I must concure, I have a LT-40 & BT-20 and both from time to time will go south.
The BT-20 will not get a valid lock.
I use the BT-20 with a google maps app that my son wrote.
Many times the BT-20 has me out in the ocean off of africa below Ghana going 122-123 mph with a headding of 132 degrees.
Basically with in ~400 feet of Lat:-0.000031, Lon: 0.0004 That is Degrees and decimal.
I have captured the Data stream, and the unit is putting out that data. Although in the $GPRMC sentence does correctly have a V for data not valid.
I use the LT-40 for SA and the BT-20 for the google ap.
The LT-40 ~95% of the time lock on within <3 minutes.
The LT-40 & BT-20 are on the Dash within 4" of each other.
When the BT-20 is in "out in the ocean mode" I usually have to turn the unit off then back on again, which is a big hassle because of loosing the Bluetooth connection and the python program that parses the NMEA data has to be stoped and re-started.
Basically the BT-20 does not lock on to the satillites...
When I use the BT-20 in "out in the ocean mode" in SA-2010 the SAT INFO shows 8 sats with --T- Two or 3 sats in RED at the outer edge of the circle and Acquiring flashing in RED...
A bit on the fustrating side!!!
Almanac update problem?