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GROUND SYSTEM FOR PART 15
- Thread starter WRPO
- Start date
> I know the more, the better..but how many is practical? How
> long should they be for 1620 AM? Size of wire used and
> should they be bare copper, or will normal "electric" wire
> be OK?
_____________
Check http://www.radio-info.com/mods/board?Board=community&Post=607449&page=
Bare copper wire size probably 16 AWG or larger for better performance.
//
> long should they be for 1620 AM? Size of wire used and
> should they be bare copper, or will normal "electric" wire
> be OK?
_____________
Check http://www.radio-info.com/mods/board?Board=community&Post=607449&page=
Bare copper wire size probably 16 AWG or larger for better performance.
//
N
Neal
Guest
The minimum would be 6 radials at 150feet
in Length
I am running 8-2" straps and 112 radials of 143feet
for 1680Khz
#10 Copper Clad.
Neal
> > I know the more, the better..but how many is practical?
> How
> > long should they be for 1620 AM? Size of wire used and
> > should they be bare copper, or will normal "electric" wire
>
> > be OK?
> _____________
>
> Check
http://www> .radio-info.com/mods/board?Board=community&Post=607449&page=
>
>
> Bare copper wire size probably 16 AWG or larger for better
> performance.
> //
>
in Length
I am running 8-2" straps and 112 radials of 143feet
for 1680Khz
#10 Copper Clad.
Neal
> > I know the more, the better..but how many is practical?
> How
> > long should they be for 1620 AM? Size of wire used and
> > should they be bare copper, or will normal "electric" wire
>
> > be OK?
> _____________
>
> Check
http://www> .radio-info.com/mods/board?Board=community&Post=607449&page=
>
>
> Bare copper wire size probably 16 AWG or larger for better
> performance.
> //
>
D
DaveyC
Guest
Hey Neal
With the ground setup you have, what type of coverage area do you achieve?
With the ground setup you have, what type of coverage area do you achieve?
N
Neal
Guest
Lets just say it gets out very well
There is also a 40x40 foot Copper mesh base to help with ground current
did I forget to say I just built this for my 10kw station.
but would work Very well with a Part 15...
I have Pics up on a website if you never seen how a ground system is installed
> Hey Neal
>
> With the ground setup you have, what type of coverage area
> do you achieve?
>
There is also a 40x40 foot Copper mesh base to help with ground current
did I forget to say I just built this for my 10kw station.
but would work Very well with a Part 15...
I have Pics up on a website if you never seen how a ground system is installed
> Hey Neal
>
> With the ground setup you have, what type of coverage area
> do you achieve?
>
> I know the more, the better..but how many is practical? How
> long should they be for 1620 AM? Size of wire used and
> should they be bare copper, or will normal "electric" wire
> be OK?
>
I know everyone has a different take on ground systems, in part because each installation is different, but from personal experience with over twenty years experimenting with part 15 set ups in the AM Band, I feel that the number of radials is much more important than their length. This is stated clearly in Ken Cornell's "Long and Medium Wave Scrapbook" and in many other engineering textbooks and is due to the fact that the ground losses are higher closer to the base of the antenna. This is why many commercial broadcast stations use ground screens at the base of their antennas in addtion to the required 120 radials.
So, on a practical basis, you are better off to have say 12, fifteen-foot radials than 4, one hundred and fifty foot radials. IMHO it is the amount of copper (or other conductor) under the antenna that makes the biggest difference, not the length of the conductors.
The same has been found to be true of top hats, structures at the top of the mast than increase radiation. Through experimentation it can be easily demonstrated that you are much better off with say a 3' solid circular horizontal top hat than 2 or four horizontal wires 2-3 times the length. Try each of these while measuring both antenna current and field strength and you will be convinced.
This brings up the question as to whether or not top hats are even legal? I don't have the answer to that and there appear to be several opinions. I know a guy who claims to have a letter from the FCC saying that anything that could fit wihtin a 3 meter cube would be considered legal! This would mean that a 10' mast with a 10' diameter solid top hat, while difficult to fabricate and support, would be OK. On the other hand there are other people who believe that the radius of the top hat must be included in the 3m measurement. Both arguments have merit and it would be interesting see where the parties would agree. For instance, no one has a problem with a 3m tall mast as a legal part 15 AM antenna. What if the mast was actually a pipe that was 12" in diameter? Probably still legal, right? Now put a cap on the pipe . . . sounds OK to me. Taking this to the extreme, picture a 3m diameter cylinder, covered at the top. The antenna is still only 3m long. How is this different from a skinny mast with a 3m horizontal plate on top.
