: 121




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« Reply #1 on: September 16, 2012, 10:26:08 PM »

Mark, I hate to be the one telling you this. However, you have a serious case of RFI using your vehicle as it's playpen.
The culprit goes by the name of "Common Mode Current" and is explained in detail here ......
http://www.k0bg.com/common.html
In getting a glimpse of what you have, or don't have in your setup can be found here ......
http://www.k0bg.com/couplers.html

I would recommend you spend some time at Alan's site in the attempt of bettering your setup, and having yourself one of the best
mobile setup this side of the free world.

I speak unashamed of endorsing www.k0bg.com   because it has helped me and many others setting up our mobile station. 

Good Luck and Happy Trails!

(((73))) Milverton
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K0BG
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« Reply #2 on: September 17, 2012, 05:38:04 AM »

The issue is indeed common mode current. There is even a blurb about it in the ATAS owners manual. A common mode choke will probably cure the issue, but it has to be mounted outside the vehicle. Remember, any length of coax before the choke it part of the antenna.

There is always some common mode on every HF installation due to the fact there is always some ground loss. Low mounting exacerbates the issue. And, running ground straps hither and yon can also do more harm than good. If the antenna is solidly mounted, no further grounding is necessary.
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KE5QEO
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Posts: 8




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« Reply #3 on: September 17, 2012, 08:51:41 AM »

Thank you both for some great information.  I will work on a common mode choke and put it outside the vehicle, hopefully it will cure the problem.  The www.k0bg.com site is great, I and many others I'm sure thank you for your work.

73
Mark
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KE5QEO
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Posts: 8




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« Reply #4 on: September 19, 2012, 07:11:35 AM »

I put together a common mode choke and wound about 3 turns of coax outside the vehicle and about 5 inches from the antenna. the coax loop is about 3-4 inches in diameter.  I have some of the good dx engineering ferrite beads on order but until then I used the cheap beads you can get at radio shack.  Still getting some common mode current mostly around 40m. also around the low end of 80 m.  It is still activating the door locks all though not as bad. 

When I put the good ferrite beads on, do you think that will improve the situation?  Is there anything else I can do in the interim to help.

Thanks
73
Mark
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K0BG
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« Reply #5 on: September 19, 2012, 09:19:27 AM »

Those beads from Radio Shack are worthless for HF. They're some unknown mix, and a 5 turn coil at 50 MHz, only measures 300 ohms. You can do that with one turn through a mix 31.

If at all possible, you want the choke outside the vehicle. That's very difficult to do when using a clip mount. And it pays to remember, that the more ground loss there is, the higher the common mode current will be.
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K3GM
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« Reply #6 on: September 20, 2012, 07:44:10 AM »

Mark, I was plagued with common mode issues initially when I installed my IC-7000 with a hitch mounted screwdriver antenna.  It would scramble the BCB receiver, and actually shut the rig down if I ventured above 50 watts output.  I did a number of fixes to get rid of it, but the two things that made the most improvement were:
1) Connect the transceiver directly to the vehicle body with a 2" wide, short copper foil strap.
2) Connect two copper foil straps from the antenna ground to the vehicle body, and to the vehicle frame like so:
http://i9.photobucket.com/albums/a96/TwoSevenRight/bond4.jpg

Additionally, I bonded the doors, hood, hatch, and exhaust system to the vehicle body.  The results were remarkable, and I got the added benefit of a much lower noise floor. Ignition noise became nearly nonexistent.
http://i9.photobucket.com/albums/a96/TwoSevenRight/bond1.jpg
http://i9.photobucket.com/albums/a96/TwoSevenRight/bond2.jpg
http://i9.photobucket.com/albums/a96/TwoSevenRight/bond3.jpg
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KE5QEO
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« Reply #7 on: October 10, 2012, 10:32:43 AM »

Ok, I have connected the transceiver directly to the vehicle body with a 2" wide copper strap.  I have run another 2" copper strap from the base of the antenna to the body.  Also a ground wire from the base of the antenna to the frame.  The antenna is mounted to a steel plate which is bolted to the hitch receiver.  Anywhere metal touchs metal I have ground it down to remove any paint or dirt.  I have bonded the exhaust pipe to the frame with a ground wire.  I purchased the mix 31 ferrite beads from DX engineering and made a choke using one of the split beads and three turns on the feed coax.  The choke is outside the vehicle basically right next to the bottom of the antenna.

The door locks are, now, not activating on any of the bands except the upper part of 40 meters.   The lock activation is very strong and continual until I stop transmitting.

Any ideas why I can't seem to eliminate this problem from 40 meters?

Thanks

Mark
KE5QEO
 
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K0BG
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« Reply #8 on: October 10, 2012, 11:30:47 AM »

Mark it is still common mode! If you wish to prove this statement, then purchase one of MFJ's clamp on RF ammeters.

Everybody seemingly runs ground straps hither and yon because they believe that is a basic mobile installation requirement. It isn't! True, it is best to band the exhaust system and other horizontal surfaces, as this decreases ground losses to some extend, and also decreases ingressed and egressed RFI. But the truth is, if adding a ground strap cured or reduced some specific RFI problem, then something else in the installation is (was) amiss. Further, sometimes adding a ground strap can actually increase a specific RFI problem.

In your case, you have chosen to use a low mounting location. This fact increases ground loss due to mutual coupling to the surface under the vehicle. Thus you will have a lot more common mode that you would if the antenna was bolted to a quarter panel.

What you didn't say is how many turns of coax did you put through the split beads. 2 or 3 won't do much. If you're careful, and you're using RG8X (as big as you'll ever need), you can get 7 turns through a 3/4 inch ID bead. That results in a choke of about 2kΩ at 10 MHz, which is fairly good. If you need more, then just snap on another bead. And you might considering where you mounted the antenna.
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KE5QEO
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« Reply #9 on: October 10, 2012, 01:54:10 PM »

Thank you Alan for your suggestions.  Yes it is definately common mode.  no doubt about that.

I started with 3 turns on the coax through the split beads, now I will go back and see if I can get 7 turns in and see if that helps.  I will also consider a different mounting location like on the rear quarter panel I'm thinking just back from the wheel well and slightly above it.

One other thing this Isuzu has a rear glass hatch that opens upward.  Below the glass is a door that swings open to the left.  the upper glass hatch has a defroster grid in it, tinted glass, a brake light at the top center of the glass. the lower door has a wiper in it that wipes the upper glass part.  when the glass hatch is shut it latches in the center to the bottom door.  Could this entire area defroster grid, brake light, wiper, etc. be part of the problem as well.  I have tried transmitting with the glass hatch open and with it shut.  When it is open the locks don't activate as often, when it is shut they activate much more often.  Should I try using the split beads on this area?  If so where?

Thanks for all your help
Mark
KE5QEO
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WX7G
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« Reply #10 on: October 10, 2012, 02:07:01 PM »

Add more ferrite cores on the coax and see if it helps.
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K0BG
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« Reply #11 on: October 10, 2012, 02:08:19 PM »

One end of the grid is at ground potential, so at HF that's not too likely. The CMHSL could if it is an LED array. A small ceramic cap (≈.1) across the leads will fix that too. In any case, I still believe it is CM, and more winds could fix the issue.

In my case, I use two mix 31 beads for the CM choke, and the coil of RG8X is about 3 inches in diameter. Any tighter, and you run the risk of the core migrating.
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