Using a Beam Deflection Tube as a Mixer for an RTL-SDR Upconverter

Over on YouTube user Full spectrum technician has uploaded an interested video where he shows how he used a beam deflection tube to create an upconverter for his RTL-SDR. A beam deflection tube is a type of vacuum tube that can be used as a mixer. If you aren’t aware, a vacuum tube (a.k.a tube or valve) is an electrical component that was used in electrical equipment heavily back in the first half of the 1900’s. They could be used to implement circuits like amplifiers, mixers, switches, oscillators and more. Even today they are still used in some high end audio equipment because many people believe they produce superior audio quality. Full spectrum technician writes on his video:

A simple test using a 6ME8 beam deflection tube as a balanced mixer up converter for an RTL-SDR to enable HF reception.

The only problem I had was too much conversion gain. Even with a relatively short antenna, and literally starving the tube for voltage, the signal output levels were high enough that I had to crank back the gain of the RTL SDR and/or use padding on the input of the RTL-SDR.

The LO was feed to grid 1 for common mode input.
The antenna was feed to the two deflection plates via a transformer as a differential input.
The output was taken from the two anode plates via a transformer as a differential output.

That resulted in the LO balancing it’s self out on the output so that the LO would not overload the front end of the receiver.

Operating voltages at the time were..
20V anode.
5V deflection plates.
20V accelerator grid.
Cathode tied to ground.

RTLSDR4Everyone: Review of the Soft66RTL3

Over on his blog Akos has posted a review of the Soft66RTL3. The Soft66RTL3 is an RTL-SDR which is retrofitted with an upconverter, filters and HF RF amp. It is produced by Kazunori Miura (JA7TDO) who is based in Japan and it sells for $40 USD shipped, or $46 USD shipped with registered air mail. Previously we posted Mike Ladds review of the Soft66RTL3 here.

In his review Akos shows us the features of the Soft66RTL3 which include the switch for selecting between several HF filters, as well as a trimmer pot for adjusting the amount of gain on the HF RF filter. He shows that inside is a nano sized RTL-SDR dongle soldered on to an upconverter board.

Unfortunately it seems Akos discovered some flaws with the unit. He discovered odd frequency drift behavior and poor performance on VHF and UHF. HF performance on the other hand was decent, but still not as good as with an upconverter.

Inside the Soft66RTL3
Inside the Soft66RTL3

New RTL-SDR Blog Units Now Available in Store: HF via Direct Sampling, Software Switchable Bias Tee, Less Noise/Spurs

A few months ago we brought out a poll asking readers of this blog what they might like to see in a revised RTL-SDR dongle. We’ve now taken some of those suggestions and implemented them into a brand new dongle. For now the price of the new dongle will remain the same as before at $24.95 USD for the dongle + antenna kit and $19.95 USD for the dongle only, but we may need to increase the price by $1 – $2 within the next few weeks due to our slightly increased manufacturing costs. Worldwide shipping remains free from the Chinese international warehouse, and US customers can order either from the Chinese international warehouse or from Amazon who will give you free shipping if you are a Prime member, or spend over $49. The Chinese warehouse is currently stocked and ready to ship, and Amazon is now stocked and should be ready to ship by the end of this week.

Please go to our store page at for information on purchasing.



Here is the short version of the biggest changes:

1) HF support via direct sampling. Connect an HF antenna directly to the SMA connector and tune from 500 kHz – 24 MHz with the direct sampling mod. (No hardware modding or soldering required)
2) Lower internal noise. Less spurs, lower noise floor etc.
3) Software switchable bias tee. No need to do any soldering to enable the bias tee. Can be turned on and off in software.

We call this version three of our RTL-SDR Blog dongles. The first was version zero and was simply the standard MCX dongles with better antennas. Next came version 1 with the bias tee and SMA connector, and version two introduced the metal case.

