SDR: No longer just a budget option.

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  • This topic has 11 replies, 5 voices, and was last updated 1 week, 6 days ago by SeanT. This post has been viewed 542 times
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    • #97928
      Joe (G.W.N.S.)
      Moderator

        Software Defined Radios (SDR) have come a long way in a short time.

        I am not going to attempt to cover all there is about SDR, but will highlight some things I find interesting.

        I’ve recommended them as a budget alternative to various Radios to include Scanners and they can still fill this role in limited circumstances.

        Software and hardware options continue get more diverse and they seem limited almost by the imagination of people.

        I’ve been following the various developments in SDR for a longtime and have dabbled in them, but much of the features available were not quite up to my needs beyond redundant backups. I’ve considered building what I wanted, but really didn’t have the time to dedicate to it, so have been waiting for others work proceed.

        Depicted below is one of my basic SDR setups.

        It’s a low cost tablet (Amazon Fire HD 8 $49.00), a RTL-SDR dongle/Antenna (RTL-SDR Blog R820T2 RTL2832U 1PPM TCXO SMA Software Defined Radio with Dipole Antenna Kit $29.95), and a OTG USB Cable.

        This one is running SDR Touch App for Android, but there are many options.

        More to follow.

      • #97929
        Joe (G.W.N.S.)
        Moderator

          SDR Touch

          SDR Touch supports receiving FM radio, AM, SSB and CW broadcasts including HAM radio amateurs, police, air traffic, weather reports, fire department and emergency stations, taxi traffic, audio of analogue TV broadcasts, digital broadcasts and many more! Depending on the hardware used, its radio frequency coverage could span between 50 MHz and 2.2 GHz. Turn your mobile phone or tablet into an affordable and portable software defined radio scanner. SDR Touch currently demodulates WFM, AM, NFM, USB, LSB, DSB, CWU and CLW signals.

          RTLSDR RTL2832U DVB-T Tuner Dongles

          Briefly, our dongles come with the following improvements:

          <1 PPM temperature compensated oscillator (TCXO) – Accurate tuning and almost zero temperature drift (2 PPM max. initial offset, 0.5-1 PPM temperature drift)

          SMA female antenna port – Generic dongles use the less common MCX or PAL antenna ports. SMA is more common, so more adapters and antennas are available for it. It is also more durable and has lower RF insertion losses.

          4.5V USB powered bias tee – This allows the RTL-SDR to power low noise amplifiers (like the LNA4ALL, HABAMP, RTL-SDR Blog ADS-B LNA) and active antennas through the coax cable. Can be enabled in software (see V3 users guide).

          Experimental: HF Direct Sampling Mode – Listen to 500 kHz – 24 MHz with direct sampling. Simply connect an HF antenna to the SMA port, and choose the Q-branch mode. There is a built in 25 MHz low pass filter, but additional HF filters may be required for optimal performance (e.g. to attenuate strong MW AM).

          Aluminium case and passive cooling – These units come stock with an aluminium case and passive cooling via a silicon thermal pad. This stops reception failing due to heat above ~1.2 GHz.

          Improved Antennas – We provide an excellent dipole antenna starter kit for newbies. Use the included mounts and extension cable to mount the dipole in good position for optimal reception. Receives terrestrial and VHF satellite signals.

          Various additional improvements compared to other RTL-SDRs – R820T2 tuner, higher quality passive components, a choke on the USB line to reduce USB noise, a much improved PCB design for significantly less internal spurs and noise, various break-out pads, improved ESD protection, additional bypass capacitors and ferrite power line chokes, improved front end matching circuit and a better LDO.

          More to follow.

        • #97930
          xsquidgator
          Participant

            Have you listened to anything other than commercial FM radio with yours?
            I got one of the $20ish USB dongles and have used it as an FM radio on my PC. (running SDR#)
            I haven’t ever tried setting up my laptop out in the woods when I might be around people using handheld radios like MURS, FRS or the like, and I wonder how effective the little antenna that came with it would be for that application. Seems this thing would offer at least the potential of visually monitoring a range of frequencies.
            Thanks for sharing, until seeing this it hadn’t occurred to me to use a small tablet rather than a PC.

          • #97931
            Joe (G.W.N.S.)
            Moderator

              Have you listened to anything other than commercial FM radio with yours?

              NOAA WX, County Emergency Services, ADS-B, and I can certainly pull out commercial FM stations that can’t be received by regular radios.

              Using a tablet for mobile is the way to go, but less options in software. Note: You could even use a Phone vice tablet.

