K7MDL Amateur Radio Pages
DSP-10 2M Software Defined Radio Transceiver Kit
 
Home
Home QTH
Antenna Farm
Portable
HF/VHF Station
VHF+ Contest Rover Trip Archive

JT44/JT65 EME Log

Microwave Projects

Hohentwiel 2M SSB/CW Transceiver Kit

DSP-10 2M Software Defined Transceiver Kit
In August 2004 I received  this kit with the RF board partially built.  It consists of 2 boards, the DSP board from Analog Devices and the transceiver board kitted by TAPR (http://www.tapr.org).    This rig covers 144.000 to 148.000MHz and supports FM, SSB, CW, and several digital modes such as PUA-43.   Full details about this kit and its software are at http://www.proaxis.com/~boblark/dsp10.htm.  

The DSP board only comes fully built and requires little modification, but does need to go into a shielded box, which in turn, mounts inside the Transceiver box on standoffs above the RF board.

The output is on 2M and should be about 20mW, plenty to drive a typical RF amp module or microwave transverter.   Apart from the software defined radio aspect , this uses a 10MHz frequency reference for the PLL and is easily driven by an external highly stable source as well.   I use the external 10MHz output from my HP5342A frequency counter, which happens to have the high stability option.   For mobile use I will likely connect a surplus ovenized 10MHz oscillator (OCXO) so I can run completely off 12VDC.   I plan to lock my some of my future microwave transverters to these same references.

This kit uses a personal computer running DOS as the human interface and is feature rich.   I would like to use a USB dial, or build a microprocessor based serial interface to add a hardware tuning knob and frequency/band display and control to aid with my mobile use so I do not have to hunt for a keyboard in limited space.   I run the control  program on my old 486 75MHz IBM Thinkpad 760C color screen sub notebook.   It runs Windows 95 normally and I boot into DOS.  This laptop also serves as my rover VHF contest logging machine since it is small and runs on 12VDC. 

These pictures show the progress on the kit.  I finished it in about 2 weeks and put it on the air with very few troubles.   The biggest issue I had was the supplied molded serial cable was faulty, and mis-wired.   Once I got a good cable I was off an running.   I started with version 3.10 and had some problems with the PTT locking up when I keyed from the microphone.   I updated to Version 3.17 which fixed that problem.  To take care of an annoying microphone PTT delay, installed the fast PTT mod which is a small hardware cut and wire process and a software config file edit.  This mod is not the easiest to locate by the way.   I just happen to remember seeing this and searched every page I could find until I found it.  You can find it by following this link http://f5mi.chez.tiscali.fr/DSP-10%20_fichiers/readme20.txt.  The 2nd issue was getting my VCO to land on 126MHz.  I removed the core from the transformer L102 completely and that worked just barely.   Not satisfied, I replaced the 10pf capacitor C117 with a 7p ceramic I had in my junk box.   It allowed by to insert the core all the way to the bottom and even just off of it giving some comfort I was not on an edge of adjustment.   I measured 17mW out.  Feeding my AM-6154 2M amp, (6W in = 300W out) I squeaked out 1/2 watt which allowed me to be heard with good audio reports by close by stations.  I used a Radio Shack mic, and a Heil Pro-Set Plus! with the HC-4 and HC-5 switched elements.

 

Here is a view of the kit with the RF board completed and mounted in the case, not yet wired into the chassis.   There are only 5 toroid coils to wind, and most components are surface mounted, all on the top side.   25 wire jumpers are on the bottom side.

Above is the EZ-Kit Lite DSP evaluation board from Analog Devices.   It uses the ADSP-2181 processor.  This is the original processor used in the DSP-10 design.  There is now another DSP available from TAPR as an alternative.   The board is mounted on standoffs in the PCB shielded box.  17 feed-through capacitors bring out the DSP serial data, the PC serial control data, and the audio at about 15KHz, which is the 2nd IF of the Radio.

The DSP box mounts on 4 standoffs above the RF board.  In these pictures I have not yet wired the chassis and board interconnecting wiring.

After wiring the chassis up exactly like the article and drill templates specified, I decided I wanted SMA jacks instead of phono jacks for the TX in and out ports.   These fit in the same holes, are compatible with my existing inventory of jumpers, and are more secure.   Additionally I installed a standard 8 pin microphone connector to permit swapping microphones between my other rigs.  I put this on the front panel along with a headphone jack, power switch, Power LED,  TX LED, and a CW key jack for ease of access and a clean look on my desktop.   The microphone connector is wired to match my Elecraft K2 and Hohentwiel 2M transceivers.   I should probably switch everything over to match my Yaesu radio for more flexibility

I found the jacks located near the RS232 connector were interfering with each other since they were so close, so I abandoned 2 of the 3 holes in that area, moving them to the front.   I also added phono jacks on the back near the RF connector where there was more room breaking out the PA key and Ant relay key lines since all my radios are standardized on phono jacks for this purpose.

The photos above show the completed wired unit.  The PCB lid is in place in the first photo, and the right hand photo shows the cover off, and the aluminum angle stock heat sinks.   I am concerned about the amount of heat generated so I have one last task planned to bolt in a spacer between the DSP box 9V regulator and the outer chassis wall.