RUDAK DSP Experimentation

June & July 2002Contributions to this presentation by:

KK7P, WD0E, 4X1KX

Why DSPs?• They are an experiment. Part of the experiment was to build

themand see if they work in a satellite, next part is to see if they arecapable of doing anything worthwhile for the users

• Using the current hardware modems there are two things making itdifficult to work with RUDAK:

1. The links are more difficult to close than expected2. Signals in the remaining transmitter mix and distort each other. We

need to find out if the DSPs can improve that situation. 3. There are technically and operationally interesting opportunities to use

various coding schemes to improve the links4. We need to develop a group of proficient software engineers who

can further explore the possibilities and advance DSP techniques for use both on RUDAK and future satellites.

DSP Objectives

1. Develop enough code and software engineering expertise to prove all the hardware works

2. Gain confidence in use of DSP modulator units

3. Develop a 9k6 up and down FSK compatible modem and see how it works compared to the hardware modems

4. Develop ground hardware that facilities further software engineering

5. Develop a coded downlink and sound card demodulator to improve the links further

6. Test and characterize the mutual distortion issue

7. Write software to enable users to test ground-stations

8. Listen to ideas and implement further projects of interest.

Participants in Testing

• Jim White, WD0E – RUDAK Operator• Michael Kingery, KE4AZN – RUDAK Operator• Assi Friedman 4X1KX – DSP code• Lyle Johnson KK7P – RUDAK Support• Harold Price – SCOS Support

Development Process

• Write DSP Code using Analog device assembler tools

• Email code for upload to spacecraft

• Upload and execute code

• Test for expected results

• Report feedback for next revision

AO40

Write DSP Code

(4X1KX)

Upload to AO40

(WD0E/KE4AZN)

Test Code

(WD0E/KE4AZN)

Report Results

(WD0E/KE4AZN)

Hardware Verified

DSP:

• Interrupts tested (not all)

• Timer tested

• Host Interface Bus tested with V53

DDS (Digital Direct Synthesizer)

• FSK mode verified

• IQ modulator not verified

• Phase modulator not tested

Four DSP Modulator Test

• Four RUDAK-A modulator DSPs loaded with carriers 20KHz apart

• All DSPs were run at the same time – a first for RUDAK!

• Image shows four carriers on the left

• RUDAK 9600FSK downlink on the right

ZRO DSP Code

• Code to emulate AO-10 / AO-13 ZRO testing

• AO40 advantage: signal is generated on AO40 and does not experience uplink loss

• The current design is to generate a carrier with markers, and then begin stepping it in 3dB increments down to –20dBc (perhaps more)

• Users will be able to have a continuous test signal to evaluate ground station receive performance

• Status: timing error cause the power to change too fast. New version in work

9600 Baud FSK Modulator

• FSK generator at 9600 Baud tested

• Result is a 4800Hz square wave

• Top picture is oscilloscope monitoring the output of the FM discriminator

• Bottom picture showing the FSK signal

Need to do:

• Add randomizer

• Add power & frequency control

• Enable QAX25 to send data to DSP modulator port

Signal Generator

• Code which will give RUDAK operator a simple utility to generate test carriers on the fly

• Operator will have frequency and power agility

• Code will facilitate dynamic test of spacecraft transponders, and user ground stations

• First release of code created week of July 22nd

• Code tested on July 24th pass but a version mix up might have resulted in unexpected results

• Next try July 25th

Current Issues

• Development cycle is long– Typically, about 4 days to

test each code

– Code testing is done on the spacecraft

• Limited power restricts DSP testing

• Only one code writer

• No Ground hardware to test code on

• Interference between MB and RUDAK reduce link efficiency

RUDAK EmulatorGoal:

• Enable DSP programmers to develop and test code on the ground prior to spacecraft upload

Features:

• One full DSP Modulator

• One Full DSP Demodulator

• 100% compatible with RUDAK

• Code upload done via PC serial port

Current Status:

• Electronic design complete

• Software SDK is being put together

IF OUT

IF IN

PC

Computer

DSP

Modulator

DSP

Demodulator

Embedded

ControllerRS232

TX Data

RX Data

What's ahead long term?

• Lots of possibilities– RUDAK on at the same time as the transponders/PSK beacon

– Links easy enough for the general user/support population to use

– Coding methods that allow use with much smaller antennas and a sound card as a decoder

– Regenerative digital transponder?

– Digital voice?

– Imaging?