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Thread: VHF radio/antenna testing

  1. #1
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    pogen is offline Sailing canoe "Kūʻaupaʻa"
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    Default VHF radio/antenna testing

    After some discussion at a recent meeting, and some weirdness I saw with VHF and AIS during the LongPac, I started to think about how to test my VHF installation.

    Fortunately at my workplace I found an old school RF spectrum analyzer and something even neater, a broad band biconic antenna, all nicely 50 ohm.

    I tested them with my VHF handheld, and saw tons of signal, and when you talk you can see the structure in the spectrum. When you key the mic on but don't talk, you just see the carrier. In this case on Ch 69, the carrier is at 156.475 MHz.

    I don't know if I would trust the absolute calibration, but one idea might be for several boats moored close together to do a comparison test transmitting to the person with the receiver gear on shore about 0.5 - 1 nm away to see how much power is coming through. Maybe after the season, or during the cruise-out to Sequoia YC in the fall. I will borrow the gear. I'm not sure how to pull data off it other than making notes on paper or taking photos of the screen. But if you are uncertain about your installation, this should distinguish sheep from goats.

    Any interest?

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  2. #2
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    Quote Originally Posted by pogen View Post
    After some discussion at a recent meeting, and some weirdness I saw with VHF and AIS during the LongPac, I started to think about how to test my VHF installation.

    Fortunately at my workplace I found an old school RF spectrum analyzer and something even neater, a broad band biconic antenna, all nicely 50 ohm.

    I tested them with my VHF handheld, and saw tons of signal, and when you talk you can see the structure in the spectrum. When you key the mic on but don't talk, you just see the carrier. In this case on Ch 69, the carrier is at 156.475 MHz.

    I don't know if I would trust the absolute calibration, but one idea might be for several boats moored close together to do a comparison test transmitting to the person with the receiver gear on shore about 0.5 - 1 nm away to see how much power is coming through. Maybe after the season, or during the cruise-out to Sequoia YC in the fall. I will borrow the gear. I'm not sure how to pull data off it other than making notes on paper or taking photos of the screen. But if you are uncertain about your installation, this should distinguish sheep from goats. Any interest? Name:  antenna.jpg
Views: 304
Size:  66.7 KB Name:  scope.jpg
Views: 289
Size:  90.0 KB
    great idea, David. Dura Mater has both. We want to be sheep. Oh, and I have an emergency antenna on my stern rail, too. I'd like to see if that works, too. In case my mast falls down some day. Although how likely would that be, huh?
    Last edited by Philpott; 07-28-2015 at 09:04 PM.

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    There are numerous reasons for mast failure...some easy to fathom, others not so much. EVERYTHING will ultimately fail.....

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    Quote Originally Posted by Harrier View Post
    There are numerous reasons for mast failure...some easy to fathom, others not so much. EVERYTHING will ultimately fail.....
    Ah, Sir. My inside joke is that Dura Mater's rigging all fell down in 25 knots two years ago during the Corinthian race on the cityfront here. I was approaching Blackhaller. My rigging was brand new and had been tuned two days before. My mast, the rigging, all the new led lights and radio antenna and shrouds and running rigging jumped the deck and fell into the bay. It was an impressive failure ("oh, no no no!" she cried), but most impressive was how several nearby boats, other participants in the race, immediately dropped their sails and radioed me. Capo Gatto (Sal Balisteri and his wife, Mary) motored right over and towed me into the SF Marina. When we arrived 1/2 dozen strangers stopped their boats to help lift everything (the mast, all that spaghetti of wires and lines) onto Dura Mater for the ride back to Berkeley. On the upside: a rigging failure doesn't instill quite the same fear. Now if it were to happen offshore? Still fearful of that.

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    Based upon my experience(s), it can become exciting. Both times for me were offshore, but safe anchorage was downwind in either case. However, subsequent actions required motoring to Honolulu for a new mast (1st time) and shipping the boat back to the mainland (2nd time). First time was a wood mast...made a new one from spruce purchased in Oahu. Second time I needed Ballenger to do the job. Things do break....
    Someone once pointed out that helicopter pilots spend their flying time waiting for something to break...sorta how I sail! And, as a civil engineer, my understanding of stresses and strains in such things as sailboat rigging tends to keep me wondering when something will fail. I wish I could just ignore such things and am envious of those who can. But, otherwise, adventure could be so dull!

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    Quote Originally Posted by Harrier View Post
    Someone once pointed out that helicopter pilots spend their flying time waiting for something to break...sorta how I sail!
    Speaking of helicopter pilots, I just read The Last Run, about a Coast Guard helicopter save up in the Fairweather Grounds of Alaska. Not literature, and I didn't understand most of the technology, but interesting. By Todd Lewan.

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    pogen is offline Sailing canoe "Kūʻaupaʻa"
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    Well, I think we will do all our VHF radio testing with masts in place. Though if people want to see how well their handhelds work then we can do that too.

    I'm thinking, have someone with the receiver gear set up on the YC deck, and have interested boats motor out about 2 nm out to the Redwood City channel entrance and anchor or stand by there. The longer distance to get well away from local clutter or echo effects, and to minimize the relative distance of the boats to the receiver.

    The tricky bit will be to figure out how I can measure my own radios and also operate the gear.

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    David, I'm going down to the Sequoia Yacht Club tomorrow to reconnoiter. Should I ask for something special? A card table? Proximity to a plug? Maybe people can attempt to make contact as they approach? Prizes for people who are able to do so. It will double as a radio check/ educational experience, thus meeting our 501(c)(3) mission. Always thinking.

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    It would be nice to have some space on a deck somewhere, the higher the better, and a regular AC outlet. And a table of some sort to sit at. I would set up the receiver antenna on a tripod or improvised mast of some sort.

    Also, they might advise on a good spot 1 - 2 nm out to anchor or loiter, deep enough water, but out of everyone's way.

    It's important for the measurement that the sending boats be at some known distance away and stationary. Anchoring would be best. When one is heeled over, the radiation pattern of the antenna is different because of the angle.

    Because marine VHF is frequency modulated (FM) you tend not to notice a weak signal until it cuts out all together.

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    I'm in for testing, but it's just VHF at this time. Always been curious about the distance the 6-w handheld will travel...all variables being equal, of course.

    Jackie, you might want to mosey over to the dock at the Port of Redwood City. There's a public marina there, looks like a transit dock. It sits more catty-corner to the fairway. Better direct line of sight. Whereas Sequoia Yacht Club is tucked up inside. You can't see the fairway from the SqYC dock.

    I'm glad I don't have to worry about my rig coming down!

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