Going full duplex with amateur satellites, part 14: Switch to FUNcube Dongle Pro+ / 2019-07-20

2019-07-20 Going full duplex with amateur satellites, part 14: Switch to FUNcube Dongle Pro+ 1 month ago
FUNcube Dongle Pro+ I saw a radio amateur offering a secondhand FUNcube Dongle Pro+ for a very reasonable price and remembered my work to get into linear satellites and the problems with the input filtering on an rtl-sdr while transmitting. So I checked the specifications for that dongle and saw a lot better filtering.

I decided to go for it and a few mails later the dongle was on the way to my letterbox. Literally, as it fitted in a small package that could be delivered in the letterbox. With tracking, so I received a notification from the package tracker app after the mailman put it in the letterbox.

There is good support for the FUNcube dongle Pro+ in gqrx so I tried that first. It does give some USB errors:
[46918.612090] usb 2-1: new full-speed USB device number 10 using xhci_hcd
[46918.762268] usb 2-1: New USB device found, idVendor=04d8, idProduct=fb31
[46918.762273] usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[46918.762276] usb 2-1: Product: FUNcube Dongle V2.0  
[46918.762278] usb 2-1: Manufacturer: Hanlincrest Ltd.         
[46918.797477] usb 2-1: 1:1: cannot get freq at ep 0x81
[46918.803092] hid-generic 0003:04D8:FB31.0003: hiddev0,hidraw0: USB HID v1.11 Device [Hanlincrest Ltd.          FUNcube Dongle V2.0  ] on usb-0000:00:14.0-1/input2
[46918.917284] usb 2-1: 1:1: cannot get freq at ep 0x81
[46918.955162] usb 2-1: 1:1: cannot get freq at ep 0x81
It does show as a valid device in gqrx and I was soon decoding audio with it. The easiest decoding was in the VHF II FM broadcast band. After all the work with the 2 MHz wide spectrum from the rtl-sdr it takes a bit of adjusting to start working with 192 kHz spectrum from the FUNcube dongle but qgrx moves that bit nicely when needed.

To the computer, the dongle is an USB device with two subfunctions: an usbaudio device and a usbhid device. The audio device is used to deliver sampled radio spectrum and the hid device is used to control the dongle. This is why it's relatively easy to use softwarewise: modern operating systems have usbaudio support and usb hid control from a user application isn't too hard either.

One of the things I do want is a lot of interesting audio routing to be able to record both the downlink audio and my own audio. So I fired up pavucontrol and gqrx crashed. Restarting gqrx did not work until I closed pavucontrol. Some searching found gqrx crash with Funcube Pro+ which suggests to turn the device off for PulseAudio. Which may seem strange but PulseAudio is also using the alsa drivers which gqrx tries to use. I guess there is some conflict between gqrx and PulseAudio in dealing with the alsa drivers. After switching the FUNcube Dongle Pro+ in PulseAudio I could open the dongle in gqrx and play with audio settings for other channels in pavucontrol.

The setup with gpredict controlling the receive frequency of gqrx also worked fine, so this is looking good. Now to find out how things work on an FM or linear satellite.

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