Welcome to the N3OX (formerly N3UMH) Radio Pages.

Updates and Other Noise

October 5, 2011

More animations, which I'll just link:

• 20m Moxon Rectangle at 40 feet
• 5el 20m Monobander at 100 feet

September 16, 2011

I was working on some visualizations and made this animation of the oscillating vertical electric field E_z for the new short vertical antenna. I don't usually post big images on the front page, and I hope the animated GIF doesn't choke anyone who still has to suffer with a slow connection. But I figured I might as well put something interesting here in case I go a year or two without updating the "Updates."

Animated 7MHz electric field E_z for the new vertical out to 80ft. from the antenna and 30ft. high.

EZNEC v. 5.0+ was used to calculate the complex amplitude (amplitude and phase) for the electric field in six inch steps from near zero to eighty feet horizontally and near zero to thirty feet vertically. The antenna is in the lower left, centered on the edge of the plot; you can see one of the sloping sides of the pyramid capacitance hat, and a little stronger field near the coil. The near field data was exported and GNU Octave was used to calculate the field as a function of time by multiplying the complex amplitude by e^-jωt (0≤ωt≤2π), taking the real part, and plotting. The color scale here is nonlinearly compressed like C = sign(E_z) * |E_z|^1/5 to give more visual detail. Thanks to Karol Krizka for good information about how to do the plotting efficiently. The series of .png files created using Octave was titled, cropped, and converted to animated .gif using virtualdub.

You may notice a small anomaly in the field a little more than a quarter of the way from left to right. That's the pinger whip that I didn't take out of the model. It is just an unloaded six foot wire so it doesn't perturb things much, but with the colorscale compression it's visible.

I find this sort of field animation to be instructive. You can see the reactive near field contributions that are basically bound to the antenna structure, and you can see how they transition into radiation leaving the antenna a bit further away. I also plotted the azimuthal magnetic field H_φ (into the screen in this cross section), and I more recently did a wider view of a quarter wavelength vertical. I'll eventually build a collection of animations like this for interesting antennas and I'll also work up an explicit tutorial on how to make these from EZNEC near field results. It's quick and easy once you get the hang of it.

September 11, 2011

I just finished a big page on a three meter (10ft.) tall 40m, 30m, and 20m vertical with continuous, remotely controlled tuning using a flexible capacitance hat and rope. As three-meter objects go it's not quite as impressive as my three meter Ph.D. Experiment, but it's more practical for home build. This article gives construction details but it is also a more general article about small antennas. In my opinion, too much energy is expended on making novel-looking things that are hard to understand and don't work very well. This article is intended to be a counterpoint to that and includes a lot of information on how I modeled and measured the characteristics of this compact HF antenna. I characterized it thoroughly for the 40m band, and it should work even better on 20m and 30m.

July 30, 2009

Yeah, so just like 94% of bloggish ventures, this bit goes a long time between updates. But I've got a new project up. Check out the Stepper Tuning Switch. At the moment, it works either in standalone mode or with Ham Radio Deluxe and the computer's parallel port to change bands on my sixty foot vertical. It would also support auto band-switching with DXLab Commander or any other program that will output a bit pattern on the parallel port based on the frequency read from the radio. Soon, I plan to modify it to support acquisition of frequency info over a USB serial connection with the help of N8LP's LP-StepLink software, removing the need for the parallel port at all.

About Me

I've held an amateur license since February, 1995, and upgraded to Amateur Extra in 1999. I got the vanity call N3OX in January, 2006. I've been more or less active the whole time I've been a ham. I've been somewhat more active lately now that I'm out of apartment status and into a house where I am permitted some antennas, but I'm leaving all the apartment-specific information up for the cliff-dwellers out there.

I recently finished my Ph.D. in Physics and am working as a post-doctoral researcher at University of Maryland, College Park.

Thanks for visiting, hope you find the pages useful and interesting.