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Old 08-08-2018, 16:28   #16
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Re: HF-SSB Radio, Proper Installation Tips/Techniques, etc.

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I think it may be directly radiated RFI - the methane detector is a completely stand alone battery unit and is at least 6' away from any other wiring and is mounted on the cabin wall though I'm not sure how I can choke it - there is no external wiring!
It certainly could be caused by radiated RFI. Even with a perfect ground, you are still in the near-field of a backstay antenna, and there's not much you can do about that.

Can you try a different brand methane detector? Or, you could enclose the detector inside a copper screen box. If the edge seams are properly soldered or otherwise made RF-tight, the gas will make it through the screen but the RF won't.

But that seems like a lot of work. Try a different detector -- it might be less sensitive to RFI.
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Old 08-08-2018, 21:09   #17
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Re: HF-SSB Radio, Proper Installation Tips/Techniques, etc.

In desperation...I suppose one could test the "direct RFI" theory by simply wrapping the detector in tin foil, to shield it from RFI. In the unlikely event that works, one could then fab up a better shield, using either metal screening or staggered perforated metal, so that the detector was still able to sample the air but it had an effective Faraday cage around it.

Worth the price of the aluminium foil to try it, I'd guess.
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Old 08-08-2018, 23:50   #18
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Re: HF-SSB Radio, Proper Installation Tips/Techniques, etc.

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In the unlikely event that works
I'd say it's almost certain that a foil shield will work, as long as the seams are rolled tightly. Any sort of good Faraday cage should block a very large percentage of the RFI. It needs to be a highly-conductive material (copper or aluminum are good),with no gaps in the seams and small holes for the gas to penetrate. And I couldn't guarantee that a screen Faraday cage wouldn't block the air-flow and keep the detector from working properly.

I would still try a different detector first.
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Old 09-08-2018, 10:56   #19
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Re: HF-SSB Radio, Proper Installation Tips/Techniques, etc.

I fully agree with you, Paul. Working with an unknown possible RFI source, kludging a temporary Faraday cage of unknown effectiveness, swapping in a new gas sniffer which, of course, is adding another total unknown....

And then of course, whether to use hand perforated copper panels or unobtainable copper window screening is indicated...(G)...

I know, somewhere out there I've seen numbers that let you figure out the minimum "hole" size in screening when using it for RFI shielding but I suspect a fast "tin foil hat" is still the quickest cheapest way to get a "Hot or cold?" answer out of it.

Or perhaps...get rid of the gas sniffer, and buy a proper gilded cage with a couple of canaries in it. Traditions must be respected!
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Old 09-08-2018, 11:50   #20
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Re: HF-SSB Radio, Proper Installation Tips/Techniques, etc.

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I know, somewhere out there I've seen numbers that let you figure out the minimum "hole" size in screening when using it for RFI shielding but I suspect a fast "tin foil hat" is still the quickest cheapest way to get a "Hot or cold?" answer out of it.

Or perhaps...get rid of the gas sniffer, and buy a proper gilded cage with a couple of canaries in it. Traditions must be respected!
That gilded cage will also protect the canaries from RFI.

A different problem, but I once had a PLB trigger itself, and got a satphone call from the USCG at 4:00AM (they called my wife at home and she gave them my satphone #). The very nice officer gave me the MMSI # of the offending PLB, and it was mine, belowdeck, stuffed inside my PFD, under my wet piled-up foulies . I couldn't get it to turn off, so I wrapped it in aluminum foil. The USCG officer emailed me after the next satellite pass (we had shared contact info by then), and confirmed that the PLB had gone silent. Of course the power levels and frequencies involved are completely different from the SSB near-field EMI issue.
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Old 09-08-2018, 11:58   #21
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Re: HF-SSB Radio, Proper Installation Tips/Techniques, etc.

Good ideas.

