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Friday, April 06, 2018

Rare Aircraft Sightings: What have you "heard" lately?

Its been a busy past month and I have not had much time to tinker or play "ham radio" aside from  sporadic DMR contacts or discussion participation lately on a few of my favorite scheduled nets.

Today, I turned back on the primary ADS-B passive aircraft radar for 24/7 operation here in the Hudson Valley that feeds into and was nice to see something I have not seen before.  A new rare aircraft!

This is definitely one of my motivations behind a number of new articles for the next two months that are much more "ham radio" related focused on software defined radio, antennas, and computing.

A rare Pokemon called the Boeing OC-135-B

According to Wikipedia "The OC-135B Open Skies United States Air Force observation aircraft supports the Treaty on Open Skies.[1] The aircraft, a modified WC-135B, flies unarmed observation flights over participating parties of the treaty. 

Three OC-135B aircraft were modified by the Aeronautical Systems Center's 4950th Test Wing at Wright-Patterson Air Force Base in Ohio. The first operationally-capable OC-135B was assigned to the 24th Reconnaissance Squadron at Offutt AFB in October 1993. It is now fitted with a basic set of navigational and sensor equipment, and was placed in inviolate storage at the Aerospace Maintenance and Regeneration Center at Davis-Monthan Air Force Basenear TucsonArizona in 1997. 

Two fully operational OC-135B aircraft were delivered in 1996 with the full complement of treaty-allowed sensors, which includes an infrared line scanner, synthetic aperture radar and video scanning sensors."

How did I come across this?

More about the primary location technology used in aircraft today can be found here and one never knows what may be flying in your area, so when I saw the OC-135B appear in the real time air traffic window, I had to look into what the "OC" means.  The program that the SDR based receiver feeds into creates a database of all tracked aircraft that provides some basic analytics capability to those who have access to it. I have seen many other variants of this aircraft such as the KC series refueling aircraft, LC series used for arctic support and the EC series for electronic early warning to name just a few. The OC series was new to me and pretty rare indeed.

What does ADS-B have to do with "ham radio"?

Pretty much not a single thing. But, amateur radio is a pretty wide hobby and there is a lot of convergence between topics that the modern ham may have interest in related to ADS-B. Some of these are:

Antenna Experimentation - ADS-B operates at 1090MHz, so antennas can be pretty small. A quarter wave antenna for 1090MHz in only 6.5 centimeters tall!  For comparison, here are some common sizes for some popular ham radio bands of operation in centimeters for a reason.

If you want to try designing antennas, there are pretty much always aircraft flying overhead, so you have ready made targets to receive and see how well your 1090MHz antenna is working. Creating small directional antennas for ADS-B will often follow the same design principles and scale for other frequencies.   If you mess up an antenna for 1090MHz, its not a huge loss in material.

Linux anyone?

Setting up a Raspberry Pi based ADS-B receiver with a simple SDR as its receiver is well documented and is a good learning environment for basic Linux related operating system terminology and ham radio applications for remote receiver experimentation.

Software Defined Radio

Modern design uses software defined radio architecture where some of the more fancy features are simply implemented in code/software compared to hardware.  Experimentation in adding new features, user interfaces and more are more easy in certain circumstances.


In ham radio, most of us chase rare or distant stations. Much of that exists within what some call "planespotting" and is a natural convergence of ham radio and aviation.  If anyone has an interest in the combination of these two wide hobbies, perhaps you may be interested in joining HVDN.

List of member benefits can be found here and where you may find people interested in related topics can be found on the activity page here.

If you are not interested in joining HVDN (Free first year membership for amateur radio operators), there is also a donation option to just gain access to the HVDN ADS-B system with more info here

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