Tagged: raspberry pi

RasPad 3.0 Review: Building a Portable Raspberry Pi 4 Tablet with Built in RTL-SDR

The Raspad 3.0 is a portable tablet enclosure for the Raspberry Pi 4B. It comes with a high resolution 1280 x 800 10.1 inch touch LCD screen, built in speakers, built in battery and a plastic enclosure that houses the LCD driver board and Raspberry Pi. Accessible on the side of the enclosure are the USB, HDMI, ethernet and audio ports which connect via the LCD driver board. They also include an accelerometer shim which allows the screen to autorotate.

The Raspad 3.0 is available on Amazon USA for $259, or directly via their website for $219 with free worldwide shipping.

A few months ago SunFounder, the company behind the RasPad 3.0 reached out to us and asked if we wanted to review the product with a free sample. Normally we don't review products unrelated to SDR like this, but given the amount of RTL-SDR software available for the Raspberry Pi, and what appeared to be sufficient internal space, we were curious if there was a way to turn this into a portable RTL-SDR tablet...

The RasPad 3.0

Unboxing

A few weeks ago the Raspad 3.0 arrived, well packed and with all the advertised components. Note that the Raspad 3.0 does not come with a Raspberry Pi 4B, this is something you will need to provide on your own.

Inside was a mains power cable, 15V DC power brick, two HDMI jumpers, a USB jumper, accelerometer shim, SD card ribbon, small 5V fan, heatsinks for the Pi, screwdriver and mounting screws, a manual and the RasPad LCD screen itself.  

The Raspad 3.0 Box and Unboxing

Assembly

Assembly is straight forward. You unscrew the enclosure using the provided screw driver, insert the Pi 4B, screw it down, connect all the cables from the Pi to the LCD driver board and SD card slot, then reassemble. After inserting the Raspberry Pi 4B and attaching all the cables this is what the inside looks like.

Inside an assembled RasPad 3.0

Now we could have reassembled the enclosure here, but we wanted this to be a portable RTL-SDR tablet, with the RTL-SDR and an SMA antenna port built in. 

It turns out that the best way to fit in an RTL-SDR Blog V3 is to directly connect it to the spare USB port on the Pi. You might also consider using a micro style RTL-SDR which would fit more easily, but those do tend to get quite hot in a small package, and can be quite bad with internal noise. Also good shielding is probably quite critical in this application due to the dongles proximity with the LCD driver board which could be an RFI source.

The SMA side of the RTL-SDR Blog V3 rests nicely on top of the USB port of the LCD driver board providing some stability, and when the bottom lid is assembled there is plenty of clearance and no squashing.

Next we drilled a hole on the rear wall of the bottom half of the enclosure for the SMA female port, and tightened the SMA connector down with a nut. In the future we'll be upgrading this to a long barrel style SMA female connector, as a regular SMA female connector is a bit short. Then a short well shielded SS405 coax cable was used to connect to the RTL-SDR dongle.

RasPad 3.0 with RTL-SDR Blog V3 Inside
Raspad 3.0 with SMA port hacked in

ProTip: Do take care to remember to remove the SD card when disassembling the RasPad! If you don't you'll end up with the SDcard slot getting ripped from it's ground traces. This happened to us, but we were able to easily solder it back on. There is a sticker on the backside of the enclosure warning about this.

Software & Testing

SunFounder provide a custom Raspbian distribution designed specially for the RasPad. However, we decided to instead install the DragonOS Pi64 Distro which is an Ubuntu distribution for the Raspberry Pi 4B that has many built in SDR programs. We burnt the image to a SD card, inserted it on the side, plugged the Raspad in to the power connector, and held the power button down for a few seconds to turn it on. Despite a few initial error messages saying it cannot enable the USB ports, everything eventually booted just fine.

We then plugged in a cable going to one of our multipurpose dipole antennas mounted just outside the office window, and tested both SDR++ and GQRX. In both cases we were immediately able to connect to the RTL-SDR and receive signals with signal strength equivalent to that received by our desktop PC, indicating that LCD interference was not a problem.

The resolution of the screen is high enough and images and text are clear. The screen is also decently bright, and brightness can be adjusted using the buttons on the side.

RasPad 3.0 with built in RTL-SDR running SDR++ and GQRX

DragonOS Tablet Compatibility Issues & Fixes

As DragonOS is not designed for a tablet setup, there were a few bugs. It should be noted however that these issues are not a reflection on the Raspad hardware, as obviously the official Raspad OS will not have these issues as it's designed specifically for tablet use.

