Which USB Bandwith does a USB SDR need? - Page 1
Forum section: electronics / rf-microwave

author: Lord of nothing
author_rank: Super Contributor
timestamp: July 05, 2018, 01:11:04 pm
content: HiSry I dont know it. So which Bandwidth does a (Generic) USB SDR Dongle need?When I use an Software who connects directly to the Dongle (like ADSB, ACARSdeco2) does the need more or less USB Bandwidth then when I use SDR# to "see" the Spectrum?

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 05, 2018, 02:26:10 pm
content: Dongle bandwidth you want as big as possible, so you can see a wide band in the spectrum.Demodulator bandwidth is done in the PC while processing, for SSB ideal is about 2.5KHz.Oh wait… USB is not a modulation type in this caseSo look at sample frequency and you will have your answer (hint: it's not that much for a typical dongle)

author: Lord of nothing
author_rank: Super Contributor
timestamp: July 05, 2018, 02:48:17 pm
content: I sayed in the other Tread I will buy an USB -> Fiber -> USB Adapter and need to know how much oft them I need. I use ~6 Dongle at the moment. My small Pc run with 100% CPU Load and my Business Server with 6% or so.So the best think is buy an USB to Fiber adapter and Install an Virtual Win7 and run the Processing on my Server who run 24/7 in quite idle and save Power.For that I need to calculate how much of that Adapter I have to buy.

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 05, 2018, 03:48:11 pm
content: The maximum sample rate of an RTL-SDR dongle is 2.5MS/s so that is 2.5MB. USB 2.0 specs say 60MB/s but even if you take half of that it's still theoretically enough for 10+ dongles.

author: Lord of nothing
author_rank: Super Contributor
timestamp: July 05, 2018, 03:59:25 pm
content: perfect. That mean with an "cheap" USB 2.0 only ->http://www.icron.com/products/icron-brand/usb-extenders/fiber/usb-2-0-ranger-2324/the Dongle works?How about the HackRF with USB 3.0 and the 3.0 Converter:http://www.icron.com/products/icron-brand/usb-extenders/fiber/usb-3-0-spectra-3022/Do you (or anyone else) see an Problem with Latency and other stuff?

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 05, 2018, 05:04:23 pm
content: Quote from: Lord of nothing on July 05, 2018, 03:59:25 pmYes, I would be surprised if it would not support 6 dongles easily. (I think that is your setup?)QuoteHackRF sample speed is upto 20Msps so about 10 times the RTL-SDR dongle. Theoretical speed of USB 3.0 is 640MBps so a handful of HackRF devices should not be a problem.Don't worry about latency, most latency comes from the processing (+demodulation) in the PC anyway.

author: Lord of nothing
author_rank: Super Contributor
timestamp: July 05, 2018, 10:32:45 pm
content: perfect I will wait until the company replay to my E-Mail.

author: Wirehead
author_rank: Regular Contributor
timestamp: July 06, 2018, 05:30:41 am
content: Quote from: PA0PBZ on July 05, 2018, 03:48:11 pmShouldn't that be doubled? 2 ADC's for I/Q stream. So something like 40Mbps

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 06, 2018, 09:06:33 am
content: Quote from: Wirehead on July 06, 2018, 05:30:41 amYou are quoting what I said about the RTL-SDR but then mentioning the sample rate of the HackRF? What I could find about the last is that they mention 20MSps but it does not say if this is total or for I and Q each. If it is each then it can be 40MBps (not Mbps!), I agree. On the other hand they also say transfer rate 20MSps so... ?Anyway, the USB speed will still be enough.Did a bit more searching and found the following here:https://www.rtl-sdr.com/review-airspy-vs-sdrplay-rsp-vs-hackrf/We monitored the USB usage using Windows performance monitor and discovered that the Airspy (with bit packing at 10 MHz) used 30,000,000 bytes per second, the RSP (at 8 MHz) 25,000,000 bytes per second and the HackRF (at 20 MHz) 40,000,000 bytes per second.So yes you are right, it is 40MBps.