The venerable Command Set

UPDATED 5/8/18
Most seasoned Hams grew up with these radios: transmitters, receivers or both.  Designed for high frequency AM Voice (mostly) or CW aircraft-to-aircraft communications during WWII, they performed the function of “command”,  hence their common name.  They could also serve as “liaison” radios for comms back to base but that function was better suited for the more powerful transmitters like the BC-375 in larger aircraft.  There is a wealth of information on the Web regarding this equipment, both WWII and more modern descriptions. The best is the series by Walt Huchins in Electric Radio magazines.

Here I will discuss my particular set and its use in the field.  The following photos shows my current CW system, A BC-696 transmitter and ARC-5 receivers.  I have owned the receivers since 1964 and long-ago modified them for 12 volt filament operation.  The transmitter was a flea-market find and it had also been previously modified for 12 volt filaments and missing the “TX Select” relay. Otherwise in good mechanical shape save for the power connector (octal).  Getting hard to find pristine un-Hammered NOS radios these days so I worked with what I had.  Command Set purists would be horrified!

The TX sits in a single TX rack, the RX’s sit in what was previously a 3 RX rack that a previous owner modified to a two-RX configuration.  As yet no shock mounts, few connectors, no Control Box etc. I figured I would work with this, the results are shown.  I build a “shelf” similar to the one found in the B-17 bomber and I added the TX-RX antenna relay with RF ammeter and the 1020 cps “beam filter” that actually works pretty well on CW with these radios.  I modified an AC supply I had previously built for my TCS system and it now powers both radio systems.

Here’s our Killer Cat supervising the construction of the Command Set system. He has learned not to wag his tail around here…..

In the photo below, The left RX is 6 – 9.1 Mc (for 40 meters), the other covers 3 – 6 Mc (for 80 meters) and the transmitter shown here is the BC-696 covering 3-6 Mc (80 meters).  I have another transmitter for 40 meters that I can just plug in to replace the 80 meter TX when I change bands, just switching the RX filament voltage over to the other receiver.  Works great. 

I have since captured an MD-7 modulator and I am planning to build another “shelf” like this one to hold the modulator and an LM-14 Freq meter as well.  Still thinking about how I will power that system…going back to a 28 Volt dynamotor to power the TX/MD-7 would take some doing although I do have a 12 volt dyno for the receivers. The “Wonderful World of Tradeoff’s”…

Still looking for suitable ARC-5 transmitters to keep everything “in the same family”.   Yes, I would prefer a pristine system with all the correct (ARC-5 or SCR-274N) parts but that will take more time – I feel that getting it on the air today is better than having it sit on a shelf in the garage forever awaiting “unobtanium parts”.  I’ll get there – just takes time.

Below is a photo of the system set up at a riverside campsite; deployed for “Vintage Field Day” sponsored by Electric Radio magazine. That’s the 80 meter transmitter on the right, waiting to be plugged in upon nightfall.

I was running the system from a Honda EX-1000 generator for AC power. It’s a good “camp” generator, starts reliably, is reasonably quiet but it radiates terrible ignition noise. (See the post on the Honda EX-1000 generator for more details). A piece of bare ground wire, tied to a rock and thrown in the river makes a good ground connection.

Command Set and GRC-109 Vintage Field Day in the mountains – N6CC

The system works pretty well if the bands aren’t too crowded, the receivers of course being fairly broad. They are quite sensitive, even with a simple wire antenna laying on the ground. I usually run either a dipole or random wire. I carry a 200 pf air variable capacitor that I can connect either in series with the antenna or in parallel with the transmitter-to ground. This “simulates a B-17 bomber antenna system”. Just tune up and adjust the variable cap for desired loading on the Pa plate meter while getting max RF antenna current. Pretty flexible, non fussy tuneup. Both TX’s key pretty cleanly although I am running regulated oscillator and screen voltages from the AC power supply.

Command Set in the field – N6CC

Military Field Day Command Set and Friends N6CC

Above: My 2006 “Vintage Military Field Day” setup on Mt. Diablo (CA). The Command Set along with some vintage friends: A GRC-109 and an RS-6 being set up for CW ops.

Below: Another shot with buddy “Army Al” and our perimeter defense force in our Forward Operating Base (FOB) waiting for breakfast to cook. Yep – it’s a cheesy photo.

Army and Navy – Vintage “Military” Field Day on the river – N6CC

I have gotten good reports from home and in the field. One can imagine an enterprising Army Air Forces radio technician lashing up a system like this from parts cannibalized from crashed aircraft. An “Improvised Advanced Base” I think they would have called it until the real gear began showing up. It’s a fun campsite radio and it gets lots of curious looks from the occasional Forest Ranger who can actually find us and check for our camp fire permits.