Over on GitHub, Rakesh Peter (r4d10n) has uploaded a new terminal/ssh based console application called "retrogram~rtlsdr". This program uses an RTL-SDR and terminal window to display a spectrum analyzer drawn in ASCII art. Because it is terminal based, it is even possible to view the spectrum of a remote device over an SSH connection. The program is based on software designed for Ettus USRP SDRs, and has been adapted for RTL-SDR.
Spektrum is a popular spectrum analyzer program that is used with RTL-SDR dongles. It is based on the command line rtl_power software and is compatible with both Windows and Linux. Thanks to it's easy to use GUI it is an excellent piece of software for scanning and determining where active signals exist, or for measuring filters and antenna SWR with a noise source.
Recently SV8ARJ (George) and SV1SGK (Nick) have been working on extending the original open source Spektrum code. Their improvements focus around the UI and making it more functional and easier to use. Currently the updated branch is in alpha, and they are hoping that any testers could help report bugs, issues and wishes to them. The code is available on their GitHub and the latest Windows test build can be downloaded from their DropBox.
The changelog reads:
- 2 Cursors for Frequency axis.
- 2 Cursors for Amplitude axis.
- Absolute and differential measurements with cursors.
- Zoom functionality of the cursors's defined area (gain + frequency).
- Mouse Wheel Gain adjustment on graph (Top area for upper, low area for lower).
- Mouse Wheel Frequency adjustment on graph (left area for lower frequency, right for upper).
- Mouse Wheel in the centrer of the graph performs symetric zoom in/out.
- View/settings store/recall (elementary "back" operation, nice for quick zoomed in graph inspection).
- Right click positions primary cursors.
- Right Double Click positions primary cursors and moves secondary out of the way.
- Left Double Click zooms area defined by cursors (Amplitude + frequency).
- Left Mouse Click and Drag on a cursor moves the cursor.
- Middle (mouse wheel) Double Click resets full scale for Amplitude and Frequency.
- Middle (mouse wheel) Click and Drag, moves the graph recalculating limits accordingly.
- Reset buttons to Min/Max range next to Start and Stop frequency text boxes.
- Cursor on/off checkbox now operate on all 4 cursors.
- ZOOM and BACK buttons.
- Filled-in graph option (line or area).
- Display of frequency, Amplitude and differences for all cursors.
- Modified: Button layout.
- Fixed: Save/Reload settings on exit/start. IMPORTANT : delete the "data" folder from the installation location if you have it.
- Filling in graph option (line or area).
Steve Andrew has just released an alpha version of a Windows Spectrum Analyzer app for SDRplay SDRs that he's been working on. The app is currently still in alpha, meaning that all the features are not yet implemented. In particular, scans larger than the SDRplay's maximum bandwidth of 10 MHz are not ready yet. In the future the app will be able to scan swath's of bandwidth up to 2 GHz wide, similar to what SpectrumSpy for the Airspy and rtl_power for the RTL-SDR does.
We are pleased to announce the availability of the first cut of Spectrum Analyser software developed by Steve Andrew specifically for the RSP line of products. Please note that this is first alpha software and so it is still very much in development and some features are still to be added. Currently supported are:
This first alpha release gives a good idea as to the look and feel for the software. The main functional limitation is that sweeps of greater than 10 MHz are not currently supported. Steve is currently re-working the algorithms for providing wider sweeps than 10 MHz to improve sweep time and remove the issue of the DC spike in ZIF mode, so please bear with him.
We recommend using the software with AGC turned off and use manual control of the gain for better display stability.
Please use this forum thread to post any issues. Read the issues already raised and only post if the issue you have found hasn’t been raised. This will help Steve in his development.
Further development information can be found on the forum.
Click here to download the 0.9a Alpha release.
Over on YouTube channel Bootstrap Workbench has been running a series on using an RTL-SDR and noise source to create a poor man’s spectrum analyzer. So far he has three videos available. The first shows how to install and setup Spektrum, his preferred Windows based wideband scanner for the RTL-SDR.
The second video shows how the RTL-SDR, noise source and Spektrum can be used to tune a cavity duplexer. A cavity duplexer is an adjustable set of filters that allows you to use a single antenna for TX and RX at different frequencies. It can be tuned by adjusting screws on the unit body.
In the third video he shows how to examine the response of a dual ferrite isolator/circulator which is a device that can be used to ensure RF only travels in one direction. This could be use for example to prevent damage to a TX power amplifier from reflected signals due to high VSWR or other nearby powerful signals.
If you’re interested in this we also have our own tutorial available about setting something like this up, but using alternative software.
The LimeSDR is a new transmit capable software defined radio with a 100 kHz – 3.8 GHz frequency range, 12-bit ADC and 61.44 MHz bandwidth which is currently seeking crowdfunding. At the time of this post there is about four days left to reach the $500k goal, and it is only 80% funded. To try and reach their funding goal they have released another batch of discounted units which cost only $249 USD. After the crowd funding campaign the price will rise to $289/$299 USD. If the LimeSDR is not funded in time, they write that the project will unfortunately be put on hold and it’s future may be uncertain. We believe that this product is shaping up to be a very good TX/RX capable SDR, like the HackRF and bladeRF, but much better overall and for the same or even lower price.
