Tagged: rtl2832u

February 3, 2015

New SDR# RTL-SDR Driver with LNA/Mixer/VGA Gain Settings and Decimation

A new SDR# driver for the RTL-SDR that comes with manual settings for the LNA/Mixer and VGA gain stages as well as software decimation (in Russian use Google Translate) has been released on rtl-sdr.ru. The three seperate gain stages offer much greater control over optimization of signal SNR and interference management. The decimation feature allows you to sacrifice some bandwidth for increased ADC bit resolution. This means that using the decimation feature can significantly improve the SNR of a signal. Update: It turns out that decimation is already used in the existing SDR# code, so using decimation in the new driver won’t improve the real SNR, only the visible SNR – so there will be no audible improvement. It will however allow you to effectively zoom in on the spectrum without loosing visible resolution. Also it allows you to use a higher sample rate (2.8 MSPS) which will improve SNR, whilst maintaining a reasonably sized (small enough) visible bandwidth for narrowband signals.

The driver is based on Oliver Jowet’s modified driver so it should also have the capability to tune down to 13 MHz or lower. To use the plugin simply download the zip file and copy the files into the SDR# folder, replacing all existing files. Previously we posted about another driver with similar capabilities, but this driver was never released to the public. There was also another driver with just the three gain settings released earlier which this driver appears to be based on.

New RTL-SDR Driver with LNA/Mixer/VGA Gain Settings and Software Decimation

February 3, 2015

Testing the built in IF Filter on the R820T RTL-SDR

As seen in this previous post, the R820T tuner chip used on most RTL-SDR’s has a built in hardware tunable IF filter. Leif, the programmer of the Linrad SDR software has been experimenting with this filter and has uploaded a video of his experiments to YouTube.

In the video he shows how the R820T IF filter can be set to be as narrow as 300 kHz. Using a narrow IF filter can help to reduce the interference from strong nearby stations by up to 30 dB. Leif uses a modified RTL-SDR driver that comes with Linrad which allows the IF filter to be manually modified.

Update: Leif has posted some extra details in the Osmocom mailing list. He writes that the modified driver can be found at https://github.com/dl8aau/librtlsdr and a Windows version is at https://drive.google.com/file/d/0B9m6SAaGpewQeWtyS0lzdW1xVmM/view?usp=sharing.

R820T with IF filtering

Watch this video on YouTube

February 3, 2015

Mods and Performance of an R820T2 RTL-SDR

Over on his blog, RTL-SDR experimenter Laidukas had added a post showing how he modded his R820T2 RTL-SDR for improved noise performance. The mods he applies are:

Addition of 100nF, 1nF and 100pF bypass capacitors on the power supply rail.
Added a common mode choke to the 5V line.
Added a MuRata NFM21 EMI suppression filter to the 5V line.
Replaced the oscillator with a 0.3 ppm temperature controlled oscillator (TCXO).
Disabled the internal RTL2832U 1.2V switching supply and provided external 3.3V and 1.2V supplies.
Replaced the MCX connector with an SMA female connector.
Enclosed circuit in a metal box.

In addition to the mods, Laidukas also made some measurements on the performance of the R820T2 on some metrics. In the first test he measured the input insertion loss or SWR. He found that the SWR was below 2 between frequencies of 25 MHz to 1076 MHz. At higher frequencies the SWR reached levels up to about 8.

Another test showed that with the LNA disabled the R820T2 had a lower noise floor by about 7dB, when compared to the R820T.

SWR Plot of the RTL-SDR Antenna Input with LNA disabled

January 29, 2015

Designing a Low Noise UHF Front End with Sharp Filtering for SDR

Most wideband SDR’s do not come with any front-end filtering built in. This limits their ability to receive weak signals in the presence of strong signals. Recently Sivan, a reader of RTL-SDR.com wrote in to let us know about a paper he published through the ARRL detailing how to design a concrete front-end unit for SDR use. A front-end helps to filter out signals that are outside of the desired passband, thus reducing interference from nearby strong signals significantly. Although Sivan uses a USRP with WBX daughtercard in his paper, he writes that the same front-end design principals can be applied to the RTL-SDR as well.

