limitations of using multiple RTL-SDR dongles simultaneously
Hello dear RTL-SDR users, I whant to use multiples dongles as array for decode wspr. My problem is that I can not use more than 4 USB dongle simultaneously. I check with usbmon, each dongle uses 500kbits / s around. So I am far from the maximum bandwidth allowed by usb 2. I tried using a USB switch with external power supply but it does not work better. The default test performed is: #!/bin/bash for ((i=0;i<=4;i++)) do rtl_test -d $i -s 250000 & done First 4 is starting but last 5 doesent. And i whant to use more... Is this a limitation of the RTL-SDR library or the kernel driver? Do we have a solution to get around the problem? Thank you in advance for your valuable feedback.
Hi Oliver, On 08.01.2018 22:37, Olivier SCHMITT wrote:
Is this a limitation of the RTL-SDR library or the kernel driver? Do we have a solution to get around the problem?
This is a limitation of the Kernel, as the maximum usbfs buffer size is set to 16 MB by default. In order to disable this limit, do the following: echo 0 > /sys/module/usbcore/parameters/usbfs_memory_mb Regards, Steve
Ah, didn't know that! Interesting. This voids my previous mail. On Mon, 2018-01-08 at 22:42 +0100, Steve Markgraf wrote:
Hi Oliver,
On 08.01.2018 22:37, Olivier SCHMITT wrote:
Is this a limitation of the RTL-SDR library or the kernel driver? Do we have a solution to get around the problem?
This is a limitation of the Kernel, as the maximum usbfs buffer size is set to 16 MB by default. In order to disable this limit, do the following:
echo 0 > /sys/module/usbcore/parameters/usbfs_memory_mb
Regards, Steve
Nice MR Markgraf ! It works perfectly! Thanks you very much! :-) Thanks also to MR Muller for the Linux distrib that I did not know GNU_Radio-Live-Hamradio-binary.iso Good continuation! Le 08/01/2018 22:42, Steve Markgraf a écrit :
Hi Oliver,
On 08.01.2018 22:37, Olivier SCHMITT wrote:
Is this a limitation of the RTL-SDR library or the kernel driver? Do we have a solution to get around the problem? This is a limitation of the Kernel, as the maximum usbfs buffer size is set to 16 MB by default. In order to disable this limit, do the following:
echo 0 > /sys/module/usbcore/parameters/usbfs_memory_mb
Regards, Steve
Hi Olivier, at a sampling rate of 250 kHz, and with the usual 8 bit complex (meaning 8bit I + 8bit Q = 16 bit per sample), a single dongle will send 4 Mbit/s, not 500 kbit/s. Are you perhaps confusing bytes with bits? Anyway, you're right, the hypothetical transfer rate of USB2 HiSpeed would be 480 Mbit/s, so plenty enough for more than 4 dongles. You say the fifth RTL dongle doesn't even start. Is there a specific error? That very much doesn't sound like a data rate problem, but more like a hardware issue. Can you see (without using them) more than four dongles on your USB bus? What operating system are you using? Does it work under e.g. Linux¹? (I see you're using bash, but I'm not sure this implies this is Linux.) Best regards, Marcus ¹ you could download a USB image and try on your own. Trying in a VM doesn't make sense, so really write the image to a USB dongle or DVD: http://inpha.se/GNU_Radio-Live-Hamradio-binary.iso It's half a year old already, but I built it to include rtl_sdr tooling On Mon, 2018-01-08 at 22:37 +0100, Olivier SCHMITT wrote:
Hello dear RTL-SDR users,
I whant to use multiples dongles as array for decode wspr. My problem is that I can not use more than 4 USB dongle simultaneously.
I check with usbmon, each dongle uses 500kbits / s around. So I am far from the maximum bandwidth allowed by usb 2. I tried using a USB switch with external power supply but it does not work better.
The default test performed is:
#!/bin/bash for ((i=0;i<=4;i++)) do rtl_test -d $i -s 250000 & done
First 4 is starting but last 5 doesent. And i whant to use more...
Is this a limitation of the RTL-SDR library or the kernel driver? Do we have a solution to get around the problem?
Thank you in advance for your valuable feedback.
participants (3)
-
Müller, Marcus (CEL) -
Olivier SCHMITT -
Steve Markgraf