We initially had no sound in SDR++ from the built in speakers. After some troubleshooting we managed to get sound by disabling the headphone jack in the audio mixer settings, which appears to be the default output in DragonOS. To do this, click on the speaker icon on the bottom right task bar and click on Mixer. Then go to the Configuration tab and uncheck the second Built-in Audio entry. Close it, and open SDR++.

Disabling the headphone jack to get the built in speakers working.

In DragonOS the touch screen works fine, although it is difficult to click on small buttons. There is no onscreen keyboard available by default. We couldn't find a way to enable a tablet mode in DragonOS, so instead opted to install an onscreen keyboard called 'onboard' via 'sudo apt install onboard'. The accelerometer is also not enabled in DragonOS. We did not attempt to fix this as we have no need for screen rotation.

Interference

LCD screens are well known to be sources of RF interference, and putting an SDR in close proximity to one could result in the spectrum being very noisy. However, without an antenna connected we did not notice any interference across the spectrum from the LCD screen. It appears that the LCD RFI noise levels are not too bad, and the shielding on the RTL-SDR Blog V3 and the coax jumper cable is good enough to prevent any being received. When an antenna with a few meters of coax was connected (such as a magwhip or our portable dipole) we also didn't notice any LCD interference. 

However, when a SMA telescopic antenna was connected directly to the SMA port we did start noticing the telltale spikes across the spectrum that are typically generated from LCD screens. If the magwhip or dipole was also moved within 2-3cm of the LCD screen, we also saw these interference spikes appear.

LCD Screen interference appears with a telescopic whip connected directly to the SMA port.

So it would be recommended to use a magwhip or dipole that has a coax run that can sit a few centimeters away from the screen. This limits the handheld ability of the RasPad a little, but you'd probably want a magwhip, dipole or other antenna over a directly connected telescopic whip for better reception anyway. 

Battery Life

We tested a worst case scenario, with the RasPad running the RTL-SDR and SDR++ continuously at the brightest screen setting. With this test the battery lasted 2 hours and 10 minutes from a full charge. Presumably if the screen was dimmed and turned off for some periods of time, it would easily last 3-4 hours.

Portability

The total weight of the Raspad including our mods is just under 1 kg (2.2 lbs). About double the weight of a modern tablet, but still light enough to be easily carried.

Other Notes

The small 5V fan provided in the kit is unfortunately a bit noisy, and it's cooling ability is seems limited. We've seen these small fans on other Raspberry Pi cooling accessories and found that they are next to useless at cooling. It would be good to see a slightly larger and quieter fan, or perhaps a better passive cooling heatsink.

The power brick output is 15V, 2A. Ideally we would be able to charge the RasPad via a car/boat 12V connection as well. We're awaiting a response to see if this is possible. Update: Unfortunately 12V seems to be a no-go, quoting SunFounder "the 12v supply may cause the Raspad to fail to charge, as the minimum is 15v".

Conclusion

The RasPad 3.0 in our opinion overall a good product. It allows you to easily go portable with your Raspberry Pi 4. While it was designed for other projects, there was just enough hackability left in it for us to fit a RTL-SDR Blog V3 and antenna port into the enclosure, yielding us a clean and portable SDR solution.

With at least 2 hours of battery life when running an RTL-SDR and software, we can easily see this being taken out in the field for spectrum analysis, decoding with rtl_433, or for portable listening to the airband, trunking etc. However, some customization of DragonOS or the RaspadOS is going to be needed to get the most out of the touchscreen.

There are also alternative LCD screen products designed for the Raspberry Pi where you sit the Raspberry Pi on the back of the screen. But it's unclear if there would be enough space inside to fit an RTL-SDR, and not to mention the lack of a battery. We also previously reviewed the Elecrow CrowPi which is somewhat similar, but a lot more clunky if you're just after a pick up and go portable SDR tablet solution. There are also higher end higher priced laptop style enclosure products for the Pi, like the Pi-Top but we're unsure if they're likely to fit the RTL-SDR internally this easily.

Disclaimer: We do not receive any compensation for this review apart from a free Raspad 3.0.

We also recently came across this review from German YouTuber Manuel Lausmann who installed and ran SDR++ on the Raspad with an SDRplay RSP SDR. 

