RAN Technology

Multi Products Model CM-1 Conelrad Monitor (Motorola DS9660)


Vintage Ham Radio 0 Comments 08/13/2020 

another obscure Elmac returns to the air

Posted By: Robert Nickels (ranickels)

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!

Click on the image title or on the image itself to open the full-sized image in a separate window.

    Not much more to be said - if you can't find it here you probably don't need to know!RADIO BOOKSMany are from non-US sources, some are in languages other than English.   Included are 23 volumes of Riders manuals, Beitmans most needed diagrams up til 1967, and much more.   Incredible resource!...  READ MORE
- Robert Nickels (ranickels),  11/02/2020 
  

Ed Marriner, W6BLZ/W6XM (SK)

One of ham radio's most prolific builders and authors
Category: Historic
 This tribute to Ed Marriner will be updated over time.   Having known his writings since my earlies ham days in the 1960s, I knew about the "SSB Transceiver from a BC453" conversion article/booklet, but until I had the good fortune to acquire two homebrew SSB transceivers made by his good friend Ernie Mason W6IQY did I know that my vintage SSB friend Lynn Fisk K5LYN was a...  READ MORE
- Robert Nickels (ranickels),  10/25/2020 
   EFJ transmitter sales data from former employees....  READ MORE
- Robert Nickels (ranickels),  09/16/2020 
   Like most hams, I remembered seeing the FPM-200 at an astronomical price in the 1962 Allied Radio catalog and wondering just how rich would a person have to be to own one?    For my 11 year old self, such things may as well have been on another planet, but well...things change.I'd seen only one FPM-200 sold (to a guy ahead of me at a hamfest) and in the pre-eBay era most rare ra...  READ MORE
- Robert Nickels (ranickels),  09/12/2020 
  

why 50 ohms?

The Forgotten Impedance
Category: Technical
 Why do we use 50 ohm cables?    If you're like most hams the answer is:  "I dunno!"In fact, it's a compromise (like most things in life) - between lowest loss when handling power and voltage breakdown, as Belden engineer Steve Lampen explains hereA pdf copy can be found below as well.   And now you know!...  READ MORE
- Robert Nickels (ranickels),  09/06/2020 
  

"Crystal Plugs"

DIY version by "RAN Crystals"
Category: Crystal Replacement
Crystal sockets were popular for pluging in ... crystals, of all things!   But they were also used for other purposes, such as the antenna relay connection on some EF Johnson transmitters.    If you want to connect a VFO to a transmitter with just a crystal socket, for example, you're going to have to either carve up an old FT-243 type crystal or if you want to outboar...  READ MORE
- Robert Nickels (ranickels),  09/01/2020 
  

A visit to the D J Everett III Radio Room

Honoring the legacy of a small town radio station owner
Category: Historic
Many successful career people are grateful for mentoring they received on the way to the top. But few have honored a memory as passionately as has been done by Beth Mann.   She's the owner of Ham Broadcasting which owns five stations in western Kentucky but the story is about her mentor, the late DJ Everett III who started WKDZ in Cadiz Kentucky in 1966.   Everett worked as...  READ MORE
- Robert Nickels (ranickels),  08/14/2020 
    Jay Miller KK5IM recently wrote an article in Electric Radio magazine about fulfilling his dream of building a homebrew "AM Kilowatt" transmitter (375 watts output by today's standards).     His crystal-controlled exciter that drive the 813 was based on his Novice transmitter, which was built by his grand-uncle back in the 1960s when Novice class hams were l...  READ MORE
- Robert Nickels (ranickels),  07/09/2020 
  

Bias control of Class E amplfiers

Previously undocumented phenomenon
Category: Technical
Micro SDR innovator Guido PE1NNZ has implemented polar modulation using an Arduino MCU and a class E PA.   For more informartion on this fascinating project, join the discussion group at https://groups.io/g/ucxInitially, Guido's design implemented the polar or EER modulation scheme using modifications to the QCX CW transceiver hardware in the traditional way as described by Leonard K...  READ MORE
- Robert Nickels (ranickels),  06/20/2020 

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