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Marine Monitoring Forum - This is the place to discuss monitoring marine communications

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  #21 (permalink)  
Old 08-09-2018, 9:04 PM
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Originally Posted by devicelab View Post
That's a LNA (low noise amplifier) + bandpass filter. The amp looks to be fairly generic but the bandpass filter is tight and looks like it would be worthy. The price suggests it may not be of super high-quality (a commercial version would probably run you 300 Euro or more) but it should work fine. (Again you can verify it's effectiveness with a VHF antenna analyzer.)
Did not or do not know what I'm looking at really, thanks for pointing this out to me.

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Remember, this LNA should be mast-mounted or very close to the antenna feedpoint. I see the AIS antenna uses a UHF connector, so you'd want a short run (< 3m) UHF to N into the LNA and then coax from the LNA into the house. You also need to provide 12v DC to the LNA as well.

You don't *have* to use this at the mast but it'll be more effective there.
Yeah not sure if I want more stuff outside dealing with the elements?

Cheers,
John
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Old 08-09-2018, 9:26 PM
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Originally Posted by devicelab View Post
Yeah you're best bet is to email Dave and see if he can build you a proper LP antenna. The LP is a log periodic and they generally work across a broad range -- such as 75 Mhz thru 1000 Mhz. Yagi antennas tend to be more frequency specific.
I did contact Dave and he has discontinued making the LP due to it not being overly popular and that users still prefer omnidirectional for AIS. His explanation of the LP V Yagi was that the LP was less focused than the Yagi and therefore had better side coverage.

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The yagi antenna is like a narrow-beam flashlight and might be too focused. I don't recall how far you were from the coastline but if you're too close then the Yagi would certainly miss a lot of signals. It might pull in more distant ships along a specific path but you'd likely miss ships that were out of your line of sight.
I'm about 2.2 Km from the coastline at about 30Mt ASL.

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If you're fairly close then I would stick with your current antenna for now. I think the LNA would be a great investment (as would a VHF antenna analyzer) for maximizing your current setup and verifying your antenna efficiency.
I did contact Sirio the maker of my existing antenna and they have recommended either of these 2, but again I'm still clueless as to what it all means haha.

http://sirioantenne.it/images/pdf/ma...07-07-2006.pdf
http://sirioantenne.it/images/pdf/ma...01-07-1998.pdf

Cheers & Thanks,
John
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Old 08-10-2018, 1:14 AM
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Yeah, that Sirio antenna is what they sent me. 5/8th's wave, so it'll have about 3dB gain.

Considering I'm on the coast and up high enough, an omni-directional antenna isn't the ideal choice. If you look at the coverage plot for my station, what I hear is in an approximately 90 spread. That is due to topographical shielding (fancy way of saying "too much dirt in the way")
A directional antenna can help, but you'd want to be cautious about getting too tight a beamwidth. Something low gain, like a 3 element yagi would help. Actually a folded dipole spaced 1/4 wave off the mast would probably help a bit.

Another option is to ditch the coaxial cable all together. Mount the receiver in a waterproof box at the base of the antenna, and just send power and Ethernet up to it from below.
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Old 08-10-2018, 1:58 AM
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Originally Posted by mmckenna View Post
Yeah, that Sirio antenna is what they sent me. 5/8th's wave, so it'll have about 3dB gain.

Considering I'm on the coast and up high enough, an omni-directional antenna isn't the ideal choice. If you look at the coverage plot for my station, what I hear is in an approximately 90 spread. That is due to topographical shielding (fancy way of saying "too much dirt in the way")
I like your terminology, it's something I can understand.

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Something low gain, like a 3 element yagi would help. Actually a folded dipole spaced 1/4 wave off the mast would probably help a bit.
You may have to explain about the Yagi and the folded dipole in a bit more detail for me?

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Another option is to ditch the coaxial cable all together. Mount the receiver in a waterproof box at the base of the antenna, and just send power and Ethernet up to it from below.
For me, probably not..........

Cheers & Thanks,
John
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  #25 (permalink)  
Old 08-10-2018, 5:10 AM
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Quote:
Originally Posted by johnmw1 View Post
I did contact Sirio the maker of my existing antenna and they have recommended either of these...

http://sirioantenne.it/images/pdf/ma...07-07-2006.pdf
http://sirioantenne.it/images/pdf/ma...01-07-1998.pdf
Those are co-linear antennas meaning that they're essentially using multiple full wavelength elements. In theory, the more elements the better.

The GP22-N antenna might be a better performer and since it uses the N connector it might be slightly more efficient. The other is what you have already but with an extra element.

Remember, this is the "fun" part of playing around any radio-based application. Your specific location and goals are what determine what works best for you.

From all of my radio experiences, the most important factor (besides a large bank balance) is height. Height is what makes everything better. Get a modest antenna up high and it can work wonders...
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