#286 

Just some information that may be helpful for beginners: 0.) Programs like GNU Radio allow the use of sound-cards to learn the basics of software defined radio. Build simple digital transmitters and receivers that use the microphone and speakers instead of a SDR. 1.) There is not much difference between the blue/plastic and the silver/metal rtl-sdr. The bandwidth and the software is the same, both are useful up to 2.2 MSps but can be pushed up to 3 MSps (no difference here). The difference is, that the metal one has a _much_ better connector, SMA instead of MCX. The blue plastic one also has a really cheap crystal oscillator, it wanders around whenever the temperature changes. The silver/metal version has a temperature compensated oscillator, it measures the temperature and uses this to correct its drift, so it is much more stable. The drift normally is a few parts per million (it it is 10ppm, this would be 10 Hz at 1 MHz, but already 1000 Hz if you receive something on 100 MHz or 10 kHz if you are interested in 1000 MHz signals).The TCXO has only 0.5 ppm drift and the cheap crystal up to 20ppm. 2.) The most important things are antennas and short good coaxial cables. They decide about the signal quality. The cheapest RTL-SDR with a good antenna (and band-filters, see #3) is better than a 10000€ SDR with a crappy antenna. Beginners should go for the cheapest SDR and use the saved money for the antenna. With RTL-SDRs it is cheaper to use a long USB cable and get the SDR close to the antenna and away from the PC (which may create interfering emissions) than a good coax. An old satellite dish with LNB, a bias-t (basically a box with two coaxial connectors, a coil and a capacitor) and a power supply that can deliver 14V (a bunch of batteries) are enough to receive that satellite shown in the video. More information and WebSDR: eshail.batc.org.uk/nb/ amsat-dl.org/p4-a-nb-transponder-bandplan-and-operating-guidelines/ 3.) Almost all SDR have wide open inputs. All signals received together (in case of the HackRF everything between 1 and 6000 MHz) must not exceed the maximum allowable signal strength. It's a common source of problems for beginners. They get interested in weak signals from far away and enable the AGC (automatic gain control) to get a nice strong signal but the signal strength (including the noise floor) jumps up and down because the AGC constantly increases and decreases the gain. Then they switch the AGC off and manually set the gain to some value, but then some mystery signals appear, signals that aren't there. That is what happens if the sum of the received signals exceed the maximum allowable signal strength, which turns amplifiers and ADCs into mixers that mix different received signals and produce these mystery signals. Fortunately there is a solution to this: Filters. If the offending signals are local FM broadcast stations, there are band-stop filters for 88-108 MHz that eliminate this problem (but Airplanes, DAB, DVB-T and cellphones may still interfere and would require separate band stop filters). If your frequency of interest is clearly defined, use a band-filter that discards everything except the interesting band. And even better is a pre-selector, that is a device full of band-filters and some switches to select them depending on your needs. And the luxury variant is something like this: www.crowdsupply.com/lime-micro/limerfe It is a pre-selector that is controllable by software. ;-) Do it yourself band-stop filters however can be extremely cheap. The cheapest is the quarter wave stub. If you have only one interfering FM station at 100 MHz, which is a wavelength of 3 meters, add a 75cm (1/4 of 3 meters) piece of coax to the antenna cable. The waves will travel to the open end, get reflected and come back 180° out of phase. They will destructively interfere with the offending signal and thereby stopping it from reaching the SDR. The waves travel only 2/3 the speed of light in coax, so the 75cm will be way too long (the final length will be around 50cm). To tune such a stub, you can connect a noise source instead of the antenna and look at the dip in the noise. If the frequency of the dip will be too low, cut a bit of coax off and see how that dip rises in frequency. If it gets too high you have cut off too much (just push some copper wire into the open end of the coax). 4.) Almost all SDR have wide open outputs! The produced signal may contain spurious emissions and harmonics. If a signal is produced, say at 145 MHz, you need at least a low-pass filter above your frequency but below twice that frequency (i.e. 200 MHz) to get rid of all harmonics. Then look at the signal with a spectrum analyzer (i.e. another SDR)! If you have tuned your SDR to 145 MHz (center frequency), modulated some NFM (narrow frequency modulation) signal at +500 kHz and send it to the SDR and expect it to only transmit at 145.5 MHz, you might also see a copy of it at 144.5 MHz. This happens due to I/Q imbalance and this error can be corrected. Then you might produce a good signal and send through an amplifier, which again might add harmonics that must be filtered with another low-pass filter.

Hats off for this great video on such a complex topic. I have been staring at my sdr dab dongle for months, but after watching this episode I'm ready to experiment. Thanks!

