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From: Bruce Fortnam <bfortnam@GlobalLocate.com> - 2006-05-17 18:33:12
> On May 16, 2006, at 4:36 PM, Jon Keller wrote:
> Doesn't using a passive antenna defeat the whole purpose of having=20
> the super sensitive gps module? It seems that many of the features=20
> this module offers cant be used because of the way this board was
The high sensitivity is for tracking indoors and under difficult outdoor
conditions, such as under tree cover and in the "urban canyon". It is
implemented by fancy processing in the baseband section, and typically
requires some assistance data to help with the satellite search. You
should not expect it to work without assistance - at least by taking it
outside first to get an initial fix.
An active antenna is simply a passive antenna with an LNA very close to
the antenna terminals. The first gain stage after the antenna is the
most important in establishing the system SNR. Any losses before the
first LNA will subtract directly from the sensitivity, while cable
losses after the first LNA will have very little effect. A passive
antenna plugged directly into the gps input should have the same
performance as the same antenna with an LNA at the end of a long cable.
This is assuming that noise from the PXA255, switching P/S, memory bus,
Bluetooth, Wi-fi, etc. doesn't jam the GPS signal. Separating the
antenna from potential interference sources is always a good thing.