Here is the long list of improvements and changes, and why they were made:

1) Improved ESD protection on the radio front end. The BAV99 diode which is used on most dongles is not a true ESD rated diode. We have added a real ESD rated diode for better protection. The BAV99 remains in the circuit as a strong signal clipper, to prevent damage to the R820T2 from overly strong signals. Please remember that not even this will save your radio from a lightning strike, and any permanently outdoor mounted antenna system must have its own lightning protection.

2) Longer SMA connector. One or two customers had problems with the shorter SMA plugs which could not fit some of their antenna connectors. The longer shaft fixes this and also allows us to add a nut to fasten it to the aluminum body which provides a better low impedance connection (although this is not strictly needed as the PCB side ground tracks already provide a good connection).

3) Improved front end circuit. The standard matching circuit on the RTL-SDR was designed for DVB-T use, and tends to attenuate signals above ~1 GHz. The new matching circuit has less attenuation above 1 GHz and similar performance below. We used very high quality, high SRF, high Q inductors in this circuit.

4) Added a software switchable 4.5v bias tee. In previous versions of our units the 4.5v bias tee needed to be activated manually, by soldering a bridge between two pads on the PCB. However we found that many customers who want to use the bias tee do not have the skills or tools to be able to perform this mod. The new unit makes use of a low noise LDO and one of the GPIO pins on the RTL2832U to activate the bias tee in software. This of course requires a modification to the drivers, but we will shortly upload a program called rtl_biast and batch files to turn the bias tee on and off in Windows and Linux.

This bias tee is great for powering a remote LNA (like Adams PSA5043+ based LNA4ALL) or something like the SpyVerter upconverter. We’ve tested it with both and found them to be running just fine. 

Warning: The bias tee LDO can be damaged if you short circuit it. Before turning on the bias tee, ensure the circuit to be powered is not shorted, or that the RTL-SDR is not connected to a DC shorted antenna!

5) Added several access pads on the PCB. Access pads for the unused GPIO pins, CLK in/out, 3.3V, GND and I2C pins have been added. The CLK input/output is disconnected by default (see change 6). Access pads for the I branch have also been added as some users and industrial customers are using these in special projects. These pads are only for advanced users who need them for special projects. Take care as these pins are not ESD protected.

6) Added a clock selector jumper. By soldering in a 4 pin 1.27mm pitch jumper header and removing the default 0 Ohm resistor, one can now easily select between the onboard clock, an external clock, or having the on board clock be the output for another dongle. This is for advanced users only who want to experiment with things like passive radar, and coherent receivers.

7) Reduced noise with a modified PCB design. This significantly reduces spurs and noise pickup due much lower impedance grounding and blocking of interference. Also added a USB common mode choke to reduce USB noise, several ferrite chokes on the PCB, and a lower noise LDO. A larger ground plane also improves on heat dissipation. 

8) Added an experimental HF direct sampling circuit, which is diplexed out from the SMA connector. This has little to no effect on VHF/UHF operation, but allows us to make use of the Q branch on the RTL2832U chip for direct sampling, which allows us to receive from about 500 kHz to about 24 MHz. (Below 500 kHz is unavailable due to attenuation from the bias tee circuit). We used a ~10dB 50 Ohm preamp as a buffer and to overcome losses in the transformer and filter. We also added a strong 24 MHz low pass filter, and added an impedance matching transformer coil to ensure good direct sampling performance.

Of course direct sampling can never be as good as using an upconverter. It can overload easily if you have strong signals since there is no gain control. But this should at least give the majority of users a decent taste of what’s on HF. If you then find HF interesting, then you can consider upgrading to an upconverter like the SpyVerter (and the SpyVerter is of course compatible with our bias tee for easy operation).

We’re still classing this mode as experimental (and will be interested to hear any feedback on results), but we have had good results in our testing of this mode when receiving signals that are not too strong, getting sensitivity as good as an upconverter. We found that very good reception was obtainable with a long wire antenna and 9:1 unun combination.

