David Carey
DSP DesignLine

Imagine a downed military pilot or injured boat captain adrift during the Korean Conflict or Vietnam War. Likely, he'd reach for the Hoffman RT-159A survival radio to call for assistance.

The RT-159A we analyzed here was found on eBay, home to almost all objects mainstream and obscure. How things like a 50-year-old survival radio show up for sale on the world's largest auction site continues to amaze me, but as a confirmed collector and pack-rat I'm delighted eBay is around as a vibrant outlet for vintage electronic rarities.

The RT-159A, a crude tool by today's standards, provided a simple but critical function, transmitting a fixed tone or a pilot's voice in a rescue request. Likewise the radio could receive signals on the same two frequencies used for transmitting--121.5 MHz and 243 MHz, designated as VFH and UHF, respectively. The 121.5/243-MHz slots remain as emergency frequencies to this day. While scheduled for monitoring phase-out in 2009, transmission on these frequencies will still likely set search-and-rescue wheels in motion.

Click on image to enlarge.

A sliding band-select switch on the outside of the radio allows for the choice of desired frequency. Other controls and externals in the RT-159A include a trio of buttons for selecting Transmit, Receive and Tone (presumably overriding the default of voice input), with all three using a shared locking slidebar to avoid inadvertent calls for response. A four-pin connector on the bottom of the case provides for hook-up to the external battery.

Two extendable mast antennas reside in another locking assembly at the top of the radio. By sliding a switch, an antenna platform that can be raised above the radio is released. From that platform, the two masts can be extended to differing lengths for the two frequencies. Instructions printed on the radio show UHF mode served by laying the masts in their short, unextended form as a dipole pair (opposing directions) across the platform. Alternatively, the masts can be fully extended for use in the VHF frequency, where a longer wavelength requires a correspondingly longer antenna element for similar gain.

Given the radio's genesis in the mid-1950s--an era when electronics were still largely implemented pre-transistor --vacuum tubes supply all the active components in the RT-159A. Opening the case for the first time brought forth the aroma of heated filament-based electronics, phenolic circuit boards, aged solder flux and old component varnishes. Memories of my early--and often only marginally successful--attempts at TV repair using the old Radio Shack tube testers came flooding back.