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Fix. i Schematic for the Cubic-inch Keyer.

It would have to be small enough to fit into the rig: I didn't warn any more hoxes and cables to worry about. It needed to be simple enough to complete quickly since I have enough grandiose -and unfinished—projects around. And it would have to drau low current to minimize the load on the station batten power supply. Alter searching through literature dealing with keyer designs, I settled on the keyer ICs produced by Curtis Electro Devices. These 16- and 18-pin DIP packages handle nearly all of the keyer functions on the single chip. They are CMOS and draw almost no current. The> feature sell-completing dots, dashes, and spaces; built-in s id el one generator, weight control, key debouncing, and good if immunity. Both single-lever and iambic ¿squeeze) paddies can be used with them They sounded perfect.

Putting 4m the Squeeze

A quick call to Curtis got the differences between the various versions ot the keyer chips sorted out. They produce 4 basic keyer ICs The 8044M is an 18-pin DIP basic keyer with provisions to drive a speed meter directly The 8044R keyer chip operates with a special squeeze key mode. An cvtra element opposite the last one sent is sem when the squee/.e le\er is released. The 8iU4BM has horh ot ihcse features, and ihc K044 has nei-then Since I have never used the special squeeze technique and had neither the need or the space for a speed meter, I chose the 8044. I placed the order during the same phone call and three days later the chip arrived After ¡.i feu minutes of peering at the documentation and sample ke>er schematic supplied, I dragged out the CSC Protoboard and sat down in front of the junkbox to do some breadboarding. The circuit shown evolved.

Looking at the left side of the keyer schematic. pins 2 and 7 are the connections to the keyer paddle . The R and C networks associated with pins 3 and 6 provide the timing for the debounce circuitry. The element timing network has its resistor across pins K and 9 and the associated capacitor across pins 9 and 10 The capacitor should be a stable type such as mylar* dielectric, Curtis does not recommend ihe use of disk ceramics here. The application note suggested that C i be a Q.15uf„ and Ri and R2 be 500k and 100k. respectively I couldn t find a 0J5uf mylar

Radio Experimenter

Photo B. The Keyerand jack instatL

capacitor. no I used Kevin's firs! law of homebrewing; 4' [ i you don't have the right size, use what you have and adjust the part connected to it accordingly!"

I used a f).22uf m\ lar capacitor at CI. A 150k resistor at R2 worked well with i! on ihe breadboard to give me a comfortable speed range. High-speed CW operators might want to reduce R2 back to 100k, or lower CI to the recommended value 15uf) to shift the speed range more toward the lop end. \ mounted the speed control pot Rt on the circuit board instead of on the outside of the rig. I find that I operate at pretty much (he same speed most of the time, and if J need lo slow down I just increase the spacing between the characters pnnJucmg a Fams worth-type spacing. It would be a simple matter to run leads to a pot mounted on the rcar of the HW-S's chassis for external adjustment.

Continuing up the right side of the chip, pins 11 -) 3 are associated with the timing and drive for the sidetone generator in the chip. Since the HW-8 has its own sidetone, these pins are not used and so left open Pin 14 is the output from the keyer. It swings positive when the keyer is making an element and rests at ground during the spaces. The HW S need* to have its key line pulled low to send an element, so 01 is used to invert the signal and provide sufficient current sink capability. The base drive is limited by R5. This arrangement should work with almost any battery-powered rig that has a positive voltage that must be pulled down to key, with currents up to about 50 mA Transmitters in which all of the current in the final amplifier runs through, the key line might need a huskier transistor at Q1 and some more base drive♦

Pin 15 is ihe manual key input and also the weight control pin. The rig a I read) has provisions for a straight key. and a 1:1:3 weigh ratio is fine by me. so in the interests of simplicity, this input is unused. You can'l loudly ignore it. however: it must be pulled

On the inside rear panel of the HW-8

up to Ydd through MKIk. I forgot and the chip started breaking into spurious oscillations after a lew seconds each time it was turned on unt]l J put the resistor in.

Pin 16 ;s Vdd. the positive supply input and pin 1 is Vss, or ground. A 22uf capacitor bypasses the chip, i he zener diode is used to drop the 12-W> volt supply at the radio to within the 10 volt operating range of ihe 8044. 1 looked at several different ways of developing a fixed, stable voltage source. Unfortunately ihey all used more current by themselves than the entire keyer draws! Even though the supply voltage to the keyer will \ary as the batter> input to the HW-8 sags, 1 have not riot iced any real problem yet. 1 tested the keyer radio combination over a 16 volt range. A slighi slowdown at the lower voltage was just noticeable, but the HW -8 was sounding rather sickly at that point anyway, The circuit only draws 50 microamperes most of the time, and just about 3 mil-(¡amperes when the elements are being sent and the base of Q[ is being driven* A nine-volt battery would power it for a long time. If I had onl> a batiery clamp for a transistor battery instead of the zener on hand, the keyer might well have featured a "self-contained" power supply!

