Playing with cheap VGA dongles as a digital to analog converter for ham radio
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README.md

fl2k

Use cheap VGA dongles as a digital to analog converter for ham radio

Based on great work from Steve Markgraf

This version is on Github I have a Blog post about my experiments so far

Objective

I'm stripping back the supplied FM example and statically linking the library code to make it easy to play with.

Longer term I'd like to be able to generate a decent HF signal that can be modulated for things like WSPR.

Build

On Ubuntu you might need:

sudo apt install git build-essential libusb-1.0-0-dev

To build just type:

make

You'll need to install the software this is derived from or you'll get this error:

libusb: error [_get_usbfs_fd] libusb couldn't open USB device /dev/bus/usb/002/014: Permission denied
libusb: error [_get_usbfs_fd] libusb requires write access to USB device nodes.
usb_open error -3
Please fix the device permissions, e.g. by installing the udev rules file

Build and install the software as documented here

macOS

All builds just fine on macOS but you need libusb which I installed using homebrew

brew install libusb

USB memory

You'll get this error:

libusb: error [op_dev_mem_alloc] alloc dev mem failed errno 12
Failed to allocate zerocopy buffer for transfer 4
libusb: error [submit_bulk_transfer] submiturb failed error -1 errno=12
Failed to submit transfer 0
Please increase your allowed usbfs buffer size with the following command:
echo 0 > /sys/module/usbcore/parameters/usbfs_memory_mb

On Ubuntu you'll need increase the USB memory buffer by running:

sudo sh -c 'echo 1000 > /sys/module/usbcore/parameters/usbfs_memory_mb'

See this article for more info and how to add this to the grub command line so it's permanent.

Run

Run locally.

./vgaplay  -s 130e6 -c 7e6 

-s is the sample rate of the software DDS. The higher the sample rate the better the sine wave output. You can probably go up to about 150MS/s

-c is the carrier frequency to generate. The closer the carrier frequency gets to half the sample rate, the more the signal becomes a square wave.

Here's how the waveform looks at 7.159MHz with 150Ms/s:

Beautiful CRO capture