I’m in the process of building a amateur radio digital voice repeater (Dstar protocol). Several in the area have talked about erecting a Dstar repeater since Icom introduced equipment 6-7 years ago, but the price of Icom’s stack (repeater, controller, gateway software) exceeds $3500 and then one needs a user radio (handheld transceiver and/or mobile rig installed in car or home) which ran $500 and up.
Dstar specifies the handling (layer 3 OSI) of the data stream, but currently Icom only uses the rather old GMSK modulation scheme with no time division. This makes using off-the-shelf narrowband FM gear possible – and with commercial PMR/SMR users having to narrowband again for 2013 there is more and more quality synthesized gear on the used market from the past 20 years available on the cheap ($25-75 common for a 25 watt 150 or 450Mhz radio that can be programmed into amateur 144-148 or 440-450 ranges).
Without going into the evolution of modem hardware boards, or the discussion of using a modern computer with a soundcard to demodulate the GMSK signal from the radio’s discriminator and modulate direct FM to the transmitter, I like the simplicity and reliability of hardware encoding and decoding.
Now back to computers. I needed something small-ish, but inexpensive. Preferably running on 13.8vdc common with the radios for emergency power. I’ve had a Lenovo X120e Netbook for almost a year running the inexpensive, energy-efficient AMD Fusion chipset and processor. I thought about ‘sacrificing’ the netbook to this project, but a screen wasn’t required, and the unit took 20vdc input. I quickly decided against 24v power for all equipment – KISS principle and all.
Hey, Asus has a micro ITX form-factor board for the AMD Fusion – and with the processor installed with a big heat sink (read: no need for fans) under $115. And it consumes less than the PicoPSU power supply so off to Amazon I go:
- Asus Dual-Core AMD Fusion APU E350/ AMD FCH A50/ SATA3/ A&V&GbE/ Mini ITX Motherboard (E35M1-I) $114.99 (before $20 MIR)
- M350 Universal Mini-ITX PC enclosure PicoPSU compatible; black color $39.50
- Picopsu-90 12v Dc-dc ATX Power Supply Cyncronix Rating $31.00
- I didn’t have spare memory so Crucial CT2CP25664BA1339 4GB 2GBx2 240-pin PC3-10600 DIMM DDR3 Memory KIT for $25.34 (don’t need 4GB, but smaller modules are only $5 cheaper… meh)
- I had a spare 5400rpm 2.5” SATA drive – although I may want a SSD in the future
The computer bundles together quite nicely, and the case is nice quality metal, except for the faceplate which I consider somewhat cheesy in that you have to unscrew (one screw) the cover and slide out to remove the faceplate.
The pix. Showing the back of the case – the PicoPSU coaxial jack for 12/13vdc is on far right
Front panel sans faceplate, showing power button and two USB jacks. These are inaccessible behind faceplate, suggested use is for USB WiFi or bluetooth radio.