Everything You Need To Know About GPS L1, L2, and L5 Frequencies - GIS Resources
GPS Signal Plan - Navipedia
GNSS signal - Navipedia
First light: Broadcast of L1C by GPS III
RA-50 GPS L1 Band GPS Signal Repeater with LNA [RA-50] - $89.98 : Mobile GPS Online - Geoidsoft Inc., GPS solutions - quality & effective - global service
Some observations of GPS L1 interference from terrestrial sources
GPS L1/L2 Antenna - Sensor Systems Inc., Aircraft Antenna