Don't know whenever I search some tricky rf concept, I always find one of your videos on it ! Thanks for the great content and efforts.

Impressive overview as always You are doing a great job, of opening new doors for the community Thanks for sharing👍😀

One of the best (possibly THE best) SDR intro videos there is.

A great explanation, thank you! SDR revived my interest in a radio, and I’m now an M0 in the UK 👍

You are the teacher I never had. Keep doing what you do! :)

Thank you for the overview of the different SDR devices and the basics. I was watching the Ossmann trainings and I am completely convinced that his great stuff. Thank you for bringing it down to 27 minutes for an overview.

I'm only 6 minutes in, and I've never seen the concept of mixer and IF explained so clearly. Thanks Andreas!

Great job Mr Andreas, you have explained that as simple as possible. Respect from Morocco.

Very impressive! You're a talented teacher in capturing and ordering concepts into bins. Too good! I think it's the best orientation video on SDR out there.

Great video Andreas! I've made nodes for agricultural sensors and have used SDR with the Adafruit Feather 915MHz Hope RFM95 LoRa boards. Cheers from Australia!

Thanks Andreas again for such a great video! .. It must be incredible time consuming to deal with such a complex area and summarize it in such a great way for us!

Thanks Andreas. This was a comprehensive 1% information for those of us getting into SDR. Thank you for your time and effort!

Andreas, I chuckled when you mentioned 'we' began listening to FM radio at a young age. FM came into my life as a teenager around 1962. AM broadcast stations were king of the airwaves and it took almost a decade for FM to overtake the throne. I enjoyed this video. Thanks for taking time to present it.

Oh wow, you answered many questions for me that werent even related to SDR's. Thank You for this great compilation of knowledge.

Wow, you managed to produce an exceptionally good and in depth coverage of this topic even exceeding your usual high quality informative videos we are used to getting, bravo. I bought a couple of the cheap SDR dongles to try but I found myself lost in the sea of information and software and put it aside for later. This video has clarified so much for me that I'm ready to give it another go to see if I can't get it to work for me. My first project will be to determine if the transmitter of my weather instruments is sending a signal and if so to build a replacement receiver to get the weather data displayed again.

Digital Radios with these capabilities have been around since the 1980’s. A Software Defined Radio is a Digital Radio that has been processed by a Marketing Department. We can start calling them Digital Radios again with no loss of generality-as we say in math class. Thank you for the summary charts.

Outstandingly clear, informative and fascinating. Thank you for sharing in such a useful way.

Excellent video! This is the best video on SDR I have seen so far! I had purchased RTL2832U based SDR couple years ago but had no time to experiment until recently. I am glad to see SDR have such great software support on Linux systems!

14:50 “a treat especial” Andreas must be watching AvE too.

Great video! Small but important correction at 7:55. In order to digitize a 10.7 MHz signal, the ADC (Analog Digital Converter) sampling frequency must be at least 2*10.7 MHz (21.4 MHz) due to the Nyquist criterion. Even if you'r interested in only the 150 kHz FM signal the Nyquist criterion must be satisfied up to the highest possible frequency within your signal, otherwise you will get aliasing effects.

Great Class Andreas!!!! Really cool video!!! I ordered one RTL SDR to help me on site survey for LoRa TXs. Thank you for sharing your knowledge!

Very interesting material. I appreciate your work and good luck in further developing your passions. Being your student is pure pleasure.

Great video, with one minor oversight. The negative frequencies aren't 'cut off' as stated in the video. They are aliased, i.e. folded over the DC axis. One of these days I will get around to using an SDR to detect nearby receivers by detecting their LO leakage...

The LimeSDR has great software support, just like the HackRF One, rtl-sdr and USRP. SoapySDR unifies practically all SDR stacks, making the hardware vendor/driver provider insignificant.

Thank you for this information. As a complete novice I would be be so happy just to put FM radio on my laptop and expand from there. This presentation has been by far the most helpful in getting my head around this new innovation.

Andres - you are a brilliant educator and I learned so much from this video today. Thank you very much for doing this. I intend to purchase an RTL-SDR dongle today and get started with this fascinating technology.

Awesome job -- thanks for the links and inspiration! This old man is going to learn some higher math and all about I/Q signals!!!!

I'm now building a radiotelescope but just stared my journey on SDR-RTL a few months ago

Thank you SO MUCH for this great summary! I'm just getting into SDRs and you gave me a lot of resources.

Excellent video again. Thank you for your effort. This is a good starting point for such a complex topic.

EXCELLENT VIDEO! I'm a little jealous of your Swiss Ham Radio license card - we still carry such an A6 rag in Germany vy 73 de dl8cy 2 u hb9bla

Use sdr at work and home it's The greatest thing since sliced bread and BMW deisel with 4 turbos

Fantastic video, thank you for providing this. A lot has changed since I was in the industry!!!

