| Home |
| Search |
| Today's Posts |
|
|
|
#1
November 6th 14, 05:11 PM
posted to rec.radio.amateur.antenna
|
|||
|
|||
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? |
|
#2
November 6th 14, 05:33 PM
posted to rec.radio.amateur.antenna
|
|||
|
|||
|
A short 160M antenna
On 11/6/2014 12:11 PM, John S wrote:
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. The power "received" may be a given for the antenna, but the power (or voltage) delivered to the receiver is not set in the same way. BTW, have you seen the extremely tiny ferrite rod antennas used in the so-called Atomic wris****ches? Yes, but they are not optimal for my application where I need as large a voltage as possible. If I end up using a preamp I may consider using a ferrite antenna. -- Rick |
|
#3
November 6th 14, 06:39 PM
posted to rec.radio.amateur.antenna
|
|||
|
|||
|
A short 160M antenna
On 11/6/2014 11:33 AM, rickman wrote:
On 11/6/2014 12:11 PM, John S wrote: 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. The power "received" may be a given for the antenna, but the power (or voltage) delivered to the receiver is not set in the same way. Yes. I mentioned that a larger impedance load (the receiver input impedance) would result in a greater voltage. For example, the voltage available at the receiver terminals in my previous post was 0.001499 V for the 6' wire and 1000 ohms load. If I now increase the impedance to 1Meg + j0, the voltage is 0.01666 V, more than 10 times as much. Is that what you mean? BTW, have you seen the extremely tiny ferrite rod antennas used in the so-called Atomic wris****ches? Yes, but they are not optimal for my application where I need as large a voltage as possible. If I end up using a preamp I may consider using a ferrite antenna. Very well, I understand. John |
|
#4
November 6th 14, 06:34 PM
posted to rec.radio.amateur.antenna
|
|||
|
|||
|
A short 160M antenna
rickman wrote:
On 11/6/2014 12:11 PM, John S wrote: 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. The power "received" may be a given for the antenna, but the power (or voltage) delivered to the receiver is not set in the same way. The voltage delivered to the receiver is determined by Ohms Law. The antenna is a voltage source in series with the impedance of the antenna. If voltage = E, impedance = Ri, receiver impedance = Rl, then the receiver voltage is (E * Rl)/(Ri + Rl). -- Jim Pennino |
| Reply |
| Thread Tools | Search this Thread |
| Display Modes | |
|
|
Similar Threads
|
||||
| Thread | Forum | |||
| Antenna & Tuner on 160M Question | Antenna | |||
| 160m antenna | Antenna | |||
| Why did this work (160m antenna)? | Antenna | |||
| Outbacker ML-130 160m antenna question | Antenna | |||
| question about 160m Isotron Antenna | Antenna | |||
Hybrid Mode
