Improving the LimeSDR Performance with Portsdown Buster

Discussion about this major DATV Project. See also https://wiki.batc.org.uk/The_Portsdown_Transmitter
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Improving the LimeSDR Performance with Portsdown Buster

Post by G8GKQ » Thu Feb 13, 2020 10:19 pm

The new Portsdown Buster build is designed to be used with the LimeSDR Mini running custom DVB firmware. I have now completed initial testing of this build (202002140) and am pleased to report that it resolves many of the issues (some modes not working, transmission breaks, etc) of the old Portsdown Stretch build.

Additionally, it supports the transmission of high SR DVB-S transmissions (up to 10 MS, if you must), so is suitable for transmitting to many of the existing ATV Repeaters. The usable DVB-S2 SR is limited to about 2 MS.

The one drawback is that the LimeSDR Mini needs to have the custom DVB firmware loaded, and so cannot be instantly used to transmit with other applications such as SDR Console. However, you can reprogram the firmware easily back and forth (Menu 3, Lime Config) and it is EEPROM based, so each LimeSDR Mini has a lifetime of at least 10,000 re-writes.

I have optimised the DVB-S2 modes for QO-100 use. The 333 KS FEC 1/2 transmission will transmit good SD pictures and only needs 1 dB S/N for reception, so can be transmitted with lower power or a smaller dish. The video source can be the Pi Camera, the EasyCap (Composite Video) or the C920 webcam.

There is no upgrade path from Stretch - you will need to build a new SD Card. There is a Wiki page listing the working modes here https://wiki.batc.org.uk/Portsdown_2020_Buster_Software and the build instructions are here https://github.com/BritishAmateurTelevi ... own-buster.

Modes not listed on the Wiki page have not been tested, so please don't complain that they are not working. The software will not support the LimeSDR USB, webcams other than the C920, or the Raspberry Pi 4. It is hoped to support the LimeNET Micro and LimeRFE amplifier as development progresses.

Please report your experiences with this build in this topic.

Dave

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Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G0LJF » Fri Feb 14, 2020 11:29 am

Hi Dave,

Thanks for this update to P.

Please, seeing as I have just constructed a brand new P2019 with the latest Stretch build, would you now be advising me to go straight to this Buster release?

The reason I ask may sound stupid, but I am having problems making sure a particular mode in the exiting Stretch build does not drop Tx power and is, above all, reliable. It it does not work at all that is fine.

This is because all my other stuff (the technical phrase) is also new and I need to know what I can really rely on.

To date I have had to put my diode probe RF detector on P2019 to check if it is reliable in terms of Tx power before doing any other system testing, if you follow me.

Ta, 73, Mike

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Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G8GKQ » Fri Feb 14, 2020 12:23 pm

Hi Mike

The answer is "it depends". If you are using a Pi Cam as your video source with a LimeSDR Mini, then all should be fine on the Portsdown 2019 build. Other video sources do suffer from power drops, but if you stick to the green squares here viewtopic.php?f=103&t=6070#p19583 they are not too bad.

If you want to transmit to DVB-S2 to QO-100 using a Lime SDR Mini, then I would recommend that you use Portsdown 2020 on Buster, as that seems to be working perfectly with the Pi Cam, EasyCap (Comp Vid) or C920 as video sources. You will need to change the firmware on the LimeSDR Mini. This is easy and the instructions are on the Wiki page.

Perhaps if you describe what you are trying to achieve, and with what gear, I can give some more direct advice.

73

Dave

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Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G0LJF » Fri Feb 14, 2020 1:34 pm

OK Dave, Tnx,

I am working on Es'Hail2 exclusively, and so I think you have answered my question.

I have just bought another San Disk Ultra 16 GB card so will 'make' another SD card build now.

My problem is the lack of Tx reliability with Stretch; I initially thought that an external video source would be good (as I can just leave that playing, reliably, while I test things out). However, this is unreliable, as you no doubt know.

So I had to go for the PI Cam instead.

I could not get any decode at at all with 66 Kb Symbols/s Tx by the way (Pi Cam). MT Pro just shows a "X" on the constellation display, so that seems like a no-go option?

I am going for a full Buster build now...

Thank you, 73,

Mike

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Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G0LJF » Fri Feb 14, 2020 3:33 pm

Hi Dave,

Brand new Sandisk 16 GB Ultra card refused to boot due to a problem with init_resize.sh failing (with a -8 error).

It seems that this script is supposed to resize the SD card's partition to the maximum available space before the OS files are then expanded.

Solutions involve removing this line from the /boot/cmdline.txt file and another is to do with creating an image of the right size for the SD card.

I used win32diskimager V0.9, not V1 as this works on XP, but I cannot see how this would cause the problem.

Anyhow, as this is your project, what do you recommend, please?

Ta, 73,

Mike

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Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G8GKQ » Fri Feb 14, 2020 5:09 pm

Mike

This problem with init_resize.sh is not a Portsdown problem, but a problem with your card or disk imager.

My first thought is that you should download the Buster Lite image again (it could be corrupt), and then write it to the card again. If that does not solve it, try using Etcher (https://www.balena.io/etcher/) instead of win32diskimager.

Is it the BATC card (E80) that you are using or another one? If not the BATC one, are you sure that it is genuine?

How are you seeing the error message?

Dave, G8GKQ

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Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G0LJF » Fri Feb 14, 2020 6:36 pm

Hello Dave,

Thanks for the reply.

I am trying a SD card re-format and then to reload the Buster image.
Unfortunately Etcher requires Win7 or above and my laptop with the SD card reader is XP.
It runs on this W7 PC fine so maybe I can flash it as a remote drive.

Anyhow, I will persevere, and try again as you say, with a freshly downloaded Buster Light image (from RPi).
I did compare the old and the freshly downloaded images and they are exactly the same size but I did not run a CRC check.

But I am checking the new SD card for any errors after the re-format was completed (seems to be a long winded process).

As for the card, it was in authentic packaging from Asda. Not from eBay. Looks genuine to me.

I do have the original one you prepared that has "E80" written on i too. If all else fails.

As for where do I see this message, its shown on the 7" display as the last line of an aborted boot sequence. The OS never has the chance to load as, I presume, it never gets correctly written to the SD card.

73, Mike

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Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G8KOE » Fri Feb 14, 2020 9:44 pm

Hi Dave,
Is vMIX supported in the new image?

73's
Martin
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Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G8GKQ » Sat Feb 15, 2020 11:46 am

Hi Martin

vMix input is not something that I have tested or tried to do. Was it possible in Portsdown Stretch?

Dave

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Re: Improving the LimeSDR Performance with Portsdown Buster

Post by g8gtz » Sat Feb 15, 2020 12:41 pm


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