Portsdown pluto PTT -stop- not working

Discussion about this major DATV Project. See https://wiki.batc.org.uk/The_Portsdown_Transmitter
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keng8vdp
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Re: Portsdown pluto PTT -stop- not working

Post by keng8vdp » Sun Jun 05, 2022 2:21 pm

G8GKQ wrote:
Sun Jun 05, 2022 1:46 pm
Hi Ken

I really do not know what the problem is with your Portsdown and Pluto PTT. I'm sure we'll solve the mystery eventually. Does it do the same when you have no connector on the Pluto output - I am thinking a high current ground loop could be upsetting things?

Please could I suggest a different way of operating your QO-100 station? I use a separate physical switch for the QO-100 PA; I never turn this on until I know that the Portsdown is up and running. During QO-100 QSOs (such as the Thursday evening QO-100 Net) I leave the Portsdown set to transmit all the time (for over 2 hours) and just switch the PA on when I want to transmit. This means that there is no delay when it is your turn to transmit, and you can turn the PA off instantly if there is anything that you are worried about.

Also, I monitor 2409.75 MHz (or whatever uplink frequency is in use) locally in the shack on another receiver to make sure that all is well before switching the PA on.

Lastly, as a luxury, a switched RF attenuator with a hardware control in the transmit line between the Portsdown and the PA would enable you to adjust the power correctly without needing to stop transmission.

Hope that helps.

Dave
Dave,
Excellent suggestions. Earlier today I fitted one of the small Chinese amplifiers between my pluto & final Amplifier. This allowed me to reduce Pluto output. (intended) as I was suspecting I might be reaching saturation on the main output Amplifier. Fortunately that small amp is 5v & I had included 5v & 12v outputs on side of my Portsdown by way of 2 DC sockets via switches and LEDs. This allows me to turn the Chinese amplifier on & off. So at least I can halt the drive to final Amplifier at will. ( This then gives me more time to find a way off shutting of the output ).
The pluto output now set at -20
This gives me enough output to still get in on 333 SR &
⅓rd fec. 30w out to helical on 1.1m dish
I thought this lower output might improve the issue. Unfortunately not.

Later I will do the other check you suggested. Only the Pluto & attempt to receive it as-is.
I'll report back what happens

Once again. Many thanks . Ken

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keng8vdp
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Re: Portsdown pluto PTT -stop- not working

Post by keng8vdp » Sun Jun 05, 2022 3:02 pm

Further to post above,

I've now done pluto only test with Rx direct on 2405.75

On C920 webcam as source the tx stops ok after tapping screen 6 seconds. I was able to do this repeatedly with same result. Reception stops 6 seconds later.

On source TestCard. The tx stops at average time 54 seconds after tapping the screen. Confirmed by mer drop on miniTiouner/other Portsdown, then reception stops. Again same on several tries but varies occasionally as much as to 68 seconds

Next I added the small Chinese amplifier that's doing around 50mw out with pluto drive at -20 and the shut off after tapping screen remained to same. 6 seconds to stop using c920 & around 1 minute using built in TestCard.

Ken

PS. Reminder as mentioned earlier- My larger home made amplifier 50w as used regular with pluto in Langstone mode works perfectly switching ssb on & off with screen button or fist mic. I've never had it stick on.

This is the same amplifier I'm using to access WB transponder. But of course in ATV mode there is only the screen PTT. So, it looks like this issue is only Portsdown not Langstone

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keng8vdp
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Re: Portsdown pluto PTT -stop- not working

Post by keng8vdp » Thu Jun 09, 2022 2:26 pm

I had a message from Clive G3GJA regarding this problem. Copy paste here:

"Managed to recreate your no TX drop issue on my Portsdown during the EY net last night. Fortunately had Lyndon here and he identified the problem. The Pluto can't cope with the data rate so the cache in ffmpeg grows and grows. You can see this in an SSH session on the Portsdown if you type "htop". The amount of memory used by ffmpeg just gets bigger an and bigger because the Pluto input rate limits the data stream. The same thing happens in Windows with FreeStreamCoder / OBS. Ffmpeg used over 0.5GB of RAM after a few minutes and kept climbing. Probably won't happen on the Lime in your case because of the lower resolution (one quarter) and consequent lower data rate"

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keng8vdp
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Re: Portsdown pluto PTT -stop- not working

Post by keng8vdp » Fri Jun 10, 2022 11:44 am

Here's my Portsdown with lime-mini working fine.

https://youtu.be/FW3UxfCeQY4

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