The Feather Weight SMK
|By Brian Wingert, N7RVD
Special to The ARS Sojourner
|I was thrilled to get this from Russ: "I'm about half way through the Sprint logs, but I already have a hunch you will win the Skinny division. I thought I should double check that your station weight was 0.22 pounds."
Russ got it right - 0.22 pounds - a bit less than 4oz.
The rig here is a Norcal SMK-1 modified for 20 meters. To succeed in Spartan Sprints from the far Northwest corner of the country, I want to be on 14 mHz where I have a gain antenna and better propagation.
The SMK-1 is a 40 meter, milliwatt, direct conversion transceiver kit available from NorCal. Its assembled from surface mount components. In addition to being very light weight, the dual VXOs allow tuning to either side zero beat, minimizing QRM. This is a distinct advantage in QRP contests where everyone tends to clump within a kHz or two of each another.
I replaced the 7.040 crystals with 14.060 crystals from International Crystal Mfg. In addition, I changed the capacitors and inductors in the oscillator sections, the NE602 input, and the output low pass filter. My SMK-1 transmits from 14.059 to 14.060 and receives from 14.057 to 14.063. I couldnt find "large" 1206 package capacitors. I used 0805 size capacitors soldered at an angle with their corners barely over-lapping the solder pads.
With the NB6M "One Watt Mod", my SMK-1 started out the April Sprint with a watt and a half RF output. By the end of the two hour contest, the 9 volt alkaline battery and two AAAA batteries were nearly discharged and the output power dropped to about 700 milliwatts. The batteries are the heaviest part of the station. I havent been able to figure out how to get a full watt output from power supplies of less than 12 volts. I am open to suggestions.
To save weight, all connections to the board are made with Molex .100" pin headers. These perfectly fit the holes on the circuit board. Instead of the metal can potentiometers that came with the kit, I used plastic Piher pots available from Mouser. I incorporated a TiCK keyer because its memory function is a life saver during contests. For a paddle, I soldered two Radio Shack tact switches together and covered them with shrink wrap. The result is a paddle that weighs less than a tenth of an ounce. Unfortunately, its so small, my fingers went numb using it in the April Sprint.
Operating in Spartan Sprints is a real blast. I thoroughly enjoy the contests and tinkering with radios between contests. With a few more tweaks and mods, Ill be back next month.
Brian Wingert, N7RVD, is a resourceful homebrewer of QRP equipment who lives in Kenmore, WA.