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moRFeus: A Low Cost Wideband Signal Generator and Frequency Mixer

During development of the Outernet project the engineering team developed several tools to help them in their RF testing. One tool that they created has now been developed further into a commercial product that they are calling 'moRFeus'. moRFeus is a small handheld RF signal generator and frequency mixer. It can be used to generate an RF tone at any frequency between 85 MHz - 6 GHz and to upconvert or downconvert signals via the mixer with an input/output frequency range between 30 MHz - 6 GHz. This type of tool is useful for people working with RF hardware as it can be used for testing and prototyping.

morRFeus is currently selling for US$149 over on CrowdSupply, and the units are ready to ship out soon. They note that the current price is a special, and that it may be increased in the future. We think that this is a fairly good deal considering that similar products can cost much more. If you are interested in the technical details the datasheet includes figures on phase noise and conversion losses. There is also a user guide that explains how the buttons work, and what each screen on the menu is for.  The morRFeus press release reads:

Outernet launches sales for wideband frequency converter and signal generator with complete field-level configuration.

Today, Outernet announced the launch of moRFeus - a wideband (30MHz - 6GHz) frequency converter and signal generator with complete field-level configurability. The product is available on Crowd Supply for $149. The price will increase after the 30-day launch campaign.

The device has an LCD display and button interface for complete field-level configuration - from setting the LO frequency to toggling between mixer and generator mode, and more. It’s in a precision-milled all-aluminum enclosure for durability and aesthetics.

moRFeus was built for hams and hackers, people with a traditional amateur radio background, as well as a makers and researchers that are interested in RF experimentation. It was designed for easy integration into a wide variety of RF projects.

In mixer mode, moRFeus enables dynamic frequency up- and down-conversion. In generator mode, it is one of the most, if not the most, affordable tools to generate a stable +/-2.5 ppm CW signal. Additional information on features, specifications, and performance metrics can be found in the datasheet.

The team already has 100 units in stock and another 900 are going through final assembly and quality assurance in Chicago. The first 100 units will ship one week after launch and orders beyond the initial stock will ship within 30 days of the close of the campaign, or earlier.

Outernet has been working on novel RF projects since the founding of the company in 2014. moRFeus was developed because from an internal need for a wideband field-configurable frequency converter for testing purposes. The company identified a huge gap in the market for a solution that met the needs of others with similar problems add their own. Outernet’s founder describes the development process:

“The idea was hatched about a year ago because we needed an easy, quick way to dynamically up-and down-convert the various radios we were experimenting with for a new product. By the summer of 2017, we had our first prototype and functional firmware. The design still required some slight tweaking. The current version of moRFeus is its third iteration. Oddly enough, the last phase of the project, industrial design, ended up being the most time-consuming. We worked with a local designer/machinist with decades of experience to come up with a custom-made all-aluminum enclosure.”

For more information and to purchase moRFeus, visit Crowd Supply.

Furthermore the product features, description, and also some of the applications and use cases for moRFeus are quoted below:

Features

  • RF Input Frequency: 30MHz–6GHz
  • RF Output Frequency: 30MHz–6GHz
  • LO Frequency: 85MHz–5400MHz
  • Fractional-N Synthesizer
  • LO Step Size: 1.5–3Hz1
  • 2.5 ppm precision TCXO
  • USB programmable
  • Generator/Mixer Function Toggle
  • Input IP3 +23dBm
  • Small, Portable Form Factor
  • Adjustable Mixer Bias Current
  • LCD Display With Backlight Feature
  • Button Control Interface
  • Dimensions: 88mm x 38mm x 68mm
  • Weight: 7.4 oz

Product Description

moRFeus is a 30MHz–6GHz programmable Fractional-N wideband frequency converter and generator designed for low spurious emissions and dynamic configuring of the LO frequency. moRFeus is designed for easy integration into popular RF environments using SMA connectors and is powered using an external micro-USB 5V supply. The LCD display and button interface provide a dynamic way to program the mixer LO frequency in the field with a step size of 1.5–3Hz.1 The device is USB programmable, enabling automatic operation from a PC (must be running Linux). Dynamic toggling between mixer and generator modes adds to field-level functionality. An optional bias voltage of 5V is available via RF choke to the mixer input to supply active antenna systems.

