Wednesday, October 13, 2021



The Hudson Valley will be home again to the premier radio direction finding (RDF) event for our area and this will be taking place on October 30th 2021 at Ferncliff Forest in Rhinebeck, NY.  GPS address is 68 Mount Rutsen Rd Rhinebeck NY 12572.  

The event will take place from 9:00 AM until about 3:00 PM.  All who are interested are encouraged to pre-register. There is no fee to attend or participate.   Registration survey here.

A combination of area amateur radio clubs will be organizing and participating in this event.

Overlook Mountain Amateur Radio Club (OMARC)

With a membership focus on Ulster county and the Northern Dutchess County area, the OMARC club will be providing lunch and hospitality for the event. Lunch will be served from 11:45 AM until 12:15 PM with snacks and drinks available for the duration of the event.

OMARC will also be supplying some of the hidden transmitters for the hunt and the WA2MJM 146.805 MHz repeater will provide educational discussion relating to this event at various times of day and the entire month of October.

United States Military Academy Cadet Radio Club (W2KGY)

Building on the success of past cooperative events, the USMA Cadet Radio Club will be participating in this event to hone practical skills which can be used in real life scenarios which may involve working across civilian and government response teams.

Hudson Valley Digital Network (HVDN)

HVDN will take the lead on education, coordination and technology that will be deployed for the first multi-transmitter direction finding event in our area.  

Additional equipment may be available for those that do not possess some of the tools needed to find the hidden transmitters. Educational session will take place from 9:10 AM until 9:35 AM. Teams of hunters will start off to find the transmitters around 9:45 AM. 

Anyone is welcome to attend and you do not need to be a member of any of these clubs or have an amateur radio license.  Donations are welcome the day of the event.

Radio Direction Finding Basics

We would like to thank Josh KI6NAZ for a pair of excellent videos explaining a little about the basics of radio direction finding and using the antenna we are promoting for the event.

HVDN also has a basic information webpage found at and here is a past article that may be of interest. 

Navigation Basics: Using a map and compass

Bob KD2QAK is an experienced search and rescue and medical technician. Bob worked with Steve K2GOG to put together this introductory video.  This will teach some basic skills which will be used during our radio direction finding event on October 30th 2021. 

Using grid squares in a practical environment

If you watched Bob's video, he mentioned the UTM grid system which is often used for search and rescue activities.  Within amateur radio, we use a system called Maidenhead Grid Locator (MLS) and here is a video which Steve K2GOG created.  Grid squares are easy to use to share approximate and fairly specific location with very few characters.  

During our RDF event on October 30th, we will be incorporating MLS into the maps which will be issued to the teams who will be looking for the hidden transmitters along with some other interesting objects in the forest.  

Some of these may include hidden treasure chests, friendly gnomes, persons of interest and a new set of trail markers that Ferncliff Forest has recently installed.  

Please bring your family if this sounds like fun!

October 30th 2021 RDF Missions

Details will be kept a secret, but we will be hiding upwards of 6 different transmitters that will each have different degrees of difficulty to find during this event.   This will help appeal to the widest number of people possible.

All transmitters will be operating on the amateur 2m band (144 to 148 MHz). Some transmitters will even be sending images, so using our SSTV skills in the field will become important and will add a unique perspective to this event.

 Other training exercises to understand how to use a directional antenna and land navigation will be interwoven into this event.

Expect lots of fun and any questions can be asked in the comments below or during any of the many organized discussions taking place on the WA2MJM repeater.

Or, feel free to contact the UNDR Net team who was responsible for putting this great event together 



Monday, October 11, 2021

Map & Compass Basics with Bob KD2QAK

October 2021 is busy with many educational activities to get everyone ready for our big radio direction finding (RDF) event scheduled for October 30th 2021 at Ferncliff Forest in Rhinebeck, New York.

Here is a great video on some basic skills and understanding for using a map and compass.

Click or or on video below

Why United States amateur radio can not evolve?


The title of this post sounds a little like a "Jeopardy" answer in the category of "Famous son inventors".  Probably, the question was "Beyond silencers, this son of a different American pioneer was also known for the growth of which hobby, which involves shooting things other than bullets into the air?"

1ZT: Getting your attention!

Its always easy to poke fun at the love of all things high frequency and possibly even one of the important founders of the Amateur Radio Relay League (ARRL) who we have to credit, much like the National Rifle Association (NRA), for embedding certain hobbies and perceptions into the DNA of Americans.  

