SSTV transmission by Raspberry Pi

This is not a complete description of the way to get the R_PI to send SSTV images. For a complete set of programs and instructions please go to GitHub/F5OEO/rpitx.

I extracted the files I needed to a new directory "SSTV":

-rwxr-xr-x 1 pi pi   15512 Mar  9 11:09 pisstv
-rwxr-xr-x 1 pi pi  103644 Mar  9 11:09 rpitx
-rw-r--r-- 1 pi pi   15488 Mar  9 11:23 test1.jpg
-rw-r--r-- 1 pi pi 3968512 Mar  9 11:24 test.ft
-rw-r--r-- 1 pi pi  245760 Mar  9 11:24 test.rgb
-rw-r--r-- 1 pi pi     167 Mar  9 12:03 Usage.txt

I have described in a previous post the Arduino based SDR receiver shields that give me reception on 40m. The IQ audio outputs are connected to the iMac with a A/D converter (a Startech device). On the iMac I have running the SDR program HDSDR, a windows program running under Wine.



The audio output of the HDSDR program is fed to Soundflower, a Mac prograam to route audio from one app to another.

To view the SSTV signals (mine or anyone else's received over the air) the Mac program Multiscan 3B is used. Its audio input is taken from Soundflower so that it is listening to the HDSDR radio.

After installation of the RPITX stuff and installing the programs - see the RPITX web site README - I created a test.jpg file for trial transmissions:



This file is 320x256 pixels and a JPEG (a PNG file can be used). It was converted to RGB using the utility "convert" from imagemagic. This produces an RGB file. Which is then encoded using pisstv to create the FT file for transmission. Finally the transmission is made -m)ode RF, -i)put picture.ft on -f)requency 7171kHz. (I found that either my R_PI output is 100Hz low, or the SDR tunes 100Hz high, but to get a correct SSTV spectrum I had to offset the SDR by 100Hz).The build commands are:

  convert -depth 8 picture.jpg picture.rgb

  ./pisstv picture.rgb picture.ft

  sudo ./rpitx -m RF -i picture.ft -f 7171.0

The received picture was not perfect, but its pretty good for a Raspberry Pi acting as SSTV encode and transmitter, with RF output on GPIO18, fed via a 40m LPF to surpress harmonics.





I tried also with a photo of my wife and it came across "real bonny".