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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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  #11  
Old 01-14-2009
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We put a cell phone repeater in our work boat. It was a waste of money.
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  #12  
Old 01-15-2009
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OK....I'm going to try the "Cell Ranger" off the Active Captain site in a couple weeks . I guess I can return it if it doesn't work or so they say . I'll be sure to post results on this site for you guys . Thanks again for all the help & advice .
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Old 01-15-2009
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I didn't want to say "It'll be a waste of money" since I haven't tried one of those units for anything. However, as a radio guy, I will say that they probably WON'T work as well as they claim.

For the most part cell towers are up higher than the surrounding terrain giving them a good distance. If, however YOU are down in a valley and NOT in line of sight of a tower the chances of you getting a good signal go down very drastically.

Your antenna / cell phone / radio HAS to be in line of sight (unless we're talking HF radio in which case radio waves work slightly differently at those frequencies).

When you're talking cell phones, you're talking 800-900 MHz, thus, the radio waves really travel in a straight line for all intents and purposes and unless you can stick your antenna in the RF window up high (if you're in a valley) then you're really NOT going to get any signal other than what might be reflected from near by structures.

Repeaters - if properly designed take a signal in on one frequency and retransmit it on ANOTHER frequency.

Basically that means a little "cell phone repeater" probably isn't going to work very well since it has to be able to switch around the channels just like cellular phones do.

I'm betting (not having looked over a schematic) that those so-called amps are merely wideband amplifiers that boost the signal at either end of the antenna and passively couple it back to the other end.

That means - essentially, you can to the same job with a plain old wire, like I started telling you about before.

Rick
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Old 01-15-2009
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We had a similar problem 7 years ago when we were staying aboard weekends. At the time was suggested we try a three watt bag phone as more power would help.

So we "upgraded" from a handheld to a bag phone. If we put the phone on the coachroof or held at a particular angle over the boom it would work - an improvement over the handheld.

Next - coincidentally on the advice of Jeff H from another BBS - we purchased a Shakespeare 4801 marine cell antenna. I mounted this on the mast head and ran the antenna cable to the bag phone inside the boat. We had signal ALL THE TIME. We were the only people with cell service in the marina.

We no longer stay aboard and one of the cell companies has since installed a tower nearby eliminating the necessity of this on board phone. It worked and worked well. It was analogue and most cell companies are phasing that out now whihc is a pity - sionce analogue works far better in remote areas.

I still have the antenna but removed it from the boat a couple years ago - as the antenna cable suffers from all the same prolems as VHF antenna cable (and looks very similar) and I lost signal due to connections somewhere.

I tried an adaptor t hook up a handheld Samsung phone to my antenna but it was never as good as the 3 watt bag phone.

Still have the Shakespeare antenna - hangin on a hook in may garage unused. It was something liek $184 and the antenna cabling approx $100

mike
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Old 01-15-2009
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Those "bag phones" you meantioned (I remember using those at the White House before most people had cell phones) transmitted between 3 and 5 watts. Some were 10 watts!

They had analog service, basically full duplex radios and they worked well.

On a side note all this "cool new digital stuff" isn't really that cool.

You can get more data into a signal (on higher frequencies) BUT because it is digital it doesn't transmit as well as an analog signal. I noted as much as a 30% drop in signal strengths when I was installing systems in years past when we went from an analog signal to digital (using a digital encryption) system.
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Old 01-15-2009
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The bag phones (and real car phones) wre strictly analog service. Yes, they had way more power than handhelds, 6 watts compared to 600 milliwatts, which is about a 10-12 db signal increase. But the cell companies have largely dropped analog service (or surcharged the hell out of it) and it doesn't support fast data transfers, so that's water under the bridge.

There's also a software limit in most cell phone systems. Radio waves travel at a fast but finite speed, and if you ever listened to the old moon landing recordings you'll be familiar with the time delay on each half of the conversation? Well, the cell phone system uses that delay (much shorter but still measurable) to determine if you are near the "right" tower, and it drops all calls made from more than something like 32 miles (max) from the nearest tower. If you have a weak signal because you are hitting that distance--forget about it, you'll never get a connection even with more power.

The good news is that the bidirectional amplifiers do work. Some brands like Wilson may be just over $300. But if you are in a fixed location, you can also use a "directional gain antenna" for under $50 to get the same amount of boost. And in extreme cases, using both the bidirectional amplifier AND an outside directional antenna (which kills your signal unless it is pointed AT the tower you are using) will give you maximum power. Putting the antenna "up high" is great, in theory. Unfortunately the cable between the antenna and anything else eats up so much power, that in practical terms you won't be putting the antenna more than 6-10' away from the phone, or amplifier, whichever you hook it into.
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Old 01-15-2009
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Quote:
Unfortunately the cable between the antenna and anything else eats up so much power, that in practical terms you won't be putting the antenna more than 6-10' away from the phone, or amplifier, whichever you hook it into.
That depends on the cable type actually. Since I don't know what they would be using, the standard example for about 80% of the coaxial cable types out there is "3db per 100 feet".

That equates to a loss of 1/2 of the power being radiated into the antenna. So if you're getting something in milliwatts, you're going to have half of the power at the other end.

