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Author Topic: I Think I'm Having An RF Problem  (Read 424 times)
KD8ERE
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Posts: 42




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« on: July 31, 2009, 07:43:21 PM »

Over the last month or so, I've posted in a few different forums regarding problems I thought I was having with my antenna, then my radio. Those problems turned out to be that my microphone had taken a turn for the worse. I replaced it, and now I'm back up and running. Thank you to all who had suggestions as to how to fix my radio.

Now I'm having another problem, and I'm pretty sure it's an RF problem. I've been trying to program a few frequencies into my radio such as 145.---. Whenever I'm set on the frequency, I key up, then the radio resets itself. I have a Kenwood TM-271A. I know that with this radio, it has an RF safety feature, and will do this if there is an RF overload. I'm trying to figure out what could be causing this. Again, I'm pretty sure it's my antenna. How bad are jpoles with RF exactly? Unfortunately, I can't check it because I don't have an SWR meter. I've never used one, so I'd be lost even if I did. Does anyone else have this problem? Thanks again!

73,
Ryan KD8ERE
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KD8ERE
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« Reply #1 on: July 31, 2009, 07:44:24 PM »

BTW, when I say resets itself, I mean it'll shut off, then come back on. Thanks again!
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AD5X
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« Reply #2 on: August 01, 2009, 04:11:47 AM »

How close is your antenna to your radio?  It sounds like you're getting RF into your power supply, and the power supply is re-setting.  Try putting some snap-on ferrites on the AC cord right at the power supply, and snap-on ferrites right at the power supply output and the radio DC input.  

I used to buy cheap snap-on ferrites by the boatload from All Electronics, but they seem to have little or none now.  Another place to get cheap snap-on ferrites is www.radiodan.com.  The more trsaditional places are Amidon, Connex Electronics, Mouser, DigiKey, etc.

Phil - AD5X
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KB9CRY
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« Reply #3 on: August 01, 2009, 04:41:37 AM »

Or, is your power supply not adequate?
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KD8ERE
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Posts: 42




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« Reply #4 on: August 01, 2009, 05:12:17 AM »

The radio is just over 30 feet from the antenna. I've got it set up in the back of my garage, with the jpole mounted to an old basketball hoop poll in front. The power supply doesn't do anything when the radio reboots. I have an Astron 35 Amp supply. Wouldn't the light on the power switch flicker if the power supply was rebooting as well?
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AC5UP
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« Reply #5 on: August 01, 2009, 05:57:46 AM »

If I recall, the pilot light on Astron linear supplies is a neon jobbie wired in parallel with the primary on the transformer. The only thing that would make it go dark would be a bad power cord, line switch, or fuse.

You can test the DC output with a voltmeter or a 12 volt lamp. If you can wire up something like an automotive lamp across the supply, then key the radio on a problem frequency, it will blink if the power supply is shutting down. Likewise a voltmeter should kick down near zero momentarily.

As for chokes and such, first thing I'd do is eyeball the J-Pole installation. Coax in good shape? No chafes, pinches or other signs of distress? Connection point at the antenna in good shape? Was the coax braid properly sealed at the antenna end against water intrusion?

Hint: When I install coax that connects via a pigtail at the antenna I've gotten in the habit of soaking the exposed braid with a generous shot of spray paint rated for outdoor use. Concept is to let the braid soak up as much paint as it can which plugs up the capillaries in the braid. If the braid is plugged with paint there's less opportunity for water to wander inside.

Finally, J-Poles benefit from an RF choke at the feedpoint. Just wrap four or five turns of coax solenoid style around the mast (assuming RG-8x) and secure it with Ty-Raps. Or, in the case of half inch coax, the same number of turns on something like a 4" PVC or ABS pipe coupler.

I have a hunch your problem is at the feedpoint if this has developed over a period of time...
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AC5UP
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« Reply #6 on: August 01, 2009, 06:13:45 AM »

One more thot:

What happens when you key the radio into a dummy load? If you don't have a dummy load, buy or borrow one and check the radio at all output power settings.

And speaking of, with your antenna connected, does the radio shut down at any power setting... Or only at highest power? If it plays OK at low power only you may well have an SWR / RF feedback issue with the antenna.
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VE7REN
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« Reply #7 on: August 01, 2009, 06:59:59 AM »

check the power cable terminals,so that they are tight. i had the same problem with my 2200 icom. turned out i had a loose negative cable.
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KD8ERE
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Posts: 42




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« Reply #8 on: August 01, 2009, 07:54:08 AM »

AC5UP,

That's a good idea wiring an lamp across the supply. I never thought to do that, so that'll be on my list of things to do today. I'll check it with the voltmeter first though. This way I can try to cover all bases, and hopefully get the issue resolved. It's not a big problem, just an inconvenience that I can only operate on 146 and 147 MHz. I have eyed the jpole, and it looked to be in order, but a second and maybe third time couldn't hurt. I'll have my wife eye it too. She's usually good at finding small things that I tend to overlook.

VE7REN,

I never took that into consideration. A few years back, I put adapters on it (I can't think of the proper name off hand) so I wouldn't have to keep wrapping the wires from the radio around the positive and negative terminals. Now that I think of it, there's a chance one could be loose. Thanks again!
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KQ6Q
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Posts: 978




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« Reply #9 on: August 01, 2009, 09:17:32 PM »

Another way to check things - connect an HT to the antenna and see if you can make contacts, or at least bring up a repeater.
The problem reminds me when I built a Heath 1175 power supply (a classic regulated supply, not a switcher) to use with a TenTec Argosy, I had problems with RF getting into the supply and forcing the output voltage down. Some disc ceramic caps bypassing the AC leads to the chassis inside, and bypassing the 12V plus and minus output terminals as well, cured the problem. If you have an Astron classic PS, not a switcher, this could be your problem too.
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