Experiences working QO-100 satellite using sdrangel

Keith Laaks

Hi All,

I have been using SDRAngel (ubuntu) very successfully on the QO-100 satellite with SDRLime-Mini.
I am able to work the satellite in SSB using the LimeSDR Mini plus a small 40dB amplifier that can do max 100mW output, with 50mW at the dish after coax losses.
Thats using a home-built Helix feed into a 3.5m dish. Signal not strong, but perfectly readable in ssb.

But there are a few challenges: 

A: Each time I start the program, I need to from scratch reconfigure the SINK side of things for transmitting.
I am able to load the full RX configuration OK from saved settings. 
But not able to load any TX configurations.
Am I just doing something wrong?
Or is there some (secret) way of doing this?

I also find it quite tricky when having to enable and disable TX when having a conversation.
Normally whilst listening to another station talking, I want to see the RX window showing the received spectrum.
But then when the time comes to respond to the other station, I currently first click the TX tab to bring that into focus, (which is left top), then move the mouse over to the microphone button on the right and 'unmute' the microphone. At the end of my transmission, I have to redo this and Mute the audio again.

There is quite a pause if I try stop/start the TX itself using the 'play/pause' buttons towards the top left. So I just leave the unit in TX permanently and use the Mute/Unmute instead. As the mode is SSB, when the mic is muted, nothing gets modulated in RF, so that method works quicker.
So 2nd question - is there some other easier way (via keyboard not mouse button) for unmuting/muting the microphone when the RX pane still has focus?

Also, is there any possibility of brining the RX and TX up next to one another perhaps?

It would also be nice to be able to (right) click on the RX window on a station and have the TX frequency automatically keep in sync.
It's quite a challenge right now to get your TX on the right frequency.

The RX display also only seems to go up to maximum 9.999 GHz.
So I am not able to add the LNB offset such that the dial reflects the correct 10GHz downlink frequency.

Any suggestions from others doing same are welcome!

Best Regards


Edouard Griffiths


a few responses:

A: only the first tab (R0) is automatically saved as default when you restart the application. You can always save your Tx configuration as a preset and load it later. You have first to select the device then load the preset (presets contain device information so that you can reuse them with different devices). Using the REST API this can be automated in a script that will set up things automatically to your usual configuration. See: for an example.

B: the famous PTT question. No there is no automatic PTT nor plans to have one as such. Again you use the REST API to implement this. There are two examples
  a: this forcibly sets Rx or Tx from the command line (that can also be triggered from the GUI)
  b: this one actively listens for changes initiated from the GUI and uses the API both ways. It also has a Rx/Tx frequency synchronization option.
These may need to be further tailored to your exact needs and are just examples.

C: No. The tabbed panels will stay as they are. You can however design your own interface and use the REST API to control the SDRangel application.

D: Very complex to implement in practice. There can be more than one channel in Rx (normally not in Tx but this is still possible) so this is a nightmare to implement and a permanent source of bugs. At best you can synchronize Rx and Tx center frequencies externally (see B).

E: There is no actual use for this. No device today goes natively above ~6 GHz. You can use the transverter mode and drop non significant digits. Suppose you tune to 10450 MHz with a 9750 MHz LO. In fact you are only interested in the 450 part so you can set the transverter LO at 750 MHz. To tune to 10450 you actually tune to 10450 - 9750 = 700 MHz. With the transverter option on the dial will display 700 + 750 = 1450. You normally know where you are so I don't see the point in displaying 10450 rather than 1450. In the event you go below the 10 GHz mark it will display say 990 MHz for 9990 MHz actually. I hope that anyone can do the maths...

Brgds, Edouard.