Applications

  • Wideband Radios
  • Distributed Antenna Systems
  • Diversity Receivers
  • Software Defined Radios
  • Frequency Band Shifters
  • Point-to-Point Radios
  • WiMax/LTE Infrastructure
  • Satellite Communications
  • Wideband Jammers
  • Remote Radio Heads
  • Frequency Up/Down Conversion
  • Automated Test Equipment (ATE)
  • Wireless Communication Systems
moRFeus Block Diagram
moRFeus Block Diagram

Review and Testing

The Outernet team sent us a moRFeus unit for testing a few days ago. It comes in a portable 3.5 x 2.7 x 1.5 inch (8.9 x 6.9 x 3.8 cm) conductive milled aluminum enclosure and weighs 7.4 ounces (210 grams). The construction is very solid, and should easily survive being thrown around in a carry bag, although we'd still advise caution as the LCD screen is not protected by a window.

The unit is powered via a standard micro USB port. After connecting a USB cable the unit immediately powers up shows a frequency selection screen on the LCD display. Five small buttons are used to control the interface, and we found it very easy to adjust the output frequency using these buttons.

Using the interface the unit can be switched between the "Generator" and "Mixer" modes. In the generator mode moRFeus simply generates a CW tone at the desired frequency. In the mixer mode moRFeus takes an input signal, mixes it with the generated tone and puts the result on the out port. Mixing a signal with a tone is the core concept behind devices like upconverters, downconverters and tuners. For example, by generating a mixing tone at 2 GHz with the moRFeus, we are able to view 2.4 GHz WiFi signals at 2.4 GHz - 2 GHz = 400 MHz.

In the screenshot below we set moRFeus to run in mixer mode with the LO frequency set at 2 GHz. This allows us to view an active WiFi signal at 2.475 GHz using an Airspy and the SpectrumSpy software. The Airspy can only tune up to 1.8 GHz by itself, so it can't view the WiFi band directly. Of course to use as a proper downconverter filtering is required to remove any images and interfering signals, but by being able to easily change the LO frequency you are able to move the signals around quite easily to avoid images or interference.

Unfortunately one limitation is that moRFeus' lowest input frequency is 30 MHz, so it can't be used to upconvert HF signals.

Viewing a 2.4 GHz WiFi signal on an Airspy by using moRFeus as a downconverter.
Viewing a 2.4 GHz WiFi signal on an Airspy by using moRFeus as a downconverter with LO set to 2 GHz.

moRFeus also works well as a standard RF signal generator, and we were able to get a clean CW tone on any frequency between 85 MHz - 6 GHz.

moRFeus as a RF signal generator
moRFeus as a RF signal generator

moRFeus also shows up a a device on the PC, and the team write that it is possible to control it programatically via Linux, however documentation for this does not exist yet although it is scheduled to be released later. We would love to see a sweep feature which should be possible with PC control.

In conclusion if you are looking for a low cost signal generator or mixer to use in your experimental RF projects, then moRFeus certainly does seem like a good deal. A tool like this is very handy to have in your RF kit.

New Custom Firmware for the PlutoSDR with Several Linux SDR Programs Pre-Installed

The PlutoSDR is an Analog Devices $99 - $149 RX/TX capable SDR with 20 MHz of bandwidth and a 325 MHz to 3.8 GHz frequency range that is software hackable to 56 Mhz of bandwidth and a 70 MHz to 6000 MHz frequency. It has an on board Xilinx Zynq Z-7010 FPGA, which has a built in dual core ARM Cortex-A9 processor as well. This processor is capable of running Linux and Linux SDR software on the PlutoSDR itself. PlutoSDR's can be purchased directly from Analog Devices, or via ArrowDigiKey or Mouser.

Recently "Lama Bleu" has been working on a custom firmware image for the PlutoSDR. Installing custom firmware allows you to load up a pre-configured Linux system which already has a bunch of useful software installed. He writes that his version is not designed to have a nice GUI, but rather focuses on scripting and data acquisition software. A list of software pre-installed to the image is shown below:

To access these tools you simply connect to the PlutoSDR via a network connection and SSH. With some of the tools installed it is possible to do things on board the PlutoSDR like recording signals, demodulating signals, transmitting CW, stream demodulated audio over a network, plot the spectrum on the terminal, create an online SDR with OpenWebRX, do a long spectrum scan and transmit DATV. 

