My LimeSDR is dropping frames

I guess I have an issue with my LimeSDR - when I run it for more then 15-20 minutes it starts dropping frames.
It happens to me on Windows on both gqrx and sdr-console, any ideas how to test wether my hardware is okay or rule out software configuration issue? (I am running latest firmware on my Lime 1.4).

Another strange thing is that I am able to receive FM station much better on LNA_H than LNA_L… is that normal?

The matching network for LNA_L has a very strong attenuation at FM station frequencies (something like 50-80 dB), while the LNA_H network doesn’t by virtue of how it’s matched for ~2Ghz frequencies. Even though LNA_H ends up not being matched properly it’ll end up receiving more signal as a result (FM radio is practically DC anyways).

What is surface temp of your Lime chipset?
Try to leave fan direct on chipset :wink:

You might be right… it is probably too high temperature issue :confused:

I have a cheap infrared thermometer with laser pointer that is nice for checking chip temps. Probably $10-15 or less. I use when cooking too as the oven is not steady. :thumbsup:

SoapySDRUtil has some rate testing functions - not sure if it’ll report dropped frames.

Rate testing options:
–args[=“driver=foo”] Arguments for testing
–rate[=stream rate Sps] Rate in samples per second
–channels[=“0, 1, 2”] List of channels, default 0
–direction[=RX or TX] Specify the channel direction

Djani @9a4db, holy crap … is this true what @Kryan92 writes above? FM stns have 50-80 db atten on RX_L?


My recollection was off so I simulated 'em again. For FM Frequencies, you’re going to get about ~20 dB of loss from the matching network alone. Not nearly as bad, but not optimal unless you’re still pretty close to the tower.

No, that’s great thanks :smile:

I’m having a heck of a time getting my Lime (Lemon) to do anything and I was using FM bcst as a reference. So this that waaay interesting to me. See My Lime seems completely deaf

Two things come to mind for me
1> “Change advanced power settings” to disable “USB selective suspend setting” (at least while troubleshooting, it could be MS Windows trying to turn off or reduce power to USB devices after 15 minutes).
2> Disconnect any other USB devices that are using the same controller, to eliminate them as a possible source of the problem. I use a dedicated PCIe USB 3.0 controller card with “NEC/Renesas µPD720202” chipset for SDR (I have not used this configuration with the LimeSDR [not shipped yet], but I have with other SDR devices problem free).

Side question: Is there any recommendation for radiators and/or fan on LimeSDR? I am using @luftek designed cases (great job btw) but is causes my Lime to overheat :(. I dismounted SMA pigtails from second channel on the case hoping additional holes would increase air flow which helped a little but not enough.

Could it not be that your computer is dropping the frames and not the limeSDR? Maybe it’s just not fast enough?

1 Like

Yes, that can be the case…

I am considering to make measurement setup and plot whole available spectrum response
on modified Rx1 W input. For at last 500 kHz to 2,7 GHz with my Aglilent E7495 on
full span (500kHz-2.7GHz)

My Rx1 L input is left as is, because I have one project in relation to EU GSM bands
RF levels within urban areas.

73 Djani

doubtfully… In my recent test when I’m not dropping frames I have 30%-ish GPU usage and 15% CPU usage (4 cores i7). When I start dropping frames CPU and GPU usage decrease significantly.
I pretty sure this is due to overheating… running lime without the case and/or putting fan blowing into the board helps.

25mmx25mm heat sinks are ubiquitous as are others for the remaining hot ships on the board.
I use glue ons for my RTL-SDR boards and they work.
So far I haven’t heard much about the use of real heart sinks in the right sizes so I figured I’d throw out the obvious reminder.
Heat sink first, then fans.
That is usually the way it works. The other way around produces far less of a result and wastes energy on a fan that is not doing much to actually cool the affected chip.

Could also be USB issues on your computer. In a couple of discussions here the topic of USB3 has come up and for some early USB3 implementations there are inherent problems. Sometimes the computer vendor releases firmware updates.

Are you using USB2 or USB3?

I kind of ruled out USB issues (I’m using USB 3.0 btw) and I’m pretty sure this is overheating. When I run 10Msps it runs for hours without any problems and chips on the board are warm but can be touched with bare finger. When I do 60Msps after 15-20 minutes chips on the board are hot and barely touchable. I am going to order heatsinks for each chip and maybe mount a fan inside the case.

Hi leoha,

Did you already decide which heatsinks part number you will use?
Are you going to glue those?

I don’t know yet but I can let you know once I decide. I just probably try to fit dimension of chips to dimensions of heatsink (low profile preferably) and glue them with either heat conductive glue or some thermal pad.
I don’t have time to do this now but i’ll try to find something on the weekend.

This post is about fans, but maybe will be useful: