Almanac Injection Procedure

=== Q1] I was trying to upload an almanac into an OEM4/OEMV GPS receiver, but I am continuously getting the checksum error. What's the problem?

A1] First, you need an almanac to inject. It typically takes 15 to 20 minutes of continuous GPS tracking to download an updated almanac message. When the GPS receiver has obtained an up-to-date almanac, the almanac can be output using the following command: LOG ALMANACA The resulting output will contain the full ASCII version of the ALMANACA message, including the #ALMANACA header, the 32-bit checksum, and and a terminating [CR][LF]. An ALMANACA message can be injected into the GPS receiver using HyperTerminal's "Send Text File" option under HyperTerminal's "Transfer" menu, or via any serial interface mechanism that allows you to upload (send) straight text data to the GPS receiver. This only works for the full ASCII version of the ALMANACA message, due to some destructive bit stripping HyperTerminal does to the binary ALMANACB message. When the GPS receiver successfully processes an injected almanac, a response similar to the following example will be generated by the GPS receiver: #ALMANACR,COM1,0,0.0,SATTIME,1371,249834.000,00000000,0004,2177;OK*13be07c1

=== Q2] Is the injected almanac saved to memory automatically, or do I need to use the SAVECONFIG command to store the injected almanac?

A2] No, the injected almanac is not stored to NVRAM automatically. And no, SAVECONFIG will not save the injected almanac into NVRAM either. Only the live almanac downloaded directly from the GPS satellites will be saved into the NVRAM, and this will be done automatically. The injected almanac will be used temporarily and then be replaced with the live broadcast almanac when it becomes available after 15 to 20 minutes of continuous (uninterrupted) GPS tracking.

=== Q3.] So why would I bother to go through all this trouble injecting an older almanac into the GPS receiver?

A3.] If the injected almanac is close to up-to-date, injecting the almanac can speed initial acquisition of GPS satellites. Any application which requires rapid GPS satellite acquisition from a cold start state can benefit from an almanac injection initially prior to insertion into a live GPS satellite tracking environment.