Category: Other

Receiving VLF with a PC sound card, Miniwhip Antenna and SAQrx

Over on YouTube user Mile Kokotov has uploaded a video showing how he is able to receive Very Low Frequency (VLF) signals between 300 Hz to 30 kHz using just his PC, a Miniwhip antenna connected to his sound card input port and a program called SAQrx Panoramic VLF Receiver. This allows reception of signals between 0-48 kHz with a sound card that can sample at 96 kHz.

Using this set up he is able to receive the Alpha navigation system beacons which are at around 10-12 kHz and some other Navy navigation system beacons between 18 and 48 kHz from his home in Macedonia.

Receiving VLF with PC and software only

Roundup of Software Defined Radios

New software defined radio (SDRs) products are popping up every few months these days so we thought we'd compile a big list of available SDRs as there are a few people who were bitten by the RTL-SDR bug and are now looking to upgrade.

For each SDR we compare the cost, frequency range, ADC resolution, maximum instantaneous bandwidth, whether or not it can TX and if it has any pre selectors built in. Here is a quick guide to what some of these metrics mean.

Frequency Range: The range of frequencies the SDR can tune to.
ADC Resolution: Higher is better. More resolution means more dynamic range, less signal imaging, a lower noise floor, more sensitivity when strong signals are present and better ability to discern weak signals. Some SDR's give their resolution in ENOB which stands for effective number of bits.
Instantaneous Bandwidth: The size of the real time RF chunk available.
RX/TX: Can the radio receive and/or transmit.
Preselectors: Analogue filters on the front end to help reduce out of band interference and imaging.

* - Denotes top choice for high value

General Use Software Defined Radios

We define general use SDRs as ones with a wide frequency range and with no focus on any specific frequency band.

R820T RTL2832U a.k.a RTL-SDR*

RTLSDR_PCB

Cost: $10 - 22 USD
Frequency Range: approx. 24 MHz - 1766 MHz (below 24 MHz available on RTL-SDR.com V3 dongles)
ADC Resolution: 8 Bits
Max Bandwidth: 3.2 MHz / 2.4 or 2.8 MHz max stable.
TX/RX: RX Only
Preselectors: Uses tracking RF filters on the R820T2 chip.
Release Date: August 2016

The RTL-SDR is still the best 'bang for your buck' software defined radio out there. While it was never designed to be used as a general purpose SDR in the first place, its performance is still surprisingly good. If you're on a budget or are just starting out with SDR or radio this is the one to get. (Link)

Continue reading →

New Signal Identification Guide Wiki: sigidwiki.com

We’ve recently created a new radio signal identification guide over a www.sigidwiki.com. This is a wikipedia styled site which is editable by anyone. We hope that some readers will make a contribution by adding new reference signals, fixing mistakes or identifying unknown signals. Any comments or requests about the page are also welcome.

You can still contribute known or unknown signals to rtlsdrblog__AT__gmail__dot__com and I will add them to the sigidwiki myself.

SoftRock Lite II Build and Test Tutorial Video

The SoftRock Lite II is a (now fairly old) soundcard based software defined radio kitset that is capable of receiving on the HF bands. Over on YouTube user w2aew has uploaded a video showing the entire kitset build process for the SoftRock Lite II SDR radio. He also goes over the circuit blocks explaining their function and how they work.

This is an excellent video if you are interested in learning more about the components and circuits used in some SDRs.

#148: Software Defined Radio kit | Tutorial | Build | Test | Softrock Lite II

TeensySDR: SoftRock SDR On a Teensy Microcontroller

Amateur Radio Hobbyist VE3MKC has been working on a project involving running a SoftRock SDR on a Teensy 3.1 Microcontroller. The Teensy is a tiny microcontroller board that uses a 32-bit ARM processor and the SoftRock SDR is a HF only software defined radio kit.

VE3MKC wrote code to first digitize then multiply the signal with a digital VFO before finally applying a low pass filter. He found that the Teensy’s microcontroller has sufficient CPU power to have an LCD RF spectrum display and process the audio output at the same time. Two videos of his project have been uploaded to YouTube.

TeensySDR - a Simple Software Defined Radio using the Teensy 3.1

Teensy SDR IQ Signal Processing

Pranking Colleagues with the USRP B210 Software Defined Radio

The Ettus USRP B210 is an advanced $1,100 software defined radio that is capable of both transmit and receive. Balint, one of the researchers at Ettus, has posted a video showing how he was able to play a light hearted prank on some of his colleagues using the B210.

Earlier in the year we posted about how Oona Raisanen was able to use her RTL-SDR to receive and decode restaurant pagers (the wireless devices given out at some restaurants to notify you when your food is ready).

Balint used his USRP210 controlled by a mobile phone app to transmit a fake signal to his colleague’s pager, causing it to activate before his food was ready.

You Can Page Me Anytime - USRP B210 + GNU Radio (teaser)

Measuring the Frequency Response of a Bandpass Filter with the RTL-SDR

Lacking both an expensive signal generator and spectrum analyzer, Hans used his RTL-SDR together with a simple diode based wideband noise generator to measure the frequency response of a 137 MHz bandpass filter.

To do this he used the RTL-SDR Scanner software which allows you to create a composite spectrum over a frequency range wider than the maximum 3.2 MHz of bandwidth the RTL-SDR provides. The wideband noise generator was cleverly constructed out of a diode operating in it’s reverse breakdown mode.

Apart from the obvious excessive spurs, this method worked quite well and the shape of the filter is clearly visible.

Bandpass Filter Response
Bandpass Filter Response
Wideband diode noise source
Wideband diode noise source

Ham it up Upconverter 3D Printed Case YouTube Giveaway

Over on YouTube Eric William has posted a video about his competition where he is giving away two 3D printed ham-it-up upconverter cases. The ham-it-up is an upconverter that can be used with the RTL-SDR to allow it to receive HF (0-30 MHz) frequencies. To enter the competition you simply need to go to Erics web forum and post about what you use SDR for in the competition thread. The competition is open only for North American viewers and ends on May 19 2014.