My inverter also switches on and off when I use the radio at high frequences - would choking the inverter power cables / PC power cable make a difference?
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Old 09-08-2018, 13:26   #22
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Re: HF-SSB Radio, Proper Installation Tips/Techniques, etc.

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Good ideas.

My inverter also switches on and off when I use the radio at high frequences - would choking the inverter power cables / PC power cable make a difference?
It's quite likely that proper ferrite clamp/chokes on the cables will improve the situation. With power cables you will want to run the positive and negative leads through the same choke core if you can (this eliminates DC saturation of the cores). I've been using "31" ferrite material (see page 14 of the presentation I gave to the SHTP for more details: http://www.sailvalis.com/presentatio...ons%202012.pdf). There may be better materials out there, but be sure you use something that works well at SSB frequencies.
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Old 10-08-2018, 11:49   #23
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Re: HF-SSB Radio, Proper Installation Tips/Techniques, etc.

Paul-
I'm guessing the infernal "water contacts" on your EPIRB had been joined by some salty moisture and that tripped it. I can appreciate why they are there but that's why I also prefer "Manual" to mean "It won't do anything until I tell it to."
There was a SAR/SAT false alarm maybe ten years ago when plasma TV's were a big new thing. Apparently someone had just set up a nice big one, and it was transmitting a harmonic that the satellites decided was a distress beacon. The owner got a big knock on his door...sure puzzled everyone for a while.
To cruelly misquote Robert Heinlein, "Any sufficiently advanced technology will be indistinguishable from malevolent spirits."
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Old 10-08-2018, 12:59   #24
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Re: HF-SSB Radio, Proper Installation Tips/Techniques, etc.

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Paul-
I'm guessing the infernal "water contacts" on your EPIRB had been joined by some salty moisture and that tripped it.
It was a PLB, manual activation only. I had it inside my PFD (I'm going to call it a lifejacket to avoid TLAO -- Three Letter Acronym Overload), and had apparently leaned too hard on it and had punched something into the PLB near the big red button. There was no visible damage to the lifejacket, but there was a tiny dent in the PLB case. I sent it in to ACR and they replaced it for free, in spite of being out of warranty and with obvious physical abuse.

And the officer at the USCG who called my wife was a real pro. He had to wake her up in the early AM hours to ask if I was at sea, and then made sure to let her know that most of these events were false alarms. After I spoke with the USCG officer I called my wife to let her know we were OK.

It was a good thing that I had a list at my navstation of all the MMSI and serial numbers for my PLBs and EPIRBs -- that way I could quickly confirm that the beacon was one of mine, and who had it (me!). After that, I installed a 121.5 MHz beacon receiver on the boat. That frequency isn't being used for initial notification anymore, but the EPIRBs and PLBs still transmit it for close-in radiolocation. With my receiver I can tell instantly if any nearby beacons are triggered, on purpose, or by accident. I don't want to start a SAR operation should we again accidentally trigger a beacon.

Quote:
"Any sufficiently advanced technology will be indistinguishable from malevolent spirits."
That was an Arthur C. Clarke quote -- "indistinguishable from magic". Your version is pretty appropriate.
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Old 03-09-2018, 14:04   #25
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Re: HF-SSB Radio, Proper Installation Tips/Techniques, etc.

Hello to all,
I just recently uploaded a couple new videos, showing LIVE, real-world Ship-to-Ship HF-DSC calls...

I've added them to my HF-DSC Playlist...please have a look....(and, please watch the playlist in order, so that it all will make sense)

https://www.youtube.com/playlist?list=PLnN6ygtZ3h2n3z5nlv-ga2zYuPozhUXZX



And, for those completely familiar with their radio and with HF-DSC, here are the videos:

"Live, Ship-to-Ship HF-DSC Calling, on GMDSS HF-DSC Calling Freqs"
And, "LIVE, Routine Ship-to-Ship HF-DSC Calling, on ALTERNATIVE HF-DSC Freqs"

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