PSK31 Digital Radio
PSK31-Wikipedia
https://en.wikipedia.org/wiki/PSK31
ARRL Introduction to PSK31 Digital Communications
http://www.arrl.org/psk31-spec
The official PSK31 Website is operated by Eduardo Jacob, EA2BAJ. The PSK31 software program may be downloaded from this site.
http://aintel.bi.ehu.es/psk31.html
VK6YSE Overview of PSK31 & Operating Techniques
http://www.vk6ysf.com/psk31_overview.htm
RIGblaster Sound Card Interface
http://www.westmountainradio.com/rigblaster.php
DX Zone-PSK31 Software
https://www.dxzone.com/catalog/Software/PSK31/
D-STAR Digital Radio
D-STAR Info
http://dstarinfo.com/
D-STARusers
http://www.dstarusers.org/
Shreveport D-STAR Digital Team, W5SHV
http://w5shv.com/Home.php
D-STAR Gateway System (REGIST)
https://regist.dstargateway.org/Dstar.do
D-STAR-Wikipedia
https://en.wikipedia.org/wiki/D-STAR
ICOM D-STAR System Introduction
http://www.icomamerica.com/en/products/amateur/dstar/dstar/default.aspx
Software Defined Radio
Software Defined Radio-Wikipedia
https://en.wikipedia.org/wiki/Software-defined_radio
NooElec
http://www.nooelec.com/store/?SID=cr8uop91sulqch0kvltqd58go5
WebSDR
http://websdr.org/
Airspy
https://airspy.com/
SDR-Radio
http://www.sdr-radio.com/
All About Circuits
https://www.allaboutcircuits.com/technical-articles/introduction-to-software-defined-radio/
Flex Radio Systems
http://www.flexradio.com/