Top hats are useful in that they force antenna current. The question is is is how large say at 1610 does the hat need to be before diminishing returns? Keep experimenting.
Yes that is exactly what i have been thinking.
I bought 8x 1 metre stainless rods, but concerned about wind and weight loading, i chickened out cut them to 24" each.
Looking at how the flag pole antenna supports them now, i should have left them full size.
It would be interesting for Rich to add some valuable info here regarding capacitance hat diameter/performance.
Also for reference i would be very interested to know what radiation improvement would be for say double the antenna height, whether this would offer double, or more signal strength, and also what bandwidth improvement.
Paul.
Paul - how is the AMT-5000 configured for use of an r-f ground? The metal flagpole+top hat form part of that monopole antenna system, but the transmitter needs to have a conducting path to an r-f ground (e.g., a buried ground rod or buried radials) in order for that system to radiate with best efficiency. Could you make a simple, annotated and dimensioned drawing/pictorial of your system, scan it to a jpg, and include it in a future post here?
What is earth conductivity in the MW band for the land at/around your antenna installation?
The following graphic may answer some of your questions, even though it is not based on the system configuration you outlined.
Rich,
The transmitter's earth connection goes straight to the ground radials collective centre connection.
The ground conductivity is 4mS/m, according to online information.
Paul.
You may be able to use a cloud service that allows for sharing files. Dropbox is one. I'll see about a list of them. They work for things like this.
RE: Reply 19 above
Thanks, Paul.
Tomorrow (29 Aug 2015) I'll set up a NEC study of the configuration in your graphic, and post the results.
Below are the results of modeling the configuration described above by Paul (BOARDMAKER).
I added the 25m tower 14m from the monopole to see what effect it has on the radiated fields -- which is negligible.
The field intensity shown assumes that the monopole system is tuned to resonance at 1512 kHz, with an r-f loss in the loading coil of 15 ohms, and 90 mW of tx power applied to the input of the loading coil.
Thank you Rich for the NEC simulation, i am very surprised what little effect the steel tower 14 metres away is having !
The tower does have a large vhf beam antenna on it, approx 12 feet long, but it probably has minimal effect.
My lack of range must be caused by something, a large tree not far away, and also the back garden has an embankment that raises up approx 3-4 feet.
These are the only other possibilities for my lack of range.
Rich, what would you expect a 6' top hat to do compared to the existing 4' one, would there be any worthwhile improvement ?
Also i would be very interested to know, would doubling the height of the antenna, when using the existing groundplane and top hat double or more the range ?
Thanks again for the info,
Paul.
Paul - I took a quick look at the monopole using a 4m section below the insulator. Other conditions the same this improved the groundwave field to about 227 µV/m at 1 mile. It would be tricky trying to resonate that system with the adjustment located 4m above the earth, though.
Changing the top hat from 4' to 6' diameter would produce a small amount of change in radiated field, but I didn't bother to model that.
I doubt that a 3-4 foot embankment has much of an effect, as that dimension is very small compared to a wavelength on 1512 kHz.
While awaiting Rich's reply, I have an experience doubling the length of the antenna on an AMT3000 from sstran.com.
I erected a bamboo pole in the back yard to hold first a 10-foot wire, tuned the transmitter and checked the range in the car.
Then I extended the antenna wire to 20-feet, retuned the transmitter, and in the car noticed no difference in coverage.
At the time I did not have a useful ground nor a spectrum analyzer to view the actual signal peaks.
I assume increasing the height under the insulator would give similar results to instead increasing the length of the 102" antenna to double that, i assume that would roughly double or more the signal strength ?
I have actually made a second antenna setup that is approx 3' below the insulator, but 20' above, will have to try it out !
Carl, i wonder if the matching is the issue regarding the lack of range with double the wire length, may be the sstran efficiency falls off ?
I am tempted to buy one of the Tecsun portable radio's to test out my range, any advise on which model ?
Also what received signal strength is considered the minimum for listening, i am assuming a clear frequency and away from houses etc ?
Paul.
BOARDMAKER asked: "Carl, i wonder if the matching is the issue regarding the lack of range with double the wire length, may be the sstran efficiency falls off ?"
I know what you mean and realize there is a point of diminished return since the SSTran transmitters are expressly designed to match a short wire, so that may have happened.
I also realize that some kind of ground would have kicked it quite a bit.
And at least an S-meter could have told me if there was some increase, but I didn't have one.
I assume increasing the height under the insulator would give similar results to instead increasing the length of the 102" antenna to double that, i assume that would roughly double or more the signal strength ?
No, because antenna current on the ground conductor of the transmitter is uniform over its length, while the current on the conductor connected to the antenna output terminal tapers from that value at its base to zero at its open end.
I am tempted to buy one of the Tecsun portable radio's to test out my range, any advise on which model ?
Either a Tecsun PL-310 or Tecsun PL-880 have useful signal strength meters. The PL-880 also has a synchronous AM detector (either sideband), receives SSB signals quite well, and has much better audio quality from its speaker.
Also what received signal strength is considered the minimum for listening, i am assuming a clear frequency and away from houses etc ?
That all depends on the sensitivity of the receiver system, and the ambient r-f noise level at the receive location.
With my PL-880 in a quiet location I get useful (fairly quiet) reception of AM broadcast signals down to 100 µV/m or so.
I have just been out in my old car that has a sony head unit, that i fitted some years ago, due to fuel injector and other ecu noise, i have to kill the engine to receive properly !
Keeping in mind it is 11.30+ pm here, the furthest i could make out the music track played was 2km exactly, this would not be heard at all in any home on a domestic receiver.
At night time their is no clearer freq than 1512 khz, but during the day i am sure i could get closer to 1602 khz.
So it looks like the car radio is more sensitive than my current portable, so it looks like i need to buy the pl-880 to test further !
My ground radials, 12 of, are laid on the grass, for testing, before i commit to cutting lines in the grass and putting them out of the way.
Rich, As the antenna is near the corner of the garden, i am limited to 3 metres radial length in 90+ degrees, would using longer radials for some of the circumference be worth it, or should i just use more 3 metre ground radials, ie 24 ?
I hope you don't mind me asking all these questions !
Paul.
As the antenna is near the corner of the garden, i am limited to 3 metres radial length in 90+ degrees, would using longer radials for some of the circumference be worth it, or should i just use more 3 metre ground radials, ie 24 ?
It might be worth the effort/cost to double the number of radials in the sector where they can be longer than 3m, and to double or triple their length in that sector. But the improvement in radiated field likely will be less than 1 dB (about 12%).
I hope you don't mind me asking all these questions !
Not at all.