Signals in Space: How, Where & What

 

The 47th Annual Trenton Computer Festival took place on March 18th 2023. I was invited back to give a presentation this year alongside some amazing fellow presenters focused on related topics.

The presentation on "Signals in Space:  How, Where & What" were highly animated and included some authentic recordings from some various man-made signals of significance over the past 60+ years.

For the basic static slides, you can download a copy HERE though if you missed it live.

Timing Is Everything: 7 Days With Kerberos SDR

The long awaited Kerberos SDR arrived last month, but I only recently got a chance to really focus my full attention on this unique device this past week. This article covers my first impressions plus setup helpful tips.

What is Kerberos SDR?

A successful Indiegogo campaign which netted 8007% backing sort of is a big deal in my mind and makes for a nice introduction statement.  The Kerberos hardware and software package was under development for some time and required many people to be involved as covered in a past article in the HVDN Notebook focused on tracking radio signals this past November.

Software defined radio has been top of mind in the hobby community for some time, thanks to inexpensive USB TV tuner dongles that have found a dual purpose as wide range radio receivers, such as the RTL-SDR v3 or NooElec and its various offerings for around the same price.

The Kerberos SDR is at its core, four of these inexpensive and capable SDR receivers assembled into one circuit board along with a number of modifications and upgrades to enable some interesting applications.

As the title of the article implies, timing is everything. At the core of the Kerberos is a shared TCXO clock source which ensures all four independent receivers are synchronized with a high degree of stability.

Last month at TCF, Joe N1JTA showed how important a TCXO is to the MMDVM "hot spot" boards that amateur radio operators are using as part of modern digital voice communications.  This same concept applies with the Kerberos, but essentially on steroids.

Having synchronized receivers allows some real fancy computations to be made using newly created open source software that is packaged with the Kerberos SDR.

Computational you say?

There is an already a well written and detailed quick start guide for using a ready made disk image or how to install the packages and related dependencies to get the Kerberos SDR software up and running, so no need to rehash that here.  But, in order to get the most out of this phase coherent software defined radio receiver, here are a few tips.

     Hardware related

• Power source considerations:  Just like with the MMDVM Pi-Star hotspots, DO NOT use some old 500 mAh USB charger from an ancient Palm Pilot!  The Kerberos SDR needs its very own 2 amp or higher current USB power source that will connect into the USB C port. This is to power all 4 receivers and not for data transfer.  A best practice is to use a separate power source for the Kerberos SDR and another for the single board computer running the demo software.

• Connecting things together: The order you connect things together does matter.  Follow these steps to avoid frustration. First, connect your power source to the Kerberos and let it run for a minute or two.  DO NOT yet connect antenna or USB micro cables to the SDR.  If you peak carefully inside the SDR near the USB connectors, you will see white LED and blue LEDs flickering inside to tell you the Kerberos is powered up.  Second, now it is safe to connect a USB micro cable from the SDR to your compute device. If using the recommended RPI 3B or 3B+,  your third step should be to apply power to the RPI after you have inserted the SD card.  Reasons for this order explained later.

• Calibration:  Try not to bug some of the innovators like Corrosive from the popular SignalsEverywhere "vlog" with basic questions so he can find some more new cool stuff to tell us all about even though he may not mind your questions.  Perform the calibration using the built in noise source and 50 ohm terminations your Kerberos came with. DO NOT skip this step.  Not only will you learn more about the software in the process, but you will avoid frustration when testing out direction finding or passive radar functionality.

• Antennae:  You need four identical antennas.  My initial tests were conducted with these small magnetic mount antennas designed for near the 70cm frequency band.  The real key is identical antennae, especially for the signal location application.  The passive radar application would likely benefit from one directional and one non-directional antenna instead, thus two antennas only are needed for that application.   It would also make practical sense to source some type of metal plate if using magnetic mount antennas, so be sure to order an iron pie plate from Amazon too when ordering antennas if you do not already have one handy. Placing magnetic mount antennae on a ground plan makes a huge difference.

• Temperature:  If you have already experimented with single SDR dongles, you know they get a little hot.  The Kerberos SDR will also run warm to the touch and is normal. If using the SDR for an extended period of time, you may want to invest in a small fan to keep it cool. 

• Raspberry Pi:  The image provided on the quick start page is for the RPI 3B or 3B+.  It will not work correctly with an older Raspberry Pi, so save yourself the trouble. The software is also somewhat intensive, so either run the Kerberos on an RPI3 or a real computer. DO NOT try to use an older SBC or anything not supported that is under powered from a CPU perspective. 

• Taking Kerberos SDR apart:  You will be tempted to take Kerberos apart. DO NOT do it unless you have a good reason to do so.  The 40 pin header under the Kerberos is an alternate way to connect a RaspberryPi with an extended header, but is really not needed.  If you did want to do this, you WILL need to open your Kerberos up and remove a 2 pin jumper inside after almost total disassembly.   Also, that tempting regular size USB port is for future use and will not work UNLESS a pair of chip resistors are removed inside the Kerberos SDR.  The bottom line is, just focus on how Kerberos is configured before thinking about hacks and modifications and get the most out of the hardware as it arrived to you first. 

