RTL-SDR Blog V.3. Dongles User Guide

Version 3 of our customized RTL-SDR dongles brought out some new interesting features. In this guide we explain how to use those features:

Feature 1: Direct Sampling HF Mode

This feature allows you to listen to HF signals between about 500 kHz to 28.8 MHz.

To use direct sampling mode

  1. Connect an appropriate HF antenna to the SMA antenna port (this is the same port where you connect your VHF/UHF antenna). 
  2. In SDR# select the Q-branch in the configure menu (the cog icon next to the play button). (If it is greyed out make sure you stop the SDR first, by clicking the stop button in SDR#)
  3. Press Play and tune to 500 kHz – 28.8 MHz.

Q-branch

VHF antennas like small discones or short whip antennas will probably not pick up HF signals very well, if at all. If you have no such antenna you might get something with the large telescopic antenna to its maximum length of 1.5m, but really this is not long enough for HF. You can instead use the screw nut provided with the antenna base to clamp on a long wire antenna that is 5 meters or more in length. Ideally you should use a 9:1 unun with the long wire antenna for optimal reception. Even more ideally you’d use an antenna tuner, though this is expensive.

Other software like HDSDR and GQRX can also support direct sampling. It may entail setting a device string, and for the Q-branch, the value should be 2. In GQRX the device string would be “rtl=0,direct_samp=2” (without the quotes). Make sure that there is no space after the comma.

To go back to listening to frequencies above 28.8 MHz remember to change the sampling mode back to “Quadrature Sampling”.

Note that this feature makes use of direct sampling and so aliasing will occur. The RTL-SDR samples at 28.8 MHz, thus you may see mirrors of strong signals from 0 – 14.4 MHz while tuning to 14.4 – 28.8 MHz and the other way around as well. To remove these images you need to use a low pass filter for 0 – 14.4 MHz, and a high pass filter for 14.4 – 28.8 MHz, or simply filter your band of interest. 

Feature 2: Software Selectable Bias Tee

V.1. and V.2. of our dongles included a bias tee which could manually be enabled by opening the case and soldering two pads on the PCB together. V.3. introduces a bias tee which can be enabled entirely in software.

WARNING: Before using the bias tee please ensure that you understand that you should not use this option when the dongle is connected directly to a DC short circuited antenna. Although the bias tee circuit is dual protected against accidental shorts with a PTC automatically resetting fuse and overcurrent protection on the LDO, short circuiting the bias tee for an extended period of time (hours) could damage the LDO or fuse permanently. Only use it while connected to an actual powered device, like an LNA, active antenna or the SpyVerter.

To make things clearer: DC Short Antenna -> LNA -> Coax -> V3(bias tee on) is absolutely fine. What’s not good and makes no sense anyway is DC Short Antenna -> Coax -> V3(bias tee on). DC Short Antenna -> Coax -> V3(bias tee off) is fine.

To enable the bias tee in Windows:

  1. Download and extract all the files in this zip file to a folder on your PC. It contains two batch files that can be run.
  2. Make sure all SDR software like SDR#/HDSDR/SDR-Console etc is fully closed.
  3. Run the biastee_on.bat file to turn the bias tee on. It will run and open a CMD prompt that will briefly say “Found Rafael Micro R820T Tuner”. The CMD prompt will close soon after upon success.
  4. The bias tee is now on. To turn it off repeat steps 2 & 3, but instead run the biastee_off.bat batch file. Alternatively, simply disconnect and then reconnect the SDR to turn the bias tee off.

If you have multiple dongles connected you’ll need to edit the batch file to specify what dongle’s bias tee you want to activate. Open the bat file with any text editor, like Notepad, and add the dongle selector “-d” flag. For example to activate the bias tee on the dongle that was plugged in second you’d need to change it to “rtl_biast -b 1 -d 1”.

