# Maximum TX bandwidth

**URL:** <https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226>\
**Category:** General Discussion\
**Created:** [29 June 2021 01:36 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226 "2021-06-29T01:36:13Z")\
**Posts on this page:** 14\
**Page:** 1

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**Author:** ![canopus19652000](https://avatars.discourse-cdn.com/v4/letter/c/e5b9ba/32.png) [@canopus19652000](https://discourse.myriadrf.org/u/canopus19652000)\
**Post date:** [29 June 2021 01:36 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/1 "2021-06-29T01:36:13Z")

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Hi fellow,  
I use GNURadion (3.7) to generate signal and pass it to LimeSDR using regular block “LimeSuit Sink (TX)”.  
So, everything is straight forward.  
I observed next behavior:

1. Transmission is fine up to 50MHz bandwidth (approximately).
2. After 50MHz of bandwidth, transmission becomes unstable: board transmit approximately one minute then it stops for one minute. So, it is up and down. Absolutely NO diagnostics is coming from GNURadio.
3. I try transmission with different transmission gain, different frequencies (200MHz, 900MHz), different calibration bandwidth (see GNURadio “LimeSuit Sink (TX)” block) – results are the same: Up and Down
4. I used external power supply (12V 2A) – result is the same: transmission is Up and Down

After having this fun for couple of week I decided to ask for help:

1. What is REAL max transmission bandwidth on LimeSDR-USB?

2. How can I check whether or not external power supply is REALLY used by LimeSDR. Yes, I see light on board coming up when I connect external power supply. But I have an impression that board does not use it. I did not find any info how can I check what power source is used by board.

Thanks in advance.

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**Author:** ![yt7pwr](https://avatars.discourse-cdn.com/v4/letter/y/ecd19e/32.png) [@yt7pwr](https://discourse.myriadrf.org/u/yt7pwr)\
**Post date:** [29 June 2021 11:30 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/2 "2021-06-29T11:30:46Z")

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I did not play lot with GNURadio but I have a question: what is CPU usage when you transmit 50MS/s and what exactly GNURadio transmit? Sine wave or something more complex?

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**Author:** ![AA7QQ](https://avatars.discourse-cdn.com/v4/letter/a/13edae/32.png) [@AA7QQ](https://discourse.myriadrf.org/u/AA7QQ)\
**Post date:** [29 June 2021 11:40 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/3 "2021-06-29T11:40:54Z")

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First, keep your input voltage under 8VDC, as the voltage switching chip is at it’s failure limit with any transients on 12VDC.  
Have you added heat sinks & good cooling (Fan)?  
hHese are the basics.

Ed

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**Author:** ![canopus19652000](https://avatars.discourse-cdn.com/v4/letter/c/e5b9ba/32.png) [@canopus19652000](https://discourse.myriadrf.org/u/canopus19652000)\
**Post date:** [29 June 2021 14:20 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/4 "2021-06-29T14:20:25Z")

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Hi yt7pwr,

CPU: I have AMD R3900x. It is pretty powerful.  
When I set 60MHz (sixty MHz) bandwidth, CPU load does not exceed 30% (total). Single core load does not exceed 80%.

Signal: I try both sin wave and Gaussian noise. Results are pretty much identical.

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**Author:** ![canopus19652000](https://avatars.discourse-cdn.com/v4/letter/c/e5b9ba/32.png) [@canopus19652000](https://discourse.myriadrf.org/u/canopus19652000)\
**Post date:** [29 June 2021 14:38 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/5 "2021-06-29T14:38:46Z")

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Hi AA7QQ,

When I was failed to transmit using just USB power, I connected my DC (12V,2A). I did not find any difference. That is why I am asking about ANY methods to control which power source is currently in use by board. I did not find any utilities yet.

I did install heat sinks. Temperature reported by LimeSuite GUI is about 60C (open stand) after long time under load.  
But! I did not find any temperature dependence. When I start transmitting (and therefore board is cold 40C), and after long time load (when board is about 60C) - results is the same.

BTW, transmission is UP and DOWN with period 80sec (40sec is UP and 40sec is DOWN).

Any idea wold be high appreciated.

UPDATE: if I try to transmit Gausian noise transmission time becomes shorter. As much noise power as shorter transmission time.

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**Author:** ![yt7pwr](https://avatars.discourse-cdn.com/v4/letter/y/ecd19e/32.png) [@yt7pwr](https://discourse.myriadrf.org/u/yt7pwr)\
**Post date:** [29 June 2021 14:41 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/6 "2021-06-29T14:41:54Z")

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My CPU is R7 2700X (according to cpubenchmark twice slower than R3900X). I notice that GNURadio is not multithreaded optimise. One core is usually doing majority of DSP tasks. On 30MS/s data stream is arround 100MB/s, for 60MS/s twice that. CPU must to compute and prepare 200MB/s of I/Q data! Too much for single core! Maybe 24 threads, in your case (my CPU is 16 threads), can do the job but only in heavily optimised multithread C/C++ app.  
And, as [AA7QQ](https://discourse.myriadrf.org/u/AA7QQ) wrote, do not forget good cooling for board.