9) Antenna bases now come with a stronger magnet and a conductive copper sticker on the bottom. The stronger magnet adds very good stability when using our large 1.5m antenna and the copper sticker ensures that good electrical contact can be made between the base and whatever piece of metal you use underneath as the ground plane. This significantly improves the antenna’s performance as a quarter wave ground plane.


10) Added corner mounting holes for those who want to stack PCBs. Some customers have been building devices that require multiple RTL-SDR dongles, and these standoff holes should aid in stacking.

As from the previous innovations the units still come with:

1) SMA connector – The most common connector in the radio world. Easy to adapt to other connectors and low loss over a wide range of frequencies.
2) Thermal pad – A thin thermal pad allows heat to transfer from the PCB to the metal case easily. The metal case then cools off to the surrounding air. This helps to solve L-band insensitivity problems.
3) Metal case – Helps block out interference and provides cooling.

We now have a V3 users guide available which explains how to use the new features such as the bias tee, HF mode and CLK jumpers.

What’s coming next?

We think that our unit is now pretty much at the peak of how good a cheap R820T2 RTL-SDR can be, so apart from minor tweaks this is likely to be our last major revision of this model of the RTL-SDR. In a 1-2 months we hope to bring out a FM bandstop filter with metal enclosure and SMA plugs with a target cost of $14.95 shipped. Further into the future we also hope to bring out supporting products like a wideband bias tee powered LNA and wideband antennas. These supporting products will of course be compatible with other SDR’s like the Airspy or SDRplay, or other RTL-SDR dongles.


HamRadioScience: Why Apple’s iMac May be the Best PC for SDR Applications

Over on on the HamRadioScience blog, the author has uploaded an article that makes the case on why Apple iMac PC’s may be the best choice for SDR receivers (at least for HF frequencies). In the testing he uses an SDRplay and Elad FM-Duo to show that the plastic case of the SDRplay does not affect the picked up RFI. He shows that when the SDR’s are connected to an iMac the interference from RFI on HF frequencies is minimal. However when connected to a Core i5 PC, there is significant amounts of CPU and monitor noise generated.

The differences in generated noise probably come from the fact that the iMac is probably much better shielded with an aluminum case and that they have high build quality standards for their monitors. The author suggests that an alternative to using an iMac could be to build your own PC, ensuring that dual chamber metal enclosures are used, which ensures that the power supply is isolated in its own separate steel compartment.

RFI is visible with the SDRplay in SDRuno when using the PC. But no RFI is seen with the iMac.
RFI is visible with the SDRplay in SDRuno when using the PC. But no RFI is seen with the iMac.

SDRplay and Airspy Sales Active Now

SDRplay and Airspy are currently holding sales for their software defined radio units. The SDRplay and Airspy are competing SDR’s that sell for similar prices. See our review for more information and a comparison between the two units.

The SDRplay RSP is currently on sale at HRO at a discounted price of $139.95 USD, giving a $10 saving. This is the first time that we have seen the RSP for sale, and the sale will last until 31 August 2016.

A few days ago the Airspy team also reduced their prices for their Airspy R2 and Spyverter upconverter products. The Airspy R2 now goes for $169 USD (at both the Chinese worldwide and US distributors) and the Spyverter now only goes for $49 USD (also at both Chinese worldwide and US distributors). This is a $30 saving for the R2 and a $10 saving for the Spyverter. The Airspy Mini remains at the previous price of $99 USD.

At this low cost we strongly suggest choosing the Spyverter over other upconverters like the ham-it-up which show slightly poorer performance and don’t come with a case. Check out our previous review of the Spyverter.

