Some notes on the A.R.C. “Type 12″ VHF AM radio system used on both private and some US military aircraft in the 1950’s.
In military service they would have carried the military model number designations although the equipment itself appears to be identical.
In military service, it was primarily used in early helicopters, Liaison aircraft and even in high altitude manned balloon launches (Projects Man High/Excelsior). Built by Aircraft Radio Corporation, this is a fun little set that works great on 2 meters AM with an earsplitting 2 watts output in Ham radio service. Very “high fidelity” Super Het receiver that is tunable from 118-148 MC including of course the current aircraft freqs. The Receiver is a model R-19 (on the right), the Transmitter is a T-13A.
The military nomenclature for the T-13A transmitter in 12 VDC configuration is the T-363/ARC. The R-19 receiver in 12 VDC configuration is the R-507/ARC.
An interesting configuration as used in the military is the UHF AN/ARC-60 set. That enabled the aircraft to communicate on part of the UHF military band (228-258 mc) by integrating the R-508/ARC receiver with the CV-431/AR transverter and associated systems. The transverter converted the UHF antenna signals down to VHF for the receiver and it also contained a UHF transmitter. TM11-5821-205-12 O/M manual applies.
Also see the Radio News section for information on performance in the field on 2 meters.
Above: The A.R.C. Type 12 set sitting on the seat for some VHF mobile range tests from Mt Diablo. It was driving a 5/8 wave vertical whip on 144.450 Mc to two other stations running USMC MAW sets in a portable configuration. One in San Francisco, the other at the Suisun Mothball fleet across the river. When the APRS repeaters were not transmitting, good comms over the 25 and 15 mile LOS paths. APRS digital signals completely obliterated the receivers when they came on 144.390 Mc. (All VHF signals are strong up here – the dashboard altimeter indicates my elevation here was 2760 feet AMSL.) Too bad, otherwise a very viable radio network. And they sound great as well! As expected, the receivers slope-detect FM signals quite well too.
I am using a correct receiver panel from an aircraft that provides the tuning dial and “sensitivity” control. I don’t have a transmitter panel so I built a temporary, functional replacement shown here. I have since added a second toggle switch so I can turn off the transmitter filaments when just receiving – to save battery power when necessary. This panel includes a switch to select any of 6 installed transmit crystals although I currently have only one – 144.450 MC. That 20 Amp fuse may sound excessive for a 12 VDC system – it is, but is needed to handle the startup surge of the dyno. It is the correct rating for an aircraft-installed 12 volt system.
Above: Ready for operations in your Bird Dog. These sets are designed for quick conversion between 12 or 24 volt operation, depending upon the aircraft type. It is a simple jumper move to change the receivers and transmitters to match the primary power supply. The receiver is very sensitive and the transmitter sounds great with the issued RS-38 Mic (a T-17 works well also). The later production receivers included an effective front-panel squelch control, mine lacks it.
In the above photo I have a dynamotor installed on the receiver which is actually from an HF Command Set receiver. Its output is only 220 VDC but it works OK. I have since gotten the correct D-10A Dyno from my buddy. I am probably going to install this set in the Bronco using the remote control panels and the spline shaft for receiver tuning. Just need to find a place for it although it is kind of handy to use as a portable as well. Fun radio, sounds great.
Before I obtained the D-10A dynamotor I had designed and built a solid state dynamotor replacement that plugs into the rear of the receiver. See below. It powers the TX and RX as the original dyno did with +250 VDC. Works great….Much easier on the ‘ol battery during extended Ops….
I have a few local buddies in the San Francisco bay area that operate 2 meter AM gear, including the USMC MAW transceivers. Those are a late- WW2 design and they work pretty well once you get them tuned up. Get your buddies on 2 meters AM in your area – it’s lots of fun.
Above: Powered by a 12 Volt garden tractor battery (and hence the solid-state dyno) on a recent field op up on the mountain. Note the additional transmitter filament switch on the TX control panel. Good AM comms with a buddy down in the valley. That J-45 CW key was connected to the adjacent TRC-77 HF-CW set also along for this Op.
If your buddies don’t show up on frequency with their AM sets, try listening to the VHF aircraft frequencies from 118 – 136 Mc. Lots of activity and you can get a good “receiver check” that way. Another interesting trick is to listen to commercial A/C talking with Air Traffic Control; “United Airlines Flight XYZ climbing to Flight Level 36″….. Then look up United Airlines Flight XYZ on flightaware.com for a tracking map with their actual locations plotted. You can get an instant “range check” on your system by seeing how far away they are at the time.
For further details on the A.R.C. Type 12 equipment, see Mike Tauson’s (K3MXO SK) excellent summary writeup, Reference 56. Thanks Mike, your work carries on.