Antennas By N6LF

Antennas

The design of antennas is a rich field for investigation and innovation.  Even after over a hundred years of work in the field we can still gain new insights and create ideas with immediate practical applications.  Since I was first licensed over 50 years ago antennas have been my passion.  Over the years I have published articles on antennas and continue to study and write about them.  The purpose of this blog is to make this work available to those who might be interested.

In both amateur and commercial installations the transmitting and receiving equipment has become quite standardized and we rarely design and build our own equipment. The exception to that for me has been my participation in the ARRL 600m experiments where standard ham gear will not transmit. I've had to go back building some gear for this experiment.   Antennas however, have much greater variety and provide a means for greatly improving station performance at modest cost.  The "home brew" antenna is very much alive and well among amateurs.  With a bit of knowledge and some hard work, the amateur can usually do as good or better than standard commercially available antennas and frequently at much lower cost. Many years ago Tom Erdmann, W7DND,(SK) told me that if I had $100, I should spend the first $90 on the antenna, the next $9 for the receiver and the final $1 on the transmitter. Of course prices have gone up bit since then but those proportions are still sound advice. I can honestly say I have a lot more money invested in my antennas than in my station equipment.

This web site provides direct access to my articles and a venue for new work which will be added from time to time as I do more. Except for articles published elsewhere, much of what I'll be posting will be pretty informal and subject to change as I learn more. The work reported here is a mix of analytic (calculations), NEC modeling and field experiments on actual antennas. Each of these has it's place but the best picture will emerge when all three techniques are combined.

If you're interested in verticals and ground systems take a look at the posts on ground system design and elevated radial verticals.  For ideas on simple gain antennas for the low bands there are a wealth of ideas in the posts on single support low-band antennas and half-square antennas.  For some practical insight on what to use for conductors in wire antennas take a look at the post on conductors for HF wire antennas.  There are also articles on tower-antenna interactions and some information on my participation in the 600m experimental group. Most of the files for downloading are in .pdf format.  The file sizes and original publication are noted after each.

Please note that I try to close each post to comments. Once in a while I forget to push the right button and the post may be open. However, I assume I'm flawless and always have the posts closed and do not look for comments. Even if by accident I leave the post open for comments don't waste you time with them.

630 meter antennas

At the last World Administrative conference a new amateur band on 630m (472-479 kHz) was authorized.  Hopefully in the near future our respective FCC's will authorize amateur operation on this new band. 

Other than some experimental licenses amateurs haven't been allowed below 160m for over 100 years so few amateurs have any experience with MF antennas.  I've been part of the ARRL sponsored 600m experimental group for several years and over that time have built several antennas for 600 and 630m.  I feel that if this band is to "take off" those of us who have been operating on MF need to share our experience.  With that in mind I have begun a multi-part series of articles on antennas for 630m.  Parts 1 and 2 are now available: Download 600m verticals part 1 and Download 600m verticals part 2.  These two parts are mostly a NEC modeling study which is fine but we still need experimental confirmation.  Part 3 of the series will be a description of actual antennas which have been built and tested.  I am currently engaged in building and testing several antennas for 630m.  The results should be available late this fall and will be summarized in part 3 of the series.

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.

Short antennas for 160m and 600m

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.   Download Short 160m verticals

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 

comments on elevated radials

I recently sent a note to the QST technical correspondence editor at the ARRL concerning the effect of radial system asymmetries in elevated radial systems.  You can read this letter at: Download December 2010 letter to QST technical correspondence .  This note emphasizes some of the problems with elevated systems and some possible misinterpretation of my March 2010 QST article.

After sending this note I realized that there was a lot more to say on the subject.  So I'm in the process of writing a very extensive article on elevated wire ground systems and the effects and cures for asymmetries.  That is however, still couple of months away from being finished.  I will post it here when it's done.

73, Rudy N6LF

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

Relation between vertical height and radial length

In one of my earlier posts I had some information on the relationship between vertical height and optimum radial lengths.  That information was buried in a larger document discussing several other items an was not that easy to find, so I've pulled that discussion out as a separate download: Download Vertical height versus radial system .  What it shows is that there is a case to be made that, for a given total length of wire, more numerous shorter radials can be helpful on short verticals.  At least up to point.

QEX letter to the editor

I recently sent the attached letter to the editor of QEX.  It may answer some questions and correct some incorrect figure captions: Download QEX letter to the editor 1 

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. 

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"

New 600m station at WD2XSH/20

Last August the FCC renewed and expanded the license for the 600m experimental group so for this new season I have rebuilt my antenna and completely redone the station.  The following is a description of the current antenna and station at N6LF, WD2XZSH/20: Download 600 meter station at WD2XSH .  The file is about 300 kB.