A.R.C. Type 12 VHF AM Aircraft System

UPDATED 7/10/21
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 and into the 1960’s. These are not the AN/ARC-12 sets they are sometimes confused with, nor are they AN/ARC-60 sets, see below.

In military service, it was primarily used in early helicopters, some trainers, liaison aircraft and even in high altitude manned balloon launches (Projects Man High/Excelsior).  They were also installed in some models of the U-2 aircraft. (Reference 62). The U-2 installation is interesting, probably selected as the aircraft was designed to be as light weight as possible. The A.R.C. Type 12 would fit the bill and do the job.

Built by Aircraft Radio Corporation (A.R.C. in this context), 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. Below: My Receiver is a model R-19 (on the right), the Transmitter is a T-13A.

The military nomenclature for the T-13A transmitter in 14 VDC configuration is the T-363/ARC. The R-19 receiver in 14 VDC configuration is the R-507/ARC. My R-19 (labeled) receiver carries a green U.S. Navy acceptance stamp on the front panel. (However it is not labeled as an R-507/ARC).  28 volt transmitters/receivers are T-364/ARC and R-508/ARC respectively (Reference 56).

As procured for military service the “Type 12” components might nominally have carried the military model number designation tag although there are exceptions as in my R-19 receiver below.  The equipment itself appears to be otherwise identical. TM 11-525-10 lists the “ARC Type 12” components with their corresponding JAN A/N numerical designations, (Reference 111).

A related, interesting radio set used in the military is the UHF-only* AN/ARC-60 set. That set operated on the lower part (228-258 mc) of the UHF military band.

MIL-HDBK-161-A /TM 11-487-A-1 describes the AN/ARC-60 as consisting of the CV-431/AR UHF transverter, R-508/ARC receiver, a control head, antenna, junction box and associated accessories.   * Reference 110.

Note that the VHF A.R.C. Type 12 is a different radio set series than the UHF AN/ARC-60 set although they utilized the same VHF receiver and D-10A Dynamotor.  As in the Type 12 set the D-10A powers the UHF transverter and receiver.

The transverter converted the incoming UHF antenna signals on 228-258 mc down to 118-148 mc VHF for the receiver. The transverter also included a 0.5 watt crystal controlled UHF transmitter using crystals for operation between 228 and 258 mc. TM11-5821-205-12 O/M manual applies.

Above: The A.R.C. Type 12 utilizing the R-19 and T-13A VHF components.

Also see the Radio News section for information on performance in the field on 2 meters. Radio News

ARC Type 12 VHF AM set mobile N6CC

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.  (There are at least 28 different system control panels available for this versatile, modular set.) 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.

The crystal controlled transmitter used unique crystals (A.R.C. Part Number 14958). The crystals can be at either 1/12 or 1/18 the operating frequency; the multiplier stage tuning can accommodate either multiplier. The A.R.C. crystals have the same 1/2″ pin spacing as the FT-243’s but their pins are slightly bigger in diameter than FT-243’s. FT-243 crystals will work in the transmitter but require small shims in the crystal sockets to accommodate the smaller pins.

I used an FT-243 crystal on 8025 kc to try to put it on 144.450 mc. (18X) This FT-243 required DIY pin adapter shims. In the stock circuit, it transmitted at 144.437 mc. So I brought the otherwise grounded pin of the crystal to chassis ground via a parallel combination of a 20 pf silver mica and a 2.5-23 pf ceramic variable cap. I can tweak it right to 144.450 MC at the antenna and it has been working fine.

ARC Type 12 VHF AM Command Set N6CC

Above: Ready for operations in your Bird Dog.

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 14 volt D-10A Dyno from my buddy. (There is also a 28 VDC input dyno available.) 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….

Here’s the schematic “as built”.  Lab notebook page – please excuse the informality.  Probably not nearly enough windings to saturate the core but I had to work with the space available on the pot core bobbin.

A.R.C. Type 12 Solid State DIY Dynamotor

ARC Type 12 Solid State Dynamotor

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 Off The Beaten Path.

ARC-Type 12 in the Field

ARC-Type 12 in the Field

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 pdf writeup on the Web, Reference 56.

Update:  I have received several requests for a “systems interconnect” diagram.  This is what I did, based largely on Mike Tauson’s article.  Apologies for the poor notebook photo.

N6CC A.R.C. Type 12 System Interconnects

Do a Search for: A Users Guide to Aircraft Radio Corporation Receivers. Thanks Mike, your work carries on.

Update:  Another excellent site is Ray Robinson’s on the Type 12 equipment.  It includes detailed component and interconnect schematics.  Take a look: https://www.tuberadio.com/robinson/museum/ARC-60/