[aprssig] Cheap USB GPS available again -- more detail

[Ben Jackson]

Ok, I cracked one open.  Forgot to mention, these units have a magnet in
the bottom of the case.

It's about 1 3/8" square and a little over 1/4" thick (mostly antenna).

The chipset is the Prolific PL-6313 "GPS Baseband Processor".  You can
usually download this from Prolific's website, but it's broken at the
moment.

There's a SiGe SE 4100L RF downconverter.

The USB interface is the PL-2303X.  Same deal about the datasheet.
I found the 3.3V TTL serial on a via between the two chips.

The antenna seems to be secured only by one fat through hole, so you can
probably replace it with a vertical-mount SMA where it is with relative
ease.  The antenna lead goes to a flea-sized cap so you could also pull
that and solder to the flea-sized trace or pad.

There's a little battery which is probably to back up the almanac for
fast restart.  Another thing you might be able to remove to save weight.

Bottom of the unit says it draws 35mA.  It does have a blinking LED
(1 blink/sec while locked) and of course the USB and USB pullup resistors
which might be removable.

I poked around looking for a locked frequency standard, but I'm sure it
will be much easier to find when the PL-6313 datasheet is back online.

-- 
Ben Jackson AD7GD
<ben at ben.com>
http://www.ben.com/