An alternative custom firmware is PlutoWeb which we posted about in the past. This image is designed for creating a web interface GUI, and for running streaming software such as OpenWebRX.

A spectrum scan completed on board a PlutoSDR running Lama Bleu's custom firmware.
A spectrum scan completed on board a PlutoSDR with rx_tools, running Lama Bleu's custom firmware.
GNU Plot running on the PlutoSDR with Lama Bleu's custom firmware.
GNU Plot running on the PlutoSDR with Lama Bleu's custom firmware.

The Outernet Ku-Band LoRa Data Service

As mentioned in our previous post about the Outernet LoRa chat application, Outernet is currently holding a 33% off sale on their 'Dreamcatcher' satellite data receiver. To get the discount use the coupon "33%OFFJULY4SALE" on their store. The sale lasts until Midnight Central Time on Wednesday 4 July. The code is valid site wide, so applies to the moRFeus product as well.

In this post we'll highlight the Outernet data service which can be received in the Continental USA with the Dreamcatcher 3 hardware.

Outernet is a free download only satellite based information service that aims to be a sort of 'library in the sky'. Their aim to to have satellites constantly broadcasting down weather, news, books, radio, web pages, and files to everyone in the world. As it's satellite based, the service is censorship resistant, and useful for remote/marine areas without or with slow/capped internet access.

Currently the Outernet data service is considered to be beta, and is only available for those in the Continental United States.

The New Outernet Data Service

Originally a few years ago Outernet started with a 12 GHz DVB-S satellite service that gave 1GB of content a day, but that service required a large dish antenna which severely hampered user adoption. Their second attempt was with an L-band service that only needed a small patch antenna. This service used RTL-SDR dongles as the receiver, so it was very cheap to set up. Unfortunately the L-band service had a very slow data rates (less than 20MB of content a day), and leasing an L-band transmitter on a satellite proved to be far too expensive for Outernet to continue with. Both these services have now been discontinued.

Outernet 3.0 aims to fix their previous issues by giving us a service that provides over 300MB of data a day, with a relatively cheap receiver, computer and antenna combination that is small and easy to set up. The new receiver uses a standard Ku-Band LNB as the antenna, which is very cheaply available as they are often used for satellite TV reception. The receiver is called 'Dreamcatcher 3', and is a custom PCB containing a hardware receiver (non-SDR based) with a LoRa decoder, as well as an embedded ARM computer capable of running Linux.

LoRa is an RF protocol that is most often associated with small Internet of Things (IoT) devices, but Outernet have chosen it as their satellite protocol for Outernet 3.0 because it is very tolerant to interference. In Outernet 3.0 the LNB is pointed directly at the satellite without any directive satellite dish, meaning that interference from other satellites can be a problem. But LoRa solves that problem by being tolerant to interference.

The Data Service

Currently, Dreamcatcher 3 users are receiving data such as hundreds of daily news articles, global weather information and the top 100 most searched Wikipedia articles of the day. A new satellite radio broadcast service is also being tested (kind of similar to Sirius XM, but only one channel at the moment). Compared to the older L-band Outernet service, the larger data rates allow for a lot more data and thus articles to come down.

Like previous iterations, the Dreamcatcher 3 board runs remotely on a WiFi connection. You then connect to the Dreamcatcher 'Skylark' web interface via a PC or mobile browser. On this web interface you can browse all your downloaded files. The user guide is a good read for understanding the set up procedure. 

Some screenshots of example received data are shown below.

Conclusion

Outernet have been working hard to perfect their service over the years, and the current offering is the best compromise between ease of use and data rates that we've seen so far. Unfortunately the service is only available in the Continental USA at the moment, but we're looking forward to future expansion. 

Currently we'd only recommend purchasing the Dreamcatcher 3 receiver for the Outernet data service if you understand that the service is in beta, requires a little bit of technical know-how, and like previous Outernet iterations is subject to possible change. Support is only available via their forums.

We can see the service being popular with those who live and work in remote areas without or with expensive internet. Censorship resistance is also another big plus, but satellites would need to be rented for these areas first.

