Category: Other

Talking to Ghosts with an RTL-SDR Dongle

Back in November of last year we posted about Doug Haber’s gqrx-ghostbox which is software that turns your RTL-SDR into an electronic voice phenomenon (EVP) tool, or in other words a ‘ghost box’ or ‘spirit box’. A ghost box is essentially a device that rapidly tunes between broadcast radio stations, creating mismashed audio of multiple stations. Paranormal researchers believe that such a tool can be used to communicate with ghosts or spirits. Over on Amazon commercial ghost boxes/spirit boxes seem to retail for anywhere from $70 USD to $140 USD so an RTL-SDR can be a budget way to get into paranormal research.

Over on her blog paranormal investigator shielaaliens has uploaded a post and video demonstrating an RTL-SDR based ghost box in action. Sheila actually doesn’t use the grqx-ghostbox software, but instead she just uses SDR# with a frequency scanner plugin set to rapidly scan through the broadcast band. In the video she asks the SDR# ghost box a few control questions such as “can you say kitty cat” and “can you say Nantucket”. In response the SDR# ghost box appears to respond with those exact words. Her Facebook post with the video can be found here.

Of course this might all sound pretty far fetched for most readers of this blog, but it is an application that the RTL-SDR is now being used for nonetheless!

SDR-Console V3 Latest Update: Signal History & Receiver Panes

SDR-Console is a popular RTL-SDR compatible multi purpose SDR software package which is similar to programs like SDR#, HDSDR and SDRuno. Currently SDR-Console V2 is the stable version and SDR-Console V3 is in a beta state. A few days ago SDR-Console V3 Preview 6 was released. It comes with some very interesting new features including a built in Airspy server, a recording scheduler, a new feature called signal history and a new receivers pane.

Over on his blog Nils Schiffhauer (DK8OK) has been reviewing the new release of SDR-Conosle V3 and writes the following information about some of the new features:

  • “Signal History” takes the signal strength of the given bandwidth each 50 milliseconds, which can be saved in a CSV file. It is also shown in three different speeds on a display.
  • “Receivers’ Pane” shows up to six combos of spectrum/spectrogram of the complete up to 24 parallel demodulators (they additionally can be shown in the Matrix, as in former versions).

“Signal History” offers many applications, to name just three:

  • analyze fading and its structure with an unsurpassed time resolution of 50 ms
  • document fade-in and fade out
  • measure signal-to-noise ratio of signals

In addition Nils has also uploaded a very useful 19 page PDF where he writes step by step instructions and shows numerous examples of the new signal history tool.

DK8OK's SDR-Console V3 P6 Screenshot. Showing multiple receiver panes and the new signal history feature.
DK8OK’s SDR-Console V3 P6 Screenshot. Showing multiple receiver panes and the new signal history feature.
DK8OK's screenshot of the signal history toolbox.
DK8OK’s screenshot of the signal history toolbox.

Forum Talk Videos From Hamvention 2017

During Hamvention 2017 several presenters and myself presented SDR or radio related talks. Some were filmed and put up onto YouTube. Unfortunately the 2017 SDR Forum video seems to be missing, or not yet uploaded yet.

The first set of talks was recorded by Gary KN4AQ at the TAPR Forum. The first talk in the set was from Michael Ossmann and Dominic Spill on “Low Cost, Open Source Spectrum Monitoring”. In this talk they discussed their recent improvements on creating a fast spectrum scanner mode on their HackRF. The second talk was “Advanced SDR Algorithms for Noise Blanking and Noise Reduction” by Warren Pratt NR0V. Here Warren discussed and gave examples of the effectiveness of some new noise blanker and noise reduction algorithms used in openHPSDR. Finally the third talk was “Introduction to RTL-SDR: Ultra cheap software defined radio” by Carl Laufer (myself). This was a brief introduction to the RTL-SDR showing some typical applications that they are used for.

The second set of talks was recorded by the Ham Radio 2.0 YouTube channel at the Digital Modes forum. The first talk was from myself again and was another introduction to cheap SDRs with some slightly different material. The second talk was by Uli with Wireless Holdings who discussed the latest developments in his DV4 digital mode transceiver products. Finally Mel K0PFX gave a talk on the latest developments in the FreeDV digital voice codec.

Finally I was interviewed by Gary KN4AQ of the HamRadioNow podcast and YouTube show and Marty KC1CWF of the PhasingLine podcast about and the V3 dongles.

Just a reminder that slides from all the talks presented by myself are available on this post.

Does the FM Bandstop Filter Withstand TX Power?

