Архив за 02.07.2018

Comment on Noise Cancellation using Linrad and the Phase Coherent Capabilities of an RSPduo by AD5NL

There seems to have been a lot of discussion about phase coherence on the LimeSDR recently; the phase alignment code was merged into the main branch of LimeSuite in 18.04.

No idea if that actually works in practice. Just maybe worth playing around with.

RTL-SDR Discussion • Re: Weak reception when in movement!

ligghts,

a car radio FM receiver has some specific signal processing functions that "hide" the loss of signal from the Rayleigh path level distribution (or variations). The dongle software has none of these functions *** (a and b; see below).

It is important to distinguish between multipath with small path delay variations (flat fades, no distortion, only signal variation) and multipath with larger path delay variations (frequency response of pass-band is not flat, audio is distorted).


1. (almost every) car radio has a soft-mute function. Without signal the audio is attenuated to prevent the noise to be louder than the wanted audio. In fact: when you use a high-end HiFi FM tuner in a car you have the noise level increase also.

The loss of audio is less annoying than the loud noise bursts when the signal is weak for a fraction of a second.

2. (good) car radio has stereo channel separation that varies with the received signal level. The audio S/N difference between mono and stereo is about 20 dB (in Europe where we have 50 microseconds de-emphasis).

Figures: noise theshold for FM is in the order of 2 microvolt; audio S/N of 26 dB for FM deviation of 40 kHz is around 4 microvolt; full stereo channel separation AND audio S/N of 26 dB requires about 100 microvolt.

3. The best FM radios use antenna diversity with two or more antennas (switching diversity or power combining diversity) to reduce the probability that the signal level has a drop down to were the audio noise will rise. Just two antennas in a fixed combiner will NOT help: then you will just create a new single antenna with about the same Rayleigh distribution for signal level and the same probability for a signal level drop.

The diversity system will also reduce the amount of multipath: in fact the Rayleigh distribution is caused by different and parallel propagation path lengths. The audio distortion due to multipath is just a function of the delay spread (together with the relative amplitude of the different parallel signals).

4. Reduction of the post-demodulator audio bandwidth does also help to reduce the experienced noise at the cost of the audio clarity.


*** a and b

A squelch is a type of soft-mute that is used in stationary receivers. The soft-mute is really an improvement over a fixed-level squelch.

A stero to mono switch that is controlled by the signal level is not appreciated due to the nervous effect on the audio.
-----------


You can write some software to insert the mentioned functions in any (SDR) radio; the car radio industry did this already for you.....

Then a better LNA: when the antenna is good, the noise matching is OK and the total system noise figure is below 5 dB or system noise temperature is below 1000 kelvin, then the addition of an LNA will not improve your results. Probably your strong-signal problems (overload, intermodulation) will rise. The dongle has already a limitation in dynamic range.

Succes,
Brightnoise

Statistics: Posted by Brightnoise — Mon Jul 02, 2018 9:48 pm


Sergey777 Стоит ли брать rtl-sdr v3 и чем он лучше бюджетного донгла? Я купил 3 версию донгла. В принципе мне нравится. …

crossbreed пишет:
Sergey777 Стоит ли брать rtl-sdr v3 и чем он лучше бюджетного донгла? Я купил 3 версию донгла. В принципе мне нравится. КВ принимает, тут от антенны всё зависит: длинна и высота подвеса, и подальше о...
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Широкополосный приёмник из DVB донгла - Страница #550

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Comment on Noise Cancellation using Linrad and the Phase Coherent Capabilities of an RSPduo by mark

A similar thing can be done with phase cancelling antennas (yagi and ground plane) joined with a phasing harness. Cool that we can do that inside the receiver these days.

Is there any good tutorial for ADALM-PLUTO?

Hello, I just got an ADALM-PLUTO as a "gift" and wanted to try it out. I've a good knowledge about RF/Modulation as I've had some good theoretical classes, but I've never done anything in practice (besides some LNA/Mixer design in the transistor level for a project from school). So I would need to have some begineer oriented pratical tutorial, any recommendations?

submitted by /u/Theis159
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Noise Cancellation using Linrad and the Phase Coherent Capabilities of an RSPduo

The RSPduo is the latest product from SDRplay, and it's main defining feature is it's dual RX channels. The two channels allow you to simultaneously listen to two stations that may be at opposite ends of the spectrum. Of course the same could be done cheaper with two separate RSP1A devices, however the advantage of the RSPduo is that the two channels are phase coherent. This opens up a lot of technical possibilities such as active noise cancelling/spatial filtering of an interfering signal or unwanted RF noise.

