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Author Topic: How To Prevent RFI in the Camper or RV  (Read 6592 times)
WA3MOJ
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Posts: 28




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« on: June 18, 2012, 02:59:37 PM »

I have a 23' monopole antenna mounted on the back of my camper to operate HF. It is tuned with an Icom AH-4
antenna tuner, that then goes to my Icom 706MKII.  There are 8 ground radial wires 33' long on the ground.

I have the control cable of the AH-4 wound on a ferrite toroid, and the coax from the tuner goes into an isolation
choke by Balun Designs.  It is a dual core choke balun:

http://www.balundesigns.com/servlet/the-63/balun-designs-1-cln-1-Isolation/Detail

Issue:  The on-board radio in the camper turns on and off during transmissions, so I'm getting RFI in the shack.

What else can be done to prevent that?

Thanks.
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W8JX
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Posts: 6088




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« Reply #1 on: June 18, 2012, 04:30:57 PM »

Non resonant antennas such as this tend to be the most troublesome here. I would suggest trying a elevated feed point with a shorter mast/antenna if need be.  Others will surely chime in.
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K9ZMD
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Posts: 171




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« Reply #2 on: June 19, 2012, 12:39:46 AM »

Everything in your camper is in the near field of that antenna.  Also, the frame of the camper surrounding your domestic electronic gear is part of the return path for antenna currents (which radiate, too). Seems pointless to fight common mode RF current with a choke on your coax when radiated RF has such a short leap through the air into your domestic electronics. 

Ferrite beads and/or capacitive bypassing on all leads of your domestic stuff might diminish the symptoms; however, dealing with the cause is more effective. Diminishing the strength of the RF field around your camper requires getting some space between your camper and the antenna, or lowering your transmitter power.   

It may be sufficient to raise the antenna higher and use 4 or more tuned, elevated radials for the bands you plan to operate.  The more radials you install, the less critical it becomes to tune them.  You might find experimentally that 10 radials the same length as your vertical will do the trick.  Or not.

If higher w/elevated radials is not an option, then move the antenna far enough away to diminish the strength of the RF field surrounding the camper.

If higher and farther away are both not feasible, then reducing the RFI in your camper may depend on a combination of reduced output power and bypassing/choking all leads to your entertainment equipment. 

Gary, K9ZMD/7
Ridgefield, WA 
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WA3MOJ
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Posts: 28




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« Reply #3 on: June 19, 2012, 02:51:17 AM »

Last year I had no isolation choke or ferrite toroid in the setup.  Actually it was a dipole about 20' away from
the trailer and up 25'.  I just pulled the fuse for the radio from the fuse box to solve the problem.

The antenna base section is mounted on the rear bumper of the trailer, so moving the antenna away further
isn't a feasible option.  Maybe getting the antenna higher on a mast.  

If going higher, will that affect the location of the AH-4 tuner, or doesn't it matter with a monopole since that
extends the effective length of the radiating element?
« Last Edit: June 19, 2012, 02:53:30 AM by WA3MOJ » Logged
W8JX
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« Reply #4 on: June 19, 2012, 05:50:32 AM »

LIf going higher, will that affect the location of the AH-4 tuner, or doesn't it matter with a monopole since that
extends the effective length of the radiating element?

You need to move feed point/base of antenna higher (as high as possible) as you need to stop radiation next to trailer. Those broad band auto tuners look good in theory but in a application like this it can compound your problems when tuner is right next to shack as radiator starts at antenna terminal on turner. Have you considered trying a elevated screwdriver type antenna?
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WX7G
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Posts: 6136




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« Reply #5 on: June 19, 2012, 08:00:08 AM »

Your solution of removing the fuse from the camper on-board radio is a good solution.
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KF7CG
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Posts: 840




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« Reply #6 on: June 19, 2012, 10:16:31 AM »

Is the camper one with a metal skin or does it have a fiberglass exterior. If the camper skin is metal bond it securely to the trailer frame to use it to help as a sheild. It won't make a complete Faraday cage since most campers have rubber roofs now.

You may also want to pay some attention to your camper power lead, that is a good point for RFI entry. This one can be a little difficult since the power line configuration changes every time you change camping spots.

Good luck, and happy camping

David
KF7CG
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WA3MOJ
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Posts: 28




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« Reply #7 on: June 19, 2012, 10:33:50 AM »

Is the camper one with a metal skin or does it have a fiberglass exterior. If the camper skin is metal bond it securely to the trailer frame to use it to help as a sheild. It won't make a complete Faraday cage since most campers have rubber roofs now.

