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Old 28-07-2010, 03:13   #481
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Originally Posted by oceansoul63 View Post
Anybody ever use a "cantenna?"

A friend of mine uses one on his boat and says it works great.
I did not see a reply to your question. Cantenna's are great..in my opinion..especially for boaters. I've built many for users. Over here, I built one for my commander so he could skype home. I just finished building one for zerotocruising also.

Here are my reasoning:

On a boat/yacht you are typically moored/anchored and have an idea where the land mass is that has the Wifi. Let's say it is directly in front of you. Why would you want to use an omni-directional antenna...distributing all your available power in all directions? (talking transmitting side only of course..however the premise is somewhat true for receive). Focusing your receiver/transmitter toward the transmitting/receiving antenna is the most logical. Another added benifit of a cantenna is it's rejection ability of signals outside the focal point/apeture. I typically see a 12-18 dbi gain with cantenna's. they can also be designed for 3G/3.5G cellular network use (2.1 Ghz vs 2.4 Ghz)

I use the Alfa AWUS036H connected directly to a RP-SMA to N-Type adapter screwed into the bottom of the cantenna..coupled directly to the radiator inside. Then use a 33' active USB cable to run it to the laptop.
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Old 28-07-2010, 04:34   #482
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Directional antennas are great if you are not at anchor. At anchor where the boat is likely to drift around... not so much.

Having said that, I have in desperation, attached my bullet to a yagi and used the bullet as a handle to keep it aimed at a station on shore. This so my partner could get a quick weather report and email up/down. A bit of an inconvenience but less of one than launching the dink and going ashore.

My record so far with the Bullet is nearly 4nm offshore with an omni. They are still king of the heap in my view.

George
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Old 28-07-2010, 04:59   #483
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George,

Not all boats at achor swing around. Yes, as the wind/current shifts. I have found using the Joby gorillapod an excellant way to mount your cantenna to anything on board

Buy.com - NEW Gorillapod Flexible Tripod Gripping For DC Camera

Also, since the dispersion pattern out the front of the cantenna is just under 45 Degrees...at the distance you'll typically be from shore..you could move the cantenna left or right a good amount and not typically effect receive/trasmit performance.
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Old 28-07-2010, 06:59   #484
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But I'm sure there's much benefit to having it 75 feet above the water. I'm thinking maybe the second spreaders, or else an antenna pole on the transom.
This is not true.

Some height is important. You do need to get above you local obstacles on your boat, arches, booms, biminis, etc.

Lots of people have tested the various heights, and with a good (true) 8-9db omni antenna, height of 8 feet or 75 feet will not make a noticeable difference to what you can connect to and use. Certainly if there is an obstruction, between you and the access point, and the access point is 200' in the air, and you need height to get over the obstacle, then yes, the height on the boat would help, but this is a very specific, and rare situation. Most access points are lining the harbor you are anchored it. And most "open" access points, will not have invested money to put it up a big pole to help you out .

In general, 6-8' off the deck of a boat will give you good performance, without the hassle and inconvenience of mounting in a more inaccessible location.

Also, I am talking WiFi here, not 3G. I don't have enough real-world experience to comment on that.

Mark
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Old 03-08-2010, 08:24   #485
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Location antenna

I'm considering installing a 2HP and I would like some advise on the best location for the antenna. These could be the different options:
1) If on top of the mast, how far should it be from the VHF antenna.
2) If on the lower spreader how far from the mast and is it a problem if it would be about on the same height of the radar (I don't expect to ever have the radar and Wifi on at the same time)

Thanks for any advise
Marco
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Old 03-08-2010, 08:34   #486
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Marco

I have installed a 5 mi WIFI antenna on the first spreader and am very pleased with the performance. Previously, I had installed it on the stern rail, but have increased the range dramatically by going uo to the spreader. Any higher than that, you will experience a loss in strength through the cable. The VHF and/or radar has no impact due to different frequencies. My system is a Windows 7 computer, having no experience with Mac.
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Old 03-08-2010, 08:42   #487
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However, if you use a USB WiFi adapter that attaches at the antenna and run a active USB cable to your PC, you will have nearly zero loss.
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Old 03-08-2010, 11:20   #488
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Most of the power-over-ethernet ("PoE", like the Bullet) equipment is running at 5 volts internally, and since it is low power it is very simple & cheap to stick on a regulator chip that converts "anything reasonable" down to five volts. So 8, 12, 14, 18 volts in the far end of the cable? Doesn't matter and won't affect performance, as long as the regulator still sees about 7 volts coming into the device. (They typically need about 2 volts more than the voltage they are putting out, anything above that is dumped.)

3G, 4G, Wifi, all are essentially the same in many ways. In fact 4G is "WiMax" which is the successor to Wifi, call it "WiFi on steroids". They're all low-power microwave signals, and microwave signals are all treated the same way, subject to the same considerations, with frequencies being close enough (in these applications) so they only affect the actual length of the antenna.

