Welcome to the home of AB7E
I have lots of interests, many of which involve one aspect or another of amateur radio, especially antennas. Listed in no particular order below are several topics, most of which include links to descriptive videos on YouTube. All of the applications listed below are free to use, and my YouTube channel is not monetized.
o Using a pair of QFH antennas for making amateur radio satellite contacts
o Crude animation of a spatial interference pattern created by multipath reception
o Text-to-CW Player with Farnsworth timing
o Does an antenna tuner actually tune the antenna? I convince myself I was wrong.
o Dielectric Loading of a VHF dipole
o 3D Printing an L-Band Helical Antenna
I created a browser application with the intent of measuring and plotting the arrival angle of incoming signals using two antennas and two phase locked receivers in diversity mode The application itself works fine and makes quite accurate phase measurements, but after a lot of trials I unfortunately realized that any multipath interference completely invalidates the measurement. The application is still potentially useful for phase measurements, just not for measuring arrival angle since as a minimum we get ground reflections that create the three dimensional interference pattern that distorts the measured phase ... and is of course a significant cause of signal fading. The application can be found at https://www.ab7e.com/ArrivalAngle.html and an explanatory video can be found on YouTube at https://youtu.be/MxRaYSRMPE4.
Even though I was unable to accurately measure the arrival angle of an incoming signal, I was able to accurately measure the phase difference it created for the signal incident upon two antennas spaced some distance apart. I realized I could use that phase difference to isolate one signal out of a bunch of them occupying the same frequency as long as the signal I wanted had a phase difference that was different than the others ... i.e, as long as it came from a different direction, even if I couldn't tell which direction that was. I created another browser based application called Spatial Signal Filter to do that and it can be found at https://www.ab7e.com/SpatialSignalFilter.html. This application does not use simple sum/difference-with-a-phase shift processing ... it uses sophisticated digital MVDR beam forming techniques to get strong peaks and nulls. An explanatory video can be found at https://youtu.be/DfEjzlANWAw. This one really works as intended, and if you don't watch any other part of the video check out the portion that starts at 29:15 showing how local noise can be virtually eliminated since a point source of noise is just another signal.
Nulling a source of local noise worked so well using the Spatial Signal Filter browser application described above that I decided to create a more streamline version that only nulled local noise. By narrowing the focus on noise reduction I was able to greatly simplify the user interface and even automate some of the setup parameters that were required in the other application. You can access this application at https://www.ab7e.com/NoiseNuller.html. A useful test file can be downloaded from xxxxxxxxxx and a descriptive YouTube video is forthcoming.
Making at least one satellite contact was on my amateur radio bucket list, but I didn't want to spend money on a yagi antennas on an AZ/EL rotator. I had already had good results with a QFH antenna for receiving the NOAA and Meteor-2 VHF meteorological image transmissions so I decided to build a pair of them for the amateur radio satellites, with the goal being a repeatable design so others could make their own as well. They worked quite well, and you can view how I made them at (VHF) https://youtu.be/EgY1MHaQ_us and (UHF) https://youtu.be/AMrPPIv-bcs
Spatial Interference Pattern Animation
As part of my attempts to measure the arrival angle of incoming signals, I tried to create something that illustrated how complex the reception pattern for signals is in the presence of relatively basic multipath effects. I used ChatGPT to create the animation you can find at https://www.ab7e.com/InterferencePattern.html. The lighter shaded areas represent peaks and the darker areas represent nulls, but the key thing is that the same kind of pattern holds for both amplitude and phase. The two dark lines represent a pair of dipoles for diversity reception with the standing waves wafting over them as the arrival angles change, but each individual dipole would see similar peaks and valleys for amplitude even if only one of them were there.
Here is a basic CW player that allows you to change speed, tone, and Farnsworth spacing. It's one of my earlier software projects and it is extremely basic, but it works. It's a browser based application and you can access it at https://www.ab7e.com/CW-Player.html.
I have always thought that the argument whether an antenna tuner actually tunes the antenna was pretty silly, but at one point recently I got sucked into the debate and managed to choose the wrong side of it. Only afterwards did I take the trouble to go beyond my intuitive thinking and actually model the situation. I still think the argument is silly since everyone knows what we mean when we use the term, and there are LOTS of other ham radio terms in everyday use that are just as misleading, if not more so. But here is what I found from the modeling. https://youtu.be/o2V72EP6LCM
Dielectric
Loading of a 100 MHz Dipole
For reasons I don't fully remember, I did a comparison of modeled versus experimental results for the dielectrically loading of a 100 MHz dipole and eventually I compared that to capacitive loading. I think the results are interesting, and I posted a video of them at https://youtu.be/YJTJcWPkVdA
3D
Printing an L-Band Helical Antenna
Helical antennas have lots of advantages, among them being very nice gain per unit volume and a quite forgiving usable bandwdith. This video shows how I 3D printed the supporting structure for a helical antenna suitable for receiving marine and aviation broadcasts from the INMARSAT series of geostationary satellites. They are pretty easy to build, and if you don't have a 3D printer maybe your friend has one. Or you might be able to convince the STEM class at your local high school to print the pieces for you if you give them a quick lecture on it. Anyway, here's the video https://youtu.be/LIikJAfI-m4 that includes the link to where you can get the .STL files for the pieces.
