BATC Forum

During the expansion of GB3NQ a problem has come to light when the output on the narrow channel ( It uses 1316MHz for HD and 1318MHz for SD at 333kSR ). The problem was a long delay ( up to 2 minutes ) and mickey mouse voices due to frequency doubling of the audio on the 1318MHz signal. Bench testing was using a RPI 5 running OBS to drive a Pluto with a test signal to be received on a Ryde as a signal source for the repeater. This received signal simulated the receiver at the repeater and it's output fed to a LinkPi encoder which fed two Plutos, one for HD and one for SD. These were received on a PicotunerNW and displayed via Opentuner. I also used two further Rydes which normally monitor the two channels. This setup showed no problems and I was wondering what I had missed. Then it was pointed out that I had not put the HDMI switch used to select the various Rydes for the different received frequencies of the repeater. I put a 4 way HDMI 'seamless' switch in between the Ryde and LinkPi encoder and the fault appeared! Changing this encoder for a different make and type made the fault go away and the system worked well again. The problem with the last switch is that it is not 'seamless' so switching may cause other problems.
I made a video of the fault and the testing.
https://youtu.be/TVJ01ZOgC6I

Martin G8LCE

Here is the test setup. The HDMI switch is shown in the green box.

G8LCE

While connecting to a monitor I noticed that the Ryde output was 1080i. This may be an explaination of the 'mickey mouse' audio. The system was seeing two lots of audio data per frame maybe. Anyway I changed the Ryde output to 1920 * 1080p @ 60Hz which matches the output of other RPi I have.
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To set Rpi output to 1080P @ 60Hz
Use Putty
sudo nano /boot/config.txt
Change the lines to look like these below
# uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group=1
hdmi_mode=16
Then reboot
Menu
12 Shutdown Shutdown, Reboot or exit to the Linux command prompt
2 Reboot now Immediate Reboot
The display should now be 1920 * 1080 @ 60Hz progressive scan
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This helped alot and the audio was about the right frequency - but a little lower it seemed!
Changing the HDMI switch to another type sorted the problem out. ( ATEN VS0801H 8 port HDMI switch )

NOTE:
The main HD output was not a problem. It was the 333kSR version that caused the trouble. The other thing I found was that the newer Linkpi with the latest firmware would work well at H265 on both 1316 HD and 1318 SD at the same time using multicast. The older LinkPi would only work at H264.

Martin G8LCE