            • #97932
              SeanT
              Keymaster

                A couple years ago I did a radio talk up at MVT and had one of these. I was able to show on the screen down in the schoolhouse all the students cell phones as blips in the RF

                if you get 2
                You can use them to decode digital trunked radio systems as long as they are not also encrypted. One monitors the control channel and the softwate tunes the other to the comms freq

              • #97933
                Joe (G.W.N.S.)
                Moderator

                  You can use them to decode digital trunked…

                  :good:

                  Hasn’t been a priority since my immediate area doesn’t use trunked at this time.

                • #97934
                  FransSacco
                  Participant

                    Hi..as per my knowledge it has more resolution. More resolution means more dynamic range, less signal imaging, a lower noise floor, more sensitivity when strong signals are present and better ability to discern weak signals. Some SDR’s give their resolution in ENOB which stands for effective number of bits.

                  • #151399
                    Joe (G.W.N.S.)
                    Moderator

                      Here are some quotes from “Do you have a Radio Scanner?”

                      …would a quality SDR unit be a suitable replacement for a scanner like the SDS and similar(given the same antenna setup)?

                      If you know comms, computers, and antennas. Combine them in proper configuration and take the time to learn and tweak your system.

                      Then maybe?

                      SDR (which goes beyond mere dongles) has a place and use.

                      The real question is what are your goals and skills?

                      If your expanding your ability to exploit the electromagnetic spectrum for everything from SIGINT to early warning ESM, then SDR is a step in the right direction.

                      I’m an avid SDR user, I’ve been using scanners and SDRs for a very long time, I’ve had multiple articles and videos out about it (published under my real name) and I would not recommend SDRs at all for LLVI patrols or similarly tactical type things. You’re stuck with lugging around a laptop to make it work at the absolute minimum and at the very best, you’re having to carry a phone or tablet and remotely connecting to a raspberry pi to make it work. If you’re working from home or a safe location or are able to put up an airspy somewhere, by all means, SDR is your man. If you’re hunting weak signals such as retroreflectors or radars, SDR is your man. What it isn’t good for is throwing into your ruck and running about with.

                      Shortly I will replace lost pics of my basic mobile setup and my intended use for such a SDR option.

                      As noted by Former Sapper I too do not recommend SDR as a replacement for a handheld scanner for increased situational awareness in the field.

                      That does not mean there is no use in the field as I will detail in a later post.

                    • #151425
                      Joe (G.W.N.S.)
                      Moderator

                        Here’s a pic of one of my basic mobile SDR setups.

                        From left to right…

                        Antenna stand with a variety of antennas.

                        RTL SDR V3.

                        USB to split micro USB and female micro USB adapter.

                        USB/micro USB cable

                        Aux rechargeable battery (if powered solely by tablet it will limit useful duty cycle).

                        Amazon Fire HD8 tablet w/armored WX resistant case.

                        Not depicted are extended coax antenna cable, suction antenna mount, magnetic antenna mount, variety of different antennas, additional battery packs, and a variety of additional apps including ADS-B.

                        In the next post I’ll give an overview of my intended uses.

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                      • #151489
                        Former Sapper
                        Participant

                          On top of these, I can highly recommend running an LNA for pulling out the weaker signals from the noise floor. You can pick cheap ones up for $4-$5, they need a little soldiering to accept power from a bias-t but work well or alternatively, you can get yourself the Nooelec LaNA for $30 or there abouts. It comes in an insulated case, ready to go and works well with the RTL-SDR V3 bias-t. Alternatively, for lower noise you can run it independently with a USB power source, I have a small USB power cell that lasts a good 12 or so hours on USB power.

                          My current mobile set up:

                          rtl-sdr V3
                          Nooelec LaNA
                          “Buckshee” dipole (BNC t connector with 2 HT rubber duckies)
                          Thinkpad laptop.

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                        • #151487
                          Former Sapper
                          Participant

                            On top of these, I can highly recommend running an LNA for pulling out the weaker signals from the noise floor. You can pick cheap ones up for $4-$5, they need a little soldiering to accept power from a bias-t but work well or alternatively, you can get yourself the NooElec LaNA for $30 or there abouts. It comes in an insulated case, ready to go and works well with the RTL-SDR V3 bias-t. Alternatively, for lower noise you can run it independently with a USB power source, I have a small USB power cell that lasts a good 12 or so hours on USB power.


                            Pic related is my LaNA set up on one of my “other” antennas.

                          • #151643
                            SeanT
                            Keymaster

                              If you haven’t grasped the obvious, there are a lot of small fiddly parts involved in making these work. They are a specialty tool and quite fun to learn how things work from the comfort of your home. #1 thing is always antenna….the RIGHT antenna for what signals you intend to receive. #2 is QUALITY antenna feed line.

                              The low noise Amp Sapper is speaking of is something you can either begin right away with or learn without then see how it improves what you already can receive.

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