Again, I don't pretend to have the answer. I'm just tossing out some ideas to keep the discussion going.
Lastly, keep in mind that the thickness of the antenna does have an effect on the efficiency of the antenna, at least in theory. I've read of people getting better results by sticking a copper pipe over the fiberglass whips used on some commercially made Part 15 AM rigs and this would make sense. Some experimenters have used 8" or even 12" vent pipe with good results. Whether it is legal is not up to me to decide.
> long should they be for 1620 AM? Size of wire used and
> should they be bare copper, or will normal "electric" wire
> be OK?
>
I know everyone has a different take on ground systems, in part because each installation is different, but from personal experience with over twenty years experimenting with part 15 set ups in the AM Band, I feel that the number of radials is much more important than their length. This is stated clearly in Ken Cornell's "Long and Medium Wave Scrapbook" and in many other engineering textbooks and is due to the fact that the ground losses are higher closer to the base of the antenna. This is why many commercial broadcast stations use ground screens at the base of their antennas in addtion to the required 120 radials.
So, on a practical basis, you are better off to have say 12, fifteen-foot radials than 4, one hundred and fifty foot radials. IMHO it is the amount of copper (or other conductor) under the antenna that makes the biggest difference, not the length of the conductors.
The same has been found to be true of top hats, structures at the top of the mast than increase radiation. Through experimentation it can be easily demonstrated that you are much better off with say a 3' solid circular horizontal top hat than 2 or four horizontal wires 2-3 times the length. Try each of these while measuring both antenna current and field strength and you will be convinced.
This brings up the question as to whether or not top hats are even legal? I don't have the answer to that and there appear to be several opinions. I know a guy who claims to have a letter from the FCC saying that anything that could fit wihtin a 3 meter cube would be considered legal! This would mean that a 10' mast with a 10' diameter solid top hat, while difficult to fabricate and support, would be OK. On the other hand there are other people who believe that the radius of the top hat must be included in the 3m measurement. Both arguments have merit and it would be interesting see where the parties would agree. For instance, no one has a problem with a 3m tall mast as a legal part 15 AM antenna. What if the mast was actually a pipe that was 12" in diameter? Probably still legal, right? Now put a cap on the pipe . . . sounds OK to me. Taking this to the extreme, picture a 3m diameter cylinder, covered at the top. The antenna is still only 3m long. How is this different from a skinny mast with a 3m horizontal plate on top.
Again, I don't pretend to have the answer. I'm just tossing out some ideas to keep the discussion going.
Lastly, keep in mind that the thickness of the antenna does have an effect on the efficiency of the antenna, at least in theory. I've read of people getting better results by sticking a copper pipe over the fiberglass whips used on some commercially made Part 15 AM rigs and this would make sense. Some experimenters have used 8" or even 12" vent pipe with good results. Whether it is legal is not up to me to decide.
> Lastly, keep in mind that the thickness of the antenna does
> have an effect on the efficiency of the antenna, at least in
> theory.
__________________
Theory says that the radiation efficiency of a MW vertical is the ratio of its radiation resistance to the total r-f resistance at the feedpoint. Other sources of resistance at the feedpoint beside the natural radiation resistance of the vertical are:
- the resistance of the loading coil
- the resistance to r-f currrents induced in the earth by the radiator, as they return to the antenna/tx "ground" terminal
- the ohmic resistance of the vertical radiator itself
Analysis shows that the radiation resistance of a Part 15 3-m vertical is nominally the same for a 1/2" OD radiator as it is for a 3" OD radiator (for example). Therefore both of these two radiators would be equally efficient, if other things were equal.
What DOES change significantly with change of OD is the reactance of the radiator. Reactance is seen to be inversely proportional to OD, and also its value changes less with a change in frequency -- meaning that a radiator with a larger OD can have better SWR bandwidth.
//
> have an effect on the efficiency of the antenna, at least in
> theory.
__________________
Theory says that the radiation efficiency of a MW vertical is the ratio of its radiation resistance to the total r-f resistance at the feedpoint. Other sources of resistance at the feedpoint beside the natural radiation resistance of the vertical are:
- the resistance of the loading coil
- the resistance to r-f currrents induced in the earth by the radiator, as they return to the antenna/tx "ground" terminal
- the ohmic resistance of the vertical radiator itself
Analysis shows that the radiation resistance of a Part 15 3-m vertical is nominally the same for a 1/2" OD radiator as it is for a 3" OD radiator (for example). Therefore both of these two radiators would be equally efficient, if other things were equal.
