Help With Multiple RTL-SDRs in auto_rx

[Hasan N0AN]

I finally succeeded in getting 3 sdrs to work, after several early morning sessions of three or more hours. I'm running 1.6.0 auto_rx on a PI4.

I changed the serial numbers as specified using eeprom utility. I used 00000002, and 3, and 4 respectively. I verified this with rtl_test.. I changed the station.cfg file, accordingly and restarted auto_rx with : docker restart radiosonde_auto_rx.

The web page showed SDRs, 2, 3, and 4 . 

After running for a minute or two, I got an error reported (Critical in Red), SDR 2 was misbehaving and needed to be reset. After several attempts at a reset (initiated by the software with no intervention by me), it said it was removing SDR 2 from the list and now  the web page only showed SDRs 3 and 4.

I changed cables. I changed hubs (USB). I changed the order of SDRs defined in station.cfg

I powered down the PI4 and moved the RTL dongles to different positions on the 10 port powered USB hub.

All with the same results, I could not get more than 2 RTL dongles to work at the same time. The minute I added a 3rd and it was defined as SDR 2....I got the above failure. Very frustrating... All 3 behaved normally as single SDRs and all three behaved as 2 in  a pair of SDRs, but SDR 2 failed repeatedly when added as number 3.

I should mention two of the SDRs are RTL-SDR v3  and one is Nooelec. It so happens that the Nooelec was assigned to serial number 2, but it worked singly and in  a pair, so it was unlikely to be the cause.

Out of desperation, I reprogrammed with eeprom software, the SDR serial number which was 00000002 to 00000005, and made the corresponding change in station.cfg. I am now using serial numbers 3, 4 and 5, instead of 2, 3,and 4.

IT WORKED!  It has been working for 24 hours since and has successfully been through two launch windows without a hitch. The software is behaving  normally  now.

My question:

Why did I need to change RTL Serial Number from 2 to 5? Was it a hardware or software conflict or both?

Here is the relevant section of my station.cfg file, that is currently running  successfully: (Many comments snipped from the station.cfg file for brevity)

sdr_quantity = 3

#
# Network SDR Connection Details
#

#
sdr_hostname = localhost
sdr_port = 5555

#
# Individual RTLSDR Settings
#

[sdr_1]

# If using multiple SDRs, you MUST allocate each SDR a unique serial number using rtl_eeprom
#   The serial number must NOT be 00000000 or 00000001, as this causes big confusion to the rtl utilities.
# i.e. to set the serial number of a (single) connected RTLSDR: rtl_eeprom -s 00000002
# Then set the device_idx below to 00000002, and repeat for the other [sdr_n] sections below
#

device_idx = 00000003

# Frequency Correction (ppm offset)

ppm = 0

# SDR Gain Setting

gain = -1

# Bias Tee - Enable the bias tee in the RTLSDR v3 Dongles.
bias = False

[sdr_2]
# As above, for the next SDR, if used. Note the warning about serial numbers.
device_idx = 00000004
ppm = 0
gain = -1
bias = False

# Add more SDR definitions here if needed. ([sdr_3], [sdr_4])

[sdr_3]
# As above, for the next SDR, if used. Note the warning about serial numbers.
device_idx = 00000005
ppm = 0
gain = -1
bias = False

==============================

Would someone please explain  why this worked? I am uncomfortable with "stumbling on" to a solution without the vaguest idea why it works.

Thanks for your patience with a newbie!

73. Hasan, N0AN

[Mark Jessop]

The way the rtl_sdr utilities interpret the device number is pretty odd.

I suspect what's going on here is that it was interpreting the device id of '2' not as the device with the serial number '2', but as the third device present (remember, 0 indexing, so 0, 1, 2), and who knows how it chooses to order the devices...

So it seems the you need to start the serial number 'above' the highest device index. Alternatively, you can also use text in those serial number if you wish (e.g. SONDE001, SONDE002, SONDE003), which I think will avoid this issue too.

73

Mark VK5QI

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[Hasan N0AN]

Thanks Mark, do you mean I need to change the serial number of each SDR with eeprom to SONDE001, SONDE002,  and SONDEOO3 respectively, or only chnage the device_idx in the station.cfg file?

Hasan

[Mark Jessop]

Both! 

However what you've got working now seems to be working OK, so I wouldn't change it.

... unless you end up wanting to add another SDR, in which case you might need to change the one with a serial of '3' to something higher again.

73

Mark VK5QI

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[Hasan N0AN]

Thanks again, Mark. I'll leave it alone for now!

I have a mini-circuits 4 port sma 50 splitter following my airspy 403 preamp and this combo works very well, indeed.

My antenna is an X500 Diamond 2/70cm collinear at 60' fed with 1/2" hardline and  the preamp in the shack. Preceding the preamp is a 2/70cm duplexer used as a prefilter (2m port terminated in 50 ohms). That is a trick I learned from hamsat use. The insertion loss is < 1 dB and it keeps out overload and intermod. 

The 4 th port of the splitter feeds my AirSpy R2 and SondeMonitor on my Win10 machine running SDR Console v 3.x

Thanks for all your help. 73, Hasan, N0AN