The Final Version

After bread boarding the circuit and adjusting component values> it was time to build the final version. I used point-to-point wiring on a small piece of perforated yectorboard. The fC was socketed as recommended by Curtis, and 1 had to drill 3 holes in the board to mount the potentiometer. The resistors were mounted vertically to conserve board space. I made no attempt to seriously miniaturize ihe unit, but (he choice of a physically smaller capacitor and potentiometer and 1 '8-Watt resistors would probably allow the unit to he shrunk to half its current si/c. As it stands now. ihe keyer measures about 1.50 x 1.00 x .750 inches, or just a bit

Phi ji< * C. WB2EMS and the Cubic-tot h Keyer in tin field. .

more than a cubic inch, hence the name.

I installed the keyer in the HW-8 along the rear of the cabinet by using a smgle post and some 4-40 hardw are to support it off the rear wall. A 3-terminal jack was installed for the paddle to plug into just above the standard ke> jack. Power was taken from the power sw itch on the front panel and the key line and ground were taken from the original key jack. The unit checked out fine when first powered up. I he onl> quirk is has is that it always sends a single dash a^ Noon as it is turned on. This could be avoided by connecting the keyer power line to the battery side of the power sw itch instead of the radio ^ide. That way. whenever the batters is connected + the keyer would power up- In that ease, if the HW 8 was not uirncd on at the lime, the dash sent would have no effect I prefer to have the power switch turn off everything, so I live with the dash.

Adding the keyer to the little rig has made operating it a real pleasure. Using a paddle works out just fine when camping, and I found a lightweight second paddle to dedicate to ihe task. The first field test was on a north country fishing trip. The rig was packed up on the motorcycle and survived the bouncing ride and a flat tire to perform splendidly at a rented cabm for several days until the batter} ran down. I have even taker lo using at the home station for casual contacts instead of the "Big Rig," propping it up on the arm of my easy chair along w ith the Bencher paddle and running a piece of coax over to ihe station antennas.

My goal was to build a simple keyer w ith a low current drain of small si/e and with good performance. Wjiha maximum drain of 3 milliamperes, a size of just over a cubic inch, and performance tqual to ¡he ke>er in the "Big Rig,1" 1 feet the goals were accomplished, There's only one problem. Since they enjoy ed playing with ii so much on the fishing trip, the HW-8 and built-in keyer are now on loan to my friends, KB- VTZ and her OM KB2AUA, Oh we 11--they gave me my straight key back! 73! ¡BsJ

John K. Nulh KA3AAQ 2934 Banks St. HarrisburgPA 17103

Repeater Controller

PC Board

How to get back on the air again quickly if your microprocessor-controlled repeater dies.

In this nnxiern day of microprocessor-controlled radios. il"s rare to tlnd a repeater that doesn't speak to you in its synthesized voice. Many repeater clubs have paid thousands of dollars for these machines thai can speak hundreds of words in maJe or female voices. They do everything under the sun except fix themselves or detect a dying memory backup battery. Now, here's how to get back on the air quickly with an inexpensive repeater controller board when your repeater is on the frit2.

As useful as these silicon-based brains have become, they still have one major drawbac k: Once one dies, the repeater remains dead until someone skilled enough can fix it. his can render a busy repeater useless for days or weeks until the controller can be reinstalled and reprogrammed.

Constructing the Hoard

An inexpensive repeater controller bo^rd can now be built in Li few hours with off-the-shelf pans and kept for emergencies. It does noi have an autopatch or IDer, nor is it run by a microprocessor, but ii will get you on the air again quickly.

My repeater controller board is a combination of several basic circuits containing the standard hold-over timer (HOT) and time-out timer (TOT), it has the option of key ing up a transmitter b\ VOX. When using VOX. au dio from the receiver's audio stag^ or speaker brings up the transmitter. Il is not necessary to open a radio and dig into its squelch circuitry to fmd a point that operates a carrier-operated relay {COR}.

The heart of the circuit is a combination of two 555 timer ICs, one used as ihe HQ^ and the other the TOT , and a CMOS 4001 quad NOR gate which performs a variety of functions. I chose the 4001 because it has tour separate NOR gates—each gate with two inputs—which can accommodate one or two separate conditions to activate the repeater (such as COR and PL).

Pins 13 and 12 of NOR gate A must both be at a logic low , making pm 11 high lo activate ihe repeater. I'll call pin 13 the COR input and pin 12 the VOX/PL/Burst input. DIP switch 1 is set OFF (or open) if ihe COR input is used, and DTP switch 2 is set OFF (or open) if the VOX/PL/Burst input is used. If not using one of the inputs, setting its respective DIP switch to ON (or closed) will pull the gale low and enables it, allow ;ng transmitter keying information to activate the other gate input.

The COR gatcr if used, can be pulled low by a logic low through CR-K or b> 2 volts or more to the base of Q-l which inverts ii to a low. The VOX/PL Burst gate can be pulled low through CR-2, or by 2 volts or more through CR-2 to the base of Q-2 which inverts it to a low;. Diodes CR^t and 5 are used for different inputs to Q-2 for several functions, CR-3 and CR-4 are used if a "Tone Burst" is needed to initiate the repeater after the TO F lias timed out, either by actual carrier timeout or non-use, CR-5 is used when using VOX iCR-3 and 4 must be removed) and rectifies the audio from the LM-386 fused as the VOX driver) to turn on Q-2(

Can Repeater SchematicSkema Cor Repeater

Photo A Repeater controller PC hoard with 2 ¡COM 4A Ts in a portable repeater package, mounted on an aluminum plate.