The basic idea behind phase coherent noise cancelling is that you have one antenna pointed towards your signal of interest, and the other pointing towards the interfering signal or coupled to the unwanted noise source. The unwanted signal/noise can then be subtracted from the signal of interest, resulting in a cleaner signal. This can only be done if the two channels are phase coherent like they are on the RSPduo.

Over on YouTube and his blog, ICAS Enterprises has been experimenting with noise cancelling on his RSPduo [Part 1] [Part 2]. The blog is entirely in Japanese, but all the relevant screenshots are in English, and we have provided Google Translated links. SDRplay have also provided a description of the process on their blog. The idea is to use Linrad to process the sound output of the two RSPduo channels from SDRuno. Linrad has capabilities that allow you to subtract two signals from one another.

In his experiments he receives a known 50 MHz CW beacon, and then injects an interfering test signal into the system. Then using Linrads 'signal adaption' feature he is able to completely remove the interference. 

RSPduoでのノイズキャンセルの実験 - Linrad使用
RSPduoでのノイズキャンセルの実験 - Linrad使用

The post Noise Cancellation using Linrad and the Phase Coherent Capabilities of an RSPduo appeared first on rtl-sdr.com.

Weather Satellite’s and Spy Servers?

I was wondering if someone setup a spy server in the 137mhz range could people around the world receive NOAA signals?

submitted by /u/WarGamerJustice
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Video on Hacking 433 MHz Devices with an RTL-SDR and Raspberry Pi

Over on YouTube user Andreas Spiess has uploaded a video showing how to use an RTL-SDR to reverse engineer 433 MHz ISM band devices such as Internet of Things (IoT)/home automation sensors and actuators. 

Andreas decided to do this because he has a 433 MHz remote controlled actuated outdoor awning which he wants to have automatically retract when the wind speed gets too high. To do this he wanted to use a wireless 433 MHz ISM band weather station with wind speed sensor. But unfortunately he discovered that it has a proprietary protocol that can't talk to his awning, which also has it's own proprietary protocol.

Andreas' solution is to use an RTL-SDR and Raspberry Pi running the rtl_433 decoder software to receive the weather station data. The rtl_433 software already contained a decoder for his weather station, so no further reverse engineering was required. The data is then converted into MQTT which is a common TCP/IP protocol for IoT devices. MQTT is then read by Node-RED which is a flowgraph based programming environment for IoT devices.

Next, unlike the weather station rtl_433 did not already have a decoder implemented for his awning. So Andreas had to reverse engineer the signal from scratch using the Universal Radio Hacker software. Using the reverse engineered signal information, Andreas then uses an ESP32 processor/WiFi chip and cheap 433 MHz transmitter to implement a clone of the awning's remote control signals. The ESP32 is programmed to understand the MQTT data sent from the Raspberry Pi via WiFi, so now the weather station can control the awning with a little bit of logic code in Node-RED.

How to Hack your 433 MHz Devices with a Raspberry and a RTL-SDR Dongle (Weather Station)
How to Hack your 433 MHz Devices with a Raspberry and a RTL-SDR Dongle (Weather Station)

The post Video on Hacking 433 MHz Devices with an RTL-SDR and Raspberry Pi appeared first on rtl-sdr.com.

Comment on SDR# TETRA Decoder Plugin Updated by scansweden

Seems to be the main/control channel in the Location Area, if you click on it SDR# jumps to that frequency.

Comment on SDR# TETRA Decoder Plugin Updated by scansweden

Check that your Microsoft .NET is the latest version/patch from Microsoft.
I run 4.7.2 on my windows 10 and SDR# is very stable running the Tetra plugin.
Another computer running Windows 7 crashed with SDR#+Tetra almost immediately after I activated the plugin
and the solution there was to update .NET.

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