Using SDR Sharp in with FLdigi
I recently set up a software defined radio (SDR) on my Model B Raspberry Pi, running arch Linux. Here are the components of my set up:
NooElec NESDR Nano SDR & DVB-T USB Stick (R820T)
Ham It Up v1.2 - RF Upconverter
Raspberry Pi Model B
Desktop computer running Windows 7
I run the rtl_tcp server from the Raspberry Pi, which is streamed over the LAN to my Desktop (running Windows). The easiest software I found for this was SDR Sharp, which is free, and supports a rtl_tcp connection. SDR Sharp supports various voice modes (SSB, AM, FM, etc.). It doesn't, however, decode digital modes. I had previously used SDR-Radio v1.5 for decoding digital modes with an old receiver and an MDSR LIF, tapping the IF out of my Panasonic DR-49 (a.k.a. Panasonic RF 4900). This worked great, but I got the desire to try the DVB-T stick as an SDR. I was trying to get it working wtih the SDR-Radio v2.0, but I couldn't seem to get it working with an rtl_tcp connection, and found the digital decoding part of the software to be very hard to figure out.
The solution was the SDR Sharp software, paired with FLdigi. The requirements for FLdigi are simple - all you need is an audio stream, and it will decode the digital signal from the audio. Some sound cards have the ability to loop back their own output to their input, but I just used a temporary workaround of a mono 3.5mm cable, plugged from the Mic to the Speaker input. Here are the steps I took, after downloading and installing the FLdigi software on my Windows 7 computer:
1. Start FLdigi => Configure => Sound Card => Devices => Choose Port Audio => Capture: Microsoft Sound Mapper - Input => Playback: Microsoft Sound Mapper - Output.
And after I started the rtl_tcp server on the Raspberry Pi, started up SDR Sharp and connected to the rtl_tcp server, it just worked. The audio came in from the sound output, to the mic input, and the FLdigi software decoded the signal just great.
Next, I plan on setting up an "audio loopback device," also called a "virtual audio cable" (VAC) to replace the external 3.5mm mono cable I had plugged in. More to follow.