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

Radiation and ground loss resistances in verticals

Over the years I've had a continuing interest in vertical antennas and the many small details of how they work.  Most of the time the minutia are not of great practical importance but for those of us interested in more than casual explanations they can be very interesting.  Here is a two part QEX article on just such a detail, how the radiation resistance (Rr) and the equivalent ground loss resistance (Rg) behave as the antenna dimensions and soil characteristics are varied:  Download QEX Jul-Aug 2015  Download QEX sept-oct 2015 .  As mentioned in a earlier post, I can't put all the supporting details in a single article, it would become unreadable so I've put the supporting material into a series of appendices which you can pick through if you're interested:

Download Rr Study Appendix A

Download Rr Study Appendix B v2

Download Rr Study Appendix C rev 1

Download Rr Study Appendix D

QEX article on elevated radial ground systems

Elevated grounds systems are frequently used in place of wires on or in the ground under a vertical.  This kind of ground system can work very well but when there are only a few radials in the elevated system it can be very sensitive to asymmetries in the radial fan, nearby conductors, etc.  Here is an article which was published in the March/April and May/June 2012 issues of QEX magazine which takes a much closer look at elevated ground systems than has been done in the past.  In the end the advice is very simple: use more radials!  This is the same advice I give for systems on or in the ground.  The standard 4-radial elevated system can work well but as the article shows it can also work not so well.  The article is primarily intended to show why I suggest that 10-12 elevated radials should be used if possible.  Download QEX Mar-Apr 2012 , 1MB, Download QEX May-Jun 2012, 2.4 MB.

Some comments on chokes for 160m GP verticals

Recently I was asked about air-core coaxial chokes to be used for feedline isolation on a 160m ground-plane vertical.  The following are some comments I made: Download 160m common mode choke 

ground systems for DXpeditions

I received an query from Bill, N7OU, regarding ground systems for multi-band verticals over saltwater.  My reply to him can be found at: Download Seawater ground article .

73, Rudy

Series of QEX articles on ground system experiments

Last year I posted results from a series of experiments on ground systems for vertical antennas.  That series of reports was converted with some modifications into a series of seven articles in QEX magazine.  The ARRL has kindly given me permission to post .pdf files of these seven articles for those who do not have access to QEX.  Here they are:

Download QEX ground systems part 1

Download QEX ground systems part 2

Download QEX ground systems part 3

Download QEX ground systems part 4

Download QEX ground systems part 5

Download QEX ground systems part 6

Download QEX ground systems part 7

A summary of these articles was published in QST for March 2010, pp. 30-33.

Download QST March 2010 Ground Systems 

In QEX for May/June 2010 letters to the editor I made the following comments.  "I think too many people are taking the QST article as gospel when it should be viewed only as an interesting set of expriments which shed some light on a few questions.  Even the QEX series, which is much more detailed, raises far more questons than it answers.  I was really hoping to encourage others to expand on my work (as I expanded on Sevick's) by showing how it might be done.  73, Rudy N6LF"

Are the lengths of radials related to the height of a vertical?

I first posted this note some weeks ago with information on the relation between vertical height and radial lengths.  However, that information was buried in one of the attachments.  To make it easier to find I've extracted the parts relevant to radial length versus height and they are now a separate and much smaller download:  Download Vertical height versus radial system .

A couple of weeks back I noticed a question on the TowerTalk reflector about making the radials on a vertical the same length as the height, i.e. use shorter radials on shorter antennas.  Something along these lines has been "conventional wisdom" for a long time but I'd never seen any real justification for it.  So I did a quick modeling study and up to a point it does seem to support this idea.  I wrote this up in:

Download radial_system_design_and_efficiency_in_hf_verticals.pdf