There are also more creative uses. 'Unplugged' getaways are becoming popular in the modern world. Perhaps you want an internet free holiday, but don't want to miss out on important breaking news and weather updates for safety. In the future Outernet could also be used for Bitcoin or other Cryptocurrency blockchain transmission. In past Outernet iterations it was also possible to send a tweet that would be re-transmitted by Outernet. A similar messaging service could be used to control remote devices.

Outernet Dreamcatcher 3 Sale $99 for the Full Kit + Testing the LoRA Chat Application

The Dreamcatcher v3.0 is Outernet's latest revision of their satellite receiver hardware. The freely available Outernet ku-band satellite service aims to keep us up to date with the latest news, provide books, videos, a daily selection of Wikipedia articles and satellite radio. Compared to the internet, Outernet is download only, and is received via their Dreamcatcher 3 hardware with an an antenna pointed to a satellite. At the moment their Ku-band service is in beta testing and so is only available in the continental United States, but they hope to eventually expand to cover more areas of the world.

Starting from today Outernet are holding a 33% off sale. This means that their Dreamcatcher 3 is only US$99 each. To get the discount use the coupon "33%OFFJULY4SALE" on their store. The sale lasts until Midnight Central Time on Wednesday 4 July. The code is valid site wide, so applies to the moRFeus product as well.

Previous Dreamcatcher implementations utilized an RTL-SDR to receive their L-Band network, however that network has now been discontinued. Dreamcatcher 3 utilizes a hardware based LoRa radio to receive their new ku-band satellite LoRa data stream. However, Dreamcatcher 3 has alternative applications, and doesn't need to be used only for the Outernet data service. Dreamcatcher 3.0 is a full LoRa radio that can transmit and receive, and in this post we'll focus on testing that out.

LoRa is a popular wireless protocol that has been designed for Internet of Things (IoT) devices. It is robust against interference and can be used in low power devices.

Dreamcatcher 3 LoRa Chat

Outernet have provided a LoRa two way open source text chat application that runs on the Dreamcatcher 3. To use it you'll need two Dreamcatcher 3 boards. With the application you'll be able to chat with short text messages in real time between the boards. Amateur radio enthusiasts may be interested in the boards as an easy way to set up LoRa experiments.

We note that Outernet are not advertising the transmit features specifically as the board is not FCC approved as an intentional radiator, so it cannot legally be used as an ISM band LoRa device for transmitting and listening to LoRa IoT sensors. But as a ham you are able to transmit with it if you can ensure that the output is clean and legal and on the ham bands. 

Dreamcatcher 3.0 Running LoRa Chat App
Dreamcatcher 3.0 Running the LoRa Chat App

A brief demo of the chat running below is shown. In the video we're using the default 'spreading factor' setting which results in robust communications, but results in a latency of about 2 seconds. Later we'll show how to change the spreading factor to reduce latency.

 

The Dreamcatcher v3.0

Outernet kindly provided us with two Dreamcatcher 3 boards to test the chat application with.

Like the previous versions, the Dreamcatcher is a full computing board with radio built into it. Except this time instead of an RTL-SDR, the radio is a hardware LoRa module. Another difference is that now there is a built in LCD screen.

On the board there are two SMA ports, one labelled "Direct" and the other labelled "LNB". The direct port is what we'll need to use for the chat application as this is the port that can transmit. There are also two SD Card slots, one for the OS and one for storage, a microphone and headphone jack, a USB-A slot with a supplied WiFi adapter, and two USB micro slots, one for USB OTG and one for power.

The package also comes with an LNB that is designed to be used with the Outernet satellite service. The LNB is receive only, so cannot be used with the chat application, so you'll need to use your own antenna if experimenting with the LoRa transmitter.

Chat Setup and Usage

First we burnt the latest version of Dreamcatcher Armbian OS to two SD cards and inserted one into each board. Since Dreamcatcher 3 has a built in LCD screen, you can login and access the terminal through the screen. But as there is only one USB port available, you'll need a USB hub to be able to plug in a mouse and keyboard, and the included USB WiFi adapter. Alternatively, if you connect the USB OTG port to a PC, you can connect to it via a USB serial connection. Instructions for connecting via serial, and for setting up a WiFi connection are the same as in our previous Dreamcatcher 2.0 tutorial.