What DOES change significantly with change of OD is the reactance of the radiator. Reactance is seen to be inversely proportional to OD, and also its value changes less with a change in frequency -- meaning that a radiator with a larger OD can have better SWR bandwidth.
//
Perhaps what should have been written is that increasing the diameter can increase antenna SYSTEM efficiency, which would include the loading coil. The increased diameter will increase the capacitance to ground in nearly the same fashion as a top hat does, allowing a lower value (and more importantly in this case) a lower resistance tuning inductor to be used with a resultant increase in power to the antenna and improved system efficiency. In nearly two decades of MEDFER part 15 experimentation, I have always noted an increase in antenna current AND an increase in signal strength in the far field when I have significantly increased the diameter of a 3m antenna.
BTW: Some people take measurements in the near field but these measurements are practically meaningless when you are using an antenna that is only a small portion of a wavelength, especially in the typical Part 15 installation with a less than optimal ground and many nearby objects that may be reradiating the signal.
In MEDFER operation we run cw so antenna bandwidth isn't an issue . . . however with AM Broadcasting the added bandwidth of this kind of antenna can improve the audio fidelity significantly. The increase depends on several factors, including how the antenna is matched to the transmitter and how the transmitter behaves when operated in to complex impedance antennas.
One added benefit of a wider bandwidth antenna is that often such an antenna is less susceptable to detuning by rain and ice.
> > Lastly, keep in mind that the thickness of the antenna
> does
> > have an effect on the efficiency of the antenna, at least
> in
> > theory.
> __________________
>
> Theory says that the radiation efficiency of a MW vertical
> is the ratio of its radiation resistance to the total r-f
> resistance at the feedpoint. Other sources of resistance at
> the feedpoint beside the natural radiation resistance of the
> vertical are:
>
> - the resistance of loading coil
> - the resistance to r-f currrents induced in the earth as
> they return to the antenna/tx "ground" terminal
> - the ohmic resistance of the vertical radiator itself
>
> Analysis shows that the radiation resistance of a Part 15
> 3-m vertical is nominally the same for a 1/2" OD radiator as
> it is for a 3" OD radiator (for example). Therefore both of
> these two radiators would be equally efficient, if other
> things were equal.
>
> What DOES change significantly with change of OD is the
> reactance of the radiator. Reactance is seen to be
> inversely proportional to OD, and also its value changes
> less with a change in frequency -- meaning that a radiator
> with a larger OD can have better SWR bandwidth.
> //
>
BTW: Some people take measurements in the near field but these measurements are practically meaningless when you are using an antenna that is only a small portion of a wavelength, especially in the typical Part 15 installation with a less than optimal ground and many nearby objects that may be reradiating the signal.
In MEDFER operation we run cw so antenna bandwidth isn't an issue . . . however with AM Broadcasting the added bandwidth of this kind of antenna can improve the audio fidelity significantly. The increase depends on several factors, including how the antenna is matched to the transmitter and how the transmitter behaves when operated in to complex impedance antennas.
One added benefit of a wider bandwidth antenna is that often such an antenna is less susceptable to detuning by rain and ice.
> > Lastly, keep in mind that the thickness of the antenna
> does
> > have an effect on the efficiency of the antenna, at least
> in
> > theory.
> __________________
>
> Theory says that the radiation efficiency of a MW vertical
> is the ratio of its radiation resistance to the total r-f
> resistance at the feedpoint. Other sources of resistance at
> the feedpoint beside the natural radiation resistance of the
> vertical are:
>
> - the resistance of loading coil
> - the resistance to r-f currrents induced in the earth as
> they return to the antenna/tx "ground" terminal
> - the ohmic resistance of the vertical radiator itself
>
> Analysis shows that the radiation resistance of a Part 15
> 3-m vertical is nominally the same for a 1/2" OD radiator as
> it is for a 3" OD radiator (for example). Therefore both of
> these two radiators would be equally efficient, if other
> things were equal.
>
> What DOES change significantly with change of OD is the
> reactance of the radiator. Reactance is seen to be
> inversely proportional to OD, and also its value changes
> less with a change in frequency -- meaning that a radiator
> with a larger OD can have better SWR bandwidth.
