I came acros the site of IK0VVE with a wonderfull description of a MEPT. MEPT stands for Manned Experimental Propagation Transmitter and is usually very low power. He uses a crystal oscilator but I find them pretty expensive. So I Looked around the net for programmable oscillators. Those are even more expensive and in the most cases you need a microcontroller to programm them. The oscillators uses I²C for setting the frequency by setting the divider and table lookups, ..... I found on oscillator that can be set by a simple resistor : the LTC1799 by Linear Technology Overlooked one thing : it is a Surface Mounted Device (SMD) and I never soldered SMD's before. Oh well. I ordered twee free samples. Two weeks later my wife gave me a big A4 style letter. Just for two devices measuring 3,5 by 1,5 mm 🙂 I managed to solder wires to it. Without a magnifying glass. I'm so proud 🙂 At the moment it oscillates around 10.138 MHz. But it jumps around when my hand comes nearby, strange. It is just ttl level at the output. Will add the 74hc240 first before furter testing. My plan is to use my old Basic Stamp 2 as a keyer for the beacon. Stay tuned for the next article on this subject.

One Response to “Designing and building a Manned Beacon or MEPT, part 1 of many”

  1. Janne OH1SDR says:

    Cheers mate, long time no see!

    I think you might have some big troubles stabilizing the LTC1799. If you have not built oscillators before, you might want to know few basics: LC oscillator can be made really stable, VCO with over decade cannot. Especially when it doesn’t seem to have shielded inductance. Also VCO with such wide range will usually introduce terrbile amount of phase noise.

    According to LTC1799 specs, the temp drift is awfull. With just few C of temp change, you would have kHz drift at 10 MHz. You would be better of with traditional Hartley etc LC-oscillator. But I suspect that even LC-oscillator would not provide the long term stability required by the MEPT. Crystal oscillator, or programmable crystal oscillator might be the solution.

    http://www.amateurradio.org.za/SOTA.doc

    Good luck with the project!

    73 de Janne OH1SDR