Progress on the new 481THz beacon TX

Today I made a start on the new optical QRSS3 beacon. This time, the circuit has some improvements: a continuous sub-carrier option and a choice of audio subcarrier frequency. Also, the frequencies are now derived from an HF crystal so stability will be excellent.

The part completed new 481THz QRSS3 beacon

The oscillator/divider is a 4060 IC and this is enabled by the output of a K1EL keyer IC programmed to send "XBM" in QRSS3.  The square wave output from the 4060 feeds the gate of an IRF510 FET which switches the 280000mcd, 10mm diameter, LED in 100mm optics.

A possible refinement will be to pull the crystal using the keyer output signal so that I have a continuous carrier but FSK keyed. This would mean I'd always have a signal to aim at, but with FSK QRSS3 CW on it. I'm not sure how much pull I'd get after dividing down if I just changed one of the capacitors loading the crystal. I shall have to experiment and see. Even as little as 5Hz would be enough, but that would need 50kHz shift at crystal frequency! A better way may be to key the frequency out of the 4060, so mark is, say 550Hz and space 1100Hz or vice versa. Plenty to try tomorrow.

Stable audio frequency tone generation (for VLF QRSS)

Next week I want to try QRSS3 with my earth mode VLF system to extend the range. As in the test this week,  Spectran software will be used my PC to filter and decode it. For a stable source I'll use a crystal and divide this down to sub-9kHz. Looking around for a suitable simple circuit I found G4HCL's very simple 1750Hz toneburst circuit which uses a 455kHz ceramic resonator (pulled slightly) and a 4060 IC as a divide by 256. With a crystal instead of the ceramic oscillator this should be perfect if followed by some filtering to produce a decent sine wave output. See M1GUR's page for more details.