RTL-SDR Samplerate

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DL2KN
Posts: 1
Joined: Tue Apr 02, 2019 12:34 pm

RTL-SDR Samplerate

Post by DL2KN » Tue Apr 02, 2019 12:54 pm

Hi, I would like to use my SDR # over the Internet. For the Internet I have a line of 16 Mbit download and 1 Mbit upload available. The Osmocom RTL-SDR server is installed on a Raspberry Pi 3.
In its own LAN network SDR # works fine, but my upload on the Internet is not enough. I have already reduced the samplerate to 0.25 MSPS. Unfortunately, only audio fragments arrive.
I installed OpenWebRX parallel. This is a perfect transfer possible. Unfortunately, OpenWebRX is limited to a frequency entered in the config file.
Is there a way to operate SDR # with 1 Mbit upload?
The bandwidth for this would be unimportant, the main thing the frequency range from VHF/UHF MHz is receivable.

Thanks for your help

Greetings Michael

hotpaw2
Posts: 144
Joined: Sat Jan 14, 2017 11:07 pm
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Re: RTL-SDR Samplerate

Post by hotpaw2 » Tue Apr 02, 2019 4:44 pm

An RTL-SDR outputs 8-bit IQ components, which, at 2 components per sample, adds up to 16 bits per IQ sample. The lowest sample rate the RTL2832U supports for USB data is 240ksps. To stay under 1 a megabit network cap would require a sample rate of under 1M/16, or 62.5k samples per second (or 0.0625 Msps), which is about 1/4th the lowest RTL2832U rate.

Now, it might be possible to lower the network sample rate by adding a filter inside or after rtl_tcp to allow by decimating by 4 or by 8. An anti-aliasing/low-pass filter followed by a decimation by 4 or 8 would allow running the RTL-SDR a USB sample rate of 240k, but streaming from an rtl_tcp server over the network at a sample rate as low as 60k or 30k, both of which are under 1 megabit per second. 30ksps is probably enough to demodulate AM and NFM, but likely not enough to demodulate broadcast FM.

tim_rtd
Posts: 155
Joined: Fri Jun 30, 2017 11:34 am

Re: RTL-SDR Samplerate

Post by tim_rtd » Tue Apr 09, 2019 1:19 pm

What you believe about OpenWebRX is not exactly correct. When viewing openwebrx on the website you can select any freq within the bandwidth sampling rate you entered in the config, Not just the center frequency.

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