John's Musings


Yeah, Me Neither

A Newbie's Primer for SDR Radio

I like to think I take a very common sense approach to things and I also like to think I take note of THE SMALL THINGS. So what I'm shooting for here is that you're new to SDR radio, and you see all these fancy SDR's and you wonder which one to buy but you'd like a common sense shakedown to SDR so you don't waste a ton of money (as I have. Oh boy, have I).


First of all ......... Welcome. SDR is AMAZING. You are surrounded by radio signals all day and all night, every day and every night. If it is a signal people have at least attempted to discover what it is and decode it if it is in fact encoded. So what is out there? AM and FM radio for sure. No surprise there. Short wave radio, CB radio. HF radio. VHF radio, UHF radio. that includes but certainly not limited to, Police, Fire, Ambulance, Aircraft, Airport beacons, pager traffic, ships at sea, tracking of Aircraft transponders, tracking of ships. Tracking of satellites. Wireless headphones. The baby monitor, your tire pressure sensors, your key fobs, wireless doorbells. Your smart gas meter emits a radio signal. You can tune in to the local NOAA weather frequency as in my pic below. You can use an SDR to detect whether there is a wireless transmitter SPYING ON YOU. etc, etc, etc.


I probably left off 25 other great things. Ok. You'd like to try. At the very least you can listen to FM radio and I do just that thing in my office. Radio's are cheap but an SDR is a CONVERSATION PIECE. Nobody will say "Nice Radio" if you have a table top radio in your office but if you have an SDR with GQRX streaming a big signal people will say "WHAT'S THAT?"




So you'd like to try SDR. Which one do you buy? The age old question. The first thing I'd recommend is to spend some time on rtl-sdr.com which is the definitive website for SDR radio. Read the forums, browse through the really great articles and then try to answer the question.....


IF I GET ONE OF THESE THINGS WHAT DO I PLAN TO DO WITH IT?


Well I promise you that no matter what the first thing you'll do after you get one is tune into a known audio signal that you can readily identify just to see if the thing is working. And for most people that is going to be a local AM or FM radio station. Once you master that you'll just find yourself drifting around trying to identify signals that are out there and sometimes you'll get lucky and hear audio, like from an aircraft overhead or from a Ham Radio on an analog channel.


So let's get back to the million dollar question. What are you going to do with it? Are you a HAM radio operator? Or a CB enthusiast? Are you a military geek or an airport geek? Perhaps you're somewhat of a spy and think you can listen to the neighbors cordless phone or their baby monitor............


Most folks will probably want to jump in cheaply to see if they like it. No need to spend $200 on an SDR only to figure out you have no idea how to use it.


I strongly recommend starting the hobby with this device. I call this one "The Blue One" It's almost the cheapest one out there.




Technically it is an RTL2832U and it works like a champ and even has a little antenna with it that is suitable for most very general and very local listening. The principal advantage of this receiver is that it is inexpensive. The main disadvantage of this is the frequency can vary a little bit with heat which means you usually have to provide a correction value in ppm before it is displaying perfectly accurate information. In my experience that is only an issue when you do more advanced stuff.






I have one of "The Blue Ones", take that back, I have several of the blue ones. One I use in my office to just plain old listen to FM radio and VHF radio traffic. I work at a Marine Corps Air Station and I'm a civilian tech rep that supports aircraft recovery operations. Translation: I can listen to the tower and ground controllers at the Air Station on one of these. Here's my best SDR military story. When an aircraft approaches an airport it can tune to something called ATIS. That is the robot dude voice that says what the airport conditions are, what runways are open, if there are any closures, if the radar approach systems are up or down or what frequency they are on, if the visual landing aid systems are on or off. You know, all the stuff a pilot wants to know....... I'm a Visual Landing Aid tech rep and one day I hear the ATIS call one of my systems as being non-operational when I know darn good and well that it is functioning perfectly. I go tell the Operations guys who say "Thanks......pause........hey, how'd you know?"


I also use the blue one with something called Pi-Aware. Airplanes release transponder signals on 1090 MHz called ADSB. You can track aircraft and even be a feeder station to Flightaware. It looks like this:



That's pretty cool, huh? A $35 Raspberry Pi and a $15 SDR and you're tracking aircraft. I've been running my station for a couple of years.


So the "Blue One" is all you need to have a little fun and for most people it might be enough. Now the Blue Guy won't go below 25 MHz or so and quite frankly there is a lot of cool stuff to be heard below 25 MHz. For starters basically all of Ham Radio and short wave radio. Also your AM radio is down there as well. Can't listen to AM radio on the Blue Guy. If you want to download NOAA WeFax transmissions, yep, you guessed it, that is down below 25 MHz as well. How about Digital Radio from other countries? Yep. Below 25 MHz.


To get below 25 MHz you need an up converter. This is a good one. The Nooelec Ham It Up Upconverter. Slap this between the Blue Guy and the antenna and suddenly you are listening to Amateur Radio and short wave radio in all its glory. So that costs another $40-$50 or so and it doesn't even have a case.


