[TangerineSDR] New Dual-Freq GPS Module

[John Ackermann N8UR]

Just FYI --

I just discovered that SkyTraq has a new GPS module, PX1122R, that seems
very comparable to the uBlox ZED-F9P, with a couple of exceptions noted
below.

It's dual frequency and has a built-in RTK processing engine -- that
means you can feed it correction data and get corrected results in
real-time.  The claimed accuracy is 1.5m CEP autonomous, or 1 cm plus 1
ppm when in RTK mode.

There is a PPS signal with claimed 12 ns accuracy.

The good news is that the module is $99 quantity 1 (they also have a
breakout board for $125 and an evaluation board for $150).

The bad news is that, at least from the data sheet, it's unclear what
data outputs it provides -- there are a limited number of NMEA sentences
listed, but it also supports RTCM 3.1 and "Skytraq raw data binary".

I *think* but am not sure that the RTCM message output provides the raw
data needed to create RINEX files and generate TEC (I'm happy for input
on that point).  And I don't know whether the binary protocol provides a
sawtooth or quantization error correction message to improve the PPS
quality.

I ordered one of the evaluation boards to test, but depending on the
data output capabilities this device may not be well suited for
timekeeping or the TangerineSDR.

Links:
Data sheet:	http://navspark.mybigcommerce.com/content/PX1122R_DS.pdf

Module:	
http://navspark.mybigcommerce.com/px1122r-multi-band-quad-gnss-rtk-module/

Breakout board:
http://navspark.mybigcommerce.com/ns-hp-gn2-px1122r-multi-band-quad-gnss-rtk-breakout-board/

Eval Board:
http://navspark.mybigcommerce.com/px1122r-evb-px1122r-multi-band-quad-gnss-rtk-evaluation-board/

John