Ham Band Conditions: hamqsl.com/solar3.html
DX / Propagation Activity: dxmaps.com
Frequencies for common digital modes: qsl.net/sv1grb/psk31.htm
Study for ham exam: hamexam.org
NVIS / Critical Frequency: hamwaves.com/nvis/en/index.html
Listen to Ham Radio Live Online: na5b.com:8901/
https://www.hamradiosecrets.com/listen-to-ham-radio-online.html
http://www.websdr.org/
Search for vanity call-sign: radioqth.net/vanity/available
Grayline propagation map: dx.qsl.net/propagation/greyline.html
Coax Calculator: timesmicrowave.com/calculator
End Fed Half Wave Antenna (EFHW): gnarc.org/wp-content/uploads/The-End-Fed-Half-Wave-Antenna.pdf
List of DTMF commands: echolink.org/Help/dtmf_functions.htm
View reach and signal reports: https://pskreporter.info/pskmap.html
Magnetic Loop Antenna: https://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm
Building a Band-Pass Filter: http://www.arrl.org/files/file/Technology/tis/info/pdf/8809017.pdf