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  #1  
Old 11-27-2010
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WiFi and VHF of the masthead

I would like to install both a hi-gain VHF antenna and a hi-gain WiFi antenna on my masthead.


1: Is there a significant interference/shadowing problem doing this?

2: Is there a separation distance I need? How do you get it?

3: Is there a better way?

4: Will the cable loss up to the masthead negate all of the gain in the antennas?

5: Will the tighter lobes of the high gain antennas give me a false gain when one factors in the mast movement?

Charles
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Old 11-28-2010
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Quote:
Originally Posted by micheck View Post
I would like to install both a hi-gain VHF antenna and a hi-gain WiFi antenna on my masthead.
That'll work for the VHF (with caveats), but not for the WiFi.


Quote:
Originally Posted by micheck View Post
1: Is there a significant interference/shadowing problem doing this?
Unlikely to be appreciable RF interference between the two. 802.11g would be at over the 14th harmonic of the marine band. 802.11a would be at over the 22nd and 30th harmonics.

Radiation pattern interference: Probably. Probably not an issue for the WiFi antenna, as there are much bigger issues, there.

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Originally Posted by micheck View Post
2: Is there a separation distance I need? How do you get it?
Brackets. Long brackets.

I've been out of the craft for years and years, so I'm a bit rusty, but, if I recall correctly: You want at least 1/2 wavelength separation between the two elements at the longest wavelength (lowest frequency). That would be on the order of 1m for the marine radio antenna.

Ugly.

Quote:
Originally Posted by micheck View Post
3: Is there a better way?
Yes. Forget putting a WiFi antenna atop the mast.

Quote:
Originally Posted by micheck View Post
4: Will the cable loss up to the masthead negate all of the gain in the antennas?
For the VHF: Depends. If you use Belden 8214 or equivalent, your loss, by the time you add connectorization, will probably be about 2dB. Height is king on VHF, so that's probably acceptable. Even if you want to avoid the weight aloft and go with RG8x, it would probably still be a net win. I you go RG8x: Offset the increased loss, some, by using BNC connectors where you can, rather than the so-called "UHF" style commonly used.

But the WiFi... The WiFi is a whole 'nother ball of wax. That's 3.7 and 5GHz for 802.11a, 2.4GHz for 802.11b/g, and 2.4 and 5GHz for 802.11n. Even with Belden 9913 (expensive and a PITA to work with), loss would be on the order of 9dB or more at 2.4GHz once you added connectorization, and in excess of 12dB at 5GHz. Belden 7810 wouldn't be a whole lot better.

And don't forget: That loss works both ways: Both transmitted and received signals.

All loss figures based on 100' of coax.

Quote:
Originally Posted by micheck View Post
5: Will the tighter lobes of the high gain antennas give me a false gain when one factors in the mast movement?
Gain has gotta come from somewhere. For omni-directional antennas it comes from flattening the radiation pattern on the vertical axis. Thus, when you heel, the windward radiation heads for space and the leeward radiation heads right into the water.

For your WiFi: Put a high-gain antenna up 40 feet and, never minding the loss figures quoted above, all your signal will be headed for the horizon... 40' up. Sitting right under the antenna, down on the deck, you might see nothing. (I'm just guessing, never having tried this.)

Jim
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Old 11-28-2010
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Thank you - SEMIjim - your analysis and thoughts have given me much to think about - I probably will do as you suggested and put the VHF antenna on the masthead and install the WiFi antenna at the deck level or on a short post off the stern pullpit

Charles
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Old 11-28-2010
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You might find some ideas over in this thread: Long Range WiFi -- Posting right now using "long range" wireless.

This is honestly something I've never spent much time researching. So far we only day-sail and race. During neither of those activities are we the least bit interested in WiFi, other than perhaps checking the weather just before a race.

Jim
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Old 01-09-2011
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Quote:
Originally Posted by micheck View Post
I would like to install both a hi-gain VHF antenna and a hi-gain WiFi antenna on my masthead.


1: Is there a significant interference/shadowing problem doing this?

2: Is there a separation distance I need? How do you get it?

3: Is there a better way?

4: Will the cable loss up to the masthead negate all of the gain in the antennas?

5: Will the tighter lobes of the high gain antennas give me a false gain when one factors in the mast movement?

Charles

the VHF is a whole different discussion, but the comments on using standard cable for the WiFi is just nuts, as noted in one of the followups.


Even with a honking great amp (such as Air802), your signal loss is severe over any significant distance. Much better is to get an integrated system which has NO cable loss: Marine PC's & WiFi by IslandTime PC is my vendor; my setup (including standoff brackets for VHF and WiFi) is one of the subsections found by mousing over his WiFi section.

My setup is an amplified WiFi adapter screwed directly to a lightning arrestor, screwed directly to the antenna. The LA is good practice in any event but allowed the deeper profile of my bracket to be accommodated when attaching the antenna to the adapter. Standard with the system will be a bracket you can mount directly to the mast. The boat next to me in this anchorage (tinyurl.com/flyingpigspot - click on the hybrid tab top right to see a satellite and map view combined) has that exact setup - he bought it based on seeing how mine worked last year here.

Plenty of standoff (original - earlier, with a board rather than the waterproof unit I have now - was in a NEMA box right next to the VHF antenna, and still worked well) for both (total length of the bracket, free for salvage at a fabricator, about 3') between the antennas, and nice separation from the wind instrument, the Windex and TriLight with my bracket setup...

The adapter runs over POE (power over ethernet) on boat power; no data loss in ethernet cable (at least not if you're not a ship with over 1000 feet of it, anyway!!), and the power goes up the unused two pairs in the cable.

Dead simple.

As to VHF cable, I chose low loss, waterproof cable, continuous between antenna and radio. A bit heavier, but much better throughput.

If you're interested in my pix of the way it/they are set up, follow the links in my gallery from 2009 refit, upgrades, electronics. You'll have to wade through the other pix in there, but you'll see all the setup I did for both. BTW, the earlier pix show my old white cable for the VHF; it determined how far out I could put the bracket while I waited for my new cable to arrive. Later pix show it all installed.

L8R

Skip, over WiFi in the middle of Elizabeth Harbour, George Town Exuma Bahamas

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Old 01-10-2011
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Instead of WiFi have you considered Mobile Broadband? The adapter is $79 @ WalMart (Virgin mobile USB stick) and it's only $40 a month for unlimited 3g anyplace you have Sprint reception.
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Old 01-10-2011
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I intend to install a bullet 2 with antenna at my missen mast head.
Why?
Where I sail because of the mountains even VHF can be localised but I can access telephone linked local wifi wherever there is a coastal population centre.
So for coastal sailing I can for example access weather forcasts which may not even be VHF available.
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