SDR ++ mit dem RASPAD 3 -Raspberry PI 4-

Installing Remote SDR V2 on a Raspberry Pi 4B

Remote SDR V2 is software that allows you to easily remotely access either a PlutoSDR, HackRF or RTL-SDR software defined radio. It was originally designed to be used with the amateur radio QO-100 satellite, but version 2.0 includes multiple demodulation modes, NBFM/SSB transmission capability, CTCSS and DTMF encoders, modulation compression and a programmable frequency shift for relays.

Over on the programmers blog, F1ATB has put out a new post showing how to install Remote SDR V2 on a Raspberry Pi 4B. The installation has been made simple thanks for a ready to use SD card image.

If you're interested in an overview of Remote SDR V2, we have posted previously about a Tech Minds review of the software.

Remote SDR V2 with a PlutoSDR

CaribouLite: A 30-6000 MHz 13-bit 4MHz SDR HAT for the Raspberry Pi

Thank you to David for submitting news about his company Caribou Labs' new product called "CaribouLite" which will be a software defined radio HAT for the Raspberry Pi. The product is currently in the pre-launch stage over on Crowd Funding platform CrowdSupply and you can sign up for future updates on the release. David writes:

I'd like to inform you of a product we have developed called CaribouLite board, which is essentially a Raspberry Pi HAT that enabled up to 6GHz SDR capabilities Tx and Rx, and an additional TxRx Sub 1GHz channel.

It uses Microchip's modem AT86RF215 as an I/Q ADC, DAC and frequency conversion is done using Qorvo's RFFC5072 IC. An FPGA (ICE40) is used to stream data packets (I/Q @ 13 bit x2 / sample) back and forth between the Raspberry Pi and the Modem, over an interesting fast interface called SMI.

I think this project brings new ideas to the table and would be interesting to the SDR community.

The use of the SMI interface is an interesting idea and not something we see utilized often as apparently the official documentation is sparse and poor. But David notes how it allows for up to 500Mbit/s of data to be exchanged between the FPGA and Raspberry Pi, although the true throughput depends on the specific Raspberry Pi model used. Regardless the SMI data rate is more than enough for the 120 MBit/s required by the two streams of 13-bit IQ data that the CaribouLite generates.

The campaign also notes that the sample rate is 4 MSPS, with 4 MHz bandwidth, and up to 14 dBm of transmit power is possible. They also note that they are planning to release a wide range of library code that allows for use cases such as wide range spectrum analysis, a signal / protocol generator, an analog / digital DAB+ receiver, an ADS-B receiver and more.

The software and hardware design is also fully open source and available on GitHub.

The CaribouLite SDR HAT mounted on a Raspberry Pi Zero

European GNU Radio Days: Presentation on gr-rpitx

J.-M Friedt has created a block for GNU Radio called gr-rpitx which allows a Raspberry Pi to be used directly as an output RF sink in GNU Radio. If you were unaware, RPiTX is software that allows you to turn your Raspberry Pi into a transmit capable SDR without any additional hardware apart from a wire antenna connected to a GPIO pin. It works by modulating a GPIO pin in a way to generate any arbitrary signal modulation. gr-rpitx allows this software to be used directly within GNU Radio.

In his presentation uploaded early for the upcoming online European GNU Radio Days conference, J.-M Friedt explains how gr-rpitx works, and shows how you can easily connect any flowgraph to the gr-rpitx output sink. His examples demonstrate retransmitting broadcast FM using an RTL-SDR, broadcasting digital signals like DRM, and how gr-rpitx and RTL-SDR could be used as part of a basic scalar network analyzer.

gr-rpitx uses the GPIO4 output of the Raspberry Pi to generate a radiofrequency stream fed by a GNU Radio signal processing flowchart with sample rates up to 400 kS/s.

European GNU Radio Days/SDRA presentation about gr-rpitx (J.-M Friedt)

An Expansion Board with SMA Output for the Raspberry Pi and RPiTX

Thank you to Ihar Yatsevich for writing in and sharing his open source project called "rpitx-coax-pcb" which is an expansion board for the Raspberry Pi that converts the GPIO pin used by RPiTX into a coaxial SMA connector for easily connecting the output to an antenna. He notes that there are two revisions. One includes a filter in the in the GP1212 / GP731 case and the other does not. Filters in this type of enclosure can be found from Minicircuits. Finally he notes that he has not yet fully tested the design, but believes that there will be no problems.

The GitHub contains the EasyEDA design files, schematics and gerbers which you can use to print and build the PCB yourself.