If you get a Smart Screen message, click on More Info, and then on Run Anyway. Also note that some versions of Windows may fail to run batch files due to misconfiguration or aggressive antivirus software. If you cannot fix these problems with Windows or your antivirus, run the command manually on the CMD line.

To run it manually on the CMD line first browse to the directory where the bias tee software is stored using “cd” (e.g. cd C:\SDR\bias_tee_folder), and then run:

  1. ON: rtl_biast -b 1
  2. OFF: rtl_biast -b 0
  3. If needed select a particular RTL-SDR device with the -d flag.

In Linux or MacOS download the source from git, compile it the same way you do the regular RTL-SDR drivers, and then run ./rtl_biast -b 1 to turn the bias tee on and ./rtl_biast -b 0 to turn the bias tee off. The procedure is:

git clone https://github.com/rtlsdrblog/rtl_biast
cd rtl_biast
mkdir build
cd build
cmake ..
make
cd src
./rtl_biast -b 1

If you want to be able to run the bias tee program from anywhere on the command line you can also run “sudo make install”.

If you have trouble running the bias tee check with a multimeter if there is 4.5V at the SMA port, and that your powered device is actually capable of receiving power. Remember that not all LNA’s can accept bias tee power. We recommend Adam 9A4QV’s LNA4ALL, as you can order this from his store with the bias tee power option enabled. If you need further help please contact us at rtlsdrblog_AT_gmail_DOT_com.

Feature 3: Selectable Clock & Expansion Headers

This is for advanced users who need to daisy chain clocks together for coherent experiments, or need to access other ports. You can either bridge the clock selector the directly with a solder bridge, or solder on a 1.27mm 2×2 header pin jumper.

To add a jumper to the CLK selector header.

  1. Carefully remove the 0 Ohm resistor.
  2. Very carefully solder a 1.27mm 2×2 header onto the clock selector pads.
  3. You can now select your clock input.

How to connect the CLK jumpers:

CLK_1

 The first position allows you to output the dongles clock to the CLK pads. The second position allows you to input an external clock.

CLK2

An example of CLK daisy chaining is shown below. One dongles TCXO is connected to two other dongles who have disconnected clocks.

CLK3

LF Improvement / Bias Tee Disable Mod:

If you want to improve the performance at LF and do not require the bias tee, then you can remove the bias tee inductor at L13. Of course remember that if you are interested in VLF/LF, it might be a better idea to use an upconverter like the SpyVerter, which can be powered by the bias tee on the dongle.

Current Known Issues:

We’re constantly trying to improve our units and we always make note of what issues exist and how to fix them.

Please remember that these units do get hot to the touch when used in warm climates. This is not an issue and is expected. We have improved the thermal bonding and heat transfer between the chips and the metal case. This results in making the metal case hotter, but it keeps the chips much cooler, resulting in better performance. To lengthen the life of the dongle we recommend keeping the unit away from direct hot sunlight.

Batch 2 and newer (Shipping Now):

No known issues. 

Known V3 Batch 1 Issues:

  1. Increased sideband noise on very strong narrowband signals. This should not be a significant problem as it only affects very strong signals. The hardware fix is to add about 100-220uF of capacitance on the 3.3V power line. Batch 2 will reduce this noise.
  2. The bias tee when turned on adds a large spur in direct sampling HF mode. This may be problematic only if you intend to use a bias tee powered HF LNA in direct sampling mode. This can be fixed by adding about 2.2uF of capacitance to the output of the LDO, before the inductor. Batch 2 will fix this.
  3. The bias tee can be damaged by accidentally short circuiting the output for a few seconds while it is on. This damage only occurs on USB3.0 and USB2.0 ports that can provide up to 1A or more or current. Batch 2 will add a resettable fuse to prevent damage.

 

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138 comments

  1. stephen

    Does anyone know how much current the bias-t can handle? I want to play with some old C-Band LNAs. I can hardly wait for my V3 to arrive. Thanks.

