DSP Card 4 ( DSP 4 )

This is the famous DSP Card 4 by Finnish Alef Null group.

The DSP Card 4 is a product of the Alef Null group. DSP Card 4 is a general purpose signal processing card, dedicated mainly to the amateur radio use.

The DSP Card 4 contains the Motorola 27 Mhz DSP56001 digital signal processor with 13.5 MIPS processing power. The card has 96 kB high speed RAM. The DSP56001 has 24-bit word length, giving a dynamic range of 144 dB. The DSP Card 4 use CS4215 stereo codec as A/D and D/A convertter. Maximum sample rate of codec is 48 Khz ( 2 inputs / 2 outputs ). DSP Card 4 is contained on a single Eurocard ( 160mm X 100mm ), four layered, trough plated PCB. The card has a single EURO-64 connector, which contains all the needed connections.

Try to play this audio file: dsp4.wav (112kb), it is a booting message from my DSP 4
Get a full 840x610 picture: dsp4.gif (104kb).

At the moment I am using this card for QPSK HF-modem at 3590.0 khz LSB 25 w on oh2rbj LinuxFBB BBS, but there are also available 1200 bit/s FSK and 9600 bit/s G3RUH packet modems, various filter softwares for amateur radio use and 2400 bit/s LPC vocoder. An intresting new modem is QPSK with 15 tones.. This modem is still in progress.

QPSK modem has some fine features as:

  • KISS interface for different AX25 solutions ( Linux, BPQ, NOS, Terminals with KISS interface or emulator etc... )
  • two phase preamble for frequency shift correction and fast symbol sync.
  • Forward Error Correction ( 3 levels, can be changed with kiss command )
  • Time/frequency diversity to de-localize burst errors
  • Automatic radio tuning using mic connector UP/DOWN pins
  • RX audio level AGC
  • Modem reports heard QPSK signals signal/noise levels for all 15 tones ( Nice radio TX/RX audio bandwidth tester ! )
  • Modem reports heard QPSK signals frequency difference in Hz ( You love this one if you don't have auto tuning ;-)

    Here is an example of modem reporting messages, they are KISS frames: 

    Port dsp: AX25: MODEM->HOST [UI C] pid=Text
0000  Tune tones: 15/+00 16/+00 08/+01 13/+00 dB/Hz

Port dsp: AX25: MODEM->HOST [UI C] pid=Text
0000  Preamble at +06 Hz

Port dsp: AX25: OH5LEP->OH2NJR [DM R F]

Port dsp: AX25: MODEM->HOST [UI C] pid=Text
0000  S/N: 10 09 10 10 08 09 09 09 07 08 08 09 06 08 05 dB

    And it sounds like this on 80m SSB: qpsk.wav(221kb)
    ( This is recorded from my FT-840 when connected to OH5LEP-10 so the signals heard are from OH5LEP )

    We have tested this modem between two FBB BBS's on 80m, it worked great and forwarding was sometimes faster than on local 1200 bit/s packet channel !!! Think about 3000 bit/s raw data transfer over HF SSB radio contact. The FEC code reduces the maximum bit/s rate but gives better performance under noisy HF frequencies. Testing is still in progress....

    If you want to do some QPSK testing on HF, feel free to mail me !!!

    Tomi Manninen, OH2BNS (oh2bns@sral.fi) released alpha newqpsk drivers for Linux soundmodem program running with soundcard. This driver works quite well together with DSP4/EVM56 modems. You can find this fine piece of work here

    Tested with following radios so far:

  • FT 757GX: ( with amtor TX/RX mods ) Works fine. TX/RX audio ok. Autotune works.
  • FT 840: Works fine. TX/RX audio ok. Autotune works
  • FT 847: Works fine. TX/RX audio ok. Autotune works. Tested also with Tomis newqpsk soundcard drivers for sounmodem Linux
  • IC 735: Works poorly. Some problems with TX audio bandwidth. ( This rig is maybe broken ;-). Autotune don't work without modifications.
  • IC 706: Works fine. Minor problems with TX audio bandwidth. Autotune don't work without modifications.

    For more information about the board you can mail to Alef Null group.

    There is also DSP4 ftp site available, maintained by Jarkko "the DSP guru" Vuori.

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