Ten-Tec RX-340/ RX-331 History

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Ten-Tec Development History

I’ve encountered stories around the internet that portend to tell the story of how the Ten-Tec RX-340 Receiver came to be. I have to chuckle at the effort put into fiction. Honestly, the true story about how this radio came to be is interesting enough without the need to make it up.

Because the RX-340 is closely related to the RX-330 receivers it could be assumed that the RX-340 is derived from those products. The reality is, a product like the RX-340 was under development before the RX-330.

In the late 1980’s and early 1990’s shortwave listening was still a significant market and monitoring of the HF spectrum was being done extensively by hobbyists and government entities alike. And as in most product markets there are multiple levels of business… base, mid-level and top-tier, which encompasses consumer, commercial & government of all types. To be sure, Ten-Tec was not new to shortwave receivers, having previously designed and manufactured an analog radio for the Navy, the model SP-325. The SP indicating it was for the Shore Patrol.

In 1991 we started looking again at designing a shortwave radio that might be attractive to high-end consumer, commercial and government users. At that time, the leader in the high-end market was the Watkins-Johnson, WJ-8711. WJ also produced a black box version, the 8712, which had no front panel.

In late 1991, we were just beginning to play with Digital Signal Processing (DSP) and became interested in creating a radio that would use DSP to perform traditional analog functions At the time there wasn’t a great deal of information available on how to do that. So we set out to develop our methods and algorithms from scratch. It was slow at first but once we had developed the demodulator algorithms we felt confident we could design a DSP radio with great performance and at a significant lower bill-of-material (BOM) cost than if it were an analog design.

That radio, which would eventually birth the RX-340, was internally referred to as the “DSP Monitor Receiver”, and was assigned the model number RX-336. In addition to DSP performing many of the analog functions, the radio would feature a removable and remotable front panel assembly. The radio without the front panel would be designated model RX-335.  In early development, the front panel was a simple Encoder/Display with multi-layered menus as our focus was on the RF/DSP hardware which was the critical element. Much later, a more elaborate panel would be designed for the RX-340.

Initially, we started DSP development with the Texas Instruments TMS320 series processors which proved difficult to use. The tools available were rather primitive and TI offered little support. Serendipitously, there was a ham that worked for Analog Devices that just happened to contact us to see if we would be interested in the ADSP-21xx processors which lead to our changing to Analog Devices processors. Ironically, it was the limited memory of those processors that would lead to many design achievements that we might not otherwise have pursued. For example. the ADSP-21xx processor could load and run 8K words of memory, forcing us to think small and streamlined.

It was in late 1992, during developing of the “DSP Monitor Receiver”, when we were approached by a government contractor that was tasked with finding options to replace their aging monitor receivers. We demonstrated our prototype radio and though they were interested, they were not interested in a front panel radio. They were specifically seeking a black-box, rack mount HF receiver in a 1U rack mount chassis that was a drop-in replacement for their existing RACAL radios. And it had to be COTS (Commercial Off The Shelf). Meaning that no government funding was available to support development and we would be fully at-risk for the investment. Despite the risks, we felt confident we could do it and decided to develop the black-box monitor receiver. Internally, the project became known as the “black-box receiver” and designated the RX-330.

You should know that one thing Ten-Tec had going for it was its extensive in-house design and manufacturing capability. We manufactured most parts of the products we sold. Transformer winding, metal work, plastic injection, tool & die, painting, labeling, cabling, PCB etching and electronic assembly were all within arms reach. As an engineer, anything you designed could be physically produced within days or even hours if necessary. Having these kind of resources just changes the way you think because you didn’t need to waste time on the ‘how’ and were able to stay focused on the ‘what’.  

The first of the “black-box receivers” was the RX-330 produced in early 1994. The product met or exceeded all specifications and expectations and the government customer moved quickly to make a purchase. Thanks to feedback from the customers, it was followed soon by the RX-330A which featured quarter-turn fasteners on the lid and a new power supply. Further enhancements lead to the RX-330B and the RX-331. 


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