Radio Room

Military radio and wireline communications equipment, and related stuff.

Aug 122012
A Half-Track Ride

Yesterday I was out at Fort MacArthur for an MRCG event. While I was there, I had a rare opportunity to ride in the fort’s half-track, complete with a quad .50 caliber antiaircraft gun in the back. I sat shotgun and operated the SCR-609 radio set. Some video may show up on YouTube someday. For now, here are a few pictures of the half-track.

Updated: Video of the event is embedded below.

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Jul 052012
AN/APQ-171 Radar Antennas

For a long time, I’ve had a passing interest in radar antennas. Not so much the antennas themselves, but mostly their azimuth-elevation (az-el) drives. Every now and then, I’d search on eBay for any such az-el drives that looked both interesting and inexpensive, with or without antennas. I finally found one to buy about a month ago, and here’s a little bit about it.

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Feb 042012
MT-702/U Radio Mount

I’ve just obtained a WW2-style packboard with an MT-702/U radio mount fastened to it. It’s similar to the FT-505 pack mount that I wrote about previously, and a BC-1335 transceiver will fit on it. However, unlike the FT-505 which has a wide spot for the BC-1335 and a narrow spot for a CH-191 battery box, this MT-702/U has two wide spots, each of which is the right size for a BC-1335.

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Jan 212012
T-368C On the Air!

I’m very happy to report that thanks to a NOS pair of Eimac 4-125A modulator tubes from Antique Electronic Supply, my T-368C is back on the air for the first time since I got it! I’ll still have plenty of tinkering to enjoy on it, and plenty of work integrating it into a full system with my R-390A receiver. I’m also happy that my antenna BALUN didn’t burst into flame upon encountering the hefty output of this small monster of a transmitter.

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Jan 072012
T-368C Firebottles

My T-368C transmitter uses three impressively large transmitting tubes. The power amplifier (PA) uses an Eimac 4-400A, while the modulator uses a pair of Eimac 4-125A tubes. These big tubes are beautiful in my opinion, especially when they’re operating with the plates glowing red. Sadly, they’re not normally visible in operation due to the transmitter’s opaque steel cabinet, studded with interlocks to keep folks away from the lethal high voltage that lurks inside. Even with the interlocks bypassed for debugging purposes (which is dangerous, and should be avoided when possible!), the big 4-400A tube is further obscured by an opaque metal chimney which ducts cooling air around it.

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Jan 022012
T-368C Transmitter Progress!

I’ve made some good progress on my T-368C transmitter already. The arcing problems have subsided on their own, though they may come back later. I traced down the modulator problem to a single resistor in the speech amplifier which failed open, thus removing power to the clipper tube’s plates and breaking the audio path. The transmitter is now working on CW and AM at full power into a dummy load! I also replaced another resistor in the same speech amplifier circuit, but I think it was actually OK and I just had a measurement error due to residual charge in the circuit.

There are still some kinks to work out…

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Dec 312011
T-368C: First Smoke Test

I bought a T-368C HF transmitter project back in October, 2007 for $1575.42, and finally started seriously working on it a couple months or so ago. This evening, it got its first taste of power in many years! It’s semi-alive, but needs more work:

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Dec 172011
FT-505 Pack Mount for the SCR-619

TheĀ SCR-619 radio set could be deployed in several different configurations, including vehicular and man-portable. In a man-portable configuration, the BC-1335 transceiver and CH-191 battery box would be installed on a common pack frame with an FT-505 mount. These mounts seem to be quite rare, as I’ve only found about two or three collectors who have them or have ever seen one for sale. A few months before the 2010 West Coast Military Radio Collector’s Group annual meeting, Paul Thekan kindly loaned me his FT-505 so that I could photograph it, measure it, and display it with my SCR-619 set at the meeting. I didn’t just photograph it, though… I also created a 3D CAD model of it, with thoughts of someday fabricating a reproduction.

