by WB4AIO on February 23, 2010
The AM-864/U broadcast peak limiter
by Kevin Strom, WB4AIO
THE AM-864/U broadcast peak limiter, which I purchased “new surplus” from John Meshna and Company in about 1974, was my first foray into true broadcast audio processing for amateur radio. Like my TCS transmitter purchase from them, the unit was beautiful and flawless out of the box. It cost me $35. I sold it in the 90s (probably a mistake) for about $100. It now has acquired a “reputation” in the recording industry, and good ones sell for over a thousand dollars.
It’s 600 ohms transformer-coupled balanced in and out, with a simple all-vacuum-tube and all-balanced audio amplifier and peak rectification and gain reduction circuit. It was built in the 1950s by the Federal Television Corporation (some were built by other contractors, I am told) for use in AM and shortwave transmitters run by AFRTS, the Armed Forces Radio and Television Service. It came with a manual, the most hilarious aspect of which was its instructions on how to destroy it (“use axes, knives, machetes, flamethrowers, incendiary grenades” etc.) in case it fell into “enemy hands.”
AM-864/U destruction instructions, from the operator's manual (click for the full-size image). And yes, the "enemy us" typo is in the original!
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by WB4AIO on February 16, 2010
The TCS transmitter: Notice the RF output terminals on the upper left of the front panel, right next to the "antenna coupling" control. (click for a larger image)
by Kevin Strom, WB4AIO
RECENTLY I was listening to WA1HLR use his modified Navy TCS transmitter on 75 meters, and it brought back memories of my early days on the amateur bands. In 1972 I bought a World War II surplus Navy TCS transmitter, built by Collins, from military surplus dealer John Meshna, via mail order.
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by Kevin Strom, WB4AIO
I’VE JUST DISCOVERED a new and worthwhile amateur radio net, meeting Saturday mornings on or around 3872 kHz in the AM mode. It’s the Flex Radio Users Net, devoted to discussions of the software-defined transceivers manufactured by Flex Radio Systems and related topics.
Flex Radio Users Net - 2 January 2010 - 3872 kHz
This week, the group was discussing both the theoretical and practical aspects of symmetrical versus asymmetrical modulation, modulation levels generally, and audio processing for HF amplitude modulation transmission.
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by WB4AIO on December 16, 2009
Here we see HD Radio sidebands on either side of an analogue FM broadcast signal, as shown on a spectrum analyzer.
by Kevin Strom, WB4AIO
WITH 2010 APPROACHING, CNET just released its “The Decade’s 30 Biggest Tech Flops” anti-awards, and “HD Radio” was among the “winners.”
HD Radio was not only doomed from the start, it was such a serious blunder that it may well lead to the death of thousands of radio stations and the permanent stunting of the industry itself.
There is nothing wrong with the concept of digital radio.
Using modern firmware-upgradeable codecs, orthogonal FDM transmission, and a network of community transmitters in a dedicated digital band, great things could have been done:
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