New ExtIO For rtl_tcp: Control R820T Bandwidth, Decimation, Auto Reconnect

A few days ago we posted about Hayati and others' work in creating a new release of the librtlsdr drivers which implemented some new interesting features. However, at the time of the post there was no GUI for actually making use of the features easily. Now Hayati has released a new rtl_tcp ExtIO interface

The interface exposes the ability to manually adjust the filtering within the R820T tuner. This is quite useful for managing out of band interference and raising overall dynamic range especially when trying to listen to a narrowband signal. It also exposes decimation controls, tcp connection features like auto reconnect and persistent connection, manual IF gain control, the ability to choose USB vs LSB tuning, and the ability to choose the highest stable sample rate of 2.56 MSPS.

The ExtIO interface is only available for SDR programs that support ExtIO, such as HDSDR. To test the ExtIO, first download and extract the latest librtlsdr release then run rtl_tcp from the command line. Extract and run the new ExtIO dll into the HDSDR folder, then run HDSDR, making sure to select the new dll when it asks on startup. You can then set the desired bandwidth and the matching decimation settings for that bandwidth.

The new ExtIO exposing new features
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How does one update rtl_tcp on Rasbian?


You will probably have to recompile.


If I just follow the instructions here:
does that get me the updated version or is there something special that I need to do?

I did try re-installing per those instructions but I’m unable to connect to the server (it doesn’t appear that it’s listening on the proper ip address)

pi@raspberrypi:~/rtl-sdr-blog/build/src $ rtl_tcp -T -a
Found 1 device(s):
0: Realtek, RTL2838UHIDIR, SN: 00000001

Using device 0: Generic RTL2832U OEM
Found Rafael Micro R820T tuner
[R82XX] PLL not locked!
Tuned to 100000000 Hz.
activated bias-T on GPIO PIN 0
Use the device argument 'rtl_tcp=' in OsmoSDR (gr-osmosdr) source
to receive samples in GRC and control rtl_tcp parameters (frequency, gain, ...).


To start I want to thank Rodrigo the collage kid for sending some instructions on how to do this . I will spend the weekend to try to get this running .


Hi OM;

These instructions hopefully will get you a up & running HDSDR version, with latest Hayati Ayguen ExtIO. Without further ado:

1) Download the software package from
2) Unzip the stuff at some folder in your computer
3) Setup the RTL-SDR drivers using the zadig.exe file following these instructions:
4) Step 1-3 is one-time only, just for setup. Now let’s run the stuff.
5) FIRST, double-click the rtl_tcp.exe file
6) Then; double-click the hdsdr.exe file – you’re up& running.
7) For the extra ExtIO functionality, in HDSDR hit F8
8) Fiddle with the “R820T/2-Tuner Bandwidth” settings to wipe out lateral unneeded signals
9) Ensure to keep the gains (both RF and IF) as low as possible. Excessive gain will spew signal images all across the board
10) If you dont know what a Bias Tee is STEER CLEAR from the “4.5V BIAS TEE” checkbox, under the risk of damaging your SDR dongle, your tenna or whatever else your antenna is connected to.

‘Sall done; I couldn’t think of anything simpler.

73 de PY2RAF.


Okay guy’s I am pushing the hell out of seventy six years old and a lot of the sdr software is above my pay grade .
Is it possible that you collage kids could use the kiss principal ( keep it simple stupid! ) and put all of this in a folder that can be copied and pasted in the hdsdr folder . Us old fart’s would like to play with this program also .