Practical Antenna Models (Volume I)
Keith Rawlings G4MIU recommends another antenna book for your radio library.
IPW,
This excellent book covered modelling techniques for use with the software package EZNEC from Roy Lewallen W7EL and also the additional package of AutoEZ (Automated use of EZNEC) from Dan AC6LA.
Needless to say, when I became aware of a new book from Marcel entitled Practical Antenna Models Volume One I was very interested to see what was within.
Description
This new book is of some 216 pages and comes in a slightly smaller format than the previous publication.
Its content is taken from the series of columns that Marcel wrote for the AntenneX online antenna magazine between 2009 and 2017 and this volume concentrates on the various forms of the dipole family.
As well as the hard copy, owners can download a pdf version of the complete book, which has colour illustrations, and this is ideal for those wishing to read the book on something like a phone or tablet.
Also, the many associated files for each section of the book are also downloadable. These consist of pre-built EZNEC models, Excel spreadsheets, Auto EZ files and neat little .exe files called Wizards, which are animated diagrams demonstrating how parameters can change as designs are altered. These files are accessed from Marcel’s website.
Practical Antenna Models Volume One is effectively written in two parts. The first part, Chapter One, is termed Antenna Fundamentals and takes the reader through the very basics of antenna theory in a series of ‘Episodes’.
With generous use of use of diagrams, the reader is introduced to subjects such as the Electric and Magnetic fields and also the Induction and Radiation fields associated with every antenna.
Basic calculations are included and, naturally, subjects such as Impedance, Resistance and SWR are described in detail. Also included is a detailed discussion on the decibel along with a very useful ‘quick reference’ decibel/power ratio chart.
Chapter Two (the second part) gets to grips with the dipole in its many forms. From the basic horizontal dipole through versions such as inverted, OCF (Off Centre
Fed), folded, multiple, doublet, bent dipoles, making a dipole fit into available space and more, just about every configuration is covered.
Based on the use of EZNEC and AutoEZ, with diagrams, charts, and text the reader is taken through a detailed design stage and analysis of the results.
I mentioned Wizards earlier and as an example, in the case of the bent dipole, a wizard has been produced of an 80m dipole at 15m/50ft, which animates the predicted SWR, Elevation and Azimuth Polar plots as the elements position is changed, Fig. 1.
Many readers will be interested in the indepth study of the OCF and also the doublet, with both the G5RV and ZS6BKW variants compared.
Conclusions
I thought that like Advanced Antenna Modelling the book was detailed, well laid out and informative.
Like the previous book, there is a heavy reliance on diagrams, and these go a long way towards making the descriptions understandable.
To be honest I found that even without taking the modelling aspects into consideration, the book alone is a wealth of information because the text and diagrams give a good insight into what can be expected from the variations of the dipole family. If you couple this with the extras that go with the book, such as pre-built models, animations, spreadsheets and so on, then the book represents excellent value and, I think, deserves a place on any antenna experimenter’s bookshelf.
Availability
The book is available from Amazon and at the time of writing is priced at £17.99 for the paperback edition and £7.62 for the Kindle Edition: https://tinyurl.com/y5yvuqde
It is also available from the author: https://tinyurl.com/y4tczafw
References
EZNEC: www.eznec.com/index.shtml AutoEZ: https://ac6la.com/autoez.html
This month I have a few more operating tips that may improve your FT8 success. Let’s start with filtering and signal processing. While many rigs have sophisticated noise reduction, noise blankers and filters to tailor the audio response, it’s best to try to avoid these when you start FT8. This is because they have the potential to reduce the decodability of data signals. The ideal audio signal, to begin with, is a clean, ‘brick wall’ filtered, audio spectrum from around 200Hz to 3kHz. Selecting the Data output in older rigs and selecting Data Modes USB in a modern rig is often a good start point. I suggest you check the operating manual for your rig, because some models reduce the receive bandwidth when selecting data modes and you’ll need to modify that. On the transmit side, you need to make sure the speech processor is not being applied to your signal.
While the settings I’ve just described make a good start point, you may have specific local problems that might benefit from some filtering or noise reduction. That’s fine, and you should go ahead and experiment. It’s just important that you start with a clean setup and then make considered adjustments from that reference.
Those with SDR-based rigs can often make use of their excellent customisable filtering to overcome reception problems. For example, if you have a powerful local station that’s swamping part of the band you may be able to improve your result by pulling the filter side in to exclude that station.
Next month I’ll run through Fox and Hounds operation plus how to make the most of FT4.
Pi News
I have two significant Raspberry Pi items this month. First up is the all new Pi 400, which is an integrated keyboard and Pi 4 (4GB) computer. You only need to add a display, mouse and a microSD card for the operating system, Fig. 1. This makes for a remarkably compact and tidy computer installation. As a bonus, the processing power has been given a boost through a higher clock speed. To build the Pi into the profile of a standard keyboard, the Pi team have developed an entirely new PCB and used an updated Pi 4 processor. Those of you that have been using a Pi-4 will be aware that it gets quite hot when it’s working hard or housed in a case. As a result, it is common practice to add a fan or large heatsink to stop the processor throttling back. The Pi team have solved this issue by including a large metal heatsink that runs the full width of the keyboard. The heatsink is so effective that they have been able to boost the standard processor speed to 1.8GHz and there is still scope for further overclocking. I’ve been using a Pi 400 for a few weeks now and I can confirm that the heatsink does a great job.
Another helpful goodie in the Pi 400 is the provision of a soft power button. This uses the Function + F10 key combination. When you press and hold these two keys for more than two seconds, the Pi will gracefully close down. I’ve checked my Pi 400 and it appears to be a real power-down because all voltages are removed from the GPIO port, including the 3.3V and 5V supply lines, thus leaving the GPIO safe to work on. To power-up, a short press of the same two buttons does the job. The new Pi 400 would make a great radio computer for the shack or to take on holiday. It is also ideal as a main computer for students that are studying at home and don’t have access to an expensive Windows laptop or PC. The price is just £67 for the Pi 400 or £94 for the kit that contains the Pi 400, mouse, preloaded microSD card, power supply and a copy of the Pi Beginner’s Guide.
Another important Pi-4 update, that slipped through the news, was the release of the much anticipated ‘boot from USB’ firmware. While the use of a microSD card for the operating system is perfect for experimenters, those using the Pi as a general computer or as a radio terminal have wanted the speed and reliability of a hard drive for the operating system. While there have been some workarounds, we have been waiting for the Pi Foundation to release the official USB boot firmware into the main distribution. That has now happened, and the new firmware has been released for both the Pi 4 and 400. You should note, though, that the Pi3B already supported boot from USB. You can update your existing system for USB boot by entering the following in a terminal session: sudo apt update && sudo dist-update -y As SSDs (Solid State Drives) are currently so cheap, I suggest you use a USB3 SSD to replace the SD card. I’ve recently been using