Beacon Keyer Specifications


Power Supply
+9 to 15V DC unregulated at 35mA (plugpack or battery)
100mm x 100mm x 15mm (Veroboard construction) - smaller with a PCB.
Continuous duty 0C to 75C
Active Devices
Atmel AT90S4433 28 pin DIL RISC microprocessor, 78L05 regulator, three transistors (2N7000, BC547B, BC557B).
Cost to build
Approximately $US25 for all components, less printed circuit board.
Developed by ZL1BPU. Interrupt driven A-D converter and interrupt driven timing for precise signal generation. Command interpreter. Two control outputs. Reprogrammable software in FRAM. User programmable beacon message kept in EEPROM, and independently field programmable using simple tools - a PC with a terminal program or a dumb terminal (300-N-8-1). Purchase price of software is very modest.
Six 10 bit A-D channels 0 - 5V DC (0.1% accuracy). Four digital inputs suitable for switches. Sampling rate well in excess of telemetry rate. Two digital outputs suitable for switching antennas, transmitter power, external sensors or even operating frequency.
NORMAL MODE - Feld-Hell, 122.5 bps 7 x 5 dot matrix using Mosaic II 5 x 5 proportional font, single spaced
DX MODE - Feld-Hell, 7 x 10 dot matrix double spaced, and can be used with all speeds
SLO MODE - Feld-Hell, 61.25 bps single and double spaced Feld-Hell
SUPERSLO MODE - Feld-Hell, 30.625 bps. Can be combined with SLO mode for 15.3125 bps! (That's 1/8 normal speed). Very slow speeds are very sensitive and quite immune to multi-path effects. At 1/8 normal speed the bit time is 65.3 ms, longer than most multi-path timing variations. 1/4 normal speed is also very effective.
MORSE 20 - Morse code at 20 WPM, using standard weighting and spacing with one dot element of added Farnsworth spacing between characters (NORMAL mode)
MORSE 10 - Morse code at 10 WPM, as above, (SLO mode)
MORSE 5 - Morse code at 5 WPM, as above, (SUPERSLO mode)
MORSE 2.5 - Morse code at 2.5 WPM, as above, (SLO mode plus SUPERSLO mode)
Keying - Both Feld-Hell and Morse modes can be on-off keyed or FSK keyed on the AUDIO output. OOK carrier 980 Hz, FSK is 980 Hz (MARK), 1165 Hz (SPACE), 185 Hz shift. Frequencies and shifts can be changed by special request.
Morse Speeds - Morse speeds were chosen for Hell compatibility, i.e. the dot time is equal to one Hell column period. This allows the Morse to be read by eye as it is synchronous with the Hell. It also allows the Hell timing to be preserved either side of a Morse phrase. Digital (ON/OFF) and audio subcarrier (980 Hz tone or FSK) outputs are provided.
Hell Accuracy - Baud rates in Hell modes are accurate to about 0.1%, achieved using software control of the timing. The speed is adjustable in 0.1% steps during software compilation.
INHIBIT - prevents start of transmission sequence if high. Tristate CMOS input. Pulled up internally while PTT is active. Transmission can be delayed by placing a large capacitor and parallel resistor to 0V at this point, (for example about 10 uF and 10 megohm for one minute delay) or by driving the pin with a Squelch or detected audio signal. Delays can also be added within the message in 2 second increments, with or without carrier.
AUX0 ... AUX3 - General purpose digital inputs for telemetry. CMOS inputs with pullup, suitable for switches or TTL/CMOS drive.
AD0 ... AD5 - 10 bit A-D inputs, 0 - 5V DC, multiplexed. Reference is the +5V supply, provided on the input connector for ratiometric measurements.
PTT - Open drain output which pulls low 250 ms before start of transmission, and releases 250 ms after end of transmission. Will sink 100mA. Intended to drive the PTT input of most modern rigs. Protected against relay spikes. Not suited to negative voltages.
AUDIO - Modified square wave output from the microprocessor tone generator, keyed with Hell or Morse data. Consists of a moderately rounded tone 500 mV p-p at about 1 kHz, AC coupled. 3rd harmonic is -15dB, 5th is -20dB, 2nd and other harmonics -40dB or better. No DC shift during keying (output is tristate when not sending). This output is keyed by the Hell or Morse data, and can be used as a sidetone or to key an SSB transmitter, with no thump or excessive click.
DATA - Positive true Hell or Morse data. Can be used to key a QRP CW transmitter or to key an external sinewave modulator using a CMOS gate.
PD2, PD3 - Two general purpose digital outputs, 5V CMOS. The outputs default low, and revert to low on mode change or end of message. Independently turned on by $7 and $8 commands respectively. Use an external 2N7000 transistor to drive a relay or audio attenuator.
SERIAL - Commands and data for message recording are received at 300-N-8-1. Message is retransmitted at 300-N-8-1 character by character (as the message is sent by radio), terminated by <CR><LF>, which will trigger transmission of a UI frame from an appropriately set up packet radio TNC.


Copyright M. Greenman 1997-2005. All rights reserved. Contact the author before using any of this material.