The SCR-274N “Command Sets” were installed on numerous WW II era aircraft including the B-17 Flying Fortress and the B-29 Superfortress. These radios were used for short range plane-to-plane and plane-to-ground communications.
Dave Germeyer W3BJG informs me that the ARC-5 (Naval version of these radios) were used on the WV-2 Lockheed Constellations that he crewed. The WV-2 Airborne Early Warning aircraft is the Naval variant of the Air Force EC-121 Warning Star and entered service in 1954.
My introduction to using Command Sets was in the middle of 2012 when I acquired a a US Army Signal Corp BC-454-B receiver and a Navy T-19 transmitter, both covering the 80M band. After working on the radios and building the required power supplies, I got the pair on the air for Straight Key Night at the end of 2012. Here's my first setup:
My very first QSO using Command Sets was with my good friend Ken N3CU at 0057Z on 31 Dec 2012.
During Straight Key Night 2012 I worked Bill KA8VIT onboard the WW II Submarine USS COD docked in Cleveland OH . Bill was kind enough to record the QSO! Listen here! I also had a nice ARC-5 to ARC-5 QSO with Chris AJ1G!
Well, I was hooked! I decided I wanted to build a complete SCR-274N system. Acquisitions and restorations started in January 2013. I had my setup on the air for the first time on September 23, 2013 (just) in time for the Fall 2013 Classic Exchange (CX) contest, and I had a blast on 40M and 80M CW. Here's the setup back then:
I'm getting 25W out on 40M and about 40W out on 80M. My antenna is an HF-2V ground mounted vertical with 32 radials. The radios feed the antenna through a series capacitor and a 4:1 UNUN. On 80M the capacitor is about 200 pF and on 40m it is about 67 pF.
I was worried about making any QSOs, and was delighted when I maded 15 QSOs on 40M and 17 QSOs on 80M.
States worked on 40M: MA, NJ, NC, MI, NY, OH VA, PA, WA
States worked on 80M: MI, NJ, NC, OH, PA, VA, MO, WI, and VE3.
Here's my SCR-274N system as it is today (November 2015):
The receivers as well as the transmitters can be powered by their dynamotors. Due to the noise (and heat in the summer - my shack is not air conditioned.....) I run everything off of power supplies.
The bottom shelf of the rack contains two transmitters on the left and three receivers on the right.
The transmitters are a BC-459-A (7.0 – 9.1 Mc.) and BC-696-A (3.0 – 4.0 Mc.).
The receivers are a BC-455-B (6.0 – 9.1 Mc.), BC-453-B (190 Kc to 550 Kc), and a BC-454-B (3.0 – 6.0 Mc.). The BC-453 is a Navigation Beacon receiver.
Notice the white tape on the receiver dials. These signify 7.040 to 7.060 Mc. and 3.540 to 3.560 Mc.; each a 20 Kc. inverval represented by just under 1/8 of an inch on the dial! On top of that, the selectivity is in excess of 10 Kc, so you'll always be hearing multiple tones from different CW signals and you have to be able to concentrate on the one you're working - your "Cerebral Filter" needs to be in top shape!
The top of the rack contains, starting from the left, the BC-442-A antenna relay (containing an RF Ammeter), and an antenna tuner & monitoring box. The gray panel contains (top) the BC-451-A transmitter control box, and (bottom) the BC-450-A receiver control box. Behind the gray panel is the BC-456 Modulator.
While a straight key can be plugged into a jack in the bottom of the BC-451 transmitter control box, the flat button on top of the box is the "built in key"!
The antenna tuner contains a 4:1 UNUN in series with an old Hallicrafters HT-37 tuning capacitor. The capacitor provides the nominal 50 pF on 40M and 200 pF on 80M.
The bottom meter on the "monitoring box" displays plate current. The three position switch in the center allows me to view plate, screen, or oscillator voltage on the top meter. This handy little unit is well worth the time to build -- it is indispensible in troubleshooting a transmitter problem in the rack!
The little black box between the "monitoring box" and the BC-456 modulator is just a switch that allows me to select which of the receivers gets high voltage. Each receiver has a DM-32 base on it that connects to the switch which connects to an HP-23 power supply via a dropping resistor (actually a pot). I adjust the pot to bring the receiver HV down to about 190V. 28V To the receivers is inserted in the standard way, being injected into the FT-220A rack and then on to the BC-450 receiver control box.
550V HV For the transmitter is inserted into the two DM-33 Dynamotor pins on the BC-456 Modulator. 28V is inserted normally into the BC-456 modulator which then goes to the BC-451.
"Kerchunking" is a word that suits Command Sets! When a transmitter is selected via the BC-451, two relays in the selected transmitter will close, and if the other was previously selected the two relays in it will open. You get a rather loud "Kerchunk" as you switch between transmitters.
Each time you close the straight key, two relays will close. One is located in the BC-456 and supplies HV to the transmitter, and the other is in the BC-442 antenna (TR) relay unit! In case that wasn't clear, these two relays close and open for dot or dash you send!
I do not use the receiver rack’s mute line as I need a side tone for CW, so I’m actively changing the gain control on the receiver control box when transmitting or receiving. It works pretty well...and headphones are a must!
Stay tuned for updates!
80M: 8 QSOs, OH, PA, MN, FL, WI, GA, IA, VA
40M: 5 QSOs, NC, ONT, OH, KY, FL
TX: T-22 (40M), T-19 (80M)
RX: Hallicrafters SX-101A
Ant: Vertical
Key: J-38
ARC-5 (T-19/T-22) Tuning Notes
ARC-5 (T-19/T-22) Tuning Notes
Copyright (c) Mark S. Bell 2013 - 2017