AF7NX Antenna and Radio Page

Slide Presentations

Variations on a Dipole 8/5/2017
An overview of HF antennas, how they work, how patterns change with height and length of radiator.  A good place to start when considering what to put up.

Practical Antenna Modeling 5/3/2019
With Examples of HF Wire Antennas and 4NEC2. How to define and edit models, run simulations, includes examples using variables, how to handle feed lines and grounds, do optimizations, etc.

Antenna Modeling

Many of the articles have links to the 4NEC2 model files for the antennas described.

A Simple Pull-up Mono-Band Verticle Dipole Antenna Design – and 4NEC2 Tutorial 4/21/2016
A simple antenna with good performance and low cost uses a resonant feed line choke and 75 ohm coax.

The Off-Center-Fed Dipole Antenna – Design 10/25/2015
A careful look at the off-center-fed dipole. This was my first antenna and this is how I thought about it.

Revisiting the GR5V and ZS6BKW Multi-band Antennas 4/9/2019
These symmetrically fed antennas use a length of to aid the match to coax for a multiband design. The parameters for the traditional designs, and one more, are rediscovered.

Optimizing Multi-band Wire Antennas 4/22/2018
A systematic approach is needed to find an optimum design for multiband wires. Here is how I do it using the tools in 4NEC2.

An Optimized 20 Meter Vertical Collinear Antenna 8/27/2017
This high-performance antenna offers robust mono-band performance if you have a tall tree.

Performance of a 20 Meter Vertical Collinear Antenna 7/7/2020
This antenna is built and tested with good results. Model runs look at expected performance on other bands as well.

Modeling Baluns and Transformers with NEC Codes 3/1/2020
Occasionally a modeling task requires more realistic handling of impedance transformations. We explore how to do this with NEC elements. A balanced inverting splitter suitable for driving phased pairs of antennas is introduced.

Modeling the J-Pole 10/27/2020
Wonder how the J-pole really works? Me too, so I modeled it. Optimizing two parameters gives perfect match, but beware of feed line currents.

Using NEC2 for Antenna Feed Design 9/22/2015
My first antenna didn’t work at all. A little study with the modeling program reveals why and suggests a solution.

Self Resonant Coil Calculator Spread Sheet Use this calculator to aid in designing resonant traps for your antennas.

Antenna Construction Projects

A 30 Meter Bamboo Pull-up Hex Beam 9/13/2020
This multi-band hex beam becomes my best antenna for the upper bands.

A Pull-up Bamboo Moxon Antenna for 20m 6/18/2020
A Moxon antenna with bamboo spreaders is my first “beam” antenna that I pulled up into the branches of my tall trees.

Measuring & Testing Things

Mapping the Radiation Pattern of a Fixed Long Wire Antenna 6/14/2016
Comparing the strength of digital signals between pairs of antennas allows quantitative determination of the radiation pattern.

Fast Avalanche Transistor Pulser 12/18/16 This is a handy one-transistor pulse generator that you can use to measure the electrical length of cables.

Comparing RTL-SDR and IC-751A Receivers Using JT65 & JT9 Signals 2/6/2016
The SNR report that comes along with each decode from the WSJT-X modes provides a quantitative way to compare reception.

Coax, Connections, Calculations, Coils and CATV Cable 6/29/2019 Some discussion about coax and why I use a lot of the 75 ohm stuff.

Modifying Radios

Modifications to the IC-751A for the Digital Modes 3/6/2017
The IC-751A remains a very good radio to the present day, but a few updates and modifications bring it into the new century.

Modifications to the IC-745 for the Digital Modes 7/29/2017
The IC-745 does not have CAT capability, but a few small mods can help you get more out of this 40 year old radio with its good receiver.

RTL-SDR Pan-adapter using HDSDR with the IC-751A 1/11/2016
Having a good “click tune” pan-adapter for the old IC-751A is a tremendous operation aid. An inexpensive RTL-SDR dongle, with a signal from the 751A’s first IF stage, works very well.

Using the RTL-SDR Pan-adapter 9/16/2016
There are quite a few things you can do with a functional pan-adapter. We go over a few of them.


Radio Daze 9/4/15
A latecomer to ham radio – this is the beginning.

Ham Lingo 10/11/2015
Radio operators have their idiosyncratic vocabulary.