Thanks to PY2RAF for writing in and sharing some tests that he did on our RTL-SDR Blog BCFM bandstop filter. The RTL-SDR Blog filters were designed for RX purposes only, and no provisions were made for TX with only small SMD components being used. However PY2RAF wanted to test to see if the filter could at least handle 5W. The gist of his results is that the filter seems to handle 5W just fine, but as a precaution we wouldn’t recommend that anyone do this unless you really know what you are doing! 

As he does not have a blog, we present PY2RAF’s write up here:


I am a Ham Radio Operator (PY2RAF), live in a metropolitan and very RF-polluted area.

Recently, I bought a handheld device and was back to the ether, after a 12-year hiatus. I assembled myself a 3-band quarter-wave “cat whisker” antenna for 144, 220 and 430 MHz (, calibrated it using a VNA and was quickly back up in the air.

Despite great and complimentary reports of good audio and transmission reports, my reception was sub-par: Lots of interference (QRM), static, squelch closing despite high S-bar signal.

I got intrigued by that, it just did not make sense: Had the VX-8 large mouth but bad ears? After a couple of days puzzled, I got a good idea: Put my filter in the antenna.

The result was great: It immediately reduced the idle band noise from 6-7 S-bars to 3-4 S-bars. The squelched interrupted audio also stopped happening.

So, I could conclude that the strong FM BC band was overloading the receiving stage of the radio. Culprit found.

However, it brought another problem: the filter is NOT designed to cope with TX power (it is actually expressly stated at the product description page). However, the enhancement was just too good and I reached Carl asking about TX support or tests. Carl explained me that while the filter was not designed with TX power in mind, it withstand some minor current, because it supports Bias Tee currents.

I took it as a ‘good enough, I’ll test it’. See the results below.


The Device Under Test (DUT) is a FM Bandstop Filter. The transceiver is a Yaesu VX-8DR. I used a PocketVNA Vector Network Analyzer for checking the filter S21 characteristics and antenna S11 VSWR and impedance figures.  The realtime VSWR and TX power were monitored by a Diamond SX-200. I also used a SDR dongle and GQRX software to check for any transmission distortion. The radiant system (antenna) is a homebrew 3-band multiple dipole antenna, with VSWR < 1:1.3 in frequencies under test.


Prior to any transmission, I put the DUT in the VNA and noted its frequency and attenuation figures.

Next step, assembled the test environment:

Transceiver – wattmeter – DUT – antenna.

I did then the first test: set the radio to its lowest power (0.05 W) and transmitted in frequency 144.320 MHz. I have also tuned the SDR dongle in the same frequency and watched the  waterfall pattern, while listening for the resulting audio. Then, repeated the very same test now adding the DUT before the antenna. The waterfall signature and the audio quality was pretty much the same and coherent. Transmitted for approx. 30 seconds using the Filter.

In the next step, I repeated the tests raising the TX power to 1W and 2.5W. I requested feedback from a fellow Ham operator and got report that the audio quality was pretty much the same with and without the filter, with no changes in RX S-units figures. It means, it did not distort the audio nor put significant attenuation into the signal.

The next test was the real world conditions test. I switched to the repeater 146.910 MHz, negative shift (actual TX 146.310, This repeater is located circa 100 KM north from my residence. After introducing myself to the repeater and stating the device test, I started transmitting first with a single watt: successfully hit the repeater. After around 7 comms averaging around 2 minutes, I asked for feedback with and without the filter: The reports that I have heard were of no change in the quality or fidelity of the transmission. The SWR was being continuously monitored by the Diamond SX-200, paying attention for any component disruption and sudden SWR raise: The operation was just normal. The filter also did not present any temperature change noticeable by touch.

Finally, I raised the TX power to 5W and requested report. I did a 1’30” TX and got report of normal transmission.


This test validated, to me, the useful and robustness of the bandstop filter in my antenna as a permanent solution: It did not change the SWR figure, produced heating, noticeable attenuation or signal distortion: It became, since then, a permanent item between my radio and the antenna.

After the tests, I ran another round of DUT tests in VNA and the attenuation of the filter were the same as original: Working the way it should be.

Next day, I joined the repeater net again and spent around two hours ragchewing in the radio, accumulating something around 25 minutes of TX. Nothing wrong was noticed.

A Final Note

It is important to register that the DUT is working in a nicely matched (VSWR < 1:1.5) antenna system. Unmatched or higher VSWR figures can result in higher voltage, enough to break down the isolation. High-Q antenna systems might also present the same issue.

The New England Workshop for SDR (NEWSDR) Accepting Poster Submissions

Thanks to Michael Rahaim a Postdoctoral Researcher at Boston University for letting us know about the New England Workshop for SDR (NEWSDR) which will be held on June 1 & 2 and Tufts University in Medford, MA. They write:

A few of my colleagues and I are organizing the New England Workshop for SDR (NEWSDR) next month and we are currently accepting submissions for poster presentations. The event will be held at Tufts University and is sponsored by MathWorks, Ettus/NI, MediaTek and Analog Devices. It is the 7th time we’ve held the workshop and we typically have attendance of 80-100 people from industry, academia, and government.

