Re: [Gumstix-users] GPS antennae

[Alexandre P. N. <al...@om...>]

Jon Keller escreveu:

> Doesn't using a passive antenna defeat the whole purpose of having the 
> super sensitive gps module? It seems that many of the features this 
> module offers cant be used because of the way this board was designed. 
> I guess thats what first revisions are for.
>
> Just for reference, I found it much easier to solder a small piece of 
> wire to the gps's pad, and then solder the wire to the resister and 
> then the resister to the vcc. I'm by no means an expert solder'er 
> however after this mod I'm much better than I was. All my attempts at 
> soldering the resister straight to the pad only lasted about a day 
> before it broke off, but soldering the wire to the pad has been solid.
>
> Heres a picture before the added heat shrink...  
> http://defy.net/balloon/gpstix.jpg
>
>    -Jon
>

The primary goal of an active antenna is to compensate for the loss that 
happens on the cable. The shorter the cable, the lesser the need for an 
LNA (low-noise amplifier) on the antenna itself. The module has itself a 
built-in LNA.

The module author's claims that starting with some amount (which I can't 
remember), any extra amplification from the active antenna's LNA is 
useless and can even saturate the module's one. It recomends paying 
special attention by the antenna gain, and warns about many active 
antenna's suppliers only mentioning the LNA gain, an antenna with a poor 
gain will not be compensated by a good LNA.

Once we have that clear, however, and generally speaking, your chances 
of success with standard-quality antennas are greater when using a good 
active antenna, even with a relatively short cable, since if it (the 
cable) is less than perfect, on low-signal conditions it can be an 
obstacle as well.

But if the cable is very good, the built-in module's LNA can do the job. 
Under these circusntances, a passive antenna with a good natural gain 
would be better than a worse antenna with a good built-in LNA.

In another words, your mileage may vary.

As for the module, I'm with you, with the current design it's quite 
limited and may be a no-go under some circunstances. I'm quite sure 
however that the 2nd generation will cover the know flaws.

Alexandre