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The R390A/URR |
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Ultimate Performance, General Coverage AM & CW Receiver |
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Home On the WWW |
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R390A/URR Receiver Site Pages Accessible from Left Hand Navigation Bar |
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The R390A was designed in a period when two prime modes of emission were AM (A3) and CW (A1). The quality of construction combined with the
performance of the receiver necessitated that it be adapted to a new, more efficient mode, SSB (A3J). Accomplishing this was not so simple. The symetrical design of the Collins mechanical filters worked
well for AM but asymetrically filters capable of selecting an individual sideband were required for true SSB reception. Also, the AGC time constants would require modification to accommodate the most readable
audio recovery possible. Finally, the existing BFO neither provided sufficient injection level or was stable enough to properly detect an SSB signal. The most common approach was to team an R390A with a CV-591
SSB converter. These were manufactured by several contractors perhaps the most common being the vacuum tube Technical Materiel Corporation (TMC) famous for the GPR-90 general coverage receiver. Much more
rare were the newer soild state SSB converters such as the Delta Electronics, ISB-1 in use by this author. |
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By far the most rare configuration for an R390A capable of receiving SSB was a receiver configured by the manufacturer with extra circuitry for
detection of A3J emissions. A 7th module containing a single 6EA8 tube and two crystals was added just behind the front panel and in front of the audio module.
Although a compromise due to the lack of both assymetrical filters and AGC time constant changes, this modification worked quite well and had the
additional advantage of being completely self-contained within the receiver chassis. |
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The module interfaced with the radio by plugging into the IFdeck and also the front panel wiring harness from where it received B+ and filament
voltages. |
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