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Old 02-04-2007, 22:08   #1
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SSB Ground Loop Situation

So a funny thing was happening with my SSB. Occasionally tuning or transmitting on the higher frequencies -20000 khz and up - would turn on the stereo. The story started this summer going to Hawaii. Later in the trip the radio, an Icom m600 with a 120 tuner would take 45 seconds to return from transmitting to receive mode. We installed another radio for the return and with the same tuner it seemed to be OK. The 600 went to Icom and with some minor adjustments it was reinstalled. This lead to the stereo lighting off occasionally as stated above. Being the clever but not overly knowledgeable type I installed a line isolater this weekend. The tuning/stereo thing went away at the higher frequencies, but it is now in the delay mode ocassionally in the 8000 khz range.

With this back ground the real question I have is on power consumption. When the mike is keyed above 12000, the power consuption climbs to the 14 amp range. This is with out transmitting. Transmitting might move the amps up a bit, but not significantly. In the lower frequencies, the amps don't climb when keyed, but do when transmitting voice or a tone.

Does this seem like normal behavior. I haven't used the radio enough when it has not had other issues to know. Any insight into this would be appreciated.
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Old 02-04-2007, 22:39   #2
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First off, that doesn't seem like normal behaviour.
Secondly, why do you assume it's a ground loop problem?

You have not said whether or not you can use the radio to communicate.

Can you contact another station and ask for a signal report?

Are you transmitting noise or hum on the higher frequencies?

Did you send the mic with the radio when you had it "repaired"? Did you use the current mic with the "replacement" radio?

Have you grounded the radio "Gnd" connection to the rf counterpoise (ground). If so, disconnect that connection.

Do you see the same symptoms when the batteries are under charge as you do when they are at a lower voltage?

Do you have a ferrite core on the coax near the antenna tuner? Ferrite cores on the coax and on the power lines can solve a lot of problems.

Good luck...
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Old 02-04-2007, 22:54   #3
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In no particular order. The line isolator is near the tuner with ferrites on both sides of it. I have not been able to contact another boat to carry on a conversation. Transmitting has consisted of requesting a radio check on the different frequencies. The mic went with the repair, but the other radio did not use it. The ground loop was a possibility mentioned by ICOM when I took the radio to them. The radio itself is not grounded to the antenna system. I don't seem to be getting any hum out of the speaker when transmitting. Thanks for the questions. Larry
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Old 03-04-2007, 00:47   #4
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Regarding the current consumption, it is possible that the higher frequency transmitted signal is interfering with your current-measuring device, and the RFI is causing it to indicate erroneously. Of course, when you key the mic without talking there should be little or no RF being transmitted (assuming you are in SSB and not AM mode). This high-current behavior does sound like a radio problem, not an installation problem.

With my Icom 710-rt / AT120 system I do get output from the stereo speakers on some bands. I suspect that this is RFI and not power-line conducted noise, and that it could be cured by putting some ferrites on the speaker leads. The noise occurs if there is power applied to the stereo, even ig the front-panel switch is off (which only powers down portions of the stereo). It disappears when the stereo circuit breaker is switched off.
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Old 03-04-2007, 06:42   #5
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If you are getting 14A current draw and you are NOT in AM mode (USB Only) you are having RF Feedback problems internal to the radio. It needs to be re-repaired...
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Old 03-04-2007, 09:21   #6
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It seemed the draw was too high for just keying the mike. The only change was adding the line isolator near the tuner. I'll retest next time to the boat with and without the isolator.
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Old 03-04-2007, 12:26   #7
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Antares-
" When the mike is keyed above 12000, the power consuption climbs to the 14 amp range. This is with out transmitting. "
What kind of radio allows you to key the mic and NOT transmit? Normally keying the mic, whether you are talking or not, engages the transmitter and the radio is transmitting.
A 14 amp draw would not be high for an SSB radio, the typical ham radio rated at 100-200 watts output draws 20A on transmit, as soon as you key the mic.

I'd suspect as Paul mentions that you are seeing RFI tricking whatever you are using to measure amps. Just how/where are you measuring amps, anyway?

WRT ground loops, you should be able to inspect your equipment, as routine maintenance, and confirm that your grounds are set up in a way that doesn't allow for group looping. If each component is grounded directly to one common point--there's no opportunity for ground loops. If you are using a daisy chain or running grounds to the DC power distribution, that's a possible problem.

" This lead to the stereo lighting off occasionally " That sure sounds like RFI. Maybe you could describe the entire setup and the way it is connected, to give us a better idea or what the wiring is like? I have no idea what kind of antenna you are using, or what kind of tuner, much less how you've hooked it all up.
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Old 03-04-2007, 12:47   #8
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Quote:
Originally Posted by hellosailor
Antares-
" When the mike is keyed above 12000, the power consuption climbs to the 14 amp range. This is with out transmitting. "
What kind of radio allows you to key the mic and NOT transmit? Normally keying the mic, whether you are talking or not, engages the transmitter and the radio is transmitting.
A 14 amp draw would not be high for an SSB radio, the typical ham radio rated at 100-200 watts output draws 20A on transmit, as soon as you key the mic.
Sorry, but this is just plain wrong. If you are in SSB mode, either upper or lower sideband, there is only a tiny bit of power transmitted when you push the mic button, and until you talk into the mic. SSB means "single sideband suppressed carrier". Usually the carrier is 40-60db down. When you modulate the transmitter with voice or noise or whatever, THEN and only then are you going to see high amperage draws. On voice peaks, a 100 watt transmitter may draw 18 amps or so, a marine 150-watt transmitter may draw amperage in the upper 20's during voice peaks.