    • Beer It

      Did you check the datasheet ?

      https://www.rtl-sdr.com/wp-content/uploads/2017/06/RTL-SDR-Blog-V3-Datasheet.pdf

      “The V3 makes use of a low noise LDO and one of the GPIO pins on the RTL2832U to provide a 4.5V bias tee that can be activatedin software. The bias tee can pull about 100 mA continuously so is suitable for the majority of 3-5V powered LNAs that are popular with RTL-SDR devices. The bias tee is protected against accidental short circuits at the LDO level, and with a thermal auto-resetting PTC fuse. See ‘Activating the Bias Tee’ for more nformationon software for activating the bias tee.”

    • Lee

      you’re probably all over this, but but i thought i’d throw this out there for general public; be aware of what you have; old c band LNAs are just that, and good for 4ghz. c band lnb’s often have a LO at 5150mhz, which means the modulation is inverted since the lo is higher than the downlink. no biggie for some modulation types but deadly for others. also be advised that the old old DRO LNBs are drifty as hell. the thinking was that since carriers at the time often took a whole transponder, you’d achieve lock even if you’re a few megs off. Power for most of these are 12-24v, 300ma.

      • stephen

        Not only that, but the newer LNBFs use voltage to change polarity (~15v for Vertical and up to 24v for Horizontal.). Some however, use two bands worth of freq’s to provide both polarities at once. Definitely research what you have before playing with it.
        Happy happy joy joy.

  2. Sauro

    Hello.

    I’m a blind bcl listener, I plugged the RTLSDR Blog 3 dongle on Adroid with SDR Touch app, because the Windows and Mac programs are not accessible with the screen reader software.
    I would like to receive some BCL signal in am, and ham radio in ssb, but unfortunately I do not get any useful signal.
    I connect the smartphone to the rtlsdr with an otg cable that powered both devices.
    I set preference / direct sampling to the “branch q direct sampling” function useful for short waves,
    I use a wire antenna of 10 meters, and with my Sony icf 7600 I received many signals in same frequences.

    Tanks.

    • Max

      The simoultaneous view of all the signals in the band. You don’t need to scan at the speed of light to catch some signal, you see them all.

  3. Paul Rodenhuis

    Hi. I have just ordered a V3 and awaiting its arrival. Some questions if I may:
    1. I have a Vista PC (old, I know) with Vista and Ubuntu 16.xx. Is one better/quicker than the other? Is Windows easier to setup and get going than Linux? I also have this 8.1 laptop, an XP netbook and several Android tablets.
    Apart from the laptop, are the others useful?
    2. Is SDR# the best s/w to install?

    • admin

      1) Either Windows or Linux can be used. They’re both quite easy to setup, but it depends on what software you want to use, and what OS you’re most familiar with. Laptops and Android can be used too.
      2) I recommend starting with SDR#, seems to be the most beginner friendly with the most intuitive interface.

  4. Eric Faden

    So if I have a LNA4ALL with the bias-t mod done, can I safely place it on the RTL SDR before enabling the Bias-T? I am trying to figure out the correct order to safely do this? I don’t want to burn anything up, but I thought I wasn’t supposed to place a bias-t enabled device on the RTLSDR before bias-t was enabled, and not to enable it without a bias-t enabled device… but this seems like a catch-22 since it is software enabled.

    • admin

      You can connect a powered device without turning on the bias tee, it won’t destroy anything. You can do whatever you want as long as you don’t create a short circuit. Even if you do short it, it’s protected by the fuse, so no worries. Just don’t short it for a long period of time or the fuse will eventually degrade.

  5. Phil

    G’day,
    I’m having an issue with the bias-t stopping when i run gr-iridium or multimon-ng in ubuntu 16.04. When i use any other program (gqrx + decoders for example), the bias-t stays active. Thought it might be a blacklist issue, so i have done that. Any ideas please?

