The Up-Converted SST
Special to The ARS Sojourner
The station consists of a Whiterook MK-65 keyer, keyer cable, Sony earbuds and an SST with internal power supply. The internal power is provided by four AAA batteries to a 12V DC-DC converter. I whipped up the converter using the National Semi LM2621 dc-dc step-up converter chip. The circuit is per the example in their data sheet.
The converter is under that sheet metal shield below the batteries in the photo. That funny black round thing is a mini speaker that doesn't really work all that great but has saved me a time or two when I've forgotten the earbuds. As you can see, I've added a SPST switch on the front panel to turn on and off the converter. You do need to choke all power lines and make sure the converter is well shielded or you WILL hear switching noise in the RX.
The SST puts out 2 watts with the converter and runs 5 to 6 hours with the typical QSO duty cycle. This seems to last the typical weekend back country adventure. The nice thing about using 12V vs. a 9V battery is you don't have to change the 8V regulator to 6V thus preserving the already limited tuning range. Also the audio amp runs off that regulator so you get more audio out.
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John Ceccherelli, KC4TXR, is an accomplished outdoorsman and low power operator. He is a Senior Engineer in GPS Product Development for IBM Microelectronics, Hopewell Junction, NY.