I guess before I move on to “blogging” about some of my own home-brew radio projects I’d best do another quick book review. Well four books in fact. And the reason for doing this up-front is because many of my personal shack projects come from one of these publications.
I’m talking about “Radio Projects for the Amateur” available in no less than four volumes. All created by Drew Diamond VK3XU. To say Drew is prolific in publishing first class radio construction articles is probably something of an understatement.
Much of the content (but by no means all) contained in these books originally appeared in “Amateur Radio” magazine. The journal of the Wireless Institue of Australia (WIA).
For a long time certain volumes were out of print and unobtainable unless you got lucky on the second hand market. At the time of writing all volumes appear to be available from the Wireless Institute of Australia (WIA) Bookshop. I would happily encourage anyone interested in home-brewing to grab all four while they are still available. 100% pure gold!
Here are some (very poor quality) photos of the current project. An ozQRP, MST400 the MST standing for “Minimalist Sideband Transceiver”. Available as a partial kit in two versions, 40m and 80m. I’m building the 40m version designated MST400. The kit comes with the PCB and optionally some hard to find parts. You source the rest of the parts yourself. The parts sourcing issue elevates this kit to an intermediate level of difficulty. This is not a beginners kit.
Front view. Plastic box (finding good, cheap metal boxes is so hard – sigh). Metal front and rear plates. Silver knobs from a very old defunct crystal CB radio (Yeah, I know, never use metal knobs!). The fact that the two smaller knobs don’t line up properly shows up in the photo! It’s not so noticeable when your holding the radio. I’ll have to do something about that. The misalignment is due to the way I mounted the pots (more on that in a minute). The signal strength meter is from the same discarded CB radio.
Top view. Speaker grill is a sink drain filter. Not sure if I like the look or not. But it’s functional. Next time I might just use it as a template and drill holes in the plastic. The construction manual is alongside. The manual is absolutely excellent! Not quite the Elecraft “step-by-step” gold standard but very good for the intended audience.
I had a roll of aluminium foil (flashing) with adhesive backing. Available from hardware stores and used for insulation. I used it to insulate the box from RF. I mounted the DDS VFO, a separate but matching kit (you can supply your own VFO if you prefer) and the controls to a PCB set rearwards from the front panel. Rather than mounting them directly to the front panel. This makes it easier to keep the front panel looking neat and builds a RF shield between the DDS VFO and the main transceiver PCB. Probably not required but it seemed like a good idea.
Another shot of the case top cover. Showing speaker, sink drain speaker grill and aluminium insulation.
Front panel and DDS control board. Upside down. Not only can I not take in-focus pictures I get them upside down as well! I’ll fix it later.
Here is the cause of the pot alignment problem. Because of the pot shaft length that I had on hand I decided to try and solder the pot body directly to the PCB. It works. But the precise alignment is quite difficult without building an alignment jig to hold the pots in place while soldering. And if you build that jig, out of say PCB material, then you may as well make it permanent! Ah, well, live and learn.
Some time back I read about an Amateur who had discovered a copper foil with an adhesive backing. He was experimenting with using it for PCB
construction. At the time I thought;- “I must try that”. It took quite some time but I finally found some to play with.
Now I wish I could properly credit where the original idea came from (It was not mine) but it was so long ago I’ve forgotten which Journal I was reading. Perhaps GQRP Sprat or maybe even VK-QRP Lo-Key.
Anyway, I finally found some copper foil. The like of which I think was being referred to in the original article. I found it on eBay (where else) and ordered a small roll. I gather it’s intended purpose is for creating RF shielding for enclosures.
The blurred image above (Sorry, I’ll take some better photo’s later) shows the result. A paper hole punch for creating confetti dots was used to punch out some pads. Three dots were then stuck to a white sticky label on top of the PCB. Then a transistor was soldered to the dots.
So “Yes”, it works.
Is it quick and easy? So much so that I won’t be picking up my Dremel again? No, not yet. At least not without some refinement. The cheap hole punch causes the foil to buckle. A more expensive two-hole punch works fine but you can’t easily see to properly align the holes your punching. So you end up with a lot of wastage. Of course it is dead easy to cut odd-shaped rectangles with a pair of scissors.
Even the act of removing the backing tape from the “dot” and sticking it down is fiddly and somewhat time consuming.
I also worry about the stray capacitance between the copper foil sticker and the copper sheet of the PCB proper. The two being separated only by the width of a paper sicker. Stray capacitance could get quite high here.
But with some refinement the technique shows obvious promise. So while the Dremel may not be due for retirement any time soon I can see a “hybrid’ construction technique developing.
Utopia would be a box of 500 easily dispensed white paper dots, each containing three little copper dots.
Anyway, I’ll keep playing with the idea.