On The Bench

Bonus Post!

I've been mulling this one over for a bit and meant to post before Thanksgiving but that clearly did not happen. 

Part of the idea of this blog was an exchange of ideas and what we're actually working on at the moment. In what appears to be true for a great number of makers, designers, tech geeks, and soldersmoke inhalers (always use proper ventilation folks!), I've got a never ending list of projects on the go at any given time. Unfortunately, this is what my desk looks like, which is actually much better than it has been. At least there's only one project there, believe it or not. The three copper clad boards in the middle of that mess of wires and assorted reclaimed components are an attempt at a direct conversion 40M (~7mHz) receiver as presented by Rick Kambel KK7B in the August 1992 QST Magazine. (That link goes to a .pdf file by the way.) The left-most board is a stab at Doug Demaw W1FB's Universal Variable Frequency Oscillator (VFO) as found in his now out of print QRP Notebook (if you look at the picture in the first blog post - that's the actual signal coming out of the VFO!). The circuit is complete but not functional. I think there's a problem in the amp section before the mixer. The middle board is the filter section, and the right-most is the audio section.

That project has taken second place, however, to Ashar Farhan VU2ESE's latest offering, the BITX40. Seen here on the right, it's a fully assembled and operational 40M transceiver that can be had from India for $45. The board is assembled by a women's collective in an effort to help people get on their feet financially. I love this.





The BITX40 is made with (radio) homebrewers and modification in mind, so all you get is the board and the bits and pieces to tune it up and get it on the air. You're on your own for an enclosure and any other modifications you may wish to make, such as a direct digital synthesis (DDS) tuner, digital frequency readout, automatic gain control (AGC) or any other refinements. This is how I'm getting around the cheating feeling I get for putting aside the scratch-built effort in favor of a purchased board. 

Right now I'm working on the enclosure which I intend to make out of wood (still mulling over the RF shielding issues there) and recycled PCB from scrapped electronics. Here are a couple of the pieces I'm going to be using for the top and one of the sides of the enclosure. I'll be cutting holes for the digital display (powered by an arduino and SI5351 clock circuit), a rotary encoder scavenged from an old home theater receiver, the volume and power pot, and the various ins and outs. I've got a drawing that I'll be using to mark out where everything goes and then will make some attempts at cutting the board without destroying it. 

To salvage the PCBs I removed all the old components with a heat gun and a flat head screwdriver. It was a bit tedious but it gave me a couple of nice pieces of PCB to use for other projects as well as an assortment of salvaged components. The trouble is getting PCB that more or less matches. One major lesson learned in the component removal process was that it seems to work best with PCBs that have a large ground plane to distribute the heat from the gun as opposed to those with only a few copper traces across the board. Boards with only a few scattered traces tended to warp and burn. I had to stop the process on a couple pieces as smoke began to pour off of them. Nothing ignited, thankfully, but I can't image the smoke from burning PCB is terribly good for you. 

OK, I've gone on more than long enough. Your turn! What are you working on?

73 de KB1VNA