Recently they also released some new updates that show off some LimeSDR features. In a post previously featured on our blog beta tester Alexandru showed how he was able to get the LimeSDR to transmit DVB-S2 HDTV. In later updates they showed how the LimeSDR can be used to:
- Reverse engineer and then control an off the shelf RF mains switch. They then combined it with a Bluetooth LE wireless temperature sensor and used Pothos to create a program that automatically turns the mains switch on or off depending on temperature.
- Control LoRa based IoT devices. In this post they used the LimeSDR to demonstrate how it can be used to transmit to, receive and simulate IoT devices running the popular LoRa wireless protocol
- Create a 10 MHz LTE cellular site. In this post they also show a mobile phone connecting to the cell site and using LTE mobile internet at 20MSPS.
- Create a spectrum analyzer, oscilloscope and signal generator in GNU Octave. Here they show how the LimeSDR can be used as an “all-in-one” lab tool replacement for several expensive devices.
- Create a Vector Network Analyzer. With the help of a directional coupler the LimeSDR can also be turned into a Vector Network Analyzer to measure parameters such as gain, insertion loss, return loss and VSWR.
- Build a remote radio head. By mounting the LimeSDR near the antenna and streaming the data back over an IP link, coax feed losses can be eliminated.
Over on his blog VK4ZXI has been testing the Airspy with the Spectrum Spy software. The Airspy is a $199USD software defined radio that can be considered as a high end upgrade to the RTL-SDR as it has 10 MHz of bandwidth and a 12-bit ADC. The Spectrum Spy software allows the Airspy to be used as wideband spectrum analyzer. In a previous post we reviewed the Spectrum Spy software with the Airspy and found it to have an extremely fast refresh rate. Recent updates since the review have made it even faster.
In his first post VK4ZXI compares the Airspy + Spectrum Spy with the RTL-SDR running RTLSDR-Scanner and Rtl_power, two spectrum analyzer programs written for the RTL-SDR. In his tests he finds that the RTL-SDR and Airspy can obtain similar scans, but the Airspy can scan and refresh the spectrum at much faster speeds than the RTL-SDR, thanks to its 10MHz bandwidth.
In his second post VK4ZXI uses the Airspy + Spectrum Spy together with a cheap BG7TBL noise source to measure the response of a cavity RF filter. This is the same BG7TBL noise source that we used in our “Measuring Filter Characteristics and Antenna SWR with an RTL-SDR and Noise Source” tutorial. The results from the cavity filter measurement show that the Airspy can potentially perform on a level close to an expensive spectrum analyzer.
Software defined radio's can easily be used a very wideband spectrum analyzers by quickly stepping through the spectrum at the largest stable bandwidth supported. The RTL-SDR has had this functionality for some time now through software such as rtl_power and RTL Scanner.
Now Youssef, co-creator of the Airspy and programmer of SDR# has released a similar program for the Airspy called Spectrum Spy. The software comes bundled with the latest SDR# download which can be obtained from airspy.com.
The Airspy is a $199 USD software defined radio with a similar tuning range to the RTL-SDR, but it is significantly better with its 12-bit ADC and up to 10 MHz of instantaneous bandwidth. We review the Airspy, SDRplay RSP and HackRF in this post. With its large instantaneous bandwidth and fast retuning speed the Airspy makes an excellent spectrum analyzer that refreshes very quickly.
Youssef stresses that the software is still in proof of concept stages, and various features are still to be added in the future. He writes:
A new utility app is available for download with the standard SDR# package. It allows the visualization of larger frequency spans by exploiting Airspy's fast frequency tuning capability. The scanning speed is comparable to real spectrum analyzers (may be faster even!) The project is still in a PoC state, but the basic functionality provided is fully operational.
It all started when some customer wanted an example code to implement their own SA using Airspy, so I did more than a code snippet. I hope you enjoy!
We tested the Spectrum Spy software on several bands, and recorded short videos shown below to show how fast it is.
20 MHz Bandwidth Mobile Phone Band
50 MHz BCFM Band
100 MHz Bandwidth Mobile Phone Band
Includes the uplink and downlink portions. We used our mobile phone to make a call and you can see the uplink at 895 MHz.
1 GHz Full Spectrum
Over on Twitter @uhf_satcom has also been testing out Spectrum Spy and has got some good shots of Ku and L-band satellite bands.
Here @supertrack_it has been using Spectrum Spy to help with the tuning of his 1420 MHz filter.
Recently a reader of RTL-SDR.com, Pavel wrote in to let us know about a new program called “Spektrum” which he has written. Spektrum runs on Windows and Linux and turns an RTL-SDR dongle into a spectrum analyzer in a similar way to rtl_power GUI front ends and RTLSDR Scanner. However one key improvement is that it is based on a version of rtl_power that has been modified by Pavel in order to make it more responsive and remove the need to wait until a full sweep is completed before you can see any results. The modified version of rtl_power can be found at https://github.com/pavels/rtl-sdr.
Spektrum also has an additional “relative mode” feature. This allows Spektrum to be easily used together with a wideband noise source to measure things like filter characteristics and the VSWR of antennas. See our previous tutorial on this here, but note that in our tutorial we used Excel instead of Spektrum to do relative measurements.
The Processing language was used to create Spektrum and Pavel has also released his processing library for accessing rtl_power functionality over at https://github.com/
Ready to use releases of Spektrum for Windows and Linux 64-Bit OSes can be downloaded from https://github.com/pavels/spektrum/releases. Note that there may be a bug with the current release which causes only a gray window to show, but we’ve contacted the author about it and it may be fixed soon.