You may also want to pay some attention to your camper power lead, that is a good point for RFI entry. This one can be a little difficult since the power line configuration changes every time you change camping spots.

Good luck, and happy camping

David
KF7CG

My camper has fiberglass walls and rubber roof. I did bond to the steel frame chassis.
Not sure about your comment about the power lead...
When I hook-up, I plug the 30A A/C cord into the campsite power outlet.

I run the Icom 706 transceiver with a Samlex power supply.
Are you suggesting beads on the 30A power cable?
Are beads at the Xcvr & PS wothwhile?

Thanks
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WX7G
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Posts: 6136




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« Reply #8 on: June 19, 2012, 11:38:10 AM »

With the only susceptible piece of equipment being the Camper radio that is where I would focus my efforts. Ferrites on the power leads, ferrites on the antenna lead, and ferrites on the speaker leads are worthwhile things to try.

Or add a toggle switch to remove power from the radio and the problem is fixed.
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WA3MOJ
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Posts: 28




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« Reply #9 on: June 19, 2012, 06:12:57 PM »

. . . . Or add a toggle switch to remove power from the radio and the problem is fixed.

Are you referring to the camper radio, or the ham radio ??    Roll Eyes

  Wink
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KF7CG
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Posts: 840




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« Reply #10 on: June 20, 2012, 10:58:23 AM »

Having owned a few different campers and still having an older travel trailer, I must comment that much of the problem is the camper radio itself. I have never seen a good radio/entertainment system come with a camper.

If you want to maintain a camper radio. Try finding an automotive type unit that will fint in the camper radio space if that is possible and then replace the original. You should get better sound and less interference.

And ferrites or other RFI removal on your camper main service are not a bad idea either. Camper power leads tend to be good antennas. The switching type battery inverters used also tend to be a source of RFI going the other way too.

KF7CG
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WA3MOJ
Member

Posts: 28




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« Reply #11 on: June 20, 2012, 11:45:16 AM »

Having owned a few different campers and still having an older travel trailer, I must comment that much of the problem is the camper radio itself. I have never seen a good radio/entertainment system come with a camper.

If you want to maintain a camper radio. Try finding an automotive type unit that will fint in the camper radio space if that is possible and then replace the original. You should get better sound and less interference.

And ferrites or other RFI removal on your camper main service are not a bad idea either. Camper power leads tend to be good antennas. The switching type battery inverters used also tend to be a source of RFI going the other way too.

KF7CG


Agreed.  The OEM radio in the camper is of the POS variety.  Surprisingly poor, given the overall cost of the trailer. 

Do you have any suggestions for a replacement radio?  I presume it is a double DIN style.

Where on the camper main would I place a ferrite or wind a toroid?  On the main 30A power cable ?

.
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WB2WIK
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« Reply #12 on: June 21, 2012, 09:29:45 AM »

In a different thread I saw posted photos of the installation which showed a long leader (insulated) wire between the automatic tuner and the base of the antenna.

That's usually a pretty big "no-no" for a good HF installation; you'd want the tuner ground and the antenna ground return (where radials attach) to be at exactly the same point, which means the tuner should be right at the base of the antenna and not someplace else.

Simply relocating the tuner to closer to the vertical, and bonding the grounds together very well, could take care of the whole problem.
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WA3MOJ
Member

Posts: 28




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« Reply #13 on: June 21, 2012, 02:41:16 PM »

In a different thread I saw posted photos of the installation which showed a long leader (insulated) wire between the automatic tuner and the base of the antenna.

That's usually a pretty big "no-no" for a good HF installation; you'd want the tuner ground and the antenna ground return (where radials attach) to be at exactly the same point, which means the tuner should be right at the base of the antenna and not someplace else.

Simply relocating the tuner to closer to the vertical, and bonding the grounds together very well, could take care of the whole problem.


Yes. That's the plan. Moving the tuner & choke balun up on to the top of the rear bumper and just under the base of the antenna. 

Here's how it would look. . .

How bad is this problem (?) . . . the mounting stud of the antenna is about 16" above the base of the antenna.  That would make the feeder line from the antenna to the tuner about 12" long.  ( ?? )

http://i252.photobucket.com/albums/hh33/gb3zub/001-7.jpg
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