Lime Mini shoulders ?

[G4WIM]

Hi guys,

While checking over my QRO amplifier for linearity I found the performance of the Lime Mini to be a contributing factor - more than expected.

Just been doing some tests with the Lime Mini at various symbol rates and power outputs but the best shoulder performance I could measure was -30dB with the Portsdown power control set to 95.

Interestingly reducing the power setting on Portsdown to 80 actually made the shoulders worse at -28dB.
I was wondering if these figures are typical ?

Symbol rate didn't seem to make much difference as you might expect.

Certainly my DATV Express is much cleaner.

Regards Tim

[G8GKQ]

Tim

The shoulders should be better than that out of the LimeSDR Mini. Please could you tell me:

What Portsdown Software version you are running (Menu 2, Info)

What LimeSDR Firmware Version, Gateware Version and Revision (Menu 3, Lime Config, Lime FW Info).

Are you running stock Portsdown software unmodified?

Thanks

Dave, G8GKQ

[G8GKQ]

This is my Lime Mini, 2408 MHz, Lime Gain 85, 500KS. Image is 500 kHz/div, 10 dB/div. So at least 45 dB shoulders, but it's only a homebrew analyser....

Dave, G8GKQ

[G4WIM]

Hi Dave,

I'll get back to you tomorrow (Saturday) with the data as it's too hot and too late in the shack right now !

I'll use the same settings as you have above for the tests.

Regards Tim

[G4WIM]

Hi Dave,

Good news I got exactly the same results as you at 500k but as soon as I increased the SR to 2MS the shoulders came up to -30dB.

Same results if I have the Lime directly on the RPI or via Jetson.

See attached pictures.

On the RPI I'm running Stretch 201906060, Lime reports FW version 6, HW version 2 Protocol Version 1, Gateware version 1 and Gateware revision 29.

Regards Tim

[G8GKQ]

Hi Tim

That is good news and explainable. At lower symbol rates, the RPi has the computer power to send the Lime more samples - giving it a better waveform/spectrum. At higher symbol rates, it simply does not have enough processing power, so it does not oversample. Here is the switching code:

Code: Select all

    if [ "$SYMBOLRATE_K" -lt 990 ] ; then
      UPSAMPLE=2
      LIME_GAINF=`echo - | awk '{print '$LIME_GAIN' / 100}'`
    elif [ "$SYMBOLRATE_K" -lt 1500 ] && [ "$MODULATION" == "DVB-S" ] ; then
      UPSAMPLE=2
      LIME_GAINF=`echo - | awk '{print '$LIME_GAIN' / 100}'`
    else
      UPSAMPLE=1
      if [ "$LIME_GAIN" -lt 6 ]; then
        LIMEGAIN=6
      fi
      LIME_GAINF=`echo - | awk '{print ( '$LIME_GAIN' - 6 ) / 100}'`
    fi

The even better news is that Evariste and a colleague have been working on a custom FPGA build for the LimeSDR Mini (not the LimeSDR USB) that will allow 2 or possibly even 4 times upsampling at 2MS. I've been testing it, but there is a lot of integration work to be done to get it into the Portsdown.

Dave, G8GKQ

[G4WIM]

Thanks for the explanation - makes perfect sense.

Out of interest I'll repeat the experiment but use the jetson to drive the Lime.

On an unrelated manner I'm still having trouble getting my LKV to play nicely with the rpi / jetson - I think I may have messed up the FW in the lkv so have another LKV arriving in the next day or two.

Question - will the LKV work with jetson / rpi using the stock FW or is it mandatory to upgrade the FW in the lkv as per the wiki ?

Regards Tim

[G8GKQ]

The Jetson should do better - but check the UPSAMPLE factor in the script.

Problems with the LKV can often be due to the network router being unhappy abouit the broadcast UDP traffic that the LKV generates. I have one router that totally fails to do any routing if the LKV is connected. Others are patchy, and I have one (a TP-Link TL-WR841N) that is perfectly happy.

I have now put the LKV and Jetson on an isolated network using that router. I have also set up a port-forward for SSH from the WAN port so that I can connect the WAN port to my home network and control the Jetson from the Portsdown, but do not spray broadcast UDP packets around my home network.

I think that the LKV does work unmodified, but I'm not sure that it does full HD in that state.

Dave, G8GKQ

[g0mjw]

I think it does Dave, but better with the right firmware.

Mike

[G4WIM]

A bit off topic, but I've set up a VLAN on my Draytek 2860n just for the LKV, RPI and Jetson as without it the LKV multi cast traffic was reeking havoc on the domestic network taking out the Sonos audio system and breaking youtube to the TV's etc !

The LKV / Jetson did work for a while then stopped again - despite there being multicast available for the Jetson.

Going to dig into the Jetson / gstreamer code to see what I can discover while I wait for the new LKV to arrive - with my luck it'll exhibit the same problem !

Will check out what the Jetson can do once I get it working properly.

Regards Tim