Monday, June 22, 2009

Repairs and receiver experimentation

Its been a while since there was some progress on the workbench. This last weekend kicked off by reassembling the frequency counter after re-soldering every joint on the board. It took about two hours to do, but it has all paid off, its now working comparing against a known working source.

I started tweaking the direct conversion receiver, with less success, but got to test out a number of other crystals along the way. 2MHz oscillates stably at 1.999999MHz, while the 25MHz crystal does not. I changed a number of different inductors and NPO capacitors to similar values to other circuits I've seen, but to no avail for 25MHz... So much for the idea of 25MHz +/- 3-4MHz VFO. There are plenty more options to come though. Found what looks like a pair of FT37-43's. Will have to check the datasheet but they look about the right size and came from a mystery box from a junk sale a while back. Will tinker with it some more.

The DC receiver picks up a lot of terrible noise around 1.8MHz which I assume is AM broadcast with the 2MHz crystal. Need to tinker more with that, and see if I can find a better way to link up the front end, not using a band pass filter to give me more tuning range. Not really sure how this works yet, but theres a lot of draw design found from the net and build. Probably hitting impedance mismatch issues. I'm sure I'll figure it out eventually.

I think its time to migrate the DC receiver from the breadboar to a manhattan board. I'm finding that the more I tinker with it the less it works. Probably connections of the components being dragged around by CRO probes, etc... Well its too colder to hang around in the radio shack any longer.

Monday, June 08, 2009

mashup ideas: solar powered radio

From the maker blog a while back they ran a series of posts on joule theif.

Bill on the SolderSmoke blog ran a couple of articles on mechanically keyed transmitters, like the ET phone home rig, also a rew ideas around clock powered keying.

So my brain was buzzing away recently and it wasn't until I spotted the solar powered garden lights, that ceased to work a couple of months ago, that I thought about re-using them. The little solar cells only put out 0.8-1.1 volts. Three in series put out around 3.2 volts in full sun light. I need to go back and see what kind of current they can sink though...

To power something like an arduino keyed tx or a DC receiver with NE612, I would need a solid and regulated 5 volts.

It wasn't until this morning, on the irc channel of our local homebrewers, that I thought about mashing up the joule theif and the 80 meter DC receiver to make a solar powered radio =) It would make it limited to day light hours, but its certainly workable. Still have some other things to work on first, but certainly the next project on the list =)