Tuesday, April 30, 2013

The Killer Watt Radio

Dave Benson is awesome.
Dave runs Small Wonder Labs, and creates some of the best kits. They just work, and they tend to just work right the first time. I've owned several over the years. My first HF CW QSO was on a borrowed SW-40. I had to modify it to work in the "Novice" part of the band because I was only a Tech plus at the time. Shortly after getting my general I purchased a built SW-30 off of QRP-L. I had that radio a while, didn't sell it until after we moved to the current QTH, and I had an SW-40+ to build.

In 2006 I got an SW-40+ for my birthday. I built that radio, and started thinking of all the ways you can make this already awesome radio cooler. First, I decided to limit my output to one watt under battery power. I did this because I wanted to qualify for certain point multipliers in QRP contests, but my schedule at work has kept me from being as contest active as I would like. I also did it because I wanted to be able to tell people my output was "One Killer Watt". At bench supply, the output is a higher, a watt with a lil lagniappe. After I built this radio, I put it in the genuine SW+ enclosure I had received with the SW-30, and have enjoyed it immensely!

One day, looking at the radio, I decided to ask myself what I could do to make this radio better for my situation. First thing was that the packaging had to be redesigned. I like to operate from a pelican case, I got it from a package deal when I bought "The Mighty FT-817" back in 2001. When I sold the radio, the case stayed with me, and I use it when I work from the field. I wanted to be able to use whatever is in the case without having to reach around the radio for wires, etc. In short, I wanted all controls and connections on the front. I have this vision in my head of one day having the radio in a pocket or something, using it in the field to sling dits and scatter dahs all over the globe, with my "One Killer Watt" of raw, unadulterated Morse code power.

The board for the radio is slightly bigger than would comfortably fit in a standard pocket, but I gladly wear cargo pants, and have at various times, large enough pockets for a small radio like the SW+ series. The board will very narrowly fit in a Radio Shack Aluminium box, model 270-238. It takes a little effort to get it to fit, but fit it will!
Ready for Action!
 The pic has the SW-40 in the front, I have speakers, key, and antenna hooked to it. This was right before I used it to QSO with KO1U. The big knob controls tuning, and the little knob controls RF gain. All the way up, and the little speakers pop when the QRN is high.


In the future I plan on seeing how far out I can spread the bandwidth without loosing too much linearity. I replaced the standard tuning pot with a 10 turn job I had left over from a failed project and you definitely notice a less linear tuning rate at the top of the tuning range. Linearity is lost because the radio uses varactor tuning. A varactor is a special diode used to take advantage of a characteristic all diodes exhibit, when reversed biased, the two halves of the diode act as a capacitor. This capacitance is predictable for a given voltage, and a varactor diode is made so that as the reverse bias voltage changes, the capacitance changes in a predictable manner. I also notice that tuning a signal is a lot easier. Right now, I have about a 30KHz tuning range. It tunes from just below 7030 to just below 7060. I would like to make it so that it tunes from the low sevens to over 7040.

Unfortunately Dave has decided to mostly give up the kitting business. You can still buy new rockmite kits, and I'm due to build another coupla those. You can also get the freqmite kit and install it too.
Possible future articles that will cover other mods I make to this radio:
1. The Killer Watt deconstructed: modularizing the board to further compact size.
2. Modding the VFO for greater tuning flexibility, adding a cap and a switch to go from lower part of band (where the DX is) to the upper part of the band (where the SKCC guys hang out for rag chewing.)
3. Adding an onboard audio amp and internal speaker.
4. making digi-friendly.
5. Taking suggestions.

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