Speaking of which, a "cantenna" is a popular 1970's term for a microwave feedguide made from a coffee can. Yes, coffee, before Pringles existed. There's no magic to a cantenna, any can, tube, duct, of metal or metal lined can be used as a feed guide for microwave signals IF the dimesions (length and width and position of the actual cable connection) are right. If they are wrong...performance suffers instead of getting better. When you can find a "can" that is the right dimension for your specific frequency, it makes construction very easy and cantennas a very good thing. But if the size isn't exactly right--it's just a waste of time.

Antenna theory and construction aren't very complicated, there are many good references online, and many good construction plans. If you can solder plumbing, or assemble backyard accessories, you can DIY. Getting durable marine-grade materials is of course a whole other problem.
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Old 03-08-2010, 11:27   #489
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Originally Posted by hellosailor View Post
Speaking of which, a "cantenna" is a popular 1970's term for a microwave feedguide made from a coffee can.
My favorite antenna design. Although a bi-quad looks better to some..maybe even inside a nice looking square patch plastic box..charging big $$...I'll take a fine-tuned 4 times the waveguide length cantenna with a horn mounted on the front for an additional 2-3 dbi
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Old 03-08-2010, 11:31   #490
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Originally Posted by Bluenote View Post
I'm considering installing a 2HP and I would like some advise on the best location for the antenna. These could be the different options:
1) If on top of the mast, how far should it be from the VHF antenna.
2) If on the lower spreader how far from the mast and is it a problem if it would be about on the same height of the radar (I don't expect to ever have the radar and Wifi on at the same time)

Thanks for any advise
Marco
Hi Marco,

The VHF antenna and radar should have minimal impact. The VHF antenna is grounded, but the cross section is very small. The mast will present more of a blind spot, so you should mount it out on the spreader as far as practical. It definitely shouldn't be mounted against the mast.

Personally, I would mount it either ~10ft off deck or at the top of the mast. Do you have an arch or other raised structure to put it on? Simplest thing might be to just mount a 8' aluminum or stainless tube (PVC?) as a post on the back rail. It wouldn't need to be very large or strong - it is just going to hold the bullet and antenna. I'm thinking something along the lines of two u-bolts mounted high and low on a pulpit stanchion holding a 1" pole upright.

Mounting it at the top of the mast will require running the cable. There have been times when I wish ours was mounted up there. Particularly here in the Caribe where we often find ourselves behind small hills and other obstacles where the height would make a difference.

Mark
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Old 03-08-2010, 11:42   #491
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However, if you use a USB WiFi adapter that attaches at the antenna and run a active USB cable to your PC, you will have nearly zero loss.
That is good advice as far as it goes, but if you want a long run (like to the spreaders) you are limited to 75' total length and that length will be made up from 5 separate active USB cables with 4 connections between them. It is difficult to find weatherproof USB cables and difficult to keep the interconnections weatherproof. And the connection adapters are large - requiring 1" holes in the mast, deck, anywhere you need a pass-through. You can't easily run the cable and make the connections yourself like ethernet or coax cable.

Moral of the story is coax is bad and long runs are difficult (and sometimes impossible). If you use a USB client adapter, best to go with one that doesn't use coax (well, not more than a few inches to make the antenna connection), and keep the mounting runs reasonable so that you only need one or two USB cables to operate it.

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Old 03-08-2010, 11:49   #492
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That is good advice as far as it goes, but if you want a long run (like to the spreaders) you are limited to 75' total length and that length will be made up from 5 separate active USB cables with 4 connections between them.
You got me there Mark..not sure how high the gentleman wanted to mount his antenna. I thought some people posted that the height made little if any difference. However, I did find a 32' cable, so you could lower your example in half and only use two cables

Amazon.com: 10 Meters (32.8 Feet) USB 2.0 Active Extension /

Doug
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Old 03-08-2010, 15:17   #493
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Good find Doug,

I haven't seen them longer than 5 meters before. These would be very useful on a boat for several applications.

I got confused and thought you were responding to someone about mounting the system at the spreaders or masthead.

Mark
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Old 03-08-2010, 16:42   #494
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The 5 mile WiFI is a good unit, much better than the RV system I previously used. as I stated in a previous post, my best reception has been from the first spreader, no higher, with no loss of signal. Service could be better, but the product is fine.
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Old 11-08-2010, 08:10   #495
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Originally Posted by ArmyChief View Post
You got me there Mark..not sure how high the gentleman wanted to mount his antenna. I thought some people posted that the height made little if any difference. However, I did find a 32' cable, so you could lower your example in half and only use two cables

Amazon.com: 10 Meters (32.8 Feet) USB 2.0 Active Extension /

Doug
A common problem is that longrange WiFi (read high power) such as 5milewifi an 6-MileWiFi uses more electrical current from the USB port. Therefore the use of extentioncables is mostly not succesfull with this units because of the extra voltagedrop. The supplied 5 meter heavy-duty cable is just good enough for use with de X-MileWiFi units. beside that is the regular quality from the chinese cables very, very bad and every monky's hair of copper in that cable is left away.
The only sollution is a special custom made (expensive) cable up to 50 meters or any length between with a diameter from 10-12mm.

Be wise, do not use extention cables with the X-mileWiFi units.


With regards, Jugo
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