Optical red/IR 3mW 15kHz FM beacon

back panel front panel


Since the North East nanowave group often use FM modulation of a subcarrier, a self-powered beacon operating at 15kHz was seen as being useful (15kHz, because the current transceiver here, which included FM, had a conversation crystal to produce/detect that). A warble tone was included as internal modulation of the sub-carrier, but this can be switched out to allow external modulation. At this point, no pre-emphasis is provided.

FM beacon circuit

The internal re-chargeable PP3 should draw 20mA from a 12v charger. A KF50 5v regulator was used because it was to hand and has both low quiescent current/low  voltage drop-out characteristics. 555's were used used because - well, they are cheap perfect for the job(s)!. A little pcb was etched on which to house the circuitry.

box innards