BATC Forum

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.




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 .

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.

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

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

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

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

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.