So I can share a little more experience on this topic than I think you'll find in my other posts here. As you guys know, at this point I’m using that amp from Criterion. It's a good unit and I'll say more about it below. I have also had opportunity to use of couple of other setups and I'll talk about them as well.
First of all you need to understand the signal you're trying to use is basically a LOS (line of site) signal. This is unfortunately bad news
what it really boils down to is that no amp will be a miracle worker. A RF signal in the range we are considering here has a limited ability to travel and a very limited ability to penetrate certain materials. This is why you will get noticeable better reception in the winter when there are no leaves on the trees and the air is dryer.
In order to establish a connection there must be a signal present no matter how good your gear is. These amps are a way to establish a connection using less signal. Ill talk about other signal aids in a sec. What this really means is with a good setup in your car you can expect a 1-3 bar (I know that term is technically meaningless) improvement over the phone alone. This is very useful if you frequently drive through areas where calls get very broken or they drop and then you can dial again. These are referred to a fringe areas. Depending on the geography and the tower density these fringe areas may transition back into good coverage areas or just out into no signal areas. No amp is gonna help you there. Good news is that for the most part in populated areas the cell co's tried real hard to avoid the dead areas.
The name of the game in extending out the good coverage area as far as possible is maximizing the usefulness of the signal available at any given spot while minimizing the noise. By using an amp we boost the signal (and some but hopefully not too much noise) Another big part of this will be the antenna you put on your car, where you put it and it's orientation. You will need to use an omnidirrectional antenna if you intend to ever move your car but it will get the signal outside the metal box you're sitting in and a quality one will provide a good signal boost as well. You can think of an antenna helping your signal by only "looking" in certain places in space. All antennas are compared to a perfectly spherical radiator when their gains are given. The higher the gain the smaller the beam that the antenna is "looking" in. In the case of an omnidirrectional antenna that we would use here we take advantage of the fact that the earth is mostly flat and our antenna's beam looks like a disk. This is why it is very important to get your antenna above your roof line and to make sure it is vertical vice inclined. Higher gain directional antennas have increasingly narrow beams that need to be pointed at the tower and are only appropriate for fixed installations.
So there are a couple of other things to consider as we get the signal to our phone. Cable and connectors are a huge deal. All cable has a certain amount of loss per foot. In general as cable get's better it gets thicker less flexible and more expensive. This is why a number of cheap antennas out there provide a zero net gain or even some times a net loss. All the benefit of the antenna is counteracted by a 20' piece of cheap cable. Connectors are another big problem here. Each one represents another point where signal is lost. Their number should be minimized and when possible lower loss connectors are preferred. Also the shielding of the cables varies very much. Most heavier high quality cable is shielded very good but many of the pigtails that cell phone manufactures sell to connect to the phones aren't shielded very well so it is critical to keep them away from power cables and other sources of noise in your car.
There are a number of systems that do not require a connection to your phone. These systems receive the signal from the tower and rebroadcast it locally so it is stronger for your phone. One of my friends has a system like this installed in his house. It doesn't work very well even though he has a nice high gain antenna (aimed correctly) on his roof. This is because in practice the original signal from the tower is still present at the location of the phone and is now noise. This is why I feel that a system that plugs into your phone is the only way to go it you want to get a real benefit from it.
Bla Bla Bla. Sorry to go on for so long but believe me I have only scratched the surface of this topic thus far. I’ll reward those of you who read this far with a little cookbook description of a good sys.
First thing you need is a phone there is a lot of variation in the RF performance of the available phones but unfortunately the manufactures have a strong interest in keeping testing data under wraps and virtually all the info available on the internet in this topic is worthless placebo effect crap… This means it pretty much a crap shoot so there are a couple of other attributes you need to look for. The phone needs to have an antenna port (sometimes called a test port) so you can plug an external antenna up to it. Another thing you’ll really want from a phone is the availability of a nice car cradle you can drop it into to easily hold it and make that connection. I am using an Erricson T610, it has the plug and a nice cradle available. It’s rf is ok but there are phones out there who I’d expect perform better. (Nokia is a good place to look for good rf)
Next you need a pigtail to go from the cradle to the amp. You’re not gonna have a lot of control over this piece as it’s likely gonna be made and sold by the manufacture of the phone and no one else. In a perfect world it would be as short as possible and have just the right connector to hook to the amp without using an adapter. IT IS CRITICAL TO KEEP THIS CABLE AWAY FROM NOISE SOURCES as it is likely the weak link in the cabling and everything that gets into it will be amplified by the amp.
Next you need an amp. You need to be sure you get one that covers the frequency band that is used by your phone. The person selling it to you should be able to help you here. It should be a quality amp and have a good SNR. Also be forewarned that there is a max FCC legal power for any given antenna and you want to stay below it. Ask the dealer about this as well. I like the amp I got from Criterion but there are others available as well that I’m sure work well.
Next is the cable that goes from the amp to the antenna. Use a nice quality cable terminated with the right connectors to avoid adapters and don’t make it any longer than it needs to be. Remember that as length goes up so does signal loss and noise pickup.
Last we have the antenna. It is a really important piece, as is it’s location and orientation. You are going to run into two basic types that are appropriate for car installations. There are the through glass type that have a piece that sticks to the outside of a window and another for the inside. They have a little loss in the connector and need to be installed very carefully or that loss is huge. But they don’t require a hole in your car and I see that as a huge plus. Remember that they aren’t gonna work through tint, so if you’re tinted you’ll need to cut a small square of it out. Also be sure that the whole antenna extends above the roof line. The other type mounts either in a hole in the roof or with a magnet. These antennas will likely perform a little better as there is no through glass connection and they will typically end up in a better location. Note that in general that they expect your roof to be metal and assume it will provide a ground plane. If your car is made of glass you may need to add a 1’ square of sheet metal up there.
So there really is a lot to consider here in putting together a system that will actually benefit you. I’ve worked as a RF engineer in the past so a lot of this was easy for me. I know that that is not generally the case so I recommend you talk to a shop that is small enough to care about you individually and design something that would work for you. I really had a good experience with the guys at Criterion give them a call and they will help you get a complete set of all the stuff you need to do a good install.
In my car I have a Sony/Erricson T610, the pigtail they sell, the S/E car cradle, the Criterion amp and a nice glass mount antenna I got from them as well. Before I put the system in my car I was only able to use my phone for the first 7-9 min of my 20 min commute home. Now I’m good from door to door though it sometimes gets a little edgy at one particular place in the summer. I’m happy with what I’ve got…
Wow, I’ve been typing for almost an hour. I should really get back to work. I hope this helps and sorry for the long post.
Dave
ed and only saw a couple of threads and all were from StationRocket about his.
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