In this configuration with the top hat and other things equal, there wouldn't be much practical difference in radiated field vs. the location of the transmitter along the 3m vertical radiator.
Rich,
Could you please do one last simulation of my diagram in post#19, but change the antenna length from the original 101" to 202" length, all other components remain the same.
I would be very interested to know what the field strength would be at 1 mile (was 124uv/m), and so what the extended distance would be for 124uv/m ?
Thanks again,
Paul.
but I won't be going on with more revisions of this project.
Hopefully you have more understanding of it now than before.
Hi Rich,
I thought you may have kept the simulation file, and could easily be altered to re run.
No problem, and thank you very much for your time and effort giving me valuable information, i appreciate it.
Paul.
I have been progressing with my tests of the flagpole antenna with top hat.
The results are getting better all the time, i have installed 32 ground radials of various lengths, over 90+ degrees these are limited to 3 metres, and the remainder of 270 degrees progressively increases to approx 10+ metres.
I did test when i had installed 16 radials, then after 32.
The biggest single difference was the top hat, this has proved to be very effective, and well worth while !
My modest 6x 2 foot top hat radials improved range, but adding a perimeter wire to the top hat radials improved it further.
Now at 1512 khz the flagpole and top hat antenna setup requires the amt5000 inductor to be at 106uh, a more serious top hat would recuce the inductance further.
I also plan to test a low loss external inductor, as well as wire mesh on the ground, around the base.
I used stainless builders banding and stainless nuts/bolts for the radial connections.
Once i am happy with the earth radials,i can tidy up the base with soil to cover the radials that are over the concrete base.
You do very beautiful work, BOARDMAKER.
Your antenna is a joy to look at.
An ordinary passer by will think it is art work.
I want my radials to look like that.
When birds land on the top hat it will be interesting.
Thanks for the kind words.
This top hat is the experimental version, the final version is going to be fabricated with stainless tubing and possible stainless mesh, so much stronger !
The next, and possible final hat version, will use 1 metre tube lengths.
Adding this current hat has doubled the range, for the same received signal strength on my car, and portable, so very worth while.
This extra range performance seems to agree with the R J Edwards simulation software, that i have been emulating this antenna setup with.
Paul.
Very nice construction! Your loading coil inductance is less than half that my antenna requires at a higher frequency. The less inductance needed the better because a lot of energy is lost in the coil.
Neil
I'm damned well IMPRESSED!!!
This is a thread worth following for sure.
I plan on venturing into AM with a C-Quam Am stereo transmitter, the antenna design is the only part that is stoping me from proceeding to going on the air. I may have to think about changing the crystal to a higher frequency though, as a hint, a full wave antenna would be about 960 feet. Trouble is my Realistic TM-152 AM stereo reciever tops out at around 1605KHz, I really don't like doing mods to old equipment, did that to CB radios back in the day, but once you cut and drill holes in equipment it sometimes ruins it for collectors.
Great job and the ground radials though, that's what I call a NEAT JOB!!!
Bruce.
This has been a nice, informative discussion, thanks to all. Neat work Boardmaker, that's a small antenna that's built like the big ones, great that you have the resolve to experiment, build, and the space in your garden for it.
I wonder what might happen if someone made an extreme top hat on a short vertical like that, say 130 feet long horizontally, in at least two directions, completing the quarter wave. You might only need a tiny coupling coil and get the full current in the 10 foot vertical section.
Here's something else to speculate on, I wonder if anyone's tried 100 milliwatts into a full length broadcast antenna tower as a test, and how much range did it get?
Very impressive construction job.
Thanks all for the kind words.
Regarding my asymmetrical ground setup, i am going to add extra ground radials on the short sides, to improve field strength best possible.
Extensive reading online tells me that the longer ground radial side does still increase signal on the shorter side, just not quite as much (1.5db less or thereabouts).
Regarding the top hat, the perimeter wire is very important, this alone all but doubles the effective capacitance !
I have just ordered some stainless tubing, and plan to use this to support a stainless mesh panel, that will be the new improved top hat.
Another option is to run a length of wire, or wires directly over the antenna, and support both ends through insulators to trees or similar (like a washing line), and connect the centre of this to the top of the antenna, this can greatly add capacitance.
Have a look at RJ Edwards tophat2 free software program, you can enter the details, and change individual values to see the effect.
With 15 ohm ground, and no top hat on my 3m flagpole, and inductor q of 200, efficiency is 0.3%.
Just adding my modest top hat of 8x 0.6 metre radials with perimeter wire increases the efficiency to 0.8%, this hat alone adds 4.4db gain over no hat.
Increasing the 8 radials to 1 metre with perimeter wire, increases efficiency to 1% over no hat, so that is 5.4db improvement !
A larger top hat capacitance gains even more, so a series of strung radials on end insulators between structures could be very interesing !
Btw, as the perimeter wire all but doubles the capacitance, you will need to emulate this by lengthening the radials by 50% in the tophat2 software.
Paul.
BOARDMAKER Paul, your experiments and their results provide the most exciting case for the place of antenna top-hats that I have seen on this site.
It was very commendable of you to present such a well detailed account of the project.
I am looking forward to further comments about this topic.
Paul, have you tried wetting down and saturating the soil where your ground radials are and doing some more tests?
Bruce.
Previously when i tested with 12x 3 metre ground radials, i noticed slight changes in current readings on the AMT500 tx over a week or two, this could well be due to the changes in ground wetness.
This was one of several reasons that why i wanted to install 32 ground radials,i assume this would help to reduce the effects of the soils surface conductivity.
My plan is to finish the ground radials (doubling the amount shortest ones), then this allows me to work on my improved top hat.
As my rf ground system must now be less than 10 ohm, the losses in the loading coil come in to focus as well.
i do have a nice 100uh coil that many years ago was salvaged from a scrapped hf transmitter from a small boat/yacht.
The coil former is made of 2 paxolin pieces slotted at 90 degrees to each other, so coil has minimum contact, it must be high q ?
The coil is approx 2.5" wide on each side, and 5" high, i can see a seperate waterproof box mounted behind the amt5000, with the coil and cap inside.
The more i look, the longer the to do list gets !
Paul.
Paul.