Analogue output & PTT

Discussion about this major DATV Project. See https://wiki.batc.org.uk/The_Portsdown_Transmitter
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KA5BBC
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Analogue output & PTT

Post by KA5BBC » Mon Sep 13, 2021 1:43 pm

Has the ability to output composite video to an analogue transmitter and to trigger the PTT been completely lost in this iteration or is there a work around?
Andy, KA5BBC/MM0BQV

g0mjw
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Re: Analogue output & PTT

Post by g0mjw » Mon Sep 13, 2021 1:49 pm

What do you mean? Iteration of what version?

KA5BBC
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Re: Analogue output & PTT

Post by KA5BBC » Mon Sep 13, 2021 2:33 pm

This current iteration of the Portsdown build.

I can find on the wiki that was running in the 2018 build but I can find a reference to it after that.

I would like to be able to include an analogue transceiver in to my build as there are still many analogue ATV users in the US as four of the, now defunct, UHF cable TV channels are within the 70cm band and therefore standard home/portable TVs can be used.
Andy, KA5BBC/MM0BQV

G3GJA
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Re: Analogue output & PTT

Post by G3GJA » Mon Sep 13, 2021 7:59 pm

The Portsdown was not primarily designed as an analogue source, so it's not a much of a priority to maintain the analogue output as things move on.

There are two dedicated analogue progams for the Pi; there is a test card program that will run on a Pi Zero that has an analogue output; see here: https://github.com/BritishAmateurTelevi ... /vidsource It will also run on the original Pi Model B (with the composite connector).

Alternatively, there is a program written for the Pi by Brian G4EWJ that can output a slide show and a scrolling banner from the baseband video output in PAL or NTSC. I can't remember which issue of CQ-TV it was published in. Sorry!

Clive G3GJA

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Re: Analogue output & PTT

Post by G8GKQ » Mon Sep 13, 2021 8:27 pm

The Portsdown 2020 software build running on a Raspberry Pi 3 (which is still fully supported) retains the ability to provide a composite video output. If configured as a stream receiver, it can be used to key a transmitter when a valid stream is received. See here https://wiki.batc.org.uk/Stream_Receiver.

The video output capability is not easily provided in the Portsdown 4 with the 7 inch screen as the touchscreen graphics had to be totally re-written due to the Raspberry Pi Foundation dropping support for OpenVG graphics in the Raspberry Pi 4. The graphics screen size is now hard-coded to 800x480 and is not easily duplicated on the 720x576 (PAL) or 720x480 (NTSC) framebuffer used by the analogue video output.

The Video Source mentioned by Clive was specifically designed to fill the capability gap left by the Portsdown 4's lack of video output.

dave

KA5BBC
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Re: Analogue output & PTT

Post by KA5BBC » Tue Sep 14, 2021 2:46 pm

I really like the stream receiver idea but I will probably apply that too an IP input to the system, It is a shame that it will not use the HDMI output with that one but I have plenty of converters.
I don't think that I'm going to be able to use the Portsdown to supply analogue signals and PTT to a VUSB modulator so will keep as purely digital and have a separate analogue system in the same rack.
On the repeater side I was hoping to be able to have output on both analogue and digital simultaneously, both in the same band would have been fantastic but just no practical. What I may be able to do is just go with digital and analogue inputs and analogue output until I can come with a better solution.
Andy, KA5BBC/MM0BQV

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