brainwagon

I haven’t even got this on the air yet, and I’m already imagining all sorts of interesting possibilities to improve and change the basic beacon design. (This is a credit to Hans for creating something simple enough to build, and yet interesting enough to inspire.) I’ve been brainstorming a bit this morning, and thought that I’d just write down some of the ideas I’ve had.

• First, there is the question of output power. I think that with the 3v supply (probably more like 2.8v) the maximum output power is somewhere around 14mw. This might suffice for reports for other DX entities in Europe, but to reach other countries from the U.S., a few additional milliwatts (say between 100 and 250mw) would be better. I suspect that I’ll have to go to a 6v supply to make that happen, but in any case, it’ll be an interesting thing to work out.
• Even without additional power, the addition of an output buffer amp is probably good. I noticed that even changing the configuration of the short wire that i was using as an antenna changed the loading of the oscillator to shift the output frequency a few hertz.
• Temperature control would probably be a good thing. Stu Phillips had some nice ideas in his own QRPp transmitter, which is probably worth emulating.
• It seems silly not to make more use of the Arduino. If I had a thermister or some other temperature sensor, I could log temperature. I could also use it to monitor battery voltage. I am also pondering using one of the cheaper processor boards: perhaps a LaunchPad ($6 is a lot cheaper than $30 or so for an Arduino).
• Using the PWM outputs of the Arduino as analog control voltages means constructing a discrete a low pass filter, or a resistor ladder. This is fine for mucking around, but using a proper DAC might also be good. Microchips makes a nice little I2C 14-bit DAC that you can get from Sparkfun on a little breakout board for $5. I suspect that if you monitored the temperature using the processor, you could calibrate the output frequency to stabilize the output with respect to temperature digitally.
  Breakout Board for MCP4725 I2C DAC – SparkFun Electronics.
• Oh, and put it in a proper metal box. With perhaps a variety of inputs and outputs. Including maybe a tap that I could use with my Norcal frequency counter.

Okay, that’s a pretty good list. Should keep me busy for quite some time.