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A short 160M antenna
I started to do some modeling on a short antenna for 160M and got what
I think are interesting results. I will post those as soon as I get a chance to write up all the data. -- Jim Pennino |
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A short 160M antenna
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#4
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A short 160M antenna
On 11/5/2014 9:32 PM, wrote:
rickman wrote: On 11/5/2014 7:28 PM, wrote: I started to do some modeling on a short antenna for 160M and got what I think are interesting results. I will post those as soon as I get a chance to write up all the data. All this stuff for short antenna is in the context of transmissions, right? For receiving a short antenna is at a disadvantage, no? I seem to recall a parameter called "effective height". For loop antenna it pertains to the signal collected irrespective of the actual dimensions of the loop. For other types of antenna I assume this is not the same and does relate directly to the length of the antenna. Is that correct? All antennas made of linear material are reciprocal in all properties. The only antennas I know of that include non-linear material are some microwave antennas with ferrite components. Generally effective height is the height of the antenna's center of radiation above the ground. How do you determine the "height of the antenna's center of radiation above the ground"? The effective height of an antenna multiplied by the incident electric field strength gives the terminal voltage at the antenna feed. -- Rick |
#5
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A short 160M antenna
rickman wrote:
On 11/5/2014 9:32 PM, wrote: rickman wrote: On 11/5/2014 7:28 PM, wrote: I started to do some modeling on a short antenna for 160M and got what I think are interesting results. I will post those as soon as I get a chance to write up all the data. All this stuff for short antenna is in the context of transmissions, right? For receiving a short antenna is at a disadvantage, no? I seem to recall a parameter called "effective height". For loop antenna it pertains to the signal collected irrespective of the actual dimensions of the loop. For other types of antenna I assume this is not the same and does relate directly to the length of the antenna. Is that correct? All antennas made of linear material are reciprocal in all properties. The only antennas I know of that include non-linear material are some microwave antennas with ferrite components. Generally effective height is the height of the antenna's center of radiation above the ground. How do you determine the "height of the antenna's center of radiation above the ground"? http://personal.ee.surrey.ac.uk/Pers...nnaheight.html http://en.wikipedia.org/wiki/Effective_height In depth treatment: http://tinyurl.com/lfee64g -- Jim Pennino |
#6
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A short 160M antenna
On 11/5/2014 10:37 PM, wrote:
rickman wrote: On 11/5/2014 9:32 PM, wrote: rickman wrote: On 11/5/2014 7:28 PM, wrote: I started to do some modeling on a short antenna for 160M and got what I think are interesting results. I will post those as soon as I get a chance to write up all the data. All this stuff for short antenna is in the context of transmissions, right? For receiving a short antenna is at a disadvantage, no? I seem to recall a parameter called "effective height". For loop antenna it pertains to the signal collected irrespective of the actual dimensions of the loop. For other types of antenna I assume this is not the same and does relate directly to the length of the antenna. Is that correct? All antennas made of linear material are reciprocal in all properties. The only antennas I know of that include non-linear material are some microwave antennas with ferrite components. Generally effective height is the height of the antenna's center of radiation above the ground. How do you determine the "height of the antenna's center of radiation above the ground"? http://personal.ee.surrey.ac.uk/Pers...nnaheight.html http://en.wikipedia.org/wiki/Effective_height In depth treatment: http://tinyurl.com/lfee64g I didn't ask for links. I'm asking you for a specific reason. Your first link relates the effective height to the "actual height" without explaining just what that is. Your second link simply states the same words that you used. Your third reference seems to be referring to transmitting antenna and does not relate this property to the antenna itself. How do you determine the "height of the antenna's center of radiation above the ground" given the physical parameters of an antenna? The effective height is a parameter that indicates the effectiveness of a receiving antenna. I dug into this for a loop antenna and it is a function of the diameter, the number of turns and if any magnetic material is used, the properties of that. I'm wondering what the nature of the equations are for other antennas? -- Rick |
#7
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A short 160M antenna
On 11/5/2014 7:16 PM, rickman wrote:
