A Versatile Automatic Keyer From Surplus

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Numerous amateur applications exist for an automatic CW keyer that will, on activation, send a predetermined transmission at a preset rate of speed. Just such a device was developed for use aboard military aircraft and was designed to automatically transmit a distress message from the normal aircraft transmitter. The complete equipment is nomen-clatured Control Keyer Group, AN/ARA-26, and consists of Keyer, KY-65/ARA-26, and two types of remote switching stations. These units have recently been declared obsolete and have been released through MARS channels. In the normal progression of such matters, they should be available through surplus dealers in the immediate future.*

The keyer is a motor driven, code disk device that is designed to turn on the aircraft transmitter, channel it to the distress frequency

Roy E. Menberg, W4WKM 3f6 Stratford Avenue Fairfax» Virginia and transmit the signals set up on the code disks. As supplied, two metal disks send SOS and bearing dashes and a third disk can be set up in the field to send the aircraft identification number. These blank disks are made of notched plastic and any desired CW message, within the capacity of the disk, may be formed by breaking out notched teeth. Two spare blank disks and a special setup tool are secured inside the cover of the keyer. The photographs show interior and exterior views of the keyer as supplied. The schematic of the unmodified unit is shown in Figure 1.

Several approaches to amateur utilization of this equipment are practical and the one selected will depend on the users requirements. Three conversions are covered in this article and they vary in complexity with their intended application. The first is very simple and

Fig. L Schematic diagram of KY-65/ARA-26 Keyer,

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with precision made tnit»rnatianut €rtisitiis

Interior of unmodified ARA-26 keyer.

its primary virtue is that it plugs in the wall and sends CW signals.. The second is a deluxe automatic caller and the last is a line break operated keyer to provide automatic transmission of CW identification following radio teletype transmissions.

Each modification consists of both mechanical and electrical work. In common with most airborne equipment, a source of dc is required to operate the PM field motor and the relays. This requirement is met by the use of a slightly unorthodox but very economical, line operated, silicon rectifier supply* The mechanical work consists of replacing the metal code disks with the plastic blanks and, in the two more complex versions, rework of the disk sequencing cams and their associated contacts. This work may be accomplished with ordinary hand tools and is not particularly difficult or time consuming.

The first step is to strip the chassis and clean up the parts which will be used in the conversion. Retain all hardware for assembly of the completed keyer. loosen the main drive unit by removing the four screws from the bottom of the case and the single screw that secures the assembly to the front panel. Locate the key contact leads and follow them to where they attach to other components. Cut these leads, leaving them as long as possible. Follow the same procedure with the yellow motor lead. Clip the blue motor lead near the housing, slip a piece of sleeving over this lead and tie to the yellow lead. This is a speed governor contact that will not be used. Unsolder the two blue leads from one end of R-101 and clean up this terminal, leaving the resistor in place with the white motor lead attached. Unsolder the leads from the homing switch, S-101, and clean up the terminals. Remove and discard the delay mechanism switch, S-102, along with its actuating lever. At the same time, remove and discard the time delay adjust ratchet spring which is mounted alongside the microswitch lever-

Remove the keying drive assembly and ex amine carefully. A little time devoted to study of the mechanism will prevent many problems later on- The key disks are driven by a small PM field dc motor through a gear train, '¡'wo friction clutches and a time delay mechanism were provided but they can not be utilized in this conversion since the timing gear ratio is not usefully related to that of the keyer drive-Keying is accomplished by three code disks fixed to a common shaft. These disks are mada with teeth and spaces around their perimeter and are arranged to actuate the keying assembly. This assembly has three sets of contacts in parallel, each operated by a blade which contacts the association disk at all times. Only one switch operates at any given time, due to cam follower levers which always hold twro of the key switch contacts open. The cam levers are operated by a set of sequence cams mounted on a common shaft along with an actuating cam which switches off the drive motor upon completion of cach cycle of operation.

:'he cam shaft is rotated by a geneva star, which is in turn actuated by a pin permanently attached to the SOS disk- Each rotation of the keying disk shaft advances the cam shaft 1/7 of a revolution and, upon completion of one revolution, switches off the drive motor-

Replacement of the metal with plastic keying disks is necessary in each conversion and may be accomplished at this time. Remove the hairpin retaining clip and the knurled nut from the end of the code disk shaft, Loosen the set screw on the outermost disk spacer and remove the complete disk assembly from the shaft. Remove the center disk and discard it.

Fig* 2, Simplified Conversion.

CI—25 mid, 50 wv dc electrolytic cond. CRl — oQQ ma silicon rect.. Sarkes-Tarzian M-GOG M-500

J1—Standard phone jack. Switchcraft C-H PI—Replacement ac line cord R1—50 ohm, 25 w variable wirewound resistor SI- SFST normally open mom. contact push button switch

Three digit parts numbers are original components

Fig* 2, Simplified Conversion.

CI—25 mid, 50 wv dc electrolytic cond. CRl — oQQ ma silicon rect.. Sarkes-Tarzian M-GOG M-500

J1—Standard phone jack. Switchcraft C-H PI—Replacement ac line cord R1—50 ohm, 25 w variable wirewound resistor SI- SFST normally open mom. contact push button switch

Three digit parts numbers are original components

Next, remove the center spacer and the SOS disk. Since the geneva star actuating pin is attached to the SOS disk is must be retained. File the code teeth flush with the inner perimeter of the disk and replace it on the sleeve assembly. Install a plastic disk flush against it. File the center spacer to a thickness of Vs" and install in its original position. Install another plastic disk and the outermost spacer.

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