another obscure Elmac returns to the air
Bob Heil's favorite radio is the Moseley CM-1 which the developer, John Clemmons, told Carl Moseley stood for Clemens Manufacturing number 1. "No", Mr. Moseley said, "That stands for Carl Moseley number 1!"
As that may be, there's yet another CM-1 receiver and it was made by the Multi Products Company of Oak Park, Michigan.
As wikipedia states: "CONELRAD (Control of Electromagnetic Radiation) was a method of emergency broadcasting to the public of the United States in the event of enemy attack during the Cold War. It was intended to allow continuous broadcast of civil defense information to the public using radio stations, while rapidly switching the transmitter stations to make the broadcasts unsuitable for Soviet bombers that might attempt to home in on the signals (as was done during World War II, when German radio stations, based in or near cities, were used as beacons by pilots of bombers".
The upshot was, to control electromagnetic radiation (aka "RF") designed AM broadcast stations were to remain on the air on either 640 or 1240 kc and would rotate transmission in a round-robin fashion so as to confuse any attempt at direction finding. Every broadcast station was assigned a primary "key" station to monitor and when commanded to do so by an alert notification, they would leave the air. This required each broadcast station to monitor their primary key station at all times, starting Dec. 10, 1951. The same requirement was extended applied to hams, effective Jan. 1, 1957. Throughout the 50's the need for CONELRAD monitoring resulted in a handful of dedicated receivers coming onto the market, from manufacturers including Miratel, Gonset, Kaar, Multi Products, and Motorola. Except the Motorola DS-9660 wasn't made by Motorola - it was in fact a private labelled version of the Multi Products CM-1.
When one showed up on eBay the light bulb came on. I've played with tunable mobile converters that were popular for HF mobiler in the 50's, but it was a hassle to set up an old car radio, power supply etc. Since the CONELRAD receiver is a fix-tuned superhet receiver with a built-in power supply and speaker it looked like the ideal IF for a mobile converter, and I happened to have a Morrow 5BR1 on hand. As things sometimes happen, a check of eBay showed a seller offering a copy of the original manual the same day I won the receiver auction.
It took nearly nothing to get going, the filter caps were fine but the rectifier tube had failed, so a couple of diodes fixed that. This receiver came from Ohio and I'd guess it came from an AM station there as the crystal channel was set to 760, which would have been WJR, Detroit. Two other crystals provide reception on 640 and 1240, but the last position switches in a variable tuning circuit, which I retuned to the output of the Morrow converter. The manual calls out sensitivity of 5 uV for "4 to 1 s/n ratio" and the converter has a lot of gain (too much, actually). Selectivity is given as 3kc at the 6dB point and 15 kc at 40dB down, which is quite good, and means it should be able to sort out signals within the AM window.
CONELRAD was probably the best system that could be devised in the late 40s but it was pretty weak. The complete alert mechanism consisted of a sequence of actions: first, the key station would drop it's carrier for five seconds, return to the air for five seconds, again shut down for five seconds,and then return to the air and transmit 1 kHz tone for 15 seconds. Decoding the full sequence would have taken equipment so expensive no one could have afforded it, so some monitors just sounded an alert whenever the key station's carrier was absent for a few seconds. This resulted in false alams when stations would switch antenna patterns or otherwise momentarily leave the air. The Multi Products receiver did both - detected the loss of carrier and the 1,000 cycle tone, and only then would the alarm be activated. Three of the 8 tubes are used for alarm detection circuitry including a 2D21 thyratron.
I didn't bother making these circuits work because what's the point? And in fact I repurposed the rear panel terminal strips to provide power to the converter and for muting. Morrow suggests very strongly that and RF gain control be added to the car radio their converter is used with since the AGC loop obviously does not include the front-end (converter) and that's something I may yet do. I was able to give it it's first on-air test on the Mighty Elmac Net on 8/12/20 and despite poor propagation it worked well.
Another Elmac has returned to the air!
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International Crystal and the crystal synthesizerHow a crystal company reduced the number of crystals neededCategory: Vintage Radio
- Robert Nickels (ranickels), 02/19/2021
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Hams, especially those who enjoy operating AM and QRP should be aware of the pioneering efforts of the US Forest Service to adopt and advance the radio art in the early decades of the 20th century.The history of radio in the USFS literally takes a book to cover, but an interesting example can be found in station KBCX, the Region 1 Radio Operations Center in Missoula Montana. It w... READ MORE
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The R-1451 HF Manual Receiver aka WLR-6 "Water Boy" SystemESM-ELINT receiver from the 1960sCategory: Vintage Radio
- Robert Nickels (ranickels), 02/09/2021
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The John Meck T-60 Transmitterthe only ham product from this famous radio/TV manufacturerCategory: Vintage Ham Radio
- Robert Nickels (ranickels), 01/30/2021
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If, like me, you enjoy flipping through old issues of 73 magazine from the 60s, you're bound to have at least seen the ads for the Transcom SBT-3 three-band SSB tranceiver. Being made in Escondido CA in the mid-60s, my guess has always been that engineers from other San Diego SSB compnanies such as Don Stoner, Les Earnshaw from Southcom, Herb Johnson, founder of Swan or Faust Gonsett may... READ MORE
- Robert Nickels (ranickels), 01/16/2021
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This short article about the AWA Forestphone was the last one put on the Midwest Classic Radio Net website by for former webmaster George K9GDT before he unfortunately became a Silent Key. MCRN articleNow that a longer version has been published in Electric Radio magazine I thought I'd include it here as well.Throughout most of the 20th century AWA was Australia's leading electr... READ MORE
- Robert Nickels (ranickels), 01/13/2021
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Alexander M. Lewyt died in 1988 at the age of 79, a holder of patents on scores of inventions. His penchant for invention, he once said, was so strong that he had chronic insomnia from lying awake at night envisioning new products. When he learned of undertakers’ difficulty in fastening neckties on corpses, the teen-age Lewyt devised a new kind of bow tie that clipped on. He sold 50,000 of t... READ MORE
- Robert Nickels (ranickels), 01/08/2021
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The Korean-war vintage AN/GRC-9 is one of the most useful and fun military field radios for ham use, as with AM and CW modes and 2-12 MHz coverage and a VFO it's all ready to go on several ham bands. The battery tube superhet receiver is also power-friendly and sensitive and stable enough to copy CW and SSB but has one annoying flaw - the 4 volt bias battery used by the audio... READ MORE
- Robert Nickels (ranickels), 01/03/2021
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Halogen type MR-16 lamps are commonly used in track lights and other spot lighting applications so what would be cooler than to drop in LED replacements! A lot, as it turns out. The LED replacements are HORRIBLE RFI emitters that totally trashed several ham bands when I unknowingly installed them.Halogen spot lights are 12 volt devices so it's long been common prac... READ MORE
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Ham radio operators honor legacy of Mars Hill companyHammarlund was an industry leader for generationsCategory: Historic
- Robert Nickels (ranickels), 12/12/2020
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