If the device is an amplifier then this is made up for by the amp making the received signal larger and sending it out the other end.

And, no, putting the antenna "up high" is the only way to get a signal if you're in a valley.
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  #18  
Old 01-15-2009
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Upfront, I'm the co-owner and developer of ActiveCaptain. We sell a new type of amplifier that has already been discussed here. I'm going to try to stay away from "selling" anything here but I can give some significant information after working with almost 200 users of these devices.

First, we have an 18 part series about all aspects of using a mobile phone on your boat. It's all free and easy to access. The article about amplification is here:
ActiveCaptain - Going Mobile - Mobile Phones Series

This article gives some background information behind the issues of passive and active mobile phone amplification. There are a few different types. We've tested them all on a few boats in real situations over the last 5 years. In general, they work really well, except when they don't - and I'll explain why.

There are times when there just isn't enough signal to do anything with. The Pungo-Alligator Canal in North Carolina comes to mind. It's a 25 mile straight cut through the middle of nowhere. We couldn't find any mobile signal out there at all. It's a complete dead zone. There are also some situations where there is so much electrical noise, the amplification can't pull out the signal from the electromagnetic mess it is receiving.

In general and unless you have a metal superstructure, a traditional wireless amp (especially the Digital Antenna one mentioned earlier in the thread) will not provide adequate results. The problem is a feedback loop that gets created because fiberglass and wood don't provide enough separation between signals. More about that is explained in the article.

Cell Ranger is a new type of amplifier. It only amplifies half the signal - the part coming from the tower to your mobile phone. That's why is it less expensive. It turns out that for a variety of reasons, towers can pick up your tiny phone signals really well. Their huge antennas and expensive electronics can "hear" anything you send out. The problem is that your phone with it's tiny antenna and inexpensive electronics needs help to receive the signal coming from the tower. The output from the tower is limited by FCC regulations. Electronics at the phone can make up a lot of this loss.

There are still times when the problem is bi-directional - usually if you are really far away from the tower and there is something in-between. In those cases, an amp just isn't going to help. But boy, it's not easy to find those places these days.

For an example of electronic noise, here's what happened to someone who got a Cell Ranger and couldn't get it to work with his air card on the laptop. He was using the USB version of Cell Ranger which was plugged directly into the USB port on his laptop. The aircard was on the other side of the laptop. So between the two devices was the entire bulk of the laptop with a very large amount of electronic noise. When he could only get 1 bar on his cell phone, he got no connection with this setup. I had him move the Cell Ranger to the other side of the laptop with a small USB cable and guess what? Four bars.

We've been working with the manufacturer of Cell Ranger to make some changes to the product for marine use. The device is really designed for automobile use today and after providing it to a couple of hundred boaters, there are a few things that we've learned. They've responded and are close to providing us with the first units to test. If you need more bars today, Cell Ranger is fine. But if it's really something for spring, wait. The next version is more appropriate for on-the-water use and provides more flexibility and capabilities.
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Old 01-15-2009
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Quote:
Originally Posted by N0NJY View Post
... the band the cell phones are in (800-900 MHZ ...
That's true--as far as it goes. There is also GSM-1800, GSM-1900 and PCS, at 1.8GHz, 1.9GHz and 1.9GHz, respectively.

Quote:
Originally Posted by N0NJY View Post
HONESTLY - if you stand near any sort of wire going up in the air (shroud, backstay for example) you ought to see some increase in received signal strength. This is because the RF way up above you is hitting that wire and can be conducted down.
"Can" being the operative word, here. We're talking near-microwave to microwave frequencies. They don't work like "garden variety" RF works. It can happen, but the effect is completely arbitrary, because the behaviour of the "conductors" is completely arbitrary at those frequencies.

Quote:
Originally Posted by N0NJY View Post
One other thing.

Don't pay any attention to things that say "Receives up to 20 miles" or some other such crap.

A signal can be received much further than that -
Depends. In free space there's the distance squared rule. But we're not in free space, we're in the atmosphere, which is full of water and dust and stuff. Again: We're talking near-microwave and microwave frequencies. The attenuation is much greater than at lower frequencies. And that's just line-of-sight: I.e.: Nothing in the way. At these frequencies, LOS is all you have. Fixed-station microwave communications towers generally aren't placed more than 30 miles apart, and they're dealing with a good deal more power, and significantly better receivers than your average cell-to-handheld link. (Commonly, max. LOS for cellular and PCS is 10 miles, give or take, in open country or across the water.)

Quote:
Originally Posted by N0NJY View Post
...the SENSITIVITY of the front end of the receiver is the issue!)
That's not quite accurate, either. It's the sensitivity and the signal-to-noise ratio . Which brings us to...

Quote:
Originally Posted by JeffreySiegel View Post
It turns out that for a variety of reasons, towers can pick up your tiny phone signals really well. Their huge antennas and expensive electronics can "hear" anything you send out.
Mostly it's the receivers in the towers. There's no end of things you can do to increase sensitivity, improve S/N and reject interference when you aren't space-constrained .

(Ex-microwave communications systems and SatCom guy, in case you were wondering.)

Jim
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Old 01-15-2009
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Don't forget that the newer 3G networks also use 2.1 GHz as well.
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