This is none other than the old man himself, Hiram Percy Maxim, who is not only one of the co-founders of the ARRL, but also one of the early inventors of the firearm silencer and son of the mastermind behind the Maxim machine gun.

Did you know there was a more legitimate co-founder of the ARRL named Clarence Tuska?  He was also the person behind the much loved QST magazine and likely would be more apt to read an article like this compared to Mr. Maxim.  

Both of these "OM" helped evolve the world of wireless communications for hobbyists like us, but we are now at a time where we need to prevent us from facing extinction.

As an engineer,  Mr. Tuska is who promoted the use of the higher 200m and above spectrum rather then the lower 600m band and was much more focused as an experimenter with radio technology.  I like Mr. Tuska and what he did for the hobby in the United States, thanks to his awareness to share information in written form. Lets now jump into something fresh and new! 


I write this after sharing notice of an important evolution within radio technology which has not yet really come into wide spread use across amateur radio yet.  

Today, we can not wait around for QST to learn about the latest innovations.  Its right here in the digital domain is where you will learn about something new. And, by the time most people get QST in the mail, its out of date and more time is spent trying to find who to give it to! 

The Future.....

What I am talking about is known as a software definable front end preselector.  Those I shared this latest Crowd Supply project with immediately needed to point out that something like this is useless, since it does not include capability for our much beloved "HF" spectrum allocations.  

At $419 USD, it is expected to cover spectrum much lower in order to appeal to the amateur radio hobbyist to make it a worth while purchase.

This preselector is a versatile, highly useful tool for providing programmable bandpass filtering for a software-defined radio, among other applications. 

In the receive path, that filtering can be used to mitigate the effect of strong blocking signals; in the transmit path, it can be used to help reduce out-of-band radiation. 

ATEK1001 aims to provide an affordable filter bank for radio enthusiasts and SDR users. More of the technical specifications concerning the 485MHz to 7.7 GHz can be read about here

Starting so high into UHF spectrum even limits its applications for most of the amateur radio community members interested in bands such as 70cm, 1.25m, 2m, 4m, 6m and of course the rest of the HF band.

What makes the ATEK101 interesting is how small it is. 

Who cares. More money for another HF CW/DIGI Kit!!

For those interested in Software Defined Radio (SDR), this is where the market software defined radio front end (SDRFE) is really targeted.  Not the HF only operator who only chases CW contacts in South Dakota.

The popular Lime SDR and Lime SDR Mini are joined by a branded product also available via Crowd Supply called the Lime RFE which does cover the important spectrum we care about and is only a mere $699 USD and covers up to 3.5 GHz plus all the important amateur radio bands in between. 

It is however a much larger product. There is even a $549 USD option for those who do not need the cellular filtering and this will appeal more to frugal amateur radio operators looking for something new. 

If you wanted to experiment with RF filtering, the Lime RFE or the ATAK1001 are what is available today.   


SIDE NOTE:   Interested SDR for HF?   Get online for the QDX available October 11th at 2:00 PM EST until units sell out. 


Do I need a SDR Front End?

Reason here is to illustrate there are some interesting things taking place within the world of software "re-defined" radio worth keeping an eye on, but another area is the niche that the phase coherent software defined radio is filling.

We are jumping to a totally different topics here because I can not find anything about a dedicated HF only or even HF and VHF RFE to write about, but now I know I have your attention.  

A phase coherent SDR is a combination of multiple software defined radios which can act together or separate from each other to do interesting things.

Combining multiple receivers can act as a way to filter or combine signals and the provided "Kerberos" product was the first low cost way to do this with its four receivers which are identical in performance to the popular RTL-SDR V3 most who are reading this probably own already.

Software for Software Defined Radio

A challenge when the Kerberos first came to market in early 2019 was little available software to use it with and it also needed a little more horse power from a computer to utilize its capabilities.

Things changed for Kerberos when the Raspberry Pi 4 became available and it was far easier to use the Kerberos for applications like radio direction finding or using its phase coherence capability. 

Software also improved since 2019, with applications like SDRangel being one of the first to offer easy to use multiple receivers at the same time in a visual application.   

Using something like a Kerberos and its 4 separate receivers capable to tune to any approximate 2.4 MHz chunk of spectrum at one time means you can monitor multiple bands at the same time or even the same frequency via different receivers and find ways to optimize reception by using different DSP filtering tools.  