> //
>
> The increased diameter will increase the capacitance to ground
> in nearly the same fashion as a top hat does, allowing a
> lower value (and more importantly in this case) a lower resistance
> tuning inductor to be used with a resultant increase in power to
> the antenna and improved system efficiency.
______________
Reducing the resistance in the loading coil certainly is a step in the right direction, as long as system resonance of the 3-m radiator and a match to the tx both are achieved. But the coil resistance almost always is small compared to the r-f resistance of the return path for ground currents. And the radiation resistance of the vertical itself is miniscule compared to either one.
Here are some calculated parameters for the base Z of a perfect 3-m radiator at 1700 kHz:
1/2" OD: 0.1278 -j3145 ohms
3" OD: 0.1263 -j2048 ohms
A low-resistance loading coil for the 3" OD radiator might be something like 2 ohms, and a typical Part 15 ground system let's say is 20 ohms. The efficiency of the 3" OD system then is about 0.57%.
If the loading coil for the 1/2" OD radiator had 4 ohms resistance and the other parameters were the same, system radiation efficiency would be 0.53%.
The difference in the received field strengths relating only to coil loss from these two systems would be difficult to detect.
//
> in nearly the same fashion as a top hat does, allowing a
> lower value (and more importantly in this case) a lower resistance
> tuning inductor to be used with a resultant increase in power to
> the antenna and improved system efficiency.
______________
Reducing the resistance in the loading coil certainly is a step in the right direction, as long as system resonance of the 3-m radiator and a match to the tx both are achieved. But the coil resistance almost always is small compared to the r-f resistance of the return path for ground currents. And the radiation resistance of the vertical itself is miniscule compared to either one.
Here are some calculated parameters for the base Z of a perfect 3-m radiator at 1700 kHz:
1/2" OD: 0.1278 -j3145 ohms
3" OD: 0.1263 -j2048 ohms
A low-resistance loading coil for the 3" OD radiator might be something like 2 ohms, and a typical Part 15 ground system let's say is 20 ohms. The efficiency of the 3" OD system then is about 0.57%.
If the loading coil for the 1/2" OD radiator had 4 ohms resistance and the other parameters were the same, system radiation efficiency would be 0.53%.
The difference in the received field strengths relating only to coil loss from these two systems would be difficult to detect.
//
I'm not sure what program you are using to do the calculations . . .I'm sure it is a good one and the numbers look like they are in the ballpark for the loading coil. However, many of these programs become inaccurate when dealing with antennas that are only a fraction of a wavelength. If this is not the case here, than something else must explain the multiple accounts of far field signal strength improvement when the length to thickness ratio is decreased. This has been reported numerous times, not only by non-technical people on these and similar boards, but also in the LOWDOWN, the Long Wave Club of America's publication and as well as in Ken Cornell's highly regarded series of handbooks referenced in a previous post.
By no means am I challenging your calculations, I just think that there may be other factors in play that are not being taken into account. I base my reported observations on experiments I have done under controlled conditions, using a HP signal generator, a Potomac OIB and FIM-41 and a HP RF voltmeter.
Much of this is a moot point because few commercial part 15 AM operations are able to achieve a good match let alone resonance with their antenna systems.
Most Part 15 experimenters, at least those that read this board, are much more interested in broadcasting than in the technical nuances of transmission. For those people, I suggest that they concentrate their energy on creating the best possible ground system that they can and perhaps add a top hat to their antenna if possible. This will result in the most substantial imporvement in coverage with the standard 3m antenna.
> > The increased diameter will increase the capacitance to
> ground
> > in nearly the same fashion as a top hat does, allowing a
> > lower value (and more importantly in this case) a lower
> resistance
> > tuning inductor to be used with a resultant increase in
> power to
> > the antenna and improved system efficiency.
> ______________
>
> Reducing the resistance in the loading coil certainly is a
> step in the right direction, as long as system resonance of
> the 3-m radiator and a match to the tx both are achieved.
> But the coil resistance almost always is small compared to
> the r-f resistance of the return path for ground currents.
> And the radiation resistance of the vertical itself is
> miniscule compared to either one.
>
> Here are some calculated parameters for the base Z of a
> perfect 3-m radiator at 1700 kHz:
>
> 1/2" OD: 0.1278 -j3145 ohms
> 3" OD: 0.1263 -j2048 ohms
>
> A low-resistance loading coil for the 3" OD radiator might
> be something like 2 ohms, and a typical Part 15 ground
> system let's say is 20 ohms. The efficiency of the 3" OD
> system then is about 0.57%.
