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Documentation for a half-duplex digital radio link between two of the Raspberry Pi 3+ SBCs. The hardware selection is meant to allow low cost, fast and open development of an digital radio network.

We start the development with two of the SBC, one as a TX and one as an RX.

I'm goinig to attempt to recreate this tutorial in an effort to secure a workable data connection over RF.

The TX function is achieved with a simple USB to VGA adapter that was discovered to be an effective DAC for high-speed data output (sampling generation). - FL2k SDR Synthe

From this tutorial I was able to achieve this functionality (an UMTS signal rendered by the dongle, as viewed from SDR# on windows 10):

It should be noted that this was just one of a myriad of harmonics all containing effectively the same information.

The RX function is of the venerable RTL-SDR dongle type. - RTL-SDR Receiver

This is all tied together with gnu-radio at the crux.

Here is a photo of the setup as it currently stands.

The VGA cable from the FL2k has an improvised SMA connection (also pictured).

It's nothing special, but it should keep any spurious emissions (of which there are countless) off of the air. The signal is routed through cables, a variable attenuator, and then to the SDR receiver (RTL dongle).

Next steps: Design a board to provide appropriate filtering for the VGA dongle for higher-order amplification and integration into an RF signal chain. Ultimate goal is an over-the-air demonstration, but to achieve this we need to filter out some of the horrendous harmonics this device is generating.

Starting off with:

DB-15 Male connector (PCB through-hole):

I invision something like this to house the main filter:

The filter could be:


Would need a balun like:

fl2k_synth_rtl-sdr_receiver.txt · Last modified: 2019/04/12 15:19 by weilawei