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Author Topic: Radio Shut Down  (Read 449 times)
KJ9A
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Posts: 9




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« on: February 13, 2003, 05:48:17 AM »

OK...Installed a new Icom 706 in my SAAB with a trunk mounted Hamstick.  The radio is directly connected with 4ga cable to the battery etc...With fusing at the battery, distribution block and radio.  All fuses rated 30Amps.  

When I transmit at less than half power, all is well...sometimes.  At full power the rig shuts down.  Grounding is not the issue, maybe a connection problem at the battery?

Any ideas?

Thanks,

Jim (KJ9A)
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N8EMR
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Posts: 235




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« Reply #1 on: February 13, 2003, 07:59:29 AM »

Its an antenna SWR and/or grounding issue. I assume you only see this on HF and not on 2m? Worse on 20m, not so on 80m?


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K0BG
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Posts: 9865


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« Reply #2 on: February 13, 2003, 09:31:37 AM »

N8EMR may be correct especially if you are using the internal VSWR bridge to measure it. the 706, like other Icoms and some Yaesus use the same circuitry for ALC, overheat protection, and VSWR shutdown. In short they are all but worthless for resonanting your antenna.

Further, it takes more than just large wire to minimize RFI. You didn't state whether you properly grounded the trunk lid. Or what kind of mount you used. All of these have cause and effects.

About a month ago, I wrote three articles on mobiles and antennas. They are:

www.eham.net/articles/4407
www.eham.net/articles/4424
www.eham.net/articles/4425

They may give you further insight as to what may be causing your problem.

Alan, KØBG
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KJ9A
Member

Posts: 9




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« Reply #3 on: February 13, 2003, 10:02:39 AM »


Thanks for the advice guys.  I have the trunk connected to the car body in two places with copper braid.

The SWR on 20M is great (1.3-1.6 up to 14.300).

20M is the only HF band I've tried so far.

Thanks,

Jim
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K5LXP
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Posts: 4485


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« Reply #4 on: February 13, 2003, 12:19:16 PM »

You didn't mention if you were using the remote head cable kit.  If you are, make sure you use the little screw that connects the ground tab to the radio chassis and adding a ferrite or two wouldn't hurt.  The radio really wierds out when it gets RF through the remote cable.

Mark K5LXP
Albuquerque, NM
k5lxp@arrl.net

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K0BG
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« Reply #5 on: February 13, 2003, 03:17:16 PM »

Mark is dead on. I forgot to mention this. It is a well known problem and a simple snap-on ferrite bead on each end will cure the problem.

Alan, KØBG
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VE3IVM
Member

Posts: 54




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« Reply #6 on: February 14, 2003, 10:24:19 PM »

When I first used my 706 with the remote head cable at home I found "birdies" around 6.8MHz and its harmonics. Those birdies "sang the song" only when I was rotating the dial or pushing the buttons. Quick investigation showed that was the cable radiating RFIs. So I was puzzled. Anyways, I wanted to install the radio in my car, but the cable was too short so I decided to cut it in half and make an insert. After I cut it and checked the wiring with a meter, I realized why I had that RFI problem. The cable has an aluminum jacket and strain wire to do shielding job, but they do not get ground from the radio through the cable's connector. Instead, they connect to the chassis only through a small tab (as Mark mentioned in his post) and a small screw that comes with the remote kit. And at home I did not use the screw, so there was no shielding and that's why I got RFI.

So here is a piece of information for the owners of ICOM 706:

- remote head cable's shielding connects to the chassis only through the small tab, and you must use a screw to provide a contact;

- the other end of the cable (connected to the head) does NOT have the shielding wire connected anywhere ( only one end of the aluminum jacket is grounded, at the chassis side). This may also explain why to use ferrite beads- the cable is long enough to build RF on that end which is not grounded, and that RF gets directly into the remote head;

- a screw has to be used to provide ground from the chassis to the remote cable's small tab. I found that the screw that comes in the kit is black anodized and probably because of that not always makes good contact. Either make sure it is tight and check the contact with a meter, or use your own stainless screw.

Good luck with your mobile installation!

Ivan
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KJ9A
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Posts: 9




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« Reply #7 on: February 16, 2003, 08:01:02 PM »

Thanks for all the help guys.  This weekend I'll do some experimenting....

73's

Jim (KJ9A)

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WB2WIK
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Posts: 20595




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« Reply #8 on: February 17, 2003, 06:53:06 PM »

If you're really fusing at the battery, distribution block, and radio, you've got a whole lot of extra fuses in line there!  Why would you fuse the line in three places, when fuses at the battery alone would do the job perfectly and provide fewer points of failure?  Also, remember each fuse and its holder represent some series resistance.  The rig really wants to see 13.8Vdc, why add more resistance to the wiring when you don't have to?

Not that this is causing your problem (it probably isn't), just seems like using three sets of fuses in the same wiring is silly.

WB2WIK/6
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