The Hallicrafters SX-28 "Super Skyrider" was an American shortwave communications receiver produced between 1940 and 1946 that saw wide use by amateur radio, government and military services.
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In July 1940, the Hallicrafters Company announced the SX-28 "Super Skyrider", the result of a development effort by 12 staff engineers and analysis of more than 600 reports that included input from U.S. government engineers, commercial users, and amateur radio operators. The SX-28's distinctive art deco styling was considered sleek and strikingly modern in 1940. The receiver's electronic circuit utilized 15 vacuum tubes in a double preselection front end on the top four shortwave bands and single preselection on the lower two bands. The radio frequency coverage was 550 kHz (0.55 MHz) to 43 MHz in six bands. Amplified AVC, a Lamb Noise Silencer, Calibrated bandspread, and Push-Pull audio output were some of the features incorporated into the design. The SX-28 would become notable for its "high fidelity" audio together with high sensitivity, stability and selectivity, and good purchase value.[1][2]
The SX-28 saw use by various branches of U.S. and allied military and signals intelligence agencies during World War II. SX-28 and Hallicrafters S-27 and S-36 receivers were often rack mounted in British government listening posts and secret listening stations for monitoring German radar and communications during the war such as Beaumanor Hall in the English Midlands where German and Italian encrypted radio messages were intercepted and passed to Bletchley Park for decoding.[4] A number of the receivers were sent to Russia as a part of the Lend Lease Act, subsequently modified to accommodate Russian tubes.[5] The Radio Intelligence Division (RID) of the U.S. Federal Communications Commission (FCC) and the Foreign Broadcast Information Service also used them to monitor the airwaves for American intelligence agencies in both mobile and fixed listening posts in the US. The typical fixed listening post had six SX-28 receivers and one S-27. After the war, the SX-28/28A continued to be used by the FCC in both mobile and fixed installations to monitor domestic radio transmitters.[6]
Hallicrafters published that 50,000 SX-28 and SX-28A's had been built by the end of its production run in 1946, however the serial numbers appear to indicate a production figure of about half that amount, approximately 27,500 receivers.[7] Many of the SX-28/28A's that exist today are in the hands of vintage amateur radio collectors and amateur radio operators.
The name "Skyrider" was intended to bestow an aura of exotic adventure to Hallicrafters products and had a long history with the company. The first Hallicrafters set to be dubbed with the name was the 1932 S-1, and several early Skyriders were regenerative sets. The "Super" was added with the introduction of the first Hallicrafters superheterodyne model, the S-4/ SX-4 in 1934. The last Hallicrafters sets to use Skyrider as part of the name were the SX-28A and the 1947 S-41 Skyrider Jr. receiver.[8]
Variations and special versions of the SX-28 were produced over the years. During WWII, Hallicrafters continued to redesign portions of the SX-28 and, at the beginning of 1944, a major redesign to the receiver's front end prompted a designation change to SX-28A. The old front-end coils were replaced by smaller, Hi-Q Micro Set types that were mounted on removable chassis. The new coil design eliminated the majority of brass parts that were used in the early style coils. After WWII, Hallicrafters had nothing new to sell radio amateurs as they had devoted all design and manufacturing to the war effort, so they offered the SX-28A as a 1946 model. The last 4000 SX-28As built have "SX-28A" indicated on the front panel which is thought to have first appeared around November 1945.[2]