Lime mini/DATV-Epress

The place to discuss the use of the LimeSDR Mini for amateur TV applications
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Lime mini/DATV-Epress

Post by G8KUZ » Mon Jan 14, 2019 12:17 pm

My Lime mini works okay with DATV-Express when I first put it into tx mode. When I drop carrier to go into rx mode and then go back into tx mode it only transmits a carrier with no video content. If I restart DATV-Epress then it works fine again. I have to restart the program each time I do this.
Is this a bug in the current software (version 12) or am I missing something.
Current setup laptop i5 with Windows 10 running DATV-Express 25/12. C920 webcam 8 Mbyts ram.

Thanks in advance for any/all replies
John G8KUZ

PS I’m useless with computers especially pc’s with Windows 10. :roll: :roll:

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Re: Lime mini/DATV-Epress

Post by g8vpg » Tue Jan 15, 2019 9:29 am

I've only used my Lime SDR Mini and DATV Express using Vmix as the video source, and it definitely doesn't do what you report then. I will try it with my c920 direct, but you might see if Vmix works with your set up. I'm using Express v1.25LP12. Have you upgraded the Lime firmware? You need to do this and it can be done using the Portsdown software.
73 Shaun.

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Re: Lime mini/DATV-Epress

Post by dl6rcg » Sat Apr 04, 2020 5:27 pm

Hi Shaun,

I am using LimeSDR mini with Firmware 1.30 (updated with Portsdown) and DATV-Express V1.25lp14. Video/audio source is vMix.
When I look to the stream with VLC Player the video quality is perfect with my USB webcam. Transmitting this stream with my LimeSDR mini ends in a pixeled video (looks like low resolution). I have the same result with Portsdown (IPTS).
It is very hard to find informations to setup such a system correctly. Could you please give me some hints how to adjust the system to get a video without pixels? Thank you in advance.

73 de Tom, DL6RCG

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Re: Lime mini/DATV-Epress

Post by G8GKQ » Sat Apr 04, 2020 8:07 pm

Hi Tom

What Symbol Rate and FEC are you using?

It will be pixelated at low SRs and low FECs because there just aren't enough video bits for the information.

If it is a C920 webcam, you should get good results with the latest Portsdown build as long as you use a powered USB Hub for it and the LimeSDR, then select DVB-S, 333 kS, 9/10 FEC. As you adjust FEC downwards, the picture will degrade as there are less bits available to carry it.

Dave, G8GKQ

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Re: Lime mini/DATV-Epress

Post by g0mjw » Sat Apr 04, 2020 9:32 pm

Hi All,

With Express, the CODEC it is using goes into a weird pixillated mode if the input resolution is too high. You need to set the input resolution to something sensible. If it's H264 and 333ks you probably want something like 640x360 as a good starting point.

Those of us sending resolutions of 1080p and higher in narrow bandwidths are using different hardware based coding schemes and specifically H265 encoding. H265 is great but very hard to do without hardware help.


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