Photo B. Repeater controller PC board attaches to an ICOM HT with a rubber hand for fast emergency repeater use.

4001 555 Repeater

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Proper conditions of pins 12 and 13 make the gate's output, pin 11 - assume a high logic state. Subsequently, the logic high goes to the base of transistor Q-3. which pulK down the liming capacitor of the HOT 555 timer to a low logic state, The timer's output ai pin 3 then turns on as long as the output of NOR "A" gate is high. The time delay* usually about 3 seconds, es set using C-6 and R-13. The timer's output turns on transistor Q^ and keys the transmitter.

The output of NOR gate "A". pin 11, also affects the input ol NOR gate B"\ This gate now acts as an inverter and its output ai pin 3 goes low to discharges capacitor C-11. As this capacitor discharges NOR "C" input pins 5 and 6 momentarily assume a low logic state. The gate inputs stay low until C-l 1 is again charged through R-14, During this low state the gate's output., pin 4. goes high lor several milliseconds and turns on Q4.

Transistor Q-4 then discharges the timing capacitor ol the i O IT, C-JOf and causes the TOT 555 output pin 3 to go high. This output is connected to pm 4 (RESET) ol the HOT 555. enabling tt to key the transmitter. The TOT resets to its maximum time (typically 90 seconds to 3 minutes) even lime the output of NOR gate *\V% goes high (i.e., every time a carrier is initially detected) If the beginning of a carrier is not detected within the allotted time envelope of the TOT, its output will go low. The HOT s reset pin will assume a tow logic state thereby turning off the transmitter, In the event of timeout a momentary break in the repeater user s transmission will re-enable the repeater.

Note the unusual wiring configuration of both 555 limers. Pins 2 (trigger) and 6 (discharge) are tied together, and pin 7

(threshold) is not used. Also note that both timing capacitors, C-7 in the HOT and C-10 in the TOT. are connected to the working voltage fVcc) bus and NOT ground. This allows U* to use the 555s as "Missing Pulse Detectors" without using additional components shown in manufacturers' information manuals. The same timing formula is still used,

where the timing in seconds = capacitance in mF times resistance in megohms times l.L Use only high quality tantalum capacitors with values up to 100 uF. The timing resistors should not exceed resistance values over 10 M.

If a TOT is not desired, do not install the TOT 555 on the PC board, or use iC sockets and simply remove it. The HOT will work as long as its pin reset pin, 4. is held high. This pin is internally pulled high, but good design practices say it should be tied high externally to the + supply line.

The LM-386 is a general purpose 400 mW audio amp requiring a minimum ot external components. It can be used for a variety of applications: A VOX driver. a line driver, an amplifier to drive a smal! speaker, and as an audio preamp for some transmitters requiring amplified mikes. Pins I and 8 of the LM-386 determine its gain If the two pins arc not used, the voltage gain is about 22. If a capacitor (any value of 2.2 to 10 uF> is connected ro these two pins, the voltage gain is ahout 200. For our purposes we usually will not need the extra capacitor.

The LM-386 will operate anywhere from 5 to 12 volts; be certain not to subject it to more than 15 volts. The output of the LM-386 is pin 1 i of the edge connector. If using the LM-

386 as a VOX driver, Í recommend using a in to 12 volt working voltage. This wilt produce peak voltages high enough to turn on Q-2 after being rectified b> díode CR-4. Also, if using VOX. make sure there is a load on the LM-386 output. If a loudspeaker is not needed, the output MUST he terminated with R-6. a lü-Ohm resistor. If the output is not terminated, C-17 will charge high enough to keep Q-2 turned on.

Assembly and Testing

The Repeater Controller can be assembled on small, single-sided PC hoard with a standard E5-pinh .156spacing edge connector for easy installation. There are several t^pes of switches available for the power and repeal off/test switch. If not needed, simply place jumpers in the proper holes. The repeat/off test switch can be vertically mounted, or, if using the board in a "card cage", can be a W-degree ty pe to make it accessible from the backplane Í designed the PC board to accommodate switches and eliminate the need for an additional control panel.

There are three jumpers required on the board: Each 555 requires a jumper on the solder side of ihe PC board between pins 2 and 6 (JUMP-1 and JUMP-2). Use inflated wire or sleeving, JUMP-3 is on the component side of the board and connects the LM-386 to the Vcc line.

The voltage regulator is only required for input voltages over i 3 volts, Except for using VOX, all circuits will work equally well an>-Where from 5 to 12 volts, if using VOX. the working voltage should be from 9 to 13 volts to dcri\e a higher peak output ^alue to be rectified and turn on Q-2.

i he 400] quad NOR gate has an unused spare gate which can be used for custom

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