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.