Wednesday, April 21, 2010

80 meter DC Rx step 1 - Diode ring mixer

Decided to take a break from the QRSS Rx. Its doing _something_ but I don't know if its on frequency or if the bandpass filter is obliterating the incoming RF or if my antenna is really crap.

So I hunted around for another project to keep myself busy with in the mean time. Picked up a copy of Practical Wireless, February 2010. George Dobbs G3RJV, has a receiver first built in 1968 that he re-explores. An 80 meter DC Rx.

Thought it might be a simpler project to work my way through. Also if it pans out, would be good to take it along to the AHARS Show and Tell night.

We just had the AHARS Members Buy and Sell night, a week ago and I purchased a handful of T37's and T50's. This will help move along a bunch of projects I have been wanting to do for ages =)

So here is the first step, the diode ring mixer in the middle of the copper clad board...

I think I will put the band pass filter on one side and the oscillator on the other and shield them both. Then add the audio board on another copper clad board. Perhaps build it up in a Haighs tin...?


Sunday, April 11, 2010

just finished a colpits oscillator for the DC Rx

Spent a couple of enjoyable hours here on the workbench building up a colpits oscillator, which is very similar to the one recently build by Bill, N2CQR, see over at the SolderSmoke blog.

You can see the frequency counter, 10.13805 MHz. I spent some time mucking around with the variable capacitor in series with the crystal. At best all the options I had would move the rock up or down by 100Hz. Although later when I mounted the variable capacitor in parallel with the impedance matching transformer, I noticed that it would pull it a total of 4Khz. Not sure if this is the right way to tune it, but it seems to work for now. So set it up for 10.140MHz, assembled the LO board into the little case. Hooked the audio and power up to the peecee and fired up QRSS-VD.

So much noise! I turned off everything that I didn't absolutely need and went around rearranging cables. So now the capture is cleaner. However there don't appear to be any QRSS signals in the air ...

Will do more tinkering later and check the clipboard. May need to do a lot more work on the dipole.


Monday, April 05, 2010

QRSS receiver up and running

Well its taken a good long while, but I've finished off the QRSS receiver and have a grabber running. I'm not picking up any obvious signals. I have not checked the clipboard, but thought I'd tinker around anyway.

Seems to be something weird going on with the oscillator, I can't get the frequency counter to pick anything up under 66MHz, which is way out of the ball park. I noticed that when I bump the crystal or hold my finger on the crystal the capture changes significantly.

So may need to move the oscillator off the main board and box it up and put a high impedance buffer on it to be able to check the frequency with the external counter.

Friday, April 02, 2010

stage one prototype working

well the first prototype for the magic lantern has blinken licthen =) am pretty happy with how it turned out. it has six banks of three LEDs spaced evenly around the gap between the external ground rail and the internal power rail...

the arduino will sit in the middle of the inner ring, and all the transistors will be driven from the PWM pins.the leds will draw about 200mA when on full, need to figure out how much current the arduino draws. still need to work out a simple charging method. four AA cells should last several hours. this means that we can charge them from the solar panels directly with a suitable regulator. or we can pull the AA cells out and charge them from a 240v system powered by solar.

so, this is the first part of the magic lantern. todays work was all about displaying patters of light. the second part is interacting with other lanterns. this will require an RF module. however i haven't made up my mind about which module to use yet. it looks like the lobethal lights festival is already using a zigbee for another project, but these puppies start around $40 each. little bird electronics has a $9 module that might work quite well, but we would like to interact with other projects. more on the that later...

Photos here.