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 Chapter 1  LF-MF overview

Download Chapter 2  Simple verticals w/o top-loading

Download Chapter 3   Top-loaded verticals

Download Chapter 4   Inductive loading and multiple tuning

Download Chapter 5  Ground systems

 Download Chapter 6  tuning inductor design

 

 

Comments on Ed Laport's book

Some years ago I was asked if Ed Laport's book, Radio Antenna Engineering, gave reasonably accurate estimates for radiation resistance and current distribution for short verticals.  I did a short modeling study with NEC to see how the results compared with Laport.  Recently Neil Klagge, W0YSE, asked me if I still had these notes which had not been put up on this web page.  The following are my comments on the comparison between Laport and NEC: Download Comments on Laport .

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 B

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

630m Antenna Support Poles at N6LF

I have recently moved to a new QTH with several acres of clear farmland but no trees for antenna supports.  So I had to come up with a means to support a large 630m umbrella vertical and other experiments with wire antennas.  Here's what I did: Download Saginaw antenna support poles . 

Short antennas for 160m and 600m

Download QEX short verticals for 160m Often it's not possible to erect a full 1/4-wave vertical, especially on 160m or even more so at 600m.  It appears that we will be getting a 600m band 472-479 kHz where the wavelengths is about 2000'.  That makes the antennas a serious challenge.  I've written the following article on verticals with heights between 0.05 and 0.125 wavelengths.  The modeling was done at 1.83 MHz but most of the discussion uses dimensions in wavelengths and is applicable at any frequency including 600m.  The discussion illustrates how critical the height of a vertical is and the absolute need to use some form of capactive top-loading if any reasonable efficiency is to be achieved.  The article focuses on the mult-wire umbrella type of top-loading but also discusses the critical issues relating to ground systems and conductor loss.  As I always try to do, the article includes some experimental confirmation of the NEC modeling results.   

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

 

Short antennas and ground systems

In June I gave a four hour antenna workshop at the Seapac hamfest in Seaside, OR.  There were 200 plus slides and the file was too large (21 MB) to post on this blog but I've gone through and pulled out those parts which apply to short antennas and ground systems.  This may be of some help to those working with the 600 m experimental group and on 80/160 m also. 

Download seaside_2007_antenna_workshop_mod_3.pdf .  This is about a 1.4 MB file.