RX-320 Front Panel - no lights or switches
RX-320 Rear Panel
Note: Ten-Tec ceased production of the RX-320D in September, 2013
The Ten-Tec RX-320 is a HF DSP computer-controlled receiver. It is quite literally a "black box", with no knobs or traditional front panel. It originally listed for under $300 direct from Ten-Tec, and it's performance on HF rivals that of receivers costing up to $1000. I have had a dozen other "serious" communications receivers in the shack, and have been very pleasantly surprised by the RX-320's performance. It is a bargain if you don't mind the lack of a front panel. The more recent RX-320D model adds a 12 KHz IF output for use with Digital Radio Mondiale and other SDR software applications. Used RX-320's are available for $160 - $340.
While the audio output of a RX-320 can be connected directly to most "passive" external speakers, it doesn't seem to work well when connected to the grounded input of an audio amplifier or distribution system. An 1:1 ratio audio transformer can be used to isolate the output from ground. The Radio Shack "Audio System Ground Loop Isolator", 270-054A, works well in this role.
A variant of the RX-320, the RX-321, was customized for maritime communications as a secondary receiver in shipboard GMDSS suites. Globe Wireless was the only customer, and they were not offered to the general public. While they look similar, there are both internal and external differences between the 320 and 321. Only about 100 were made. Additional RX-321 details may be found here. The same RX-320 software applications and cabling may be used to control RX-321s.
More information on the mil-spec/professional grade RX-331 can be found here, including manual, schematics, and brochure.
There have been many questions about the RX-320's performance on medium wave. There is a fixed filter which reduces the receiver sensitivity below 1 MHz, but I find there is plenty of sensitivity for dx listening when using external antennas. In fact, I normally use 10 to 20 dB of attenuation on the input of the RX-320 above 800 kHz to reduce overload from strong signals when using HF dipoles and long wires. An AMRAD modification to increase VLF/LF sensitivity can be found here.
Ten-Tec should receive kudos for publishing the RS-232 and command sequence specifications. In addition to the Windows GUI control program provided with the receiver, the Ten-Tec web site provides a BASIC text mode control program (source code). One unusual aspect of the interface is that it is almost entirely "write only". The firmware version number and signal strength, but none of the other operating parameters, can be retrieved from the receiver. The specs invite software innovators, and there are many third party software applications for controlling the RX-320. A good example is DXTRA's WorldStation.
One Linux control program version is rx320. It uses the Xclass library routines to provide "windows-like" GUI components. Another Linux control program is GRIG, an application that has a common graphical front end to many radios, including the RX-320.
Gnu Rig (GRIG) main window.
There are at least two PalmOS RX-320 control programs. The very affordable Palm PDAs, with the serial/RS-232 cradle and null modem adapter, provide a very affordable "soft" front panel for the receiver.
Additional details, such as full specifications, the latest RX-320 software, Programmer's Reference Guide, Schematic Diagrams and Material List are available from Ten-Tec's Web Site. In addition, there are photos/details on their high-end RX-331, RX-340, and RX-400 receivers.
PDF of AMRAD LF/VLF Mods for the RX-320.
Medium Wave Circle review of the RX-320, originally from Radio Netherlands.
eHam reviews of the RX-320.