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Follow up to Spike ;Bent dipoles?
In rec.radio.amateur.antenna Spike wrote:
On 29/11/2015 23:24, wrote: OK, I added radials for a total of 5 in a 45 degree spread and optimized for minimum reactance. radiator: 203 inches, radial: 186 inches, R: 52.4 Ohms, X: 0.4 Ohms SWR: 1.1, Maximum gain: -.18 dBi in the direction of the radial and an elevation angle of 30 degrees, Reverse gain: -3.7 dBi Note with one radial the F/B ratio is about 5 dB and with five radials it is about 3dB. About the only thing I can see worth noting about this antenna is that it shows more radials are better, but everyone already knows that. Imagine a case whereby someone digs up the soil around the base of a vertical antenna, a couple of feet deep and as far out as the antenna is tall. Into this they mix 2 percent of high-aspect-ratio thin conducting fibres, say about a foot long, and then replace the soil. 2 percent of conducting fibres in an essentially non-conducting medium is about the minimum proportion necessary to reach the percolation threshold.. What results from your modelling exercise do you get in this case? Modeling thing buried in the soil requires professional software that costs on the order of $1,000. To do this with reasonably priced (for a hobby) software requires that effective soil conductivity be determined. Send me either $1,000.00 or the effective soil conductivity and I'll be glad to do it. -- Jim Pennino |
Follow up to Spike ;Bent dipoles?
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Follow up to Spike ;Bent dipoles?
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Follow up to Spike ;Bent dipoles?
In rec.radio.amateur.antenna Spike wrote:
On 30/11/2015 18:34, wrote: In rec.radio.amateur.antenna Spike wrote: Imagine a case whereby someone digs up the soil around the base of a vertical antenna, a couple of feet deep and as far out as the antenna is tall. Into this they mix 2 percent of high-aspect-ratio thin conducting fibres, say about a foot long, and then replace the soil. 2 percent of conducting fibres in an essentially non-conducting medium is about the minimum proportion necessary to reach the percolation threshold.. What results from your modelling exercise do you get in this case? Modeling thing buried in the soil requires professional software that costs on the order of $1,000. To do this with reasonably priced (for a hobby) software requires that effective soil conductivity be determined. Send me either $1,000.00 or the effective soil conductivity and I'll be glad to do it. The effective soil conductivity will be close to the fully conductive value of the fibres - that's what percolation does. The high aspect ratio fibres are a method of achieving that in a poorly conductive medium such as soil. One can not enter text into a model; numbers please. -- Jim Pennino |
Follow up to Spike ;Bent dipoles?
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Follow up to Spike ;Bent dipoles?
In message , Spike
writes On 30/11/2015 23:53, wrote: In rec.radio.amateur.antenna Spike wrote: The effective soil conductivity will be close to the fully conductive value of the fibres - that's what percolation does. The high aspect ratio fibres are a method of achieving that in a poorly conductive medium such as soil. One can not enter text into a model; numbers please. Much of this has already been done, 'this' meaning studying the effects of ground conductivity and number of radials (going up to 64) by N6LF in QEX with the latest version being published in September/October this year. Note for Brian Howie: the study encompasses 472 kHz, and it should be noted that below 1MHz the soil electromagnetic parameters diverge significantly from HF values. This implies that a different approach is needed, and one of the articles looks at this - you might find this of interest. Thanks I've had a look at them . If I ever get round to transmitting there, I'll need a lot of earth. I'm still using my 5 foot loop for receive, but it's now series tuned, rather than parallel with a coupling loop and seems to work a bit better. By coincidence my morning training run took me near the EDN NDB http://www.b-howie.demon.co.uk/lfbcon.htm It's a top loaded vertical, but looking over the fence, I could see a lot green earth wire radials on the surface. It's possible there are buried ones too , but there are only about 6 and they can't be more than 15ft long, Brian -- Brian Howie |
Follow up to Spike ;Bent dipoles?
