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Discrepancy Sheet

Found in the Attic: B&W 410 Distortion and Voltmeter

Posted by Tom Vernon on June 7, 2016

B&W 410 Distortion & VoltmeterA recent trip to the attic reminded me of the long-forgotten ritual of an annual proof-of-performance, required of all stations by the FCC. Sitting in a dusty corner was a B&W 410 distortion and voltmeter. Time to bring it down for a general cleanup and photoshoot.

The theory of total harmonic distortion measurement is simple. Feed a low-distortion sine wave into the device under test. Connect the output to the distortion analyzer. Filter out the fundamental frequency. What's left is second and higher order harmonics and noise. Of course, when theory is put into practice, things can get complicated.

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Topics: Vintage Technology

Found in the Attic: MSI CP-803 Composite Processor

Posted by Tom Vernon on March 2, 2016

CP-803The first AGC and peak limiter amps for broadcast audio were designed to maintain a station's modulation within FCC limits. Starting in the mid-1960s, they evolved into tools to create a unique 'sound', and to win loudness wars. By 1980, it seemed that audio had been squeezed and squashed as much as possible, and listener fatigue was a common topic for articles and discussions. Then, the composite processor appeared on the scene, and new heights of loudness seemed possible for FM broadcasters. This installment of Found in the Attic contains a brief history of composite processors, and discusses the Modulation Sciences Inc. CP-803 in particular.

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Topics: Vintage Radio Technology

Found in the Attic: Radio Down on the Farm

Posted by Tom Vernon on February 18, 2016

Philco 40-90This episode of Found in the Attic features a 1940 tabletop radio with a twist. This Philco model 40-90 is a farm radio. Although they were an important part of radio history, these radios are largely forgotten today.

When radio came on the scene in the 1920s, it was the first mass media. It brought Americans together as never before. Suddenly, geographic boundaries didn't matter. Once the sun went down, clear channel AM radio stations sent their signals coast to coast.

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Topics: Vintage Electronics

Found in the Attic: Broadcast Electronics 500

Posted by Tom Vernon on January 26, 2016

Spotmaster 500An earlier installment of Found in the Attic looked at the ATC/Collins P-190 cart machine, which was the first commercially available tape cartridge deck, and the hit of the show at NAB '59. Around that time, Ross Beville, Chief Engineer of WWDC in Washington, DC had the same idea, and also began to develop tape cartridge machines. He apparently did not know about the work of ATC's Bailey and Jenkins until NAB '59. In June of 1959, Beville founded Broadcast Electronics in Silver Springs, MD, to manufacture Spotmaster cart machines. The first production runs were built in the station's garage.

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Topics: Vintage Radio Technology

Found in the Attic: Yaesu FRG-7

Posted by Tom Vernon on December 30, 2015

Yaesu FRG-7The hobby of short wave listening is not dead. OK, there aren't as many choices as there once were. Many European short wave broadcasters have abandoned their transmitters and towers in favor of online streaming as the economic slowdown strangled the budgets of many operations. Still, there are enough stations out there to keep the hobby alive. So, put on your bellbottoms as we go tripping back to the 1970s to check out a Yaesu FRG-7 communications receiver, affectionately nicknamed the 'FROG 7'.

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