Isn't there an SDR that does those lower frequencies and the higher ones? You betcha there is! The RTL-SDR v3





This will go from about 0 MHz to about 1.3 GHz or so. That is huge. HOWEVER, there is a big however here...... Natively the device tunes to about 25 MHz lowest which is the same as the blue one but you can tune it down lower by doing something called "Direct Sampling" which means you apply a device string command in software such as GQRX and an LNB offset value and viola' you are listening to Amateur and Short wave radio. Another caveat here is that once you apply those values you are stuck between 0 and 25 MHz until you put your settings back to "normal".


If you are a newbie I bet you have no idea what that means and I explain it better here. Ok this is getting complicated. Isn't there an SDR that tunes to the lower bands AND the upper bands without having to be a computer scientist?









Again, you betcha there is. It is an SDRPlay RSP 1, RSP 2. As of this writing the RSP1 is discontinued however I bet you can still find them. An RSP 2 will set you back about $170 though. Suddenly it gets expensive but remember you want a device that is simple to use. SDRPlay RSP2 is an AWESOME device however if you are using anything but Windows it becomes not so awesome. Building software and installing drivers for Linux or Mac is a very involved process but nothing a geek can't handle.





The RSP 2 software is called SDRUno and it has a bit of a learning curve but it is extremely powerful once you've learned it. Another gigantic advantage of the RSP2 is it has a huge useable bandwidth of 10 MHz. That means if you are using your SDR as a scanner it can cover 10 MHz worth of frequencies. One of the most popular scanner programs is called SDRTrunk but alas the RSP 2 does NOT WORK with SDRTrunk. I'm pretty sure that it doesn't work with the other popular trunking program which is called Unitrunker.


Welcome to Suckville. Population: You.








So the RSP 2 is just as sweet a device as can be but because of the drivers and software development it doesn't play nice with all the software. My understanding is that the SDRPlay software, SDRUno will soon have scanner support. And that's COOL! But again, SDRUno is Windows only. If you are a Linux geek like me you're still kind of left in the dark.


If you need 10 MHz of useable bandwidth to make a police scanner you need to investigate getting an AIrspy R2. Looks like it is just about at the end of its support life and Airspy will be selling a newer device soon. Airspy plays nicely with SDRtrunk and Unitrunker so having an Airspy in my opinion is preferable to having an RSP 2 (for trunking scanners).


What's the bad news about the Airspy R2? You know there is bad news, right? Airspy R2 doesn't go below 25 MHz and you need an up converter to use with it. Their upconverter, the Spyverter. The price for an Airspy and Spyverter.............$250 or so. Oucheth. But by and large you can do more with Airspy and it comes with a free software program called SDR# that is probably the best SDR software out there that there is. Sadly it is Windows only and I generally despise Windows. But push come to shove if I really want to do something tricky I'll grab the Airspy and my Windows laptop.



These are all receivers. If you decide you need to transmit, well number 1 you need an FCC license and number 2 you need something called a HackRF, an Adalm-Pluto or a LimeSDR or LimeSDR-mini


I won't say much about the transmitters because this is a primer for newbies but an Adalm Pluto needs special drivers that generally have to be compiled and built and it again doesn't play with all software natively. Ditto for LimeSDR and LimeSDR-mini. I just bought a LimeSDR-mini and it is barely useable because the software and support just isn't out there yet because it is so new. HackRF works with pretty much everything and it has 20 MHz worth of useable bandwidth. If you want to dabble with transmitting but you're still a newbie do yourself a favor and buy a HackRF.


To recap briefly. An inexpensive SDR will do most things however it won't tune below 25 MHz. You need an up converter to reach those frequencies. An inexpensive SDR that will do direct sampling and reach those HF frequencies is available but it is just a little geeky to get working and once you are set below 25 MHz, you are stuck there until you undo what you did to get there in the first place. To have it all costs bigger money but having bandwidth and a giant frequency spread means little if the software support isn't available.


Buy a cheap stick, play, learn a little and THEN AND ONLY THEN, spend the money on the greater receivers.


1. If you just want to dabble pick up a generic RTL-SDR as cheap as you can. There are a bunch of different ones out there and they all work. Some better than others.

2. If you want to inexpensively listen to HF, Shortwave, and Amateur Radio buy an RTL-SDR v3.

3. If you want HF, Shortwave, Amateur radio and want to listen to VHF and UHF without having to set device strings and LNB offsets buy an SDRPlay RSP2 or RSP1A.

4. If you want to follow trunking radio systems such as your local police, fire, ambulance, city services buy an Airspy R2.

5. If you want to transmit and do cool experiments like trying to break into your own car by hacking the keyfob buy a HackRF.

6. If you want to track L band satellites and the such get the SDRPlay RSP2 or RSP1A (or Airspy).


I probably own 2 dozen SDR Radios. If I had to start fresh knowing what I know now I'd buy generic ones for long term projects like PiAware. I'd buy an Airspy and Spyverter for bigger game, and I'd buy a RTL-SDR v3 for the laptop bag for traveling.


Enjoy.


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