For quite some time I have been reading arround about SDR, which seems to be a very interesting subject. But it always seemed to be something too complex to achieve and I never had time to do so. Plus, living in Argentina, means that you don't have easy access to electronic components, and shipping from the north via UPS, DHL, whatever, is ridiculously expensive, plus you have not only to pay customs on the items but on the shipping as well!.
The begining of this year, everything changed, and I found about the SoftRock kits. Not only there were receivers and software available, but even a transceiver. As I use radio to do digimodes, this involves precisely always having a laptop PC available, so depending on it wasn't a problem for me, while a transceiver would allow me to do radio wherever I go, something I currently don't do, because I wouldn't take the hassle to move my rig out from my home. Finally, these kits where certainly accesible! Arround USD 30, shipping included. This was excellent, because anything a little bit more expensive, would mean I would have to deal with customs, a loose a whole day in a line (Argentina is synonym of many ridiculous things, yes...), instead the kit arrived home right with the mail. Finally, there were plenty of sources and a huge community in the Yahoo group softrock40, ready to help.
So I ordered, and in a week I had the kit at home. I ordered as well a Si570 XTALL kit that would allow me to have access to many wide bands and not just a little piece arround a frequency given by a crytal. The next thing would be to actually build it. But there was a problem to solve first. SMT soldering was synonym of nightmare for me. After much reading, I found that there were techniques to do this quite easily, and all what was needed was an extremely expensive soldering paste. I asked at the shops here, and it meant spending over $100, for an amount that would allow me to build thousands of kits... but I wanted only 1... Internet gave me the answer as well, thanks to somebody who sells small syringes for $5 shipping included! See here. So I immediately bought it, and one week later I had it.
Now I had all the elements, the next step, was to solder the small SMT capacitors and ICs to the board. To do this I aquired a used toaster, for $5, I disabled the mechanical thing that makes the bread slices jump, and then I had my soldering station. I used a Variac and an ammeter to control the current and temperature. And I made a test first with a piece of PCB and a drop of the paste. Except for the PCB flying to the opposite side of the kitchen (yes, the lever wasn't correctly disabled after all), everything went ok. So now, I had the experience to try it for real with the RXTX. Half an hour later, I had the PCB ready, with those precious little chips correctly soldered. It was a success, really easy and completely effortless! Just one tip, don't put too much paste or you will get bridges, and be extremely careful in controlling the temperature according to the color of the paste.
One little thing to consider, is that if you use a soldering paste method to assemble this kit, then you are obligued to do that first, and only once. This means you cannot go, section by section and controlling that every single step went ok. Such procedure is a lot more recommended, but you will have to solder the ICs manually, and to do that you really need to know what you are doing, and you must have a very steady hand (not my case).
The next weekend I spent a whole day, doing the rest. The most difficult part certainly was to make the coils. The cores are really small, and to get them right, without scratching the isolation, was painfull. Yet I did it quite well after all.
I would like to talk about performance, tips, and everything, but this is quite recent, and I don't have the time yet to do so.
So... to be continued...
Here you have some photos. Click on them to open them full size.
Placing SMT components
Board with SMT components already soldered
Resistor pin forrest
My soldering assistant
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