If you are unfamiliar with it, RPiTX is a program for Raspberry Pi single board computers that allows you to transmit almost any type of signal on frequencies between 5 kHz up to 1500 MHz with nothing more than a wire connected to a GPIO pin. However, it is highly recommended that appropriate filtering be used if you are transmitting with an amplifier or longer range antenna as the RPiTX contains harmonics that can cause interference with other devices.

RPiTX Coaxial PCB Expansion Board for the Raspberry Pi

Raspberry-NOAA V2: Raspberry Pi Automated NOAA and Meteor Weather Satellite Capture

Raspberry-NOAA is open source code and a set of scripts that allows you to set up a Raspberry Pi as an automated NOAA and Meteor weather satellite station with an SDR like an RTL-SDR. The software makes use of the Raspberry Pi version of WXtoIMG and meteor_decoder for decoding the satellites, a program called predict for predicting satellite passes, and various automatically generated cron scripts to schedule recording and processing.

Recently V2 has been released by Justin Karimi who builds on the work of the original creators. It seems that the webpanel has been upgraded and made mobile friendly, as well as many more enhancements that can be seen on the Release page notes.

Raspberry-NOAA V2 Web Panel

Recent Podcasts on Software Defined Radio from Scanner School

Scanner School is an online resource that aims to teach subscribers all about radio scanning. They also run a weekly podcast discussing various topics in the scanning hobby. Recently they've had a bit of a focus on software defined radios, with several of the last podcasts being SDR related.

Episode 170 - SDRplay with Jon Hudson

On today’s episode, host Phil Lichtenberger interviews Jon Hudson, the co-creator of the SDRplay devices. They talk about the evolution of radio scanning software, the advantages of SDRplay and SDRuno, where they think the scanner hobby is headed, and more.

What You Need To Know

Jon Hudson is a co-creator of the SDRplay device. SDRplay manufactures both hardware and software. Before about 20 years ago, processing the radio chain was done exclusively on the hardware. Now computers are powerful enough to support doing most of this work with software. SDRplay was founded in 2014. The RSPDX has multiple antennae, which allows users to switch from one antenna to another quickly and easily. Because SDRplay makes their own software for Windows, they take a lot of time to make sure it works seamlessly out of the box. SDRplay acquired a company called Studio One that manufactured software about five years ago. SDRplay is releasing a scheduler, which will function as an audio recorder for a specific channel at a specific time. An advantage of the scheduler is that it allows users to tune in to certain frequencies at a specified time and then turn it off or move on to something else. All session notes with links to the items we talked about can be found on our website at www.scannerschool.com/session170

170 - SDRplay with Jon Hudson

Episode 169 - SDR++ with Alex Rouma

A cross platform, open source, free SDR software!

In this episode, Phil talks to Alex Rouma, author and creator of SDR++. They discuss how Alex got into SDRs, where SDR++ is now and where he hopes it can go, and how you can contribute to this open source software’s development, whether you’re a programmer or not.

What You Need To Know

SDR++ is free, open-source, cross-platform software for your SDR. Alex got into SDRs after watching a video of someone receiving weather satellites, piquing his interest in radio in general. Alex is currently building SDR++ as general purpose SDR receiver software with more modern functionality like multi-VFO and multi-platform support. SDR++ supports anything Alex has or that companies have sent him, including SDR Play, HackRF, RTLTCP, and more. Alex considers the software still in beta, but thinks he’ll have stable code with the features he wants within 3-4 months. He wants to add audio filtering features and more options for the file source. SDR++ is fully modular so you can add plugins as you need them. Alex aims to make the software as automatic as possible. All session notes with links to the items we talked about can be found on our website at www.scannerschool.com/session169

169 - SDR++ with Alex Rouma

Episode 168 - Using a SDR as Your Scanner

In this episode, Phil talks to listener Greg Weamer about his SDR setup. They get into the history of SDR development, what you can do with an SDR that you can’t do with a hardware-based scanner, and where they think the future of SDRs is heading.

