[aspicer]

Yacht Cellular WiFi Antennas - dB gain and dB Myth/Marketing

When a yacht Internet Connection system of the WiFi or Cellular type is installed on a yacht, usually there is an amplifier a coaxial cable and a marine type omni-directional antenna. That will be one of those 2 to 4 foot (approx.) white vertical antennas. They have to be made specifically for the application, which means the purpose and frequency band or band(s) that it will be used for. Often these antennas have a specification as to Gain. Antennas don't really amplify a signal, they cannot. They are not an active electronic component, meaning there is no powered electronic components in them that could amplify a signal. They are basically just a radiator of radio frequency (r.f.) energy. Now, grant it they are a very special kind of radiator. The intention being to put as much of the energy in the best possible area, and to try and concentrate also on receiving from the best possible area. This area has to be 360 degrees around because a yacht can and does move. And you never know which way you are going to dock or anchor the vessel. So the antenna has to be able to cover "all around."

Vertical Omni-Directional antennas have "Gain" by pulling in the vertical rf beam width. They gain by concentrating more energy where it is needed rather than wasting it more up and down where it is not needed. The gain works in both directions, transmit and receive. Such antennas are usually compared to a non-gain antenna (either theoretical "isotropic" or a common "dipole" antennas). In this case comparison is "dBi" so comparison is to Isotropic. There's a funny PUN on the dB-whatever used in marketing. The call it "dbM" for db-Marketing. 8 to 9 dB gain in marine wifi or cellular is pretty much standard stuff. They've got to be careful not to pull the vertical beam width pattern in Too Much or you could miss the access point (or cell tower as the case may be) altogether either by under or over shooting it. Antenna should be placed as high as possible on a yacht... hopefully with nothing close by on the same height level. Sometimes there are tradeoffs to get it up there somewhere. But generally you don't want anything like a large radar or satellite antenna to be in its path.

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Alan Spicer (a_spicer (at) bellsouth.net)
http://telecom.dyndns.biz/

[CaptPKilbride]

So, any words of wisdom on using the cellular amplifiers with such an antenna?

[aspicer]

Originally Posted by CaptPKilbride

So, any words of wisdom on using the cellular amplifiers with such an antenna?

Wisdom, oh yah...

Digital Antenna out of Fort Lauderdale, Florida has been the popular one for that. Direct inline amplifier requires that you have a cellular card (or device) that can take an external antenna. Digital Antenna is a manufacturer and won't sell to the public directly. The direct inline amplifier is a lot less expensive than the repeater amplifier that a lot of yachts use. Of course the repeater comes as a kit with the coax cable and omni antenna. So that sort of justifies the cost. (Other companies make these as well, such as Wilson, but I haven't tried them.)

I prefer LMR 400 coax cable for all WiFI and Cellular installs. But the repeater kit uses a smaller coax cable that comes with it. The repeater has a little inside antenna and eliminates the need for direct inline connection. People report varying luck with how well the repeater works. So try it right away if you buy one. In my experience for Internet Data cards the repeater "likes" to be close to the data card or it doesn't work so well. By close I mean 1 or 2 foot away from the inside antenna.

There are cellular routers available as well. They can take many different cellular internet cards. That allows flexibility to change cellular carriers and cards. Be careful not to get a router stuck on one technology such as CDMA EVDO only unless you are sure you'll never need to switch. Cellular routers allows to share the cellular connection to multiple computers wirelessly and wired. They typically can be expanded to a multiple access point wireless system on a yacht. I've done a lot of cellular + wifi systems. My systems designs are proprietary to me.

Sony Ericsson has new gear out... if you like GSM, the W20 series is much improved over the old F221 and F251 series. They now have HSDPA and WCDMA as well as built-in ethernet (wired network) and wireless. No more messing with 9-pin serial ports for slow GPRS speeds and Dial-Up Networking in Windows or such. They've been slow supplying them though. Delays upon delays. And trying to push the G series boxes instead which don't go all the way to the faster Internet Tecnologies.

On the Voice over IP or Broadband Telephone front... Vonage has been in patent lawsuits from Verizon. (Why can't the "V"'s just Get Along?) And obviously Skype has surged in popularity. Skype is a bit more confusing to get the whole in/out to PSTN (Public Switched Telephone Network) thing. You have to get Skype IN which is having a phone number with area code. You have to get Skype OUT to call out to PSTN numbers. With Vonage you just got one thing and you were on. They are still advertising so I guess they are still "floating". There are newer devices to let you divorce your Skype Service from the Main PC computer and the Skype program. (Usually you had to leave a computer running with the Skype Software program running even with some USB connected devices.) I did a Netgear Skype Router with cordless handset. And a carryable WiFi Skype phone for a yacht just recently.

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Alan Spicer (a_spicer (at) bellsouth.net)
http://telecom.dyndns.biz

[aspicer]

It was delayed, and delayed, and then went into FCC approvals, since they first told me we could get them LAST YEAR. Then February this year,...

It's a pretty cool unit. Panbo's blogged about it awhile back as well. I've been battling them to release the darned thing or shut up!

Well the finally just did that. And I can get them if anyone wants. You can use them with or without an outside antenna. Obviously they'd work better with the external antenna. Perhaps even an amplifier like I mentioned before. Antennas not to hard to get, or cellular amplifiers either.

These are GSM... 3G is WCDMA/HSDPA (elements of UMTS), with fallback to GSM EDGE and GPRS. The box is Tri-band HSDPA, and Quad Band GSM. Has printer server for USB printers. Built-in 4-port LAN switch. And onboard WiFi.

Now you know why I've been fighting with them to let them out the door.


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Alan Spicer

[winesk]

Wilson also makes a cell amplifier. The hard wired version works well. I think its a bit cheaper than Digital Antenna.

[aspicer]

Yah, I was aware of Wilsons stuff. I blogged about a report that I received on DA's marine repeater, that it caused interference up in the northeastern US to Altel's network. I also know an AT&T Wireless engineer and they don't like the DA repeaters at all either. I've not heard anything about the direct inline DA amplifiers. Correction: just heard a tid bit that the Ericsson W25 could burn them out because it's too powerful for the older units. Reportedly DA is handling that problem and replacing them, and newer DA direct inline amplifiers are fixed to not have that problem.

I'd have to wonder if the Wilson amplifiers would suffer the same trouble? I've been doing Ericsson W25's directly to the antenna with no amplifier lately. I'm a bit wary of amplifiers these days.