Brian Kirby, KD4FMN shows us how he implemented battery backup for his Z3801A Motorola GPS receiver. This modification will hold up the real time clock in the GPS receiver and retain the satellite almanac data. A benefit of this is to speed up the next aquisition cycle if the Z3801A loses power.

According to the Motorola manual, the GPS engine draws 5 uA at 3 volts. It is helpful to mark a date on the batteries when they are installed, so that a record of their their age is known. In this light duty application, battery life should be approximately equal to the battery shelf life.

Two AAA sized cells and a battery holder from Radio Shack (P/N 270-398B) are used. Just tack solder the leads to pin 1 (plus-battery backup) and pin 3 (common) of the GPS receiver connector. Alternately, a 3.6 volt backup battery similar to those used in personal computers may be used.

After you bring the receiver back up and it locks up, let it run about 30 minutes to an hour before you shut it back down to test the real time clock. It takes about 13 minutes for the GPS receiver to establish an almanac. When you bring the unit back up, you should see the correct real time and the GPS receiver should sucessfully lock in under 45 seconds.