  6. Lurch

    Just tried to turn BiasT on, BUT ” ‘rtl_biast’ is not recognizedas an internal or external command, operable program or batch file.”
    Downloaded the ZIP file, running on Windows 10 Pro. Using a RTL_SDR v3.

  7. Tom

    Seeking recommendations for an F-Connector Splitter with one port DC Power Pass through.

    Running 2x RTL-SDR dongles with an LNA near antenna. Seeking to have one dongle BIAS-T power the LNA.
    Splitter must be F-Connector. Any recommendations?

  8. Jim Williams

    I am new to SDR. I just purchased one of your rtl-sdr blog v3 dongles from Amazon and am trying to use it in direct sampling mode. I am using Gqrx on an iMac running macOS 10.12.5 Sierra. In normal mode, your dongle shows up as Realtek RTL2838UHDIR SN:00000001 and it receives FM broadcast signals just fine. To switch to direct sampling, I change the device string to “rtl=0,direct_samp=2” (without quotes) per the instructions above. I also set the input rate to 2048000 consistent with your instructions for SDR#. I then tune to a very strong local AM broadcast station and hit start. I get nothing at all on either display. When I go back to check I/O devices, the device has switched to “Other.” Can you tell me where I have gone wrong? (Congratulations on America’s Cup!)

    • admin

      That’s quite odd, do you have any screenshots that you can upload? Also what is the exact frequency that you are tuning to? I think it’s normal for it to show Other though.

      • Jim Williams

        1.010 mHz (WINS in NYC).

        Hopefully this will get a screenshot to you.

        /Users/jim/Desktop/Screen Shot 2017-07-07 at 2.51.53 PM.png

        • W1PJE

          Hello,

          I am using a Mac here running OS X 10.11.6 (El Capitan) so not quite the same as you. However, I found that I had to update my GQRX with the latest version. I used MacPorts, which also updates the RTL-SDR driver. When I did that, the direct sampling option worked fine. (Beforehand, it gave me nothing at all, similar to you.)

          If you are not using MacPorts, you should give it a try. After installing it (see the web page for instructions), the command would be

          sudo port install gqrx

          and then you would run GQRX from the command line as:

          gqrx

          Perhaps this will help.

  9. VAlentin

    Hello! I accidentally gave a food of the active antenna on sdr entrance (12v). Sdr works in VHF When I pereklyuat VHF of strengthening is not present and nothing is heard. I ask to prompt what detail most likely is subject to replacement. Thanks. I ask to specify the name.

    • admin

      Hello, I think your comment didn’t translate very well, but as I understand it you applied 12V DC to the front end by mistake, and you’re asking which parts need to be replaced?

      Probably ESD diode D12 is blown. It’s also possible that C23 could have blown as well. If you’re unluckly the R820T2 might also have died from the voltage, even though there are three DC blocking caps.

      • Valentin

        Yes, I accidentally applied 12 volts to the antenna input. I listened at this time to a frequency of 3600 MHz. (In the settings was Q-branch). I checked BAV99, it works. The capacitor is good. I turn on the frequency of 144 MHz, everything works well, I hear signals from the walkie-talkie. When I translate in the settings the direct conversion (Q-branch) and put the frequency of 3600 MHz the scale shows an even level and there are no signals from the antenna. There are no noises. Is there a possible cause in the stabilizer is 4.5 volts. I think I need to replace it (LP2985AIM5-4.5 / NOPB tell me this stabilizer is used in SDR). I measured the voltage at its input, it is

          • admin

            That regulator is for the bias tee, so there won’t be any output there unless you actually turn it on in software. So it’s normal for there to be no output on that one.

            At 12V it’s possible you blew the BGA2867 amplifier which is the small black chip below D12. Be aware that it’s also possible that all the caps are damaged too.

            • Valentin

              Thank you. I understood. So the stabilizer does not turn on when the Q-branch value is set. If the amplifier is damaged, then why do I receive a 144 MHz signal with good gain, the SDR works as expected, without any problems receiving the signal, and when I switch Q-brunch and put 3600, there is no gain. Is it possible in this case? Or at a frequency of 144 MHz, another amplifier is involved?

