LimeSDR Mini DVB Output shoulders

The place to discuss the use of the LimeSDR Mini for amateur TV applications
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M1SJE
Posts: 3
Joined: Fri Aug 02, 2019 6:37 am

LimeSDR Mini DVB Output shoulders

Post by M1SJE » Tue Sep 10, 2019 10:57 pm

Hi there,

Slowly getting ready to use QO-100 on WB but when I checked the output, it was barely usable.

Even with the power set really low, the shoulders that grew from it were too much (less than 20db below).

Here are 2 screen prints from the VSA, 435MHz vs 2400MHz.

Image
Image

Is there something wrong with my LimeSDR, or is there something i'm missing, because having just built a 250w PA, I'm not going to transmit with those shoulders on the sat, i'll end up consuming the channels either side :/

Thanks for any help :).
Sarah M1SJE

g4eml
Posts: 40
Joined: Thu Apr 26, 2018 9:36 am

Re: LimeSDR Mini DVB Output shoulders

Post by g4eml » Wed Sep 11, 2019 9:40 am

My Lime mini performs about the same as yours. For that reason I use it at 430MHz and then mix up to 2.4GHz. It gives me a much better signal. On local testing I get a better MER and cleaner looking constellation than using it directly on 2.4GHz.

Having said that other people have had different results so I suspect the Lime Mini performance at high frequencies varies quite a bit.

In practice shoulders that are 20dB down will not be seen on the satellite. The noise floor is only about 8-10dB down even on a strong wideband signal. So although not ideal it would still be usable and I suspect many people are getting away with it.

G8GKQ
Site Admin
Posts: 1288
Joined: Sun Mar 22, 2009 1:21 pm

Re: LimeSDR Mini DVB Output shoulders

Post by G8GKQ » Wed Sep 11, 2019 9:48 am

Hi M1SJE

First of all, what are you using to drive the LimeSDR Mini? Portsdown, DATV Express, GNURadio or custom code?

Second, what are your selected transmitting parameters?

Do try at 432 MHz as suggested by Colin.

Dave, G8GKQ

M1SJE
Posts: 3
Joined: Fri Aug 02, 2019 6:37 am

Re: LimeSDR Mini DVB Output shoulders

Post by M1SJE » Wed Sep 11, 2019 7:03 pm

Hi and thanks for the replies :)

I agree the 70cm's output is better, and i'd prefer to just go straight to 2.4ghz, but if I have to mix it up to that, then so be it :/.

The settings I used for 2.4ghz didn't really matter, as no matter what SR/FEC/power level, it was always distorted, only time it wasn't was when the signal was so low, that any of the shoulders were hidden under the noise floor of the receiver. I also used portsdown and express DVB, which suggests to me that it isn't a software issue, but a hardware issue.

I'll try sending a test signal up when it's quiet to see if it's hidden by the noise floor by the time it gets to the satellite.

If that doesn't work, i've just got a Pluto from digikey, and the output on 2.4ghz is clean as a whistle :).

Thanks for your help,

Sarah M1SJE
Sarah M1SJE

G8GKQ
Site Admin
Posts: 1288
Joined: Sun Mar 22, 2009 1:21 pm

Re: LimeSDR Mini DVB Output shoulders

Post by G8GKQ » Wed Sep 11, 2019 8:46 pm

Hi Sarah

It might be worth checking the firmware/gateware standard on your LimeSDR Mini. A mismatch between what is loaded and what is required can cause the symptoms that you are seeing. In Portsdown, try Menu 3, Lime Config, Lime FW Info. You can also try Lime Report (which runs LimeQuickTest) while you are in that menu. Details here: https://wiki.batc.org.uk/Using_LimeSDR_ ... ation_Menu

Dave, G8GKQ

BG0AUB
Posts: 12
Joined: Sat Feb 16, 2019 8:16 pm

Re: LimeSDR Mini DVB Output shoulders

Post by BG0AUB » Thu Oct 10, 2019 2:28 am

g4eml wrote:
Wed Sep 11, 2019 9:40 am
My Lime mini performs about the same as yours. For that reason I use it at 430MHz and then mix up to 2.4GHz. It gives me a much better signal. On local testing I get a better MER and cleaner looking constellation than using it directly on 2.4GHz.

Having said that other people have had different results so I suspect the Lime Mini performance at high frequencies varies quite a bit.

In practice shoulders that are 20dB down will not be seen on the satellite. The noise floor is only about 8-10dB down even on a strong wideband signal. So although not ideal it would still be usable and I suspect many people are getting away with it.
What use mixer from 430 up2400?I also want to try to do so

g4eml
Posts: 40
Joined: Thu Apr 26, 2018 9:36 am

Re: LimeSDR Mini DVB Output shoulders

Post by g4eml » Thu Oct 10, 2019 9:54 am

I use the BU500 from Hides.
I have also designed and built a simple mixer using surplus components from the U.K. Microwave group and that also works well.

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