In the paper he designs a 431 – 435 MHz front-end using low cost SAW filters, a low noise amplifier (LNA) and a limiter to protect the radio. He writes that the design could easily be adapted for other bands as well.

January 29, 2015

SDR# Frequency Scanner Plugin Updated

The popular frequency scanner plugin for SDR# has recently been updated (in Russian, use Google Translate). The frequency scanner plugin allows you to quickly scan through a definable slice of spectrum, stopping to listen on active signals. The new features are outlined below

1. Added the selection of multiple ranges to scan. Ranges can be different modulation and bandwidth scanning step. To select multiple ranges, use Ctrl .

2. The scanner operates completely independently of native squelch SDR #. To determine the end of the activity, a new parameter Hysteresis – is the level below which the signal is considered inactive. When using the option Use Mute , you can disable the squelch SDR #.

3. In setting the added options – choose the scanning signal with the maximum level and the width of the spectrum used.

4. Parameter Detect moved from the window in the panorama scanner settings.

January 28, 2015

Compressing and Filtering I/Q Data

One great feature of SDR software like SDR# is the ability to make I/Q recordings of the entire received bandwidth for later analysis. The problem is that these recordings can take up massive amounts of hard disk space. Jay Moore, the author of the RTL-SDR DX blog has recently been experimenting with methods for compressing I/Q files (2021 UPDATE: Jay's site has been abandoned, please use this archive.org link).

Jay tried compressing a test I/Q file with 7-Zip LZMA, Zip Deflate and FLAC. His results showed that FLAC compression was by far the fastest and also compressed the most in a test I/Q file with low amounts of redundant information.

Jay also discovered that it is possible to record "filtered" I/Q recordings using the RAW setting in SDR#. The RAW setting allows you to record an I/Q file from the tuned bandwidth selected within SDR# which allows for a much smaller file size.

January 28, 2015

Updates to Removing the 1.2V Switching Power Supply on the RTL-SDR

A few months ago we posted about how a Japanese RTL-SDR modder disconnected the noisy 1.2v switching power supply on the RTL-SDR and replaced it with three diodes. The diodes reduced the voltage from the 3.3v line to 1.2v. It seems that most of the improvements seen from the previous post were inconclusive, as soon after he realized that there are minor dongle to dongle variations in sensitivity, so he could not be certain if the improvement was due to his modifications.

However, he has continued to modify the RTL-SDR using the same principal (Japanese, use Google Translate). He discovered that to fully suppress the 1.2v switching regulator pin 27 on the RTL2832U chip must be connected to ground. Once this is done the switching noise present at 1 MHz disappears, although there does not seem to be any significant improvement in noise anywhere else.

The first screenshot shows an unmodded dongle with the switching regulator still connected. There is some noise present at around 1.026 MHz. The second image shows a modded dongle, the noise at 1.026 MHz is gone.

Switching regulator on. Noise can be seen at around 1.026 MHz.

Switching regulator off. Noise at 1.026 MHz is gone.

January 27, 2015

Listening to Trunked Radios with One RTL-SDR

Usually to listen to trunked radio systems, two RTL-SDR dongles are required. One for decoding the trunking control channel and another for listening to the audio channel. However if the audio channels are within the same chunk of received bandwidth as the control channel it is possible to use just one dongle to follow trunked conservations.

Recently Pawel of pewusoft wrote in to RTL-SDR.com to let us know about a tutorial he uploaded showing how to get trunking to work with just one RTL-SDR dongle. His method uses Unitrunker and SDR# together with the AuxVFO plugin and a new plugin that he wrote for interfacing with Unitrunker.

Although there is already a Unitrunker interface plugin for SDR#, Pawel wrote a new plugin based on serial port commands as he found that the original interface plugin did not work properly for him.

Unitrunker Serial Port Interface SDR# Plugin