Sunday, July 28, 2013

Amateur Radio Home Brew group - "making frequency"

The theme of today's ARNSW Home Brew group meeting was "making frequency" and we had a diverse range of approaches on show. It's fascinating how technology has moved from crystal oscillators, to phase locked loops to computer controlled DDS in a few short years.

John, VK2ASU, demonstrated how to raise the frequency of a quartz crystal by carefully grinding it to make it thinner.

This is done first with 600 grade sand paper and later directly on a glass sheet using a fine compound such as toothpaste.

The evolution of a flexible Atmel processor controlled DDS based oscillator was shown, starting with the prototype and ending with a very nicely boxed up unit with plenty of space to house perhaps an entire transceiver at a later date.

Here's the prototype:

Here's how the completed project turned out:

Stephen, VK2BLQ showed a "Huff and Puff" stabilised oscillator he had constructed.

It's amazing to me how even non-computer nerds are getting in to embedded processors for ham radio applications these days. Mostly the Arduino and Raspberry Pis are popular but here's a nice board Bob made:

Peter, VK2EMU, explained phase locked loops and DDS and the crowd had a great time.

In other news, my build of Peter, VK3YE's "Knobless Wonder" is now transmitting well - I had a good report on my audio and signal from Mal, VK2BMS.

I've been having some trouble with transmit RF oscillation - due mostly to my use of long, unshielded wires, but I'm gradually improving things. Both transmitter and receiver work but I have yet to add a relay to allow easy switching.

My transmit audio is reported to be clear but "thin", Mal does say it's very readable and "communications quality". Great progress!

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