The SDRplay RSP
The SDRplay RSP
The Airspy R2
The Airspy R2

An AIS Decoder for MATLAB and the RTL-SDR reader Mike wrote in to us today to let us know that he has released his AIS decoder for MATLAB and the RTL-SDR. MATLAB is a technical computing language used by many scientists and engineers in the world. Mike writes the following about his work:

Automatic Identification System (AIS) is a communication standard that is used by commercial and recreational maritime vessels to report a ship’s ID, position, course and other information. This data is used for collision avoidance, search and rescue and many other applications. AIS has the following characteristics:

  • Access protocol: Self-organizing Time Division Multiple Access (SOTDMA)
  • Transmission frequencies: 161.975 MHz and 162.025 MHz
  • Transmit Power: 2 W or 12.5 W
  • Modulation: Gaussian Minimum Shift Keying (GMSK)
  • Data Rate: 9600 bits per second

An AIS decoder that uses the RTL-SDR and MATLAB to capture AIS transmissions is posted on MATLAB Central, the MathWorks file sharing exchange. The decoder has three main components

  1. Software to connect MATLAB to the RTL-SDR and bring IQ data directly into the MATLAB workspace (
  2. Demodulation and decoding algorithms to convert the IQ samples into bits and decode the AIS data (
  3. A user interface to configure the RTL-SDR, launch the capture and decoding process, and display the decoded messages (

The MATLAB Central post includes MATLAB source code for the AIS decoder, captured data files from Boston and San Francisco, an app for easy configuration and operation of the decoder, and instructions for installing the RTL-SDR Hardware Support Package and AIS Decoder app.

If you want to learn how AIS works, and how to write a decoder, then a MATLAB example like this is an excellent resource.

Unlocking Almost Any Vehicle with an SDR or Arduino

Earlier this week released a story indicating that researchers from the University of Birmingham have discovered two vulnerabilities that can be used to unlock almost any car. The first vulnerability concerns Volkswagen Group vehicles (VW, Audi, SEAT, Skoda) sold since 1995. Essentially their research found that the keyless entry systems of VW Group vehicles relies only on a few global master keys which they have been able to recover through reverse engineering of an undisclosed component used in a VW car. Then by sniffing the wireless key’s signal with an RF module or SDR like the RTL-SDR or HackRF they are able to recover the cryptographic algorithms used and then using the global key clone the wireless key signal, which can then be re-transmitted with a simple Arduino.

In their second research findings, the researcher’s write how they have been able to crack the Hitag2 rolling code system which is used in many vehicles such as Alfa Romeo, Chevrolet, Citroen, Dacia, Fiat, Ford, Lancia, Mitsubishi, Nissan, Opel, Peugot and Renault. Again, the hack works by sniffing a few wireless keyfob rolling code signals with an SDR or other device. Once the signals have been sniffed a simple laptop computer can reportedly break the encryption within one minute.

Here are some interesting excerpts from the conclusions of the paper:

The results of this paper show that major manufacturers have used insecure schemes over more than 20 years. Due to the widespread use of the analyzed systems, our findings have worldwide impact. Owners of affected vehicles should be aware that unlocking the doors of their car is much simpler than commonly assumed today. Both for the VW Group and the Hitag2 rolling code schemes, it is possible to clone the original remote control and gain unauthorized access to the vehicle after eavesdropping one or a few rolling codes, respectively. The necessary equipment to receive and send rolling codes, for example SDRs like the USRP or HackRF and off-the-shelf RF modules like the TI Chronos smart watch, are widely available at low cost.

A successful attack on the RKE and anti-theft system would also enable or facilitate other crimes:

– theft of the vehicle itself by circumventing the immobilizer system or by programming a new key into the car via the OBD port with a suitable tool

– compromising the board computer of a modern vehicle, which may even affect personal safety, e.g., by deactivating the brakes while switching on the wiping system in a bend

– inconspicuously placing an object or a person inside the car. The car could be locked again after the act

– on-the-road robbery, affecting the personal safety of the driver or passengers if they (incorrectly) assume that the vehicle is securely locked

Note that due to the long range of RKE systems it is technically feasible to eavesdrop the signals of all cars on a parking lot or at a car dealer by placing an eavesdropping device there overnight. Afterwards, all vulnerable cars could be opened by the adversary. Practical experiments suggest that the receiving ranges can be substantially increased: The authors of [18] report eavesdropping of a 433 MHz RFID system, with technology comparable to RKE, from up to 1 km using low-cost equipment.