What You Need To Know

Today, Greg does not have a hardware scanner at all, but only a SDR. His area has simulcast problems that the SDR solves. Greg currently uses about 8 RTL-SDR dongles, including 3 on a Raspberry Pi, some on another Raspberry Pi, an old laptop, and more. Greg also uses Trunk Recorder, which is one of the most difficult things he’s ever configured, but he loves that it monitors every voice channel at the same time. RDIO Scanner is a web interface that takes the feeds from the virtual recorders Greg has going and cues up calls on every voice channel so you don’t miss anything. Because it’s a web interface, he can bring it up on his phone or tablet from anywhere. Greg thinks the next major SDR development will eliminate the need for any fully hardware based radios entirely. An SDR can do things that not a single hardware-based scanner out there is capable of. Greg has used his SDR to tune into his utilities smart meters for his water and gas to track his usage. One of Greg’s favorite things about SDR is that you can see the signals and whether they’re strong or not, whether they’re digital or analog, etc. The ability to visualize the signal lets you find a lot more new stuff to listen to. The flexibility of an SDR and ability to do so many things at once with it means you get the equivalent of several premium subscriptions to other services. All session notes with links to the items we talked about an be found on our website at www.scannerschool.com/session168

168 - Using a SDR as Your Scanner

Episode 165 - This is Why You Need an SDR

In this episode, Phil walks through the basics of what an SDR is, its history, and how you can get set up with one. The perfect introduction to his upcoming SDR webinar and course.

What you will take away from this week's podcast:

An SDR means that anything normally handled by the hardware of the radio is now handled by the computer, and the physical hardware serves as an interface. The only limitation on the SDR hardware you buy is the frequency range and the amount of RF it can digest. SDR receivers have come a long way since they were first hacked into existence. SDRs used to be difficult to set up, but that’s no longer true. You don’t need advanced computer skills to run SDR software. SDR software can run on PC, Linux, Mac, Raspberry PI, and even Android. An SDR is more flexible and less expensive than a traditional radio. You can turn a $30 USB stick into something as powerful as an SDS200 in an afternoon. All you need to get started is an SDR USB stick, a computer, and the free starter software SDR Sharp. Once you get set up with FM broadcast stations, aviation, and other analog systems, Phil’s SDR course will go into how to set up digital reception. If you download DSD+ Fast Lane or Unitrunker you can monitor trunking systems. All session notes with links to the items we talked about an be found on our website at www.scannerschool.com/session165

165 - This is Why You Need an SDR

Episode 164 - Raspberry PI and SDR w/ Fuzz the Pi Guy

In this episode, Phil talks to "Fuzz the Pi Guy".

Fuzz has a large YouTube channel and has a ton of SDR and Raspberry Pi Videos.

Fuzz and I discuss how he uses his Software Defined Radios and how he keeps costs down by using a Raspberry Pi as as his computer for many of these projects.

What you will take away from this week's podcast:

SDR stands for Software Defined Radio, where you plug your hardware into power on one end and your computer on the other end so the computer software can interpret the signal. The Raspberry Pi is essentially a low-cost computer to help teach computer science in schools, and is now used for things like hosting Minecraft servers, learning Linux, and running SDR programs. Fuzz has a YouTube channel where he primarily demonstrates Raspberry Pi projects and tips, as well as a wide variety of small electronics content. He’s using a new setup that involves a Raspberry Pi 3 with an RTL-SDR dongle, connected to a 2m 70cm homemade antenna to receive his local Phase 2 frequencies, uploaded to Broadcastify using the new free software OP25. Using this setup, Fuzz essentially created a Phase 2 scanner for under $100. The FlightAware website gives a good introduction to using the Raspberry Pi with an SDR that can get you set up in under 15 minutes. The Raspberry Pi has the best support system out there for any Pi hardware, but Fuzz has been working with the Atomic Pi lately. This setup provides an inexpensive alternative to buying a pricey scanner if you don’t mind troubleshooting and problem solving to get going. All session notes with links to the items we talked about an be found on our website at www.scannerschool.com/session164

164 - Raspberry PI and SDR w/ Fuzz the Pi Guy

Controlling a Wireless Ceiling Fan with an RTL-SDR and RPiTX on a Raspberry Pi

Over on YouTube River's Educational Channel has uploaded a new video showing how he uses a Raspberry Pi to control a ceiling fan via it's wireless control signal. Back in January we posted about River's first video where he shows him using and RTL-SDR and Universal Radio Hacker (URH) to reverse engineer the control signal.

In this new video River uses the RPiTX software to generate the control signal without requiring any additional transmit hardware. He first explains how RPiTX can generate an arbitrary signal from a square wave and talks a bit about the harmonics this creates. To reduce harmonics he adds a simple low pass filter to the GPIO output.

Next to control the fan he uses the "sendook" program that is included with RPiTX to transmit the binary control string that he reverse engineered in his original video. Finally he creates a simple web server so that he can control his ceiling fans via his phone and integrate it into his smart home.

Abusing Raspberry Pi GPIO pins as a radio transmitter to control my ceiling fan