              • Valentin

                I checked D12, the diode. It doesn’t pass a signal in one side. Write please brand and model of the D12 diode. And Most likely the amplifier as the signal passes very poorly burned down. It is heard but is very silent on the korotkikhkh waves. The amplifier is precisely used by BGA2867,115?

                • admin

                  D12 can be replaced by any ESD diode, rated above 5V. Or you can operate it without the diode, the BAV99 will still handle some ESD. Yes the amp is BGA2867, but BGA2866 or 2869 can also be used.

  10. willie

    wow, just wow… for the price this dongle really does it all! i’m glad i waited until V3, as the ability to get HF, along with VHF in a single small package is just fantastic! i am using gqrx under OS X 10.10.5 and also under GNU/Linux – works very well indeed – kudos!

  11. Axel DG9BEY

    Hello. I would like to use the dongle in combination with a Transcierer. Is it possible to connect a Tx line at some point on the board of the dongle, so that it is kind of muted during Transmission ! And if it is possible, how could it be done ?

  12. captcha

    Is it possible to use the V3 dongle in direct sampling mode for HF in combination with the command-line tools rtl_power or rx_power?

    • captcha

      Yes it is.. The rx_power utility accepts a -D mode argument which sets direct sampling mode. Values for mode can be set as 0 (disable/default), 1 (I-branch), 2 (Q-branch) and 3 (no-mod). I just used the V3 dongle to log activity on the 40m band with the following command: rx_power -D 2 -f 6.98M:7.21M:200 -i 10 -d driver=rtlsdr -g 50 outfile.csv

  13. Andy

    I am using a v3 to run ADSB on a RPi3 but unfortunately it doesn’t work with my ADSB program Dump1090 mutability – just causes the error usb_claim_interface error -6 when run 🙁

    Is there a way to get biasT set to on when the RPi3 is started and which is compatible with the Dump1090 program OR a way to hardware mod the unit so it is active when switched on?.

    Many thanks for your assistance.

    • admin

      What does rtl_test give? Double check that you’ve blacklisted the dvb-t drivers, and installed the rules.d file.

      You can use a script to run the rtl_biast program on boot if you always want the bias tee to be on.

  14. LINDECKER Patrick

    Hello to all,

    I tested my “RTL-SDR.COM V3” key at 1545 MHz (L band), with a patch antenna and a LNA supplied by the key. This key seems to have a very low drift and a small shift of 2 KHz from the nominal frequency, which is a pleasure not to have to consider drift and shift.

    I noted that a sampling frequency of 250 KHz introduces an additive noise of about 4 dB compared to a sampling frequency of 1 MHz, So on SDR#…, avoid this 250 KHz sampling frequency (I will switch all modes in Multipsk at a sampling frequency of 1 MHz instead of 250 KHz (except ADSB which needs 2 MHz)).

    73
    Patrick

  15. someone

    Is there a way to have the bias-t on in DVB mode in linux? I want to use the dongle as a normal TV dongle, and I have an antenna with a built-in LNA that requires bias-t to work…

  16. KU4A

    Very nice. Didn’t take long at all to set up my V.3 dongle. The only thing that tripped me up is that you have to hit “stop” to change from Quadrature Sampling to Q-Branch and vice versa. Thanks for a great set of instructions.

  17. Jeff

    Hi, still learning all this sdr stuff, can this V-3 dongle still be installed in the dolphin labeled up converter ??? I bought the V-3 as an upgrade to the cheap one that comes with the kit, thank you in advance for any answers…

    • admin

      It might be possible, but you’d need to hack it in a bit as the pads might not line up.

      Also I believe most of those kits main purpose is to connect up the direct sampling mode on a generic dongle. The V3 already has the direct sampling mode connected up and with an extra amp too, so it would make no real sense to use a V3 on that mod board.

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