There it is, my second BITX transceiver, this one for 20 and 40. Once I got the VFO sorted out, this one went together very quickly. Obviously experienced gained on the first project was a big help.
I followed Farhan's advice and characterized the 11 MHz crystals in the filter. Then I used the AADE filter design software to build a 3 KHz filter. Using my Arduino DDS signal generator and the new Rigol 'scope, I was able to do a manual sweep across the passband -- it looked very close to what was predicted by the software.
This morning I built the bandpass filter for 20. As soon as that was done, I fired up the receiver. This was an amazing experience for me: a homebrew receiver that worked right away! That never happened before. I'm listening to 20 meters now. It sounds great. I even managed to demodulate and display some SSTV. The VFO seems very stable.
I still have to build the RF amplifier stages, the bandpass filter for 40 and low pass filters for 20 and 40 (I know Steve Smith is watching!). Then it will be time for cabinetry. I guess I should put some paint or varnish on that walnut box. Any recommendations? I'll line it (on the inside) with copper flashing material.
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Don't forget your filters -- the Man is watching always...
ReplyDeleteRecord some audio and share it with us !
ReplyDeleteBill,
ReplyDeleteI'm trying to build a wobbulator using the Arduino DDS VFO and an I2C DAC to provide the sweep voltage.
The project could be built on as an add on to your VFO. I'll drop you a line when it is completed.
I'm using a sweep of +/- 2kHz from the centre frequency - giving a 4kHz sweep which takes up most of the DAC range. Do you Think 4kHz is sufficient?
Bill:
ReplyDeleteCongrats on your project! If it were my walnut box, I couldn't bear to paint it--I'd rub a coat of boiled linseed oil in, wiping off all the excess, then let that dry a few days; then I'd follow that with two or three coats of a clear wiping polyurethane finish (preferably satin), applied with a cotton cloth or rag. The boiled linseed oil will darken and bring out the grain, and the wiping poly will seal and protect the wood.
If you use the oil, be careful with the rags you use--they can catch fire all by themselves if you don't spread them out to dry.
73, Doug (AA0MS)
Just add an AD8307 logamp and use an analog input of the arduino to measure the power level directly. Well, that's what I'm planning to do anyways.
ReplyDelete