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Oct 052010
SRI-M550 Amplified Speaker

I bought this amplified communications speaker at a military surplus swap meet. It’s a nice little powered speaker which is intended for use with manpack radio sets (particularly ones with digital data capabilities). It is powered by a 9V battery which fits in a sealed compartment at the bottom of the unit. It is housed in a rugged aluminum chassis, and has a pair of clips on the back which can be used to hang the speaker from one of the “roll bar” handles which are common on these manpack sets.


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Mar 222009
KY-38 NESTOR Voice Encryption Device (Demilitarized)


The KY-38 is the manpack variant of the NESTOR family of voice security devices. Used during the Vietnam War, this family included the KY-8 vehicular unit, the KY-28 aircraft unit, and the KY-38 manpack unit. These devices permitted secure voice communications over radio.

This particular unit has been demilitarized; that is, all of the cryptographic hardware has been removed from the unit before it was released as surplus, leaving only the case, power supply, interface circuitry, and an interesting electromechanical keying device. The battery box is also missing.

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Feb 192009
Message Book M-210

Message Book M-210 was, as far as I have been able to determine, the standard form for recording message traffic during World War 2. A great deal of rigorous procedure was necessary to reliably route message traffic, and part of that procedure involved composing messages on the standardized carbon-copy forms in Message Book 210 prior to submission to message centers for routing. The same forms were used by message centers when transcribing messages (for example, after encrypting them with Converter M-209), when receiving messages sent via radio, etc.

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Nov 082007
TBY-4 Transceiver

I bought this TBY-4 transceiver in November, 2007 for the princely sum of $26. I plan to retore it to operation, and I’ll add more information about it here… someday. In the mean time, here are some pictures.

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May 292007
AN/TRC-179 "Regency Net" HF/SSB Transmitter/Receiver

The AN/TRC-179 Force Terminal is part of the “Regency Net” system, which was a radio system fielded in the 1980s. Regency Net was designed to survive the electro-magnetic pulse (EMP) from a nuclear airburst. Thus, its members are a lot more complicated than other radio systems with similar capabilities, with lots of filtering on all electrical inputs and outputs. The set covers 2.0000 to 29.9999 MHz with LSB, USB and data modes. The Regency Net members include a frequency-hopping Electronic Counter-Countermeasures (ECCM) mode. The sets can function in single-channel mode with the ECCM card removed, and they were often deployed this way to non-military users such as FEMA.

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May 252007
US Navy Microwave Protective Clothing

This conductive mesh suit was developed to protect people who need to work in strong RF fields emitted by Naval shipboard RADAR systems. It provides a minimum of 20dB of attenuation from 200 MHz to 10 GHz, in fields up to 200 mW/cm2. A complete set also includes rubber boots and gloves, a hardhat, and cotton over-clothes which prevent arcing between electrical equipment and the conductive mesh suit.

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May 242007

Instructions for Installation of Radio Sets AN/GRC-9 or SCR-694-C in Combination with Radio Sets AN/GRC-3 to 8, AN/VRQ-1 to 3, AN/VRC-8 to 10, AN/VRC-16 to 18, AN/PRC-8 to 10, or SCR-619 in Truck, 1/4 Ton, 4×4, Utility, M38 & M38A1 (Warning: 35 meg PDF file!)


Thanks go to Ken Perkins for the scans, and Wes Knettle for passing them along to me.

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May 032006
Chinese Type 102E HF Radio Set

I bought this Chinese HF transmitter/receiver set from seller redstarradio on eBay back around March, 2005. It came as a complete new set including the manuals, spares, tools, test equipment, etc. that would normally be issued with the set, all in original packaging. It was a lot of fun to unpack a brand new complete radio set in pristine condition! The historian in me felt bad about destroying the original packaging, but I just had to play with the radio! I compromised by carefully photographing everything as I unpacked it, paying special attention to packaging methods and markings.

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