This seems to be mostly an academic and industry conference type event, but a few people reading this blog may be interested. Registration is free.

This year as well as the poster presentations there will be a tutorial and introduction to using the PlutoSDR, which is an (as of yet unreleased) TX & RX capable SDR that will be priced at around $149 USD. It looks to be like a way to get started with SDR TXing very cheaply. During the workshops they are also providing tutorials on using USRP SDR devices with MATLAB Simulink, and with FPGAs. In 2016 they also had some interesting presentations including “Wireless Beyond RF: From Underwater to Intra-body Ultrasonic Software Defined Radios” and a tutorial on “Identifying Mystery Waveform Using Simulink and RTL-SDR”

Comparing Two LNA’s for HRIT/LRIT (GOES) Reception

Over on his blog Lucas Teske has been comparing the LNA4ALL and an SPF5189 LNA from eBay on HRIT/LRIT reception from GOES satellites. SPF5189 LNA’s can be found on eBay for less than $8 USD, with free shipping from China, whereas the LNA4ALL costs 27 Euros shipped from Croatia. GOES is a geosynchronous orbit weather satellite which requires a satellite dish or other high gain antenna to receive. It downlinks at about 1.7 GHz, which means that a high quality LNA with low noise figure and good PCB design is needed for reception.

In his post Lucas mentions how he saw a review on eBay stating that the SPF5189 did not work at L-band. However, he found that odd as all of his SPF5189 LNA’s seemed to work just fine with L-band reception. So he did a benchmark comparing the SPF5189 to the PSA5043+ based LNA4ALL which is known to work well on L-band.

From his comparisons he found that the SPF5189 does indeed work well on L-band, and is comparable to the LNA4ALL. He concludes that the reviewer must have received a bad unit, or didn’t know what he was doing.

Lucas also makes an important note regarding the PCB design of these LNA’s. Even though the SPF5189 and PSA5043 chips have similar specs, with LNA’s the design of the PCB is crucial, as a poor design can significantly degrade performance. With the LNA4ALL you can be sure that the design is good, although the SPF5189 LNA’s currently on eBay look to be designed okay as well. Though with some eBay sellers there is no guarantee that you will receive a good board. We note that we have seen some really poor designs for PSA5043 LNA’s out there as well.

The eBay SPF5189 LNA vs the LNA4ALL from 9A4QV
The eBay SPF5189 LNA vs the LNA4ALL from 9A4QV

Italian Language RTL-SDR Book Now Available

For our Italian readers – recently we received a submission from Marco Cardelli (IZ5IOW) who wanted to let us know that he and his friend Andrea Possemato (IZ5TLU) have published a book in the Italian language about the RTL-SDR. He writes:

The main goal is to introduce the “newbie” in this interesting world of digital radios, demonstrating that SDR is not an expensive technology. Both are the authors also of one of the firsts books about Raspberry Pi in Italian. All books are available on on-line stores, or from the publisher:

For any other information, please use the contact forms published on Marco Cardelli’s website:

The book costs 9,90€. We haven’t purchased the book ourselves as we cannot read Italian, so if you decide to purchase the book please leave a review of it in the comments section to inform others on it’s quality.

The Italian RTL-SDR Book Cover
The Italian RTL-SDR Book Cover

Titus II SDR Updates

Over on the blog we’ve seen news of an update regarding the PantronX Titus II SDR. The last update we had was in January. contributor Richard Langley writes:

There was a segment on the latest episode of AWR’s Wavescan (9 April 2017) about the Titus II DRM receiver recorded during the recent HFCC meeting in Jordan. In it, it was stated that the shipment of the first 1500 units was expected at the end of March or by the first half of April. Included some discussion of added shielding to prevent digital noise and the high-sensitivity of the receiver compared to other DRM units. 

Head over to the post to listen to the Wavescan podcast announcement,

The Titus II is an Android Tablet + SDR combination that is due to be released in the near future. Its main purpose is for reception of Digital Radio Mondiale (DRM) which is a digital broadcasting medium used on the HF frequencies, which somewhat replaces standard short wave AM radio. The Titus II hopes to be one of the first low cost receiver solutions for this market and as a wideband SDR it should work for many other applications too. From the advertised frequency range of 100 kHz – 2 GHz we speculate that it will be using the Mirics SDR chipset, which is the same chipset as used in the SDRplay. The target price is under $100 USD.

The Titus II Portable SDR
The Titus II Portable SDR