Below is a list of resources for anyone working with or interested in RF.
FCC ULS – Search the FCC Universal Licensing System.
GPS Coordinates – Find GPS coordinates of any location.
Radio ID – Register for or search for a radio ID used on numerous networked amateur radio systems.
Signal ID Wiki – Tool for identifying all sorts of digital radio modes.
Distance and Bearing – Locate the distance and heading for any two locations. Useful for beam aiming.
RTL-SDR – Excellent resource for projects and software using inexpensive software defined radios.
QRZ.com – Long standing amateur radio resource. Probably the most popular ham radio resource.
DX Heat – Real time HF spotting
SOTA watch – Summits on the Air spotting. SOTA is a group of amateur radio folks who hike up to hills and mountains attempting to contact as many stations as possible.
hamqsl.com – Excellent, long running site for detailed HF propagation information.
BatLabs – Another long running site for all kinds of information about Motorola Radio products.
Repeater Builder – This site has also been online for a long, long time. It features a ton of information on using commercial radios for repeater use.
Radio Reference – Exhaustive frequency database. If you can’t find what you’re looking for here, then try an FCC ULS search.
Sandy’s Communications – Ham friendly Motorola authorized dealer. Owned by Sandy (K7FY) and his son Jeff (N0WTF).
ADS-B Exchange – Find unfiltered ADS-B information for airborne aircraft world wide.
SCRRBA 70 cm open repeaters – The official Southern California Repeater and Remote Base Association list of open, coordinated UHF repeaters in the Southern California region.
Southern California repeater list – A more detailed listing of Southern California amateur radio repeaters, organized by county. This resource is provided by Jet Propulsion Labs Amateur Radio Club.
TASMA 2 meter repeaters – The official Two-Meter Area Spectrum Management Association listing of coordinated VHF amateur radio repeaters.