On 11/5/2014 7:28 PM, wrote: I started to do some modeling on a short antenna for 160M and got what I think are interesting results. I will post those as soon as I get a chance to write up all the data. All this stuff for short antenna is in the context of transmissions, right? For receiving a short antenna is at a disadvantage, no? I seem to recall a parameter called "effective height". For loop antenna it pertains to the signal collected irrespective of the actual dimensions of the loop. For other types of antenna I assume this is not the same and does relate directly to the length of the antenna. Is that correct? I ran a simulation to confirm that the received signal is some function of the length of a wire antenna. My model was a 6 foot zero-loss wire 10 miles from the source with a load of 1000 ohms. The frequency is 1MHz. Wire length Volts received 6' 0.001499 12' 0.005408 So, it appears that doubling the length of a short antenna captures about 3.6 times the signal. Is this what you wanted to know? |
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A short 160M antenna
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#9
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A short 160M antenna
On 11/6/2014 11:08 AM, John S wrote:
On 11/5/2014 7:16 PM, rickman wrote: On 11/5/2014 7:28 PM, wrote: I started to do some modeling on a short antenna for 160M and got what I think are interesting results. I will post those as soon as I get a chance to write up all the data. All this stuff for short antenna is in the context of transmissions, right? For receiving a short antenna is at a disadvantage, no? I seem to recall a parameter called "effective height". For loop antenna it pertains to the signal collected irrespective of the actual dimensions of the loop. For other types of antenna I assume this is not the same and does relate directly to the length of the antenna. Is that correct? I ran a simulation to confirm that the received signal is some function of the length of a wire antenna. My model was a 6 foot zero-loss wire 10 miles from the source with a load of 1000 ohms. The frequency is 1MHz. Wire length Volts received 6' 0.001499 12' 0.005408 So, it appears that doubling the length of a short antenna captures about 3.6 times the signal. Is this what you wanted to know? That is a nice experimental verification. I guess I figured this is the sort of thing that there would be an equation for. A loop antenna has a simple equation defining its effective height (ability to convert the field to a voltage). I expect there is a similar equation for each antenna type. I guess the point is that for receiving it is important to match the size of the antenna to the signal to receive the maximum power. Or is there something equivalent to the matching network that would equalize the power received? In your example you said you used a 1000 ohm load. Is there a way to improve the signal from the shorter antenna? -- Rick |
#10
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A short 160M antenna
On 11/6/2014 10:52 AM, rickman wrote:
On 11/6/2014 11:08 AM, John S wrote: On 11/5/2014 7:16 PM, rickman wrote: On 11/5/2014 7:28 PM, wrote: I started to do some modeling on a short antenna for 160M and got what I think are interesting results. I will post those as soon as I get a chance to write up all the data. All this stuff for short antenna is in the context of transmissions, right? For receiving a short antenna is at a disadvantage, no? I seem to recall a parameter called "effective height". For loop antenna it pertains to the signal collected irrespective of the actual dimensions of the loop. For other types of antenna I assume this is not the same and does relate directly to the length of the antenna. Is that correct? I ran a simulation to confirm that the received signal is some function of the length of a wire antenna. My model was a 6 foot zero-loss wire 10 miles from the source with a load of 1000 ohms. The frequency is 1MHz. Wire length Volts received 6' 0.001499 12' 0.005408 So, it appears that doubling the length of a short antenna captures about 3.6 times the signal. Is this what you wanted to know? That is a nice experimental verification. I guess I figured this is the sort of thing that there would be an equation for. A loop antenna has a simple equation defining its effective height (ability to convert the field to a voltage). I expect there is a similar equation for each antenna type. I have not used an equation. I used EZNEC. You can get a free trial version. It has limitations, but no time limit IIRC. I guess the point is that for receiving it is important to match the size of the antenna to the signal to receive the maximum power. Or is there something equivalent to the matching network that would equalize the power received? In your example you said you used a 1000 ohm load. Is there a way to improve the signal from the shorter antenna? In receiving, it seems that size matters when it comes to small antennas like we are discussing. If you could increase the (receiver) input impedance you will get more voltage. No matter what you do, you cannot increase the power received except by refining your system. The (volts/meter)^2 is fixed. It is up you to capture the available signal. And, I think it will take somewhat heroic efforts at your frequency of interest. BTW, have you seen the extremely tiny ferrite rod antennas used in the so-called Atomic wris****ches? |
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