I did my radio trade apprenticeship 40 years ago. I had heard of SDR but never lifted its skirt. You have blown my mind with the ingenuity of the people who developed it, and with the possibilities.

Great video, I would have loved the opportunity to work with you on it. Perhaps we can collaborate on a future video?

Did you really compare accustic waves with electro magnetic waves? :-) I am sure my ears cannot hear 10 kHz electro magnetic waves ... :-)

Fantastic video. I've been playing with SDR for a while, but you've just explained everything perfectly in 27 minutes. Need to step up from a SDR dongle to a HackRF One now!

A delightful summary! I was a radar systems engineer for 30 years...we were using I/Q demod in the '80's...I am retired 10 years now...this video was like going home for a nice meal and a chat! Many thanks!

If passively listening to something is illegal then the entire world has gone mad.

I think you mean 100KHz, not 1KHz at 21:13

Fantastic explanation! I now have a better understanding of I/Q signals. I grew up in the analog age and really found your video helpful.

WOW , WONDERFUL :: You have exceeded your usual very high standard and created a overview/documentation/teaching document that is of great value to the digital maker world. HOORAY!!!! ( p.s. many many thanks for pointing out the Mike Ossman video SDR playlist )

It's the swiss army. I can guarantee you that there's still some poor soul sitting there scanning frequencies by hand 😁

Congratulations Dr,Andreas...Never had a so comprehensive explanation of the SDRs we use..Keep up the good work!! 73 de SV2LLJ Ioannis

Excelent video. Been using SDR for a while for AIS and ADS-B reception. A good antenna is important.

What a way to teach and share your knowledge!!! Thank you Andreas!!

Andreas, that is a truly excellent overview! Inspired me to get my nooelec rtl out again and play with ADS-B in - thanks!!

Wow! An amazingly well designed and presented video!

Great video, of course now you have made a lot of persons longing for your version _with_ the complex numbers

Wonderful to find someone who really knows what they are talking about.

I have to present a technical seminar on SDRs tomorrow, this video is definitely a gem. Thanks for this professor.

Outstanding introduction to SDR Andreas. I think you perfectly captured the correct 1% of required facts :-).

Beautifully clear and concise, I learnt a lot from this, thanks and I've subscribed.

The best video on the subject i have seen so far. Its a one-stop shop for anyone looking to understand, 1. What is a radio? 2. What it does? (In simple terms) 3. How does SDR improve upon the prevalent solutions? And the narration and the narrator is fantastic. Thank you for the video.

I love your videos, they are always so informative!! I just got a mid roll ad. I thought I would let you know. It was at 13 minutes.

Another wonderful video covering the topic. I use an SDR to receive railroad dispatching communication. Works great for the price and size of a cheap dongle

Great explanation Mr Spiess, I’ve been experimenting with a couple of SDR’s last couple of years, although as an old school engineer which I love analog design; I think future is SDR.

Great explanation of how SDR works. Thanks!

That was very well distilled. Good work!

Fascinating video. I learned something new. Thanks for making it.

Excellent delivery of relevant information!

Thank you for this beautiful summary of Software Defined Radio! See you at GNU Radio 2020!

A timely video, I just received a Nooelec SDR receiver and "Ham It Up" up-converter a few days ago. Using it on an old Macbook Pro using the CubicSDR software. Thank you very much from KC1MC.

Thank you Andreas, a very comprehensive explanation, I'd like to add Pi-FM-RDS. As it allows for a cheap simple test FM signal, it's also a lot of fun for those learning about radio.

Fantastic well thought out video that will save many ppl a lot of time. I learnt a lot even though I've been using RTL-SDR for sniffing my sensor signals for some time. Very good round out information. Thank you :) :)

You are contributing to the technical society and saving our time, which we will be spending otherwise to do the basic research on - learning "Hello World on SDR"

This video brings down a lot of dark veils of RF. Awesome, thanks for sharing with the noobs!

Thank you - really enjoyed Wish I had more time to play with SDR

Been using one of those 10 dollar dongles to receive national emergency services pager messages in the Netherlands for a while now. Best thing I ever found out about. Playing with radio is amazing. Highly recommended

God Bless this man for simplifying such complex topics

Thanks for the effort put into this video, excellent content.. just started exploring SDR for the purpose of WiFi Spectrum analysis on 2.4GHz, 5GHz & 6-7GHz..