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**Author:** ![canopus19652000](https://avatars.discourse-cdn.com/v4/letter/c/e5b9ba/32.png) [@canopus19652000](https://discourse.myriadrf.org/u/canopus19652000)\
**Post date:** [29 June 2021 14:47 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/7 "2021-06-29T14:47:19Z")

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As far as I know, each GNURadio block occupies one core. So, one block cannot be executed on two core.  
That is why I mentioned that “Single core load does not exceed 80%”. It means that no cores reach its saturation hopefully 🙂

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**Author:** ![yt7pwr](https://avatars.discourse-cdn.com/v4/letter/y/ecd19e/32.png) [@yt7pwr](https://discourse.myriadrf.org/u/yt7pwr)\
**Post date:** [29 June 2021 15:33 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/8 "2021-06-29T15:33:55Z")

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There is a catch: modulation/demodulation is real-time job! Even if transmit process occupies only 20-30% of one CPU core there are no guarantee for success. For TX is critical DSP process called interpolation and it is possible to make it multithreaded. Did you try to stop-start GNURadio when output is silenced? Also, on Windows problem can be some time USB power management and need to be turn off.

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**Author:** ![RightHalfPlane](https://avatars.discourse-cdn.com/v4/letter/r/46a35a/32.png) [@RightHalfPlane](https://discourse.myriadrf.org/u/RightHalfPlane)\
**Post date:** [29 June 2021 18:05 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/9 "2021-06-29T18:05:43Z")

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All my machines except for the Raspberry Pi, easily handle 40 MSPS (i.e. 320 MB/s) with a single thread receiving with a LimeSDR mini - so one would think that they could handle transmission at the same rate or greater on the LimeSDR.

SdrGlut Simultaneously Running Five SDRs  
[https://www.youtube.com/watch?v=BmUNrAn1Llk](https://www.youtube.com/watch?v=BmUNrAn1Llk)

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<div class="post-metadata">

**Author:** ![canopus19652000](https://avatars.discourse-cdn.com/v4/letter/c/e5b9ba/32.png) [@canopus19652000](https://discourse.myriadrf.org/u/canopus19652000)\
**Post date:** [29 June 2021 21:16 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/10 "2021-06-29T21:16:27Z")

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Hi guys,

Thank you very much for your participation in this discussion. It seems I found problem.

The point is that, my GNUradio script originally used Osmocom sink (BladeRF micro). This board does not stop transmitting in the same environment. However, when I changes Osmocom sink to LimeSDR sink it start producing strange results. I’ve disabled one so-called “hier” block in GNURadio script (it is not needed under certain circumstance) and everything start working as expected 🙂

Couple of words about multithreadeing and performance. GNURadio does have, for example, FFT filter. Regular GNURadio 3.7 distribution (Windows precompiled) contains this block. It is a single thread. Nevertheless, this block easily handles filters with **several thousand** coefficients (on R3900x). The hier block, mentioned above, costs absolutely nothing from computational point of view, but it caused me problem.

So, I do not care why “hier block “+Osmocom(bladeRF) and “hier block”+LimeSDR sink behave differently. I know that LimeSDR works as expected 🙂

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<div class="post-metadata">

**Author:** ![yt7pwr](https://avatars.discourse-cdn.com/v4/letter/y/ecd19e/32.png) [@yt7pwr](https://discourse.myriadrf.org/u/yt7pwr)\
**Post date:** [30 June 2021 08:08 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/11 "2021-06-30T08:08:39Z")

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Great news! Can you share GNURadio gr file?

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**Author:** ![yt7pwr](https://avatars.discourse-cdn.com/v4/letter/y/ecd19e/32.png) [@yt7pwr](https://discourse.myriadrf.org/u/yt7pwr)\
**Post date:** [30 June 2021 08:17 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/12 "2021-06-30T08:17:20Z")

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Is there a install instruction for Windows version? Downloaded release but after I try to run SdrGlut error message is shown about missing library.

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**Author:** ![RightHalfPlane](https://avatars.discourse-cdn.com/v4/letter/r/46a35a/32.png) [@RightHalfPlane](https://discourse.myriadrf.org/u/RightHalfPlane)\
**Post date:** [1 July 2021 02:58 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/13 "2021-07-01T02:58:24Z")

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What library is it Complaining about ?

Near the Bottom of the Readme on -

> **[righthalfplane/SdrGlut](https://github.com/righthalfplane/SdrGlut)**
>
> SdrGlut is a simple software defined radio - using glut and glui for its interface - righthalfplane/SdrGlut

are the instruction for a Windows install. The Latest version of the PothosSDR package no longer has the problem with the Device.h file and it is missing the install for RTAudio -

[https://www.youtube.com/watch?v=DyYIKiu2zVI](https://www.youtube.com/watch?v=DyYIKiu2zVI)

I need to update the instructions - I did not realize that they were so out of date

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<div class="post-metadata">

**Author:** ![canopus19652000](https://avatars.discourse-cdn.com/v4/letter/c/e5b9ba/32.png) [@canopus19652000](https://discourse.myriadrf.org/u/canopus19652000)\
**Post date:** [1 July 2021 15:22 UTC](https://discourse.myriadrf.org/t/maximum-tx-bandwidth/7226/14 "2021-07-01T15:22:36Z")

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Hi!

I use windows distributions from here:  
[http://www.gcndevelopment.com/gnuradio/downloads.htm](http://www.gcndevelopment.com/gnuradio/downloads.htm)

In particular, I use v3.7.13.5/v1.6 with AVX2.

I did try many different versions from there. It looks like other ones are less stable.  
I did not try 3.8.2 and up.

Sorry I am not an expert in GNURadio versions/distributions and glitches.