      Software related

• Demo software:  Its not very polished, but gets the job done.  The biggest thing to be aware of is that your Kerberos WILL NOT work if you did not plug in everything correctly first.  If you see no sample rate with numbers being displayed in milliseconds or seconds, you did something wrong or do not have the right power source or good USB cables.  Do not blame the software first, check your hardware. The software is otherwise pretty straight forward.

• Computational stuff:  You may learn quickly that the RPI 3B+ is under powered at times if you are running wider bandwidth than the default setting of 250 kHz. You can trim this down closer to the width of the signal you are interested in.  You can also change the decimation from its default to any higher number for slower sampling speeds. Both changes will give you lower latency overall.   Same goes with shutting off the spectrum display as it does take a number of compute cycles to visualize 4 simultaneous views of the frequency being monitored. 

Additional stuff

There will be future articles about direction of arrival and passive radar related topics here on HVDN Notebook related to the Kerberos SDR as well as experiences running the demo software on a much more capable piece of computing hardware, but for now follow all these tips and best practices.

Feel free to share your experiences on the RTL-SDR forum for Kerberos SDR and enjoy your new toy. 

Presentation: Digital Hotspot Pi-Star MMDVM Hardware Overview

Joe N1JTA gave a presentation as part of a workshop at the Trenton Computer Festival on March 23rd.

Billed as the world's oldest computer festival,  TCF19 was the 44th year in which many hobbies converged which show how ubiquitous computers and wireless technology has become.

There is more detail about TCF on websites such as Hackaday and the official event website here.

What made Joe's presentation unique was that it focused only on open source hardware and some best practices and purchasing tips to guide newcomers into a less frustrating entry into the world of digital voice amateur radio technology.

N1JTA also focused on how the MMDVM and Pi-Star combination is an excellent learning tool for those interested in deploying a wide area digital mode repeater, but would like to first experiment on a much smaller scale thanks to a digital hot spot.

Check out the full presentation below and hopefully this enables further learning about one of the most modern incarnations of amateur radio.

HVDN Digital Hotspot Pi-Star MMDVM Hardware Overview PDF Edition (March 2019)

March 23rd: TCF19 Computer Festival

This event has a little something for everyone interested in modern technology and applications, not just related to amateur radio or even computers.

The featured keynote this year will be led by Tony Sager of the Center For Internet Security which is headquartered just outside Albany, New York.  Tony will talk about the importance of cyber-security and how it affects almost every aspect of our connected lives today.

Other featured presentations include:

• The State of Cyber Crime in New Jersey by NJ Department of Homeland Security Cyber Team!

• Maintaining the Integrity of Elections in a Digital World – Rebecca Mercuri

• Quantum Computing – Barry Burd 

• Amateur Radio Satellite Spectrum - Steve Bossert 

• WordPress Bootcamp – Lou Judice

• Cybercrime and Theremin Zen – Kip Rosser 

• MMDVM Hotspot Construction - Joe Apuzzo  

• Hands-on Arduino Workshop for Beginners – Katalin Frolio

• All Day Robotics Pavilion – Seung-yun Kim

What about amateur radio? 

HVDN's very own Joe Apuzzo N1JTA and Steve Bossert K2GOG will be among the 50+ presentations and workshops also taking place during this fantastic event.

In N1JTA's 30 minute presentation he will talk about how radio and computers has converged through the popularity of digital modes in Amateur radio and how it has grown exponentially over the last few years due to the affordability of VHF/UHF digital handheld radios and other equipment.

One of many MMDVM hot spot options, the N2BOC version 

is full duplex capable and the same size as a Raspberry Pi Zero. 

A large part of this growth can also be attributed to the impact of hot spot devices and the unique learning capability they create. A hot spot is a small access point type device that uses amateur radio spectrum and a decentralized network of servers to enable global or local  digital communication.

Joe will cover at a high level, what is needed to construct your own "micro repeater" or hot spot device and how it works, along with how to create secure connections and utilize a decentralized network maintained by a group of amateur radio operators around the world.

Brandmeister is unique in that it can route all types of digital voice traffic through its decentralized network of servers to end node devices such as hotspots and repeaters

Since the hot spot device is nothing more than a Raspberry Pi single board computer and a multi mode digital voice modem hat plus some open source software called Pi-Star it is relatively inexpensive but very complex to understand how it works.

Steve will be cover in varying detail more than 21,000 MHz of spectrum available to amateur radio operators looking to experiment with satellite communications today. While much of this spectrum is above 1.2 GHz, this still leaves over 60 MHz of varied spectrum that can be used by those holding the easiest to get Technician class amateur radio license and with minimal expense.

Your DMR radio can also be used for satellite communications
via analog FM mode you might have forgot exists.

Steve's discussion will cover the most common spectrum used today for amateur radio operators interested in satellite communications, additional spectrum users to be mindful of and a review of the most active satellites that can be used with less than $100 of invested equipment.  He will also give a "sneak peak" on this topic to attendees of the March 11th HVDN meeting in Rhinebeck, NY.

More about TCF19, the full agenda and when is Joe's presentation can be found at https://tcf-nj.org/

Interested in other interesting events? Check out the HVDN activity calendar