By the time many people got excited about the capability of the Kerberos, it was already out of production or sold at lower cost, but there is a new model called the Kraken about to be unleashed which will include five independent receivers.  so,  its time to jump onboard now if you want to do amazing things with a phase coherent receiver. 

There is a more polished software program specific for the Kraken, which can also be used with the Kerberos if you have.  

Many more traditional SDR programs like those which Rick W1RHS let us know about recently also exist now which can be used with phase coherent hardware.

During the October 19th session of the popular Northstar Digital Net managed by Jim WA2UMP,  some discussion about both phase coherent receivers and possibly other SDR topics like RFE will be mentioned. 

Steve K2GOG of HVDN will be available to share more details and field questions on some other aspects about software defined radio that hopefully, will make the likes of Mr. Tuska and Mr. Maxim proud. 

Please be sure to join us Tuesday October 19th at 8:00 PM Eastern Time on Brandmeister Talk Group 31630 if you are interested in topics like this on the evolution of amateur radio by using the future to do so thanks to DMR.

Sunday, October 10, 2021

Chasing the Dragon - Building a Signals Intelligence (SIGINT) platform with SDR


It has been ten years since software defined radio (SDR) has reached the average tech enthusiast through hacking a USB DVB-T TV Tuner. This helped accelerate existing SDR projects such as GNU Radio for signal processing and low cost transceiver platforms such as the HackRF and LimeSDR.

The more complex the signal the more demanding it is in system performance to process, decode, and sometimes decrypt. Many interesting signals transmit at very low power levels requiring you to be in close proximity to them. This makes building a highly portable dedicated SDR system the most desirable path.

Building a SDR system to participate in Wireless or RF Capture the Flag contests (WCTF and RFCTF respectively) is a use case that has the broadest spectrum requirements from a few MHz to a few GHz. Many of these events are hosted at fixed locations with the more complex modulation schemas transmitted there. Any portable requirements are for well known signals.

Because this use case requires the greatest breadth and depth of signal identification you see people use workstation-grade laptops. But people do not want to be using their best laptop as their SDR station especially if it is their "daily driver" for work/personal. Thus begins the journey for a more cost effective solution for a system dedicated to SDR. Thus began my quest such a system.


Starting with contests as my use case, I started investigation what is the most versatile signal intelligence (SIGINT) platform I can build using readily available components at a moderate cost. This is what I came up with:

  • RX coverage from 100 KHz to 6 GHz
  • TX coverage on frequencies within the RX coverage where legally and/or licensed to operate. ISM, GMRS (US), FRS (US), and Amateur Radio bands.
  • Should be able to carry every thing in nothing larger than a carry-on luggage sized case and quickly deploy the station in under 10 minutes.
  • All resources are focused on signals intelligence first. Any other intended usage of the compute platform is secondary.


I came up with the architecture and components diagrammed below. While SDR performance s well documented using a Raspberry Pi 3 Model B+, performance is centered around simple analog and digital modulation modes like OOK, ASK, FSK, PSK, and MFSK. Since I expect to be working with more complex digital modulation voice modes such as DMR, C4FM, P25, and M17 I opted to build on a Raspberry Pi 4 with 4GB RAM (RPi4) instead.

SIGbox Architecture

Since the build needs to be portable, I decided to have power sourced from 12VDC which could be delivered by a switching power supply or power supply or battery such as a 12V@20A LiFePO4.

Since the RPi4 demands 5.1V a dedicated buck converter is installed between the RPi4 and power sourc. When RPi4 are under heavy load a "Low Voltage" message will be displayed in any X-Windows session. 

USB devices are equally demanding for power so a USB 3.0 powered hub is installed. 36 watts is distributed across seven ports.

I suspect each port is limited to 2.5A but I do not expect all connected USB devices to be under load at all times - three at best. But it does beg the question whether USB power hubs vary when it comes to whether they make the entire current capacity avialble to a port. Further testing require on this.

The RTL-SDR Blog V3 R820T2 RTL2832U and HackRF SDR devicesare a good combo to satisfy broad spectrum and TX/RX requirements. The RTL-SDR performs well for HF/VHF/UHF receive, The HackRF makes a good secondary receiver for VHF/UHF for signals that require two receivers and primary up reciever for signals up to 6GHz. The HackRF also provides all our transmit requirements. 

