Remote SDR v4 – Tips

Launch of Remote SDR

In the address bar of Chrome or Edge, enter the IP address of the Orange/Raspberry Pi or one of the 2 Orange Pi if you have a dual configuration. If the system asks you, give the IP address of the orange PI of the receiver and the address of the transmitter. Put the same for a Pluto.

Go to the Remote SDR page. The ‘RX On’ indicator is red then should turn green after a few seconds, then the same for the ‘TX On’ indicator.

If one of the LEDs remains red, reload the page.

The Spectra green line should fill with a vertical line 5 times per second. This corresponds to the arrival of a spectrum frame (2048 values at the output of the FFT).

In some rare cases, the received spectrum is reversed. It must come from complex demodulation oscillators that do not start on the correct phase. Do a ‘Relaunch’ and it is fine.

Starting the Adalm Pluto

In the ‘Tools’ page there are 2 tools to check if the Pluto responds. Sometimes it gets stuck, a reboot may be necessary. The ‘help’ command gives a list of commands that can be sent to Pluto. It’s irrelevant, but it shows that it is reacting correctly.

In principle, you need a USB hub between the Pluto and the Orange PI One Plus under Armbian. This corresponds to a system bug that I cannot explain. The Orange pi zero 2 and the Raspberry Pi works connected directly.

Warning !!! An additional 5V power supply is required for the Pluto. USB power is not enough.

Starting RTL-SDR

In the Tools page, we have a tool for obtaining RTL-SDR info. This makes it possible to verify that it is responding. Be careful, some models heat up and no longer respond after a certain time.

Starting HackRF One

In the Tools page, we have a tool to obtain Hack-RF info. This makes it possible to verify that it is responding.

2 SDR connected to a Raspberry 4

If 2 HackRF One are connected to the same Raspberry Pi 4, to recognize which is the receiver and which is the transmitter, you must put in the configurationRX.js and configurationTX.js files the last 4 digits of the serial numbers. A reboot is necessary.

With an RTL-SDR key and a HackRF One, the order of plugging into the USB ports resolves the ambiguity.

Frequency drift compensation

Upper beacon

In case of traffic via QO-100, it is necessary to compensate for the drift of the LNB in the antenna. Remote SDR makes it possible to track the high and low beacons in frequency and estimate the compensation to be made. Each time Remote SDR is launched, check the beacon setting and manually compensate if necessary by turning the mouse wheel on the numbers. Then the automatic compensation will do what is necessary.

TX Manual correction

To compensate for any delay in transmission, it is necessary to listen to its signal in return. Switch to transmission and select the Sinus 800Hz generator. Look at the spectrum of the audio channel of the receiver and adjust the “Manual correction” of the transmitter to have an audio signal close to 800 Hz.

Adjusting Frequencies

For fine adjustment of the frequency of the receiver, the transmitter, the compensation of the receiver or the transmitter, there are different means:

  • turn the mouse wheel on the numbers
  • click on the figures to display a zoom and then turn the mouse wheel or slide your finger above the figures.

For the audio channel of the receiver you can use the left and right arrows on the keyboard.

RX and TX Gains Adjustment

Depending on the SDR model, the gains are different and some of the sliders are not used. Experiment to find the optimum corresponding to your configuration.

The dynamics of HackRF or RTL-SDR being only 8bits, a bad adjustment of the gains can result in the appearance of additional lines in the spectrum due to lines which saturate.

Dynamic spectra tuning

For the ‘Waterfall’ and the trace in amplitude of the spectrum, click on the arrow on the right to adjust the sliders. The setting is different for each SDR.

Receiver Squelch

By clicking on the reception mode (NBFM, WBFM or AM), you can set a squelch.

Microphone authorization

Web browsers do not give access to the microphone if the site does not have secure access in https. On your local network at home, you generally work in http simply. To get around this difficulty, the solution is to set up a derogation at the level of the web browser by accessing the “flags” parameters. you must type in the address bar:

with Chrome: chrome://flags

with Edge(2020): edge://flags

Look for the header:

Insecure origins treated as secure

Fill in the field as below with the IP address of the orange PI which provides the pages.

Reception scanning

It is possible to define one or more scanning zones of the reception band. The system automatically locks onto the correspondent and changes it every 10 seconds. With the mouse, it is possible to move the limits and the threshold.

Setting of GPIO outputs

It is possible to set the GPIO outputs according to the reception or transmission frequency. This is applicable for configurations with one or two orange PIs. This makes it possible to switch relays, for example, depending on the band worked.

To refer to the number of GPIOs and connection pins see the following articles :

For the Raspberry PI 4, in a terminal window type: pinout or go to the web page

The settings are made in the configurationRX.js and configurationTX.js files.


The definition of the transmit frequencies for which a CTCSS signal is desired can be found in the configurationTX.js file.

Software Architecture

For those who would like to open ports to communicate to the outside.

CPU cooling

With intense use, the CPU may heat up, especially if it is mounted without a heat sink. If 65 ° C is exceeded,one GPIO pin goes to 1 to control the power on of a fan.

pin 7: Orange Pi Zero 2
pin 12: Orange Pi One Plus
pin 7: Raspberry 4B
After 30s of inactivity, no more web client connected, radio signal processing stops, CPU temperature drops rapidly.

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