On 03/12/2015 12:45, Brian Howie wrote:
In message , Spike writes Note for Brian Howie: the study encompasses 472 kHz, and it should be noted that below 1MHz the soil electromagnetic parameters diverge significantly from HF values. This implies that a different approach is needed, and one of the articles looks at this - you might find this of interest. Thanks I've had a look at them . If I ever get round to transmitting there, I'll need a lot of earth. I guess it will need a lot of planning! And wire... I'm still using my 5 foot loop for receive, but it's now series tuned, rather than parallel with a coupling loop and seems to work a bit better. Do you find the S/N is improved with a loop? Have you thought of trying a shielded loop? By coincidence my morning training run took me near the EDN NDB http://www.b-howie.demon.co.uk/lfbcon.htm It's a top loaded vertical, but looking over the fence, I could see a lot green earth wire radials on the surface. It's possible there are buried ones too , but there are only about 6 and they can't be more than 15ft long, For the beacon to be of maximum use, they'll need a good sky-wave signal; it sounds like the visible radials are there to provide a DC path to earth probably in association with a ground spike, rather than for getting the main lobe lowered. -- Spike "Crime butchers innocence to secure a throne, and innocence struggles with all its might against the attempts of crime" - Maximilien Robespierre |
Follow up to Spike ;Bent dipoles?
In rec.radio.amateur.antenna Spike wrote:
On 03/12/2015 12:45, Brian Howie wrote: In message , Spike writes Note for Brian Howie: the study encompasses 472 kHz, and it should be noted that below 1MHz the soil electromagnetic parameters diverge significantly from HF values. This implies that a different approach is needed, and one of the articles looks at this - you might find this of interest. Thanks I've had a look at them . If I ever get round to transmitting there, I'll need a lot of earth. I guess it will need a lot of planning! And wire... I'm still using my 5 foot loop for receive, but it's now series tuned, rather than parallel with a coupling loop and seems to work a bit better. Do you find the S/N is improved with a loop? Have you thought of trying a shielded loop? By coincidence my morning training run took me near the EDN NDB http://www.b-howie.demon.co.uk/lfbcon.htm It's a top loaded vertical, but looking over the fence, I could see a lot green earth wire radials on the surface. It's possible there are buried ones too , but there are only about 6 and they can't be more than 15ft long, For the beacon to be of maximum use, they'll need a good sky-wave signal; it sounds like the visible radials are there to provide a DC path to earth probably in association with a ground spike, rather than for getting the main lobe lowered. Sky wave propagation doesn't happen at those frequencies for all practical purposes. Sky wave propagation was discovered when amateurs started using frequencies greater than 200 meters. -- Jim Pennino |
Follow up to Spike ;Bent dipoles?
On 05/12/2015 03:40, wrote:
In rec.radio.amateur.antenna Spike wrote: On 03/12/2015 12:45, Brian Howie wrote: By coincidence my morning training run took me near the EDN NDB http://www.b-howie.demon.co.uk/lfbcon.htm It's a top loaded vertical, but looking over the fence, I could see a lot green earth wire radials on the surface. It's possible there are buried ones too , but there are only about 6 and they can't be more than 15ft long, For the beacon to be of maximum use, they'll need a good sky-wave signal; it sounds like the visible radials are there to provide a DC path to earth probably in association with a ground spike, rather than for getting the main lobe lowered. Sky wave propagation doesn't happen at those frequencies for all practical purposes. That's amazing. So all those aircraft at 35000 feet in its service area can't hear the beacon? If it didn't have sky wave, it would merely be a ground-wave beacon, not much use as there aren't that many airports within 35 miles of Edinburgh, and the aircraft captains would know where they were anyway. Sky wave propagation was discovered when amateurs started using frequencies greater than 200 meters. What's interesting here is now much of the radiated power goes sky-wards, and how much goes into surface wave. But apparently no-one's ever thought to determine this, so it'll remain a mystery. -- Spike "Crime butchers innocence to secure a throne, and innocence struggles with all its might against the attempts of crime" - Maximilien Robespierre |
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