For signal specific requirments, Ubertooth is added for Bluetooth, a GPS to keep time and location, and an Alfa AC1200 for WiFi. A FM VHF/UHF analog/digital transceiver is optional for VHF/UHF APRS and DMR. This transceiver could be something simple like a Baofeng DM-1801.


Given the RPi4 for compute, Raspberry Pi OS Full (32-bit) is the chosen operating system given its maturity and maximum ARM hardware compatibility. While Ubuntu 20.04 was an option, sticking with "tried and true" reduces debugging points in the prototype.

SDRangel and SDR++  are SDR applications reflecting a new generation of tools that provide frameworks for plug-in development. This is necessary given the growing complexity of digital modulation modes optimized for superior noise immunity without sacrificing throughput to deliver use cases such as passive radar. SDR applications need to scale in functionality that allows peeling back the layers which can also include decryption.

SDR application frameworks are a great evolution enabling those who may not be able to cope with working at a lower level with GNU radio and GRC companion to stand on the shoulders of others through developing plug-ins. To encourage plug-in develeopment and experimentation to further the SDR "arts" I decided to focus only on SDRangel and SDR++ and include libraries, command line decoders, and other relevant tools focused on signal intelligence (SIGINT.)

To promote further development in SDR and signals intelligence you have to create an education path free of distractions best through some gamified journey. While one can create labs for simple digital modulation modes like OOK, ASK, and FSK, the established modulation modes in Amateur Radio provide a more interactive introductory education. I have done this with a workshop I presented at HOPE XII and have since archived on Github.


When people try to build their own RF related platform or distro, they tend to dump every RF related package a repo has on the topic and top it off with the latest trendy app as long as it is available as a package and does not require compiling. Without ready avilable and relevant help and education, this hurts more than helps someone getting into SIGINT. 

The best approach is establish common ground starting with the end-user already knowing how to install and configure Raspberry Pi OS Full (32-bit) and familiarity in its use as an end user. From there easy to follow instructions that to stand-u pan automated script to install the required software to build a working SDR station. Any choices the end user needs to make during installation needs to be very explicit in what they are deciding.

The end user should not be overwhelmed with first experience after the install. Any desktop changes should be incremental and not transformational. Something as simple as an updated background tells them "they have arrived", a new menu with all the applications that were part of the install, and one or two desktop links that help educate end-users in their SIGINT journey.

Gievn the above, I produced a (Bash) installer script that is run after a fresh install of Raspberry Pi Full OS and configuration (raspi-config) has occured. The end-user gets the script through cloning a Github repo which includes componetns the installation script is dependent on.


What I love about virtual machines and containers is I can quickly iterate tests and fixes build/destroying/building again images. For the RPi it means having a bunch of formatted SDcards on hand with fresh Raspberry Pi OS installs already upgraded on hand. This tends to slow down the testing iteration.

Testing has shown that RPi4 performance may not be enough when investigating signals for special uses cases that require multiple SDR devices. In those scenarios it may be better to run SDR headless servers on RPi3 B or better platforms each with their own SDR device. The SDR GUI client on a laptop or its own platform.

This laid the groundwork in porting everything into Ubuntu 20.04 for use on more potent hardware since it is available for Raspberry Pi as well. Porting to Ubuntu 20.04 also meant I could iterate through testing faster by building/destroying virtual machines instead.

Early Releases

The discussion and work to date have culminated into the following projects.

  • SIGpi. SIGINT platform for RPi4
  • SIGdeb. SIGINT platform for Ubuntu 20.04 and Debian based systems

With the exception of the workshop materials, the other two repos are early days still implementing and testing lessons learned with the SIGdeb repo as of this writing the furthest along.


If your a beginner in SIGINT and your use case is education, experimentation with well known signals, and new to contests, then adding a bunch fo RF packages from your favorite distro should suffice. But as your experience grows and you develop an affinity to certain types of signals you will find that you need to be selective in the tools you choose and your system optimized for their performance. You will also gain an appreciation for building/using the proper antennas for various signals and perhaps once you've mastered a tool like SDRangel or SDR++ get into better understanding GNU Radio.

What about Windows? There are a range of low cost PC sticks comparable to RPi4 in "price-for-performance/features." Referencing the architecture, I plan to do some testing with a Windows PC stick running Windows 10 on an Intel Atom x5-Z8350 with 4GB RAM, HDMI, Bluetooth, dual-band Wi-Fi, and USB 3.0. Subject for a future article.


- Joe, NE2Z

Search For Something