Improving the LimeSDR Performance with Portsdown Buster

Discussion about this major DATV Project. See also https://wiki.batc.org.uk/The_Portsdown_Transmitter
g4hiz
Posts: 48
Joined: Thu Oct 18, 2018 6:40 am

Re: Improving the LimeSDR Performance with Portsdown Buster

Post by g4hiz » Tue Feb 18, 2020 6:31 pm

Hi all,

some test results at my end. Programmed a 32GB SanDisk Elite card as per the Wiki procedure; upgraded the Lime firmware to 1.30 then LimeDVB ok (as reported at the time). Interestingly, the Lime report page says 1.30.

All started ok first time, with 7 inch display correct way up. Tested the power output on 3 bands, results as below. Can't seem to get any significant power output for 'Carrier' mode but DVBS-2 ok. Power measured using an HP8481 head and HP436A power meter, last calibrated a long time ago, so measurements for indication only. Power head connected directly to the Lime Tx output with one N/SMA adaptor. Lime gain 100, DVBS-2, FEC 9/10, Test Card, all powers in dBm.

Power Levels.JPG
Power Levels.JPG (39.29 KiB) Viewed 1057 times


There seems to be a reduction in power at 1000ks/s for some reason and as mentioned 'Carrier' mode seems to give a very low power (<-16dBm) even on 436MHz.

One other observation, the touch screen seems slightly sluggish. The Pi3B+ and touchscreen were supplied from a dedicated PSU, with the Lime connected via a powered hub.

Many thanks to Dave G8GKQ for all the good work. Testing continues !

73

Jen G4HIZ

G8KOE
Posts: 28
Joined: Fri Aug 09, 2019 8:14 am

Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G8KOE » Thu Feb 20, 2020 10:02 am

Hi Dave,
Just installed Buster as idiot guide all now working.
All my tests are via Oscar.
Sym Rate 333 FEC 3/5 Lime Gain 95
Mod S2QPSK H264 Lime DVB 4:3 Source Webcam C920.
Static pictures good with sound.
Sound and picture breaks up with movement in picture.
vMIX with IPTS in works well.
I can't change all the Presets.
Manually input change of frequency.

Will keep testing
Martin

g4hiz
Posts: 48
Joined: Thu Oct 18, 2018 6:40 am

Re: Improving the LimeSDR Performance with Portsdown Buster

Post by g4hiz » Thu Feb 20, 2020 12:51 pm

Hi all,

an update on my power table above. Unfortunately, the 2.4GHz results posted were for a Lime Gain of 90 not 100 as stated. The 436 and 1255MHz results were ok. It shows how you have to be careful when changing frequency as other stored settings may change. The corrected table is below. What I have also done, is to show how power output varies with Lime Gain and the effect on the spectrum, for 1Ms/s at 2.4GHz. All results DVB-S2.

73
Jen G4HIZ
Attachments
Power Level Lime Gain100.JPG
Power Level Lime Gain100.JPG (36.46 KiB) Viewed 932 times
Power Level vs Lime Gain 2.4GHz.JPG
Power Level vs Lime Gain 2.4GHz.JPG (48.03 KiB) Viewed 932 times
1Ms.JPG
1Ms.JPG (65.99 KiB) Viewed 932 times

G8GKQ
Site Admin
Posts: 1418
Joined: Sun Mar 22, 2009 1:21 pm

Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G8GKQ » Thu Feb 20, 2020 1:02 pm

Thanks for the correction Jen - I was having trouble reproducing your 2.4 GHz results!

I have identified the reason for the 1000 kS power drop and will correct it in a minor update later today. This will potentially worsen the 1000 kS spectrum at high Lime Gain levels, as the spread is quite simply caused by overload in the Lime output stage. Reduction in Lime Gain to produce the same output level as shown below will result in the same performance.

Dave

G8GKQ
Site Admin
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Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G8GKQ » Thu Feb 20, 2020 1:09 pm

Martin

Just tried to reproduce your problem with the presets, but can't find anything wrong. Please could you describe how it does not work?

Are you using VLC to view the received C920 pictures or the player in MiniTioune? MiniTioune is very fussy, but VLC does not seem to have problems when I try it.

Dave

G8KOE
Posts: 28
Joined: Fri Aug 09, 2019 8:14 am

Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G8KOE » Thu Feb 20, 2020 3:59 pm

Hi Dave,
I Have Keyboard set to 2409.750
Preset 1 2407.750
Preset 2 2408.250
Preset 3 2408.750
Preset 4 2409.250

Direct frequency entered 2409.750 TX OK
Select Preset 1 set to 2407.750 frequency changes to 2407.750 TX OK
Select Preset 2 set to 2408.250 frequency changes to 2409.750 TX OK on 2409.750
Select Preset 3 set to 2408.750 frequency changes to 2409.750 TX OK on 2409.750
Select Preset 4 set to 2409.250 frequency changes to 2409.750 TX OK on 2409.750

I am using both VLC and MiniTioune.
VLC usually handles signals better.

Just pleased to have signals to work with.

73's
Martin

G8GKQ
Site Admin
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Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G8GKQ » Thu Feb 20, 2020 4:21 pm

Hi Martin

I have just tested this exact setup and it works for me. It was fiddly to set up though!

Sorry, but I now have to ask the obvious question: Please confirm that you have changed the frequencies (by changing the manual frequency before selecting store preset and choosing the button), not just the labels of the buttons.

If there still seems to be a problem, have a look at the file

Code: Select all

/home/pi/rpidatv/scripts/portsdown_presets.txt
The preset frequencies and labels (p1freq and p1label etc) are defined very near the bottom of the file.

Dave

G8KOE
Posts: 28
Joined: Fri Aug 09, 2019 8:14 am

Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G8KOE » Thu Feb 20, 2020 4:49 pm

Hi Dave,
Yes it was me not operating your software correctly.
All working now.
I had forgotten the correct method of setting the presets.

Thanks for your help!

Sorry.
Martin

ON1BTE
Posts: 6
Joined: Tue Aug 13, 2019 6:01 pm

Re: Improving the LimeSDR Performance with Portsdown Buster

Post by ON1BTE » Sun Feb 23, 2020 2:38 pm

Hello,

today installed the Portsdown 2020 with Buster and it's great.
With the special DVB Firmware (output to Lime DVB) the spectral image for SR >500ks has been greatly improved !
With a Lime Gain of 90 you get +/-50dB.
I only use it with the IPTS. The stream is created with a Tandberg Encoder EN8090. Fantastic images ... !
I only have one remark, the 16APSK and 32APSK mode doesn't work anymore. You only see some increased noise with a carrier in the middle.

Well done !
73 - Patrick - ON1BTE

G8GKQ
Site Admin
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Re: Improving the LimeSDR Performance with Portsdown Buster

Post by G8GKQ » Sun Feb 23, 2020 5:38 pm

Hi Patrick

Thanks for the positive comments.

Yes, the custom DVB firmware only supports QPSK and 8PSK (although I have not tested 8PSK yet). I have documented all the limitations that I know of on the Wiki https://wiki.batc.org.uk/Portsdown_2020 ... B-S2_Modes. I hope to rectify some of these limitations, but I think that 16APSK and 32APSK will only ever be possible using the basic Lime firmware.

Dave

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