Antennas By N6LF

LF-MF antenna notes

 

The present draft of these notes, while far from perfect, may be helpful to many amateurs.  For that reason I've posted them in their present form with the understanding they will be revised, probably several times, in the coming years. 

By all means let me know if I've forgotten something useful and, even more importantly, if I've made a mistake!  A lot of other peoples work has been included but the mistakes are all mine!

GL and 73, Rudy N6LF, WD2XSH/20

LF-MF notes: 

Download Preface-Table of contents

Download Appendix 4- ground systems as reflectors

Download Chapter 1

Download Chapter 2

Download Chapter 3

Download Chapter 4

Download Chapter 5

Download Chapter 6

 

Universal curves for soil conductivity and permittivity

 

40 years ago Longmire and Smith suggested that the soil characteristics, conductivity and permittivity, which vary greatly with frequency, can be fitted to universal graphs.  The idea is if you know the values at one frequency you can predict the values at a different frequency.  I've had their report for many years but only recently took the time to carefully evaluate the idea.  Attached is a scan of the original report, Download Longmire and Smith scan, an EXCEL spreadsheet containing their equations compared to independent measurements, Download Longmire and Smith graphs   , and my comments on their idea,  Download Comments on Longmire and Smith .  The idea has some merit but you should decide for yourselves!

Determination of Soil Characteristics Using a Low Dipole

For many years I have used soil probes and a network analyzer to measure my soil characteristics.  It is also possible to determine soil properties using a low dipole.  While this idea has been around for years it turns out to be a bit trickier than advertised.  However, with a little care it can work just fine as I showed in my Nov/Dec 2016 QEX article: Download Soil characteristics QEX .

QEX Appendices

I will have an article on radiation resistance and ground loss resistance for verticals in the July/August and September/October 2015 issues of QEX.  For anyone who wants more detailed background information for the article there are four appendices:

Download QEX Appendix A

Download QEX Appendix C

Download QEX Appendix D

GL and 73, Rudy N6LF

Soil parameter measurements at HF

This is an update of an earlier post on the measurement of soil electrical characteristics. These are measurements at my new QTH which extend down to 100 kHz. Download Soil Measurements At N6LF

One of the basic inputs to antenna modeling programs are the ground conductivity and relative dielectric constant.  Frequently however, modelers have no real idea what their particular ground characteristics are.  It is possible to make useful soil parameter measurements at HF which are sufficiently accurate for modeling purposes.  The nice thing is that these measurements are not very difficult requiring only a very simple mechanical assembly, say a rod and a piece of screen, and an impedance bridge like an MFJ259 or similar units. The following file has a detailed discussion of this kind of measurement: ground parameter measurements, 1 MB .  I recently gave a talk at the Dayton Hamvention. Here are the slides: Dayton 2005 slides, 220 kB.

Sometimes it is handy to know the skin depth and wavelength in a particular soil.  Skin depth and wavelength in soil, 70 kB.