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.