Great video as usual Andreas! I played a lot with SDR a few years ago. I began with the softrock kits sending the IQ signals to a soundcard for the ADC. This gave a bandwith of only a few kHz. After that I had a RTLsdr and this was a great upgrade. I used it for receiving HAM Radio, boat tracking system, POCsac and also for looking of interferences! 73's de ON8NP

Great stuff, I'm new to SDR, this is just what I wanted.

What a great overview. Thanks for doing this.

Thanks for a comprehensive video on that matter :)

Great thanks for your lesson. Best regards from Uzbekistan

Probably one of the best descriptions of I/Q that I have seen because you described it in terms of the necessary local oscillator frequency. Don KC3MBK

A friend suggested that I learn the 60 to 80 abbreviations used in SDR menus as a way to get started with using SDR’s. I thanked him for the warning and pointed out that I have better things to do with my time and if a SDR is not intuitive and easy to use, I don’t want one. Such a suggestion is appropriate because during my time working as an electronic engineer, I learned that programmers could turn an intutive concept into somethng no one can understand in no time at all !!!

I am so glad I am getting into this now as opposed to 5+ years ago. There is just sooo much more content about this available to noobs! Thank you for making this!

My mind is blown. Here it is November 2019, and I am a 79 year old tech junkie but I never knew about SDR until now. I built crystal radios when I was a boy in the 1950s, worked for a while as a radio-TV technician in the early 60s, and with mainframe computers from mid 60s until I retired. I am amazed at how far technology has advanced in my lifetime. Thanks for the great info.

Thank you very much for the really precious and high-quality content

Thank you for this wonderful primer.

A long time ago in a land far away I designed I-Q equipment. The 3GHz I-Q based signal generator was the HP8780 and the IQ demodulator and display was the HP8980. I left HP after 21 years and went to a new company where we invented the first Cable Modems. Ultimately my group was bought by a big blue company that messed it all up so 20 years ago I quit. About the same time I became an inactive HAM. Now I am getting back into HAM radio. I just bought a hybrid SDR HAM radio, the FTDX10. The technology has changed so much but seeing your video here was fascinating. It brings back so many memories. I was an early proponent of the I-Q space and it is just mind boggling to see what has happened in the last 20 years. I feel like the mythical man who was on a tropical island for 20 years and returns to find the world has changed. For the last several years I have been designing equipment for my boat using Intel Edison Edison, ESP8266, and ESP32 and have enjoyed your channel for some time but somehow missed this episode until now. Really loved this video. Thank you for making it.

Great video, thank you for the effort put into this.

Andreas, you are the first to explain local oscillator and mixer and IQ in a way that made it past my thick skull. Now it seems so simple I'm going to try making a toy SDR with my FPGA to remind myself that I still don't know the other 99% :-)

Great Job! Thanks for this awesome tutorial.

Very fascinating. I always enjoy your videos.

This was GREAT. Thank you very very much. I will use your links for purchase.

Great video again. If possible I'd like to give you 5 thumbs for this video. Congrats for your 150k subscribers since last week. I'm quite sorry missing your session in Weinheim, but I had to work on IARU1-Fieldday...

Highly informative, thank you.

Great video, this video alone is well worth my Patreon contribution. Thanks Andreas

Hi Andreas, I really enjoy watching your videos. They are all extremely well done. I believe you can simply the explanation of the IQ signals. When you down-convert the signal to 0 HZ, you essentially get a DC level after the low pass filter for any signals that are exactly the same as your intermediate frequency. This level depends on the phase difference between your incoming signal and the IF. If the phase matches exactly, you will get a high level, and if it's out of phase, you will get nothing. Therefore, you can't tell the difference between an out of phase signal and no signal at all. The solution to this is to have another mixer which is 90 degrees out of phase from your primary oscillator. This way the signal will show up on one channel or the other. This also holds true for signals that are some offset from the IF. For example, if the IF is 100Mhz, both a 99.99Mhz and a 100.01Mhz signal will show up as 10Khz signal after mixing. However, these resulting 10Khz signals will have different phases between each other on the I and Q channels. This allows the demodulator to tell the difference.

Excellent. Andreas should be hired by "Masterclass". With this video, amateur radio and aviation enthusiast should now be able to understand how Flight Tracker had made a business using SDR.

Thanks! I always wanted to know how these things work.

Please make a video about encoding & encryption digital modulations. Your videos are comprehensive and informative. thanks alot .

Fun for the weekend! Thank you so much

Great video, it was just what I was looking for, i.e., a foundation I can build on.

Excellent: exactly the 1% I need to go for more steps. Great job. Thanks !!! BTW: by doubling the received/detected signal in I and Q, it would not only double the signal strength (as you also could do with just a simple amplifier) but it also halves the noise in the S/N ratio, I would guess ?