The chat software is available on GitHub at https://github.com/Outernet-Project/Dreamcatcher-Packet-Tester. To install it simply run the following commands at the Dreamcatcher's terminal:

sudo apt update
sudo apt install libsoc-dev libsoc2
git clone https://github.com/Outernet-Project/Dreamcatcher-Packet-Tester
make

Then you can run the chat program with:

sudo ./chat

Upon running the program you'll be asked to enter a MIXER frequency. This frequency doesn't really seem to matter and we're not sure why we're asked for it. But you can enter any frequency such as 300000000 Hz (300 MHz).

Once you've opened the chat program on both Dreamcatchers you should be able to type in text on the console, and have it show up on the other Dreamcatcher after pressing enter. Remember to plug an antenna in to the DIRECT port of both Dreamcatchers, or run of attenuated coax between them. The provided LNB cannot be used for the chat application.

Playing with LoRa Settings

The actual RF output frequency is by default hard coded in at 2.4 GHz. If you want to change it you can edit the main.cpp file with a terminal based text editor like nano, and look for the #define RF_FREQUENCY entry. Then you will need to recompile by running 'make' again. However note that at the time of this post, according to Outernet the software only works properly at around 2.4 GHz. Apparently this is simply a software limitation and once this is fixed you should be able to transmit at any frequency between 85 MHz to 5400 MHz.

Also by default, the LoRa 'Spreading Factor' is set to the maximum of 12. This means that there is roughly a latency of about 1 second between sending a message, and receiving it on the other unit.

The spreading factor can also be adjusted in the code by editing the "modulationParams.Params.LoRa.SpreadingFactor" variable. This determines how spread out in time the packet it. Larger spreading factors result in more robust error free communications, whereas smaller factors result in lower latency.  Below are some valid spreading factor entries for the code.

Note that if you reduce the spreading factor you'll also want to reduce the RX_TIMEOUT_VALUE and TX_TIMEOUT_VALUE #defines (you'll need to search for these lines in the code. Hint: In Nano CTRL+W is search.). For a spreading factor of 7 a timeout of 100 ms works well.

LORA_SF5 
LORA_SF6 
LORA_SF7 
LORA_SF8 
LORA_SF9 
LORA_SF10 
LORA_SF11 
LORA_SF12

It is also possible to adjust the bandwidth from 200 kHz up to 1600 kHz using the following code on the "modulationParams.Params.LoRa.Bandwidth" variable.

LORA_BW_0200 
LORA_BW_0400 
LORA_BW_0800 
LORA_BW_1600

The LoRa 'coding rate' can also be changed via the "modulationParams.Params.LoRa.CodingRate" variable.

LORA_CR_4_5 
LORA_CR_4_6 
LORA_CR_4_7 
LORA_CR_4_8 
LORA_CR_LI_4_5 
LORA_CR_LI_4_6 
LORA_CR_LI_4_7

You can also adjust the TX output power by adjusting the value specified by #define TX_OUTPUT_POWER. By default it is set to the maximum output power of 13 dBm. The lowest value available is -18 dBm. 

Remember that after making a change in the main.cpp file, you'll have to recompile the chat program by running 'make'.

Below we visualized the different LoRa spreading factors with a HackRF. It's interesting to see how the spreading factor changes the packet transmit time.

Comparing LoRA Spreading Factors
Comparing LoRa Spreading Factors

Conclusion

Overall the Dreamcatcher 3 LoRa chat software works, but is still very much in early development. Regardless it is an interesting tool for experimenting with LoRa. The hardware is ready, and software now just needs to be developed to make use of the LoRa protocol. We also note that the Dreamcatcher is not a plug and play device, and that it's mostly suited to people who enjoy tinkering with new beta products.

We'd also just like to remind that in order to legally transmit you'll need a ham licence. The board is not FCC approved for regular ISM band LoRa use. While the output power of the Dreamcatcher isn't too strong at a maximum of 13 dBm, we still recommend that you make sure to reduce the output TX power, or run a direct attenuated coax connection when testing. There are also weak signal images present at some harmonics, so any ham using this with an amplifier would be of course expected to provide sufficient filtering.