In the AM mode, of course, the radio does transmit when you push the button.

Note that this is NOT the case with a VHF-FM radio, which does transmit full power when you push the mic button.

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Old 03-04-2007, 12:59   #9
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I'm measuring by the amp meter on my DC distribution panel. All testing was done in upper side band mode. Tuning moves it to the 4-7 amp range with a background load of 1 to 2 amps. Keying the mike did not significantly increase the the draw until adding the line isolator. The DC ground for the radio is via the power cable. The chassis of the radio is not grounded or bonded to anything. The only other connections are the control wire to the tuner and the coax. The counterpoise (I had hoped to stay away from religious topics.) is a single copper foil strip to a external dynaplate aft of the keel. The run is about 15 ft forward of the tuner which is mounted inside the transom. No other direct connections in the setup although it runs by the engine. Larry
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Old 03-04-2007, 13:53   #10
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Bill is exactly right about current draw on single sideband transmit.
A correctly operating SSB or HAM when using USB or LSB won't draw significant current unless it's being modulated. The transmit current should be proportional to the modulation.

Steve B.

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Old 03-04-2007, 14:32   #11
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Larry,

Problems are hard to diagnose at a distance.

However, I'd suggest you connect your transceiver to a dummy load (buy one, like the MFJ 300-watt model for $39), borrow one, steal one. They're good to have around.

If you don't have a decent power/swr meter, get one. Daiwa's are particularly good....several models...and can be found on eBay. Others will work, too.

Make up a couple of 3' jumpers, from RG-8X cable, with a PL-259 UHF connector on each end.

OK, now you're set for basic diagnosis. Connect the antenna output of the transceiver to the power/swr meter input, and connect the power/swr meter output to the dummy load. You now have a decent test platform which is completely independent of your boat's antenna and RF ground system.

Transmit into the dummy load on several bands, e.g., 4mHz, 8mHz, 12mHz, 16mHz, 22mHz. Watch the power output on peaks (OK to whistle into the mic...you're not putting a signal on the bands which will interfere with anyone). Watch the power draw, when you just push the mic button and when you modulate (speak or whistle) into the mic.

If you are, indeed, drawing significant power (say, over 5 amps) when you just push the mic button on SSB (upper or lower), then the problem is with your transceiver. Send it for repair.

If it passes these tests OK, and behaves differently when you connect it to your boat's antenna and RF ground system, then something's wrong with the antenna/ground system.

Again, start with basics. Remove the line isolator. Carefully check all conections, and the coax itself for shorts and open circuits. Check you RF ground system...all connections...to be sure they're clean and tight.

Take your time. Write things down. Have a beer and review what you've done and learned.

While a bit tedious, these procedures will help you isolate the problem. Once that's done, you can take steps to correct it.

Good luck,

Bill
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Old 03-04-2007, 15:48   #12
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" Keying the mike did not significantly increase the the draw until adding the line isolator. "

Sounds like the isolator may be bad.....
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Old 03-04-2007, 15:50   #13
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Bill,

Thanks for the steps. A logical approach is appreciated. I'll see what I can gather in the way of gear and work through it. Larry
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Old 03-04-2007, 16:25   #14
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OK, what is this line isolator, exactly? I was thinking it was a ferrite common-mode choke (clamp-on split toroid or similar) on the coax between the radio and the tuner, but I can't imagine a way that this would cause high current when a normally-functioning transceiver is keyed.

I suppose if the isolator is indeed a common-mode choke (ferrite core or otherwise) over the radio coax cable, this would eliminate any RF grounding effect from it. Normally, this "grounding via the coax" shouldn't be necessary, but since there is no other ground connection to the radio other than through the power connections (you mention that you don't have an independent ground connected), this might make the radio chassis become hot at higher frequencies. All sorts of interesting stray paths for RF will start popping up, and these could cause internal feedback and high power consumption (among other problems).

My Icom manual is pretty insistant that I provide a solid ground connection to the radio, in addition to the power-connector ground. I've got a nice copper strap connecting the radio grounds to my boat's ground system. You might try this and see if it helps.

Bill's suggestions for isolating the problem are good ones, by the way.
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Old 03-04-2007, 16:56   #15
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Paul,
The line isolator is from Radio Works and is a tube containing a winding of coax around a ferrite core with connectors on each end. It seemed like a viable thing to try based on my original symptoms of an occasional slow return from transmit or tuning and the fun of having the stereo turned on with out human intervention.

I attended one of the Radio University sessions and that confirmed with later information made me feel leaving the radio chassis ungrounded was the right way to go. I'm still comfortable with that part of the dynamic. James remarks on perhaps a defective isolator could be true. I don't know how to test it but if removing it makes things better it would certainly seem suspect. Larry
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