Decoding MXL Cubesats

Decoding MXL Cubesats with a SDR and Sound-Modem software.

The Michigan Exploration Laboratory (MXL) ground-station software by default wants to connect to a physical TNC. For this connection they use a python based daemon that connects the RS232 TNC interface via a tcp socket on port 12500 to there final ground-station client. This solutions is used with: MCubed, MCubed-2 and GRIFEX.

Many radio amateurs such like myself use a SDR receiver and no longer make use of a  physical TNC and therefor I was looking for an alternative way to use there ground-station software. Well the python part can be swapped with another kiss server like the one that comes with the UZ7HO Sound-Modem or Direwolf (that also runs on Linux) solution.

Below a block diagram with the two different ways to connect the ground-station software.


For this to work with a SDR solution, one has to do the following:

Alter the MXL ground-station software configuration file


UZ7HO-KissServerUZ7HO, enable the kiss server option and select a ground-station software corresponding port. Select Settings -> Devices -> Server setup. In this example I used port 9100, default is 8100.

After this you can start your favorite SDR program, redirect the audio to the sound-modem software and start the MXL ground-station JAR (Java Archive) for example mcubed2_gs_client.jar when you want to decode MCubed-2.

This information can also be found at the website from JE9PEL: 9k6 decoding

Credits: UZ7HO, VB-Cable, SDR# and MXL

ISS SSTV – weekend of July 18

ARISS SSTV images were transmitted this weekend from the amateur radio station in the ISS Russian Service Module to commemorate the 40th Anniversary of the Apollo-Soyuz Mission.

40 years ago this week, the historic joint Apollo-Soyuz mission was conducted. Apollo-Soyuz (or Soyuz-Apollo in Russia) represented the first joint USA-Soviet mission and set the stage for follow-on Russia-USA space collaboration on the Space Shuttle, Mir Space Station and the International Space Station.

Below images that where received during the night between the 18th and the 19th of July with a FUNcube Dongle Pro+, SDR# and RX-SSTV.






UZ7HO Sound-Modem 0.83b

UZ7HO has updated his Sound-Modem software. The current version is 0.83b. Below a part of the latest changes.

SoundModem v0.83b changes:
- Added 12 dB PreEmphasis filter.
- Added 3 parallel decoders with NONE, 6 and 12 dB preemphasised signal.
  By default this option is ENABLED ("PreEmphasis filters - All" in "Modems"
  menu). On both ( WA8LMF's Track1 and Track2 records
  1021 frames are decoded.
- Fixed some minor bugs.


In processing electronic audio signals, pre-emphasis refers to a system process designed to increase (within a frequency band) the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as attenuation distortion or saturation of recording media in subsequent parts of the system. The mirror operation is called de-emphasis, and the system as a whole is called emphasis.

Pre -De -Emphasis

Pre-emphasis is achieved with a pre-emphasis network which is essentially a calibrated filter. The frequency response is decided by special time constants. The cutoff frequency can be calculated from that value.

In high speed digital transmission, pre-emphasis is used to improve signal quality at the output of a data transmission. In transmitting signals at high data rates, the transmission medium may introduce distortions, so pre-emphasis is used to distort the transmitted signal to correct for this distortion. When done properly this produces a received signal which more closely resembles the original or desired signal, allowing the use of higher frequencies or producing fewer bit errors.

Source: Wikipedia

UZ7HO Sound-Modem update

UZ7HO has again updated his Sound-Modem software. Below a part of the latest changes. With the current 2400 BPSK experiments on QB50p2 this version is a great improvement to decode these QP50p2 telemetry 2400 data.

High-Speed SoundModem v0.03b changes:
- Changed LPF filter in HAPN 4800 baud mode.
- Little code optimization.
- Fixed some minor bugs.

SoundModem v0.80b changes:
- Added new BPSK 2400 baud modem.
- Little code optimization.
- Fixed some minor bugs.

2400 baud BPSK QB50p2 IQ replay and the new Sound-Modem software

UZ7HO Version overview:


  • AFSK 300, 600, 1200, 2400 baud.
  • (D)BPSK 300, 600, 1200, 2400 baud.
  • (D)QPSK 2400, 3600, 4800 baud.
High-Speed SoundModem

  • G3RUH 9600, 19200 baud.
  • Manchester 1200, 2400, 3600, 7200 baud.
  • HAPN 4800 baud.

UZ7HO download page

New UZ7HO Sound modem version

UZ7HO has released a new version of his great Sound modem software.

UZ7HO Soundmodem

Here is part of the version history file, take a look at this file to get to know al the options.

SCM v0.71b changes:
- Fixed "Frame Collector" operation with MAXFRAME greater than 4 and IPOLL
  frames. By default it supports up to 6 frames into collector's buffer now.
- Added "TXFrmMode" option (that was available in 9k6/19k2 version). It allows
  to select the transmission mode of the frames.

  If set "TXFrmMode=1" then it will repeat only one frame on each of REJ acks.
  It can be useful in poor condition jointly with MAXFRAME up to 4. If another
  station uses a TNC which can operate with "Frame Collector" this option can
  improve a performance, especially on HF.

  If set "TXFrmMode=0" then it will always repeat the block of the frames, of
  which the number is limited by MAXFRAME. It can improve the efficiency in
  good condition. Especially with TNCs without "Frame Collector" function.

  By default this value is "1".

Finally got my PK-96 working

AEA-PK96PK-96 and TS-2000X

After some debugging and measurements, I finally got my PK-96 working with my Kenwood TS-2000X where I use the TS-2000X ACC2 connector. The problem was that when one uses pin 13 PTT the TX audio from the PK-96 is muted. This pin is normally used for a foot switch and not for an external modem. So after I switched pin 13 to pin 9 on the ACC2 connector everything was working. ISS packet here I come.

Image pin function remark
PK-96-Audio-connector 1 TX audio to radio
2 GND ground
3 PTT push to talk
4 RX audio from radio
5 SQ squelch
Image pin function remark
TS-2000-ACC2 1 RX audio sub radio
2 RTTY key input
3 RX audio main radio
4 GND ground
5 SQ squelch main radio
6 NC not connected
7 SQ squelch sub radio
8 GND ground
9 PTT push to talk, audio not muted
10 NC not connected
11 TX audio in radio
12 GND ground
13 PTT push to talk audio is muted