SDR Radio/GNU Radio Companion - Page 1
Forum section: electronics / general

author: Dave Turner
author_rank: Frequent Contributor
timestamp: January 11, 2019, 11:55:22 pm
content: I know it's late but I wish you all the best condiments for the seasoning.I've just started to look at the GNU Radio Companion.Does anyone know of a USB 'dongle' that will allow bi-directional communication with GNU Radio Companion?For those of us working on an extremely limited budget spectrum analysers and other instruments are a pipe dream. However with a decent computer, the GNU Radio Companion software, and an appropriate interface (ie IO dongle) one could have a lot of fun. For example send a swept frequency into discrete components such as a filter and read the results back to display them. IF the GNU Radio Companion (et al) has the ability.Any ideas/pointers please.Dave

author: bitseeker
author_rank: Super Contributor
timestamp: January 12, 2019, 07:50:44 am
content: I'm just barely sticking my toe into the SDR waters, so I'm just joining the thread to follow along.

author: awallin
author_rank: Frequent Contributor
timestamp: January 12, 2019, 08:10:50 am
content: Quote from: Dave Turner on January 11, 2019, 11:55:22 pmIf you are on a budget you should be able to start with a sound-card, both for ADC (RX) and DAC (TX).For RF-frequencies you'd then mix the sound-card signals up/down - there are "SoftRock" SDR-designs out there that use this approach.

author: scatha
author_rank: Regular Contributor
timestamp: January 12, 2019, 09:59:46 am
content: The simplest way of sweeping a filter with an SDR uses an analogue noise source in conjunction with an SDR receiver displaying an FFT.If you want to use an SDR for transmit, GNURadio certainly supports full-duplex operation however finding a cheap USB dongle capable of full duplexandwith two antenna ports with sufficient isolation might prove a challenge. It may be possible to use two dongles, one dedicated to transmit and the other to receive - this makes isolation much easier. Whether you can connect both to the same GNURadio Companion signal processing chain will depend on whether the SDR device driver supports this.

author: OwO
author_rank: Super Contributor
timestamp: January 12, 2019, 01:07:54 pm
content: An SDR isn't a very good way to measure the response of a filter/network if it even works at all. Of the low cost SDR transceivers that can do full duplex (transmit and receive at the same time) all are based on a single chip with everything integrated, and TX-RX isolation is very poor. On the other hand if you use the noise source approach the resulting graph will be, well,noisy.Really it's far easier to build your own network analyzer for fairly cheap, and there are even existing open source designs out there.

author: scatha
author_rank: Regular Contributor
timestamp: January 13, 2019, 04:40:26 am
content: Quote from: OwO on January 12, 2019, 01:07:54 pmThat's what FFT averaging is for - exactly the same if you are using a noise source in conjunction with a spectrum analyser setup (although in this case you are winding down the video bandwidth). The results are uncalibrated, probably get a lot of spurs etc., but as a ghetto method of handwaving a filter response out to 6 GHz it really is pretty useful.

author: untitelhar
author_rank: Newbie
timestamp: January 25, 2019, 06:58:03 am
content: Quote from: bitseeker on January 12, 2019, 07:50:44 amI agree with this opinion.

author: citizenrich
author_rank: Newbie
timestamp: May 29, 2019, 07:44:53 pm
content: Hi,On the original poster's use case, I'd suggest that GNU Radio is not an ideal or even rough way to understand filter response because it's not generally used to replace a swept spectrum analyzer.A helpful person posted a video on how they characterized antennas using a broadband noise source from ebay (~$20) and a directional coupler (also ~$20). He used Spektrum, an RTL-SDR spectrum analyzer that can do sweeps. I copied his exact approach and it worked to (very) roughly identify unknown antennas. It's easy to modify the setup to sweep a filter to see its response.On GNU Radio, I'm no expert but it's more for building real-time systems. It can do a few things an SA or VSA can do, but not all. It can playback files, but not scrub through them like an RTSA (e.g. Tek RSA, Signal Hound). It can be used to design and modulate carrier signals using an SDR, but it's not as convenient to pick up and use like an AWG or VSG.What GNU Radio can do that test instruments cannot is this awesomeness: radar, space monitoring, cellular base stations, satellite ground stations... you name it. It's a wireless communications system-building platform - as a friend noted.I hope The Signal Path, or W2AEW, or EEVBlog have a helpful review of of SDRs and GNU Radio and then help raise awareness about how they complement test equipment.HTH