>
> If the loading coil for the 1/2" OD radiator had 4 ohms
> resistance and the other parameters were the same, system
> radiation efficiency would be 0.53%.
>
> The difference in the received field strengths relating only
> to coil loss from these two systems would be difficult to
> detect.
> //
>
By no means am I challenging your calculations, I just think that there may be other factors in play that are not being taken into account. I base my reported observations on experiments I have done under controlled conditions, using a HP signal generator, a Potomac OIB and FIM-41 and a HP RF voltmeter.
Much of this is a moot point because few commercial part 15 AM operations are able to achieve a good match let alone resonance with their antenna systems.
Most Part 15 experimenters, at least those that read this board, are much more interested in broadcasting than in the technical nuances of transmission. For those people, I suggest that they concentrate their energy on creating the best possible ground system that they can and perhaps add a top hat to their antenna if possible. This will result in the most substantial imporvement in coverage with the standard 3m antenna.
> > The increased diameter will increase the capacitance to
> ground
> > in nearly the same fashion as a top hat does, allowing a
> > lower value (and more importantly in this case) a lower
> resistance
> > tuning inductor to be used with a resultant increase in
> power to
> > the antenna and improved system efficiency.
> ______________
>
> Reducing the resistance in the loading coil certainly is a
> step in the right direction, as long as system resonance of
> the 3-m radiator and a match to the tx both are achieved.
> But the coil resistance almost always is small compared to
> the r-f resistance of the return path for ground currents.
> And the radiation resistance of the vertical itself is
> miniscule compared to either one.
>
> Here are some calculated parameters for the base Z of a
> perfect 3-m radiator at 1700 kHz:
>
> 1/2" OD: 0.1278 -j3145 ohms
> 3" OD: 0.1263 -j2048 ohms
>
> A low-resistance loading coil for the 3" OD radiator might
> be something like 2 ohms, and a typical Part 15 ground
> system let's say is 20 ohms. The efficiency of the 3" OD
> system then is about 0.57%.
>
> If the loading coil for the 1/2" OD radiator had 4 ohms
> resistance and the other parameters were the same, system
> radiation efficiency would be 0.53%.
>
> The difference in the received field strengths relating only
> to coil loss from these two systems would be difficult to
> detect.
> //
>
> I'm not sure what program you are using to do the
> calculations
The base Z values for the two 3-m radiators at 1700 kHz that I posted were NEC-2 (Numerical Electromagnetics Code, v. 2) calculations. This computer code has proven to be quite accurate for modeling the significant parameters and electromagnetic responses of radiating structures with defined geometry, source, and load parameters. The rest of my calculation to determine system radiation efficiency was based on the "R" component of the radiator base Z calculated by NEC-2, related to the other resistances in a Part 15 AM antenna system. This is just a proven application of Ohm's Law.
>... something else must explain the multiple accounts of
> far field signal strength improvement when the length
> to thickness ratio is decreased. This has been reported
> numerous times, ... I just think that there may be other
> factors in play that are not being taken into account.
> I base my reported observations on experiments I have done
> under controlled conditions, using a HP signal generator,
> a Potomac OIB and FIM-41 and a HP RF voltmeter.
I haven't seen verified proof to this effect, only that increasing radiator cross-section increases the SWR bandwidth of the radiator. That is a valuable benefit, but by itself doesn't increase radiation efficiency, or field strength at the resonant frequency of the antenna system.
//
> calculations
The base Z values for the two 3-m radiators at 1700 kHz that I posted were NEC-2 (Numerical Electromagnetics Code, v. 2) calculations. This computer code has proven to be quite accurate for modeling the significant parameters and electromagnetic responses of radiating structures with defined geometry, source, and load parameters. The rest of my calculation to determine system radiation efficiency was based on the "R" component of the radiator base Z calculated by NEC-2, related to the other resistances in a Part 15 AM antenna system. This is just a proven application of Ohm's Law.
>... something else must explain the multiple accounts of
> far field signal strength improvement when the length
> to thickness ratio is decreased. This has been reported
> numerous times, ... I just think that there may be other
> factors in play that are not being taken into account.
> I base my reported observations on experiments I have done
> under controlled conditions, using a HP signal generator,
> a Potomac OIB and FIM-41 and a HP RF voltmeter.
I haven't seen verified proof to this effect, only that increasing radiator cross-section increases the SWR bandwidth of the radiator. That is a valuable benefit, but by itself doesn't increase radiation efficiency, or field strength at the resonant frequency of the antenna system.
//
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