November 05, 2009 in 600m experiment | Permalink | Comments (0)
Earlier this year I posted a description of a simple clamp-on RF current transformer. Since that time I have updated the design with a much larger ID and the core held in a spring-clamp that allows easy on/off in the field. The following is an update of the earlier post: Download Current transformer 2 . File size = 460 kB.
June 15, 2009 in Vertical array design ideas | Permalink | Comments (0)
Earlier I posted a report on the work done last October on the 80m 4-square at NK7U. After that work there were still many unanswered questions so I and W2VJN went back to NK7U at the end of May to run more tests. The following is report on that trip.Download Report on 29-30 May 09 measurements . size = 175 kB.
This series of tests also generate more questions than answers but I think it may be interesting to those who might have an array near a tower.
June 15, 2009 in Vertical array design ideas | Permalink | Comments (0)
It's well known that a nearby tower can affect the performance of a vertical array but I haven't seen any articles which give an actual example. Last fall I made such measurements on an 80m 4-square which clearly show just how bad the interaction can be. Attached is a summary of those measurements: Download NK7U array tests 7 Oct 08 . This file is about 73 kB.
March 15, 2009 in Vertical array design ideas | Permalink
Interaction between a vertical and a nearby tower can be a very real concern. I have done a short NEC modeling study on the subject which sheds some light on the subject. It's far from complete and I will no doubt expand it in the future but I have received a number of questions on the subject so here is the study in its present form. Download Tower coupling study The file is approximately 250 kB.
March 12, 2009 in Vertical array design ideas | Permalink
I mentioned on the towertalk reflector that I had been trying to make accurate measurements of resonance in grounded towers with large antennas systems on them. A number of people asked for the details. So here they are: Download Some notes on measuring tower resonances . These are only preliminary notes which give the general idea of what I'm about. In due course they will be updated.
73, Rudy N6LF
February 12, 2009 in Vertical array design ideas | Permalink
I just realized that my weblog was open for comments. I thought I had it closed so I have not been reading any of your comments. Please send comments to n6lf@arrl.net
October 15, 2008 | Permalink
On Friday October 17th I'll be giving a talk at Pacificon 2008 in San Ramon, CA. The talk is just an overview of my recent ground system experiments. Here is a copy of the presentation for those who attended or have an interest:
October 15, 2008 in Design of radial ground systems | Permalink | Comments (0)
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
While I was at it I took a look at the variation in radiation resistance and ground loss resistance as the radial system and/or ground characteritics were varied:
Download radiation_resistance_variation_with_radial_system_design.pdf
This one is just for fun, I don't think it has much practical application but it may help in understanding how verticals work.
October 04, 2008 in Design of radial ground systems | Permalink | Comments (0)
Over the years I have talked a lot about ground systems for HF verticals. Most of what I have said comes from modeling and calculations of my own and experimental work of others most of which was for LF or MF broadcast applications. Other than the QST articles by Sevick many years ago and the CQ articles by Arch Doty, there has been little experimental work reported in amateur literature which could be used to judge the validity of NEC modeling and whether it can actually tell us something that's real for HF verticals. Beginning about a year ago I set up a test range in my pasture and began a series of careful experiments on HF verticals with various ground systems including some with elevated radials. Two results stand out. First the NEC prediction that a few elevated radials can be as efficient as a large number of ground radials seems to be correct at least at my site with the test antennas I used. See experiment 3.
The second interesting item is that using only a few long radials can result in much higher ground losses than the same radials shortened. In the past I have often said that a few long radials might be a waste of copper but were harmless. Not so! Experiments 4 and 5 are related to this.
I also ran some experiments with the 40m+ version of the SteppIR vertical. My particular interest was developing a ground system that was effective from 40m through 10m. That work is reported in experiment 6. Some obvious ground systems don't work all that well.
I have written up my experiments in a series of reports. Nothing formal just a review of the experiment, the results and some comments.
Download antenna_ground_system_experiment_1.pdf
Download antenna_ground_system_experiment_2.pdf
Download antenna_ground_system_experiment_3.pdf
Download antenna_ground_system_experiment_4.pdf
Download antenna_ground_system_experiment_5.pdf
Download antenna_ground_system_experiment_6.pdf
Separate from the reports I have written up a detailed description of the test arrangments and instrumentation: Download antenna_ground_system_test_setup.pdf
I suggest you read the test setup description first so you can follow the experiment reports which do not contain all the test setup details.
On Saturday, August first, I gave a talk to the NW DX convention on this work. The following is the PowerPoint presentation file for that talk: Download ground_system_tests.pps
August 04, 2008 in Design of radial ground systems | Permalink | Comments (0)
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 both as an amateur and as an electrical engineer. Over the years I have published articles on antennas and continue to study and write about them.
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. Of course at least some experimental verification is vital to make the analytic and NEC modeling work believable.
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. Most of the files for downloading are in .pdf format. The file sizes and original publication are noted after each. There is also a category for the 600m work.
October 17, 2006 in Introductory comments | Permalink | Comments (0)