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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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  #1  
Old 11-30-2007
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The Great Antenna Experience

Mostly this is just funny ...

I have been doing a test of new radio equipment and I got irritated because I couldn't get good signals on it, couldn't even get WWV (time signal) very well. I wasn't even pulling in shortwave or AM broadcast stations, it was mostly just faint signals buried in the noise, even at night. Started thinking it was an antenna problem.

Tried to fix my antenna on the roof but for various reasons it broke.

Got even more irritated.

Finally I went and picked up a LOT of 16 gauge stranded wire and started running a new antenna so I could test this rig. Ran the wire out the window, over to a post, about 50 feet over to a barrel, another 30 feet to a fence post, about 150 feet over to a big post cemented in the ground, and then about 200 feet across a small field to another fence post. Total length of my antenna is like 400+ feet. I mean you should see it, looks terrible, wire strung up all over the place and it's all zig-zag'd around the property.

So then I go in and tune up the radio to some shortwave and AM broadcast stations and instead of having signals that are so faint they are buried in the noise I have these crystal clear beautiful noise free signals that sound like you are standing in the middle of a train station with about 50 people talking at the exact same time. Now my property looks like I am working for SETI and everywhere I tune now all I get is all these signals on top of each other and you can't make out a thing any of them are saying, but let me tell you, it's a truly beautiful noise free signal! lol
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Old 11-30-2007
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k1vsk will become famous soon enough
it's called a 'long wire" antenna and is notoriously good at receiving low/med wavelength signals. What radio and freq are you playing with?
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It's an Icom 706 and I was trying to pull in some pactor signals but I haven't been able to find any. I don't know if it's the wrong season, the wrong frequencies, the wrong time, or what the problem is ... but me and pactor signals just haven't met at the same point. I'm trying to test out my pactor modem by receiving some kind of a pactor transmission on it and trying to monitor it to see if everything is working right.
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wind magic

Seems like your long wire antenna is giving you more gain than your receiver, or you, is looking for. Maybe you should coil up the last 200' and hang it on the big post, and then see if your now somewhat attenuated signal allows you to separate out some of the stations when you are tuning.
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That antenna is a big longer than what will fit on most boats.. .
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Old 12-01-2007
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k1vsk will become famous soon enough
You should be able to receive Pactor mode transmissions around 14105 MHz although not constantly. As you probably know, unless you have a tuner which can deal effectively with a random length antenna such as you described, you may not be able to connect.
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I don't see any reason why you can't receive Pactor signals with your 706 and a random length wire (almost anything 15' or longer).

Perhaps it would help if you knew exactly WHERE to listen. Info for the 85 or so participating stations in the WinLink network (PMBOs) is available on the WinLink website: www.winlink.org

There is a wealth of info on that site, including a link to a frequency list compiled by a South African station: http://users.iafrica.com/z/zs/zs5s/bulls/PMBO.TXT

If you "sit" on some of these frequencies, you'll no doubt hear some activity. Even better, if you're a licensed ham download the WinLink software for free and contact one of the PMBO's directly.

Bill
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SEMIJim will become famous soon enough SEMIJim will become famous soon enough
Oh my

Looks like it's time for a bit of Basic Radio Wave Transmission and Propagation Theory. Unfortunately, I've forgotten more than I recall. (At least of the details and the "why.") But here goes, anyway.

For starters: The best antenna for a given frequency is one that is tuned for that frequency's wavelength. Wavelength is inversely proportional to frequency, following the fomula:
Code:
Wavelength in meters = 300 / Frequency in MHz

    -or-

Wavelength in feet = 984 / Frequency in MHz
(Good grief, I actually had to look those up! )

The next most efficient is quarter-of-a-wavelength lengths (3/4, 1/2, 1/4).

The next two things you need to know is, generally, radio waves that are... um... let's say "bounced off the sky" (to cut a rather long explanation short), generally end-up horizonally polarized, even if they started out vertically polarized, and man-made noise generally has more vertically-polarized components than it does horizontally-polarized ones.

Lastly, you need to understand that the ground under your antenna forms part of the antenna system.

Putting this all together: A vertical antenna on top of the house, particularly one that has no real or virtual ground-plane and is not well-grounded, to boot, that is less than 1/4 wavelength of the desired frequency will generally perform much more poorly than a (multiple) quarter-wave or better, horizontally-polarized antenna that's over a decent ground plane (e.g.: the ground).

More than this, in this venue, is simply not practical. I used to have stacks of books on antenna and transmission line theory and design, and on radio wave propagation theory and practice.

One of the easiest antennas to hoist, that is relatively efficient at a wide variety of wavelengths, is a Windom, cut to 1/2 wavelength for the middle of the desired band, with a single-wire feed 1/3 of the way from one end. (E.g.: If your interest is in 40 meters: A 20 meter Windom.) Use your favourite search engine to search for design details. I used one of these, cut for 80 meters, for years, along with an antenna tuner, on everything from 160 meters through 10 meters.

Jim
(ex-WD8ABM)
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Old 12-01-2007
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We constructed a similar antenna on an oiler I was on, although we fused it (and rightly so) for when the radio operator fired off his HF transmitter. I think we had about 200' of copper strung out; it was tough to tension. Seamen used to coil up wire, about 20', and place it in their porthole window and clip it to the antenna for AM reception.
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Oh yeah: If you're going to build long-wire antennas, use something called copperweld (I think that's both a trade name and a generically-used term) wire, which is a copper-plated steel wire, rather than actual copper throughout. Why? Copper stretches easily. Copper-clad steel, not so much .

Jim
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