The findings were presented at the Usenix Advanced Computing Systems Association conference during August 10-12, 2016 in Austin, TX. The white paper is titled “Lock It and Still Lose It—On the (In)Security of Automotive Remote Keyless Entry Systems” and can be downloaded here. Of course they did not publish the actual VW master keys in their paper and they have notified VW and NXP who make the Hitag2 chips in advance, noting that Hitag2 had actually been broken for several years prior.

Back in February we showed how Smay Kamkar was able to bypass rolling codes with his RollJam device, however the findings by these researcher’s is different in that they are actually able to generate new rolling codes, such that a simple Arduino with transmitter can act as a second wireless remote.

A $40 Arduino which can be used to record wireless rolling codes, then transmit new ones once cracked.
A $40 Arduino which can be used to record wireless rolling codes, then transmit new ones once the encryption has been broken.

New Outernet Products For Sale: E4000 RTL-SDR, L-Band Patch Antenna, L-Band LNA

Outernet is a new satellite service that aims to be a free “library in the sky”. They continuously broadcast services such as news, weather, videos and other files from satellites. Their aim is to provide up to date information to users in locations with little to no internet (rural, third world and sea), or in countries with censored internet. It may also be of interest to disaster preppers. Currently they have an active Ku (12 – 18 GHz, though due to be discontinued shortly) and C-band (4 – 8 GHz) satellite service, and now recently have their L-band (1.5 GHz) service active. The L-band signal is currently broadcasting at 1539.8725 MHz over the Americas, 1545.525 MHz over Europe/Africa/India and 1545.9525 MHz over Asia/Pacific.

To receive their L-Band service you will need an RTL-SDR capable of receiving 1.5 GHz, like a R820T/2 RTL-SDR (preferably at least passively cooled like our RTL-SDR Blog models as some R820T/2 units tend to fail at 1.5 GHz without cooling) or an E4000 dongle. You will also need an appropriate L-Band antenna and L-Band amplifier.

To help with these hardware requirements, Outernet have just released for sale an E4000 RTL-SDR with bias tee enabled ($39), an L-band satellite patch antenna ($24) and an L-Band LNA ($19). There is also a E4000 + LNA bundle ($49) available. The E4000 comes in a metal case, and has the bias tee always on. The LNA requires bias tee power and is also compatible with our RTL-SDR Blog units that have the bias tee. The patch antenna is tuned for 1525 – 1559 MHz and is the production version of the prototype antenna we used in our Inmarsat STD-C tutorial. Combined with an LNA we found that the patch antenna gives good performance and can also be used to receive other services such as Inmarsat STD-C and AERO. Currently shipping is only available within the USA, but they write that they will have international shipping available shortly.

EDIT: For international buyers the Outernet store is now started selling these products at

The L-Band Outernet signal decoders aren’t finalized yet, but we expect them to be released in a matter of days to weeks. They will have decoders available for the $9 CHIP computer and Raspberry Pi 3 platforms. They way it works is that you plug your RTL-SDR with L-band LNA and patch antenna connected into the CHIP or Raspberry Pi 3 which is running their customized image. The CHIP/Pi3 then broadcasts a WiFi access point which you can then connect to with any device, and access the files as they are downloaded. Once these decoders are released we’ll do a full tutorial on receiving the Outernet L-Band service with an RTL-SDR.

The Outernet L-Band Patch Antenna
The Outernet L-Band Patch Antenna
The Outnernet L-Band LNA
The Outernet L-Band LNA
The Outernet E4000 RTL-SDR in metal case with bias tee.
The Outernet E4000 RTL-SDR in metal case with bias tee.