A Growing Concern
Hams occasionally like to take their toys to remote locations and play radio from the top of a mountain or at a pleasant picnic in a park. This gives us a chance to set up equipment in odd places, erect antennas and generally practice for emergency communications contingencies. To encourage this practice, the ARRL (American [...]
Top Band, as 160 meters is called, presents a a challenge because the long wavelength leads to large antennas. One can always play tricks with loading to be able to use a physically shorter length of wire. There are many articles on compact 160 m antennas, but this is not one of them. Rather, I'm [...]
A lowly coil of wire can be surprisingly difficult to understand and model correctly. I use coils of wire or coils of coax cable as trap inductors for various antenna designs that I have built. In the low frequency limit, the traditional inductance calculations work okay and can give you a pretty good estimate of [...]
When you first meet the J-Pole, you are forgiven if you don't quite grok how it is supposed to work. What is that 'J' for anyhow? When I have questions like this, I get out the 4NEC2 modeling program, and see what it says. Let's start out with the basic model -- the J consisting [...]
The bamboo Moxon I built for the 20 meter band earlier this summer convinced me of the power of compact two element antennas. When I was showing the Moxon to a friend, he pointed up to a nearby tree and said "There's the place to pull from," pointing to the crotch of a tall branching [...]
A couple of years ago I designed this antenna which had the good property of substantial low elevation gain and the model generated consistent and predictable 4NEC2 results. The wire that it would replace was already "pretty good" so it's taken two years to decide to build it. But I always had the feeling that [...]
As much as I love all of the wires up in my trees, I've come to realize that a little real gain and directivity would be nice. However, my trees are really in the way for a a typical tower and a beam antenna, so I am left to consider what resources I have and [...]
Antenna modelers are often left with a question about how to handle baluns and impedance matching devices when using the NEC codes. Often we just ignore all of the feed nonsense and place the source right on the antenna wire to find the pattern, drive impedance, etc. You can also just reflect the driving impedance [...]
I've been using a spool of RG-6 CATV cable of dubious quality for quite a while as my go-to source of antenna feed line because I happened to have the spool in my junk collection. Using the 75 Ω cable got me thinking about why we care what impedance the cable is and how matching [...]
Here are the slides for a presentation given to The Valley Radio Club on May 3, 2019. The hope is that the slides contain enough detail that the reader could easily build and run the examples in 4NEC2. Practical Antenna Modeling Power Point Presentation Practical Antenna Modeling PDF format slides Using the NEC Codes With Examples [...]
