I'm glad to see that we can agree, but there's little point in discussing antennas outside the context of receivers and transmitters, which is what I was doing.
An antenna with nothing connected to it hardly qualifies as an antenna, does it? It's just a piece of conductor, it's the receiver or transmitter that makes it an antenna.
You're just wriggling. Why not just admit that my point is well taken?
w
Since everybody else is getting out their credentials, a screenshot of some software I wrote to run the anechoic chamber...
w
An externally hosted image should be here but it was not working when we last tested it.
w
I'm actually not sure which of your points you mean. So let's review them.
That post was actually pretty good.
But the first sentence seemed an odd thing to say in the OP's context. It's like saying anything will work, just not very well, when he was wanting to know what would work well.
But at least you alluded to my main point, that if it won't receive well it also won't transmit well.
This one came off as a bit snobbish, at first, but who am I to talk about that? <grin> And the random wire comment threw in a bit of a red herring. And I think that the "perfectly satisfactory on receive" is what actually tweaked me, because if the antenna had also been able to transmit well, then it would also have been even better than the previous "perfectly satisfactory" level, for reception. I see where you're coming from and what you said is not wrong. I just didn't think it told the whole story well-enough, and that as an attempt at a counterexample it was just a bit too omissive.
This one I don't really understand. But I'm interested. I probably would have guessed the opposite, if told to assume that it was valid for (only one of either) weak or strong signals.
Getting back to your last post:
I think that I accidentally wiggled too far, at one point. So here is a correction: All of the transmit and receive antenna parameters are the same (i.e. have precise reciprocity) EVEN with the antenna connected to a matched transmission line (or any fixed impedance, actually).
What performance levels you get from the overall system will, of course, also depend on the rest of the system. But all of the antenna's parameters, i.e. propagation pattern, gain, resonant frequency, bandwidth, efficiency, and polarization will be exactly the same for both transmission and reception, unless you change the impedance that the antenna sees at the feedline connection. It doesn't seem like a big deal, as far as real systems are concerned (but is certainly true, as far as it goes). So, anyway, yes, in the larger context of complete systems with antennas, I'd say that all of your points were probably well-taken.
But why should it be so conceptually difficult to separate the antenna from the receiver or transmitter? I think there is _definitely_ a point to discussing antennas by themselves. There is a great body of theory and knowledge that considers mainly or only antennas. So yes, I believe that an antenna certainly does "qualify as an antenna", even when it is not explicitly in the context of a transmitter or receiver.
I think we've beaten this dead horse long enough (but feel free to continue, of course). Worse yet, I just burned my lovingly-hand-crafted pizza to death!
Regards,
Tom
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This just does not have to be true. Many antennas yes, other antennas no. A very common misconception.
My question now is, if I just use a hunk of wire 1.154 meters long, OR SO, will it need to be straight or can I fold it over a few times to place in a whip style enclosure?
Basically what I gather here from the discussion is, an antenna built to mathematical specs to receive/transmit the set wavelength and matching the impedance of the transmitter/receiver is going to give the most optimal performance in those respects. Then of course the type of design will play a major role in performance as well.
But ultimately, sometimes dumb luck designs or rigging produce solid results as well.
The stock antenna, which was just your generic single pole telescopic, was about 10-15 inches long but broke so I replaced it with a generic of the same design that was about 20-24 inches. Worked great but is a pain in the can even if I don't bother with full extension and will undoubtedly break. Replacing it with a 1.154 meter antenna probably allow me to walk around the neighborhood playing guitar if mounted on the roof but uhhhh I already have enough groupies
Ultimately if the little whip or modifying the little whip doesn't attain the results I desire, I'll just use a hunk of wire which I don't have to worry about snapping in half.
Basically what I gather here from the discussion is, an antenna built to mathematical specs to receive/transmit the set wavelength and matching the impedance of the transmitter/receiver is going to give the most optimal performance in those respects. Then of course the type of design will play a major role in performance as well.
But ultimately, sometimes dumb luck designs or rigging produce solid results as well.
The stock antenna, which was just your generic single pole telescopic, was about 10-15 inches long but broke so I replaced it with a generic of the same design that was about 20-24 inches. Worked great but is a pain in the can even if I don't bother with full extension and will undoubtedly break. Replacing it with a 1.154 meter antenna probably allow me to walk around the neighborhood playing guitar if mounted on the roof but uhhhh I already have enough groupies
Ultimately if the little whip or modifying the little whip doesn't attain the results I desire, I'll just use a hunk of wire which I don't have to worry about snapping in half.
You can divide the 1.154 meters by 4, to get a 1/4-wavelength antenna. That would be 28.85 centimeters, or 11.35 inches, if my arithmetic is correct.
You could just use a piece of wire and let it dangle. Or you could attach it to something non-conductive to keep it straight. Or you could use a piece of stiff metal instead of a wire. Or you could buy a collapsible whip antenna and push it down until it's the right length. If you already HAVE a whip that extends to 24 inches, you can use it as a 1/2-wavelength antenna at around 22.7 inches, for better performance, or collapse it to around 11.3 inches, for convenience.
Tightly folding the 1.15 meters of wire and stuffing it into a small-diameter enclosure might be too iffy.
You could just use a piece of wire and let it dangle. Or you could attach it to something non-conductive to keep it straight. Or you could use a piece of stiff metal instead of a wire. Or you could buy a collapsible whip antenna and push it down until it's the right length. If you already HAVE a whip that extends to 24 inches, you can use it as a 1/2-wavelength antenna at around 22.7 inches, for better performance, or collapse it to around 11.3 inches, for convenience.
Tightly folding the 1.15 meters of wire and stuffing it into a small-diameter enclosure might be too iffy.
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Well, it's only true for antennas with elements that are made of metal, or some other conductive material. <smile>
Seriously, how do you propose that the antenna could know what it is being used for, so that it could suddenly change its properties?
(OK, I guess maybe we should specify that we're talking about "plain" metal antennas, not "active" antennas with built-in amplifiers etc.)
As I also said, just to be more clear about it: What performance levels you get from the overall system will, of course, also depend on the rest of the system. But all of the antenna's parameters, i.e. propagation pattern, gain, resonant frequency, bandwidth, efficiency, and polarization will be exactly the same for both transmission and reception, unless you change the impedance that the antenna sees at the feedline connection.
How could that NOT be true??
Think about it. Have you ever seen an antenna gain pattern? Of course you have. Have you ever seen two different gain patterns, one for receive and one for transmit? Of course not. Case closed.
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Well like I said in this antenna right here in transmit effectively shorts itself out and acts then as a messed up dipole. In receive what is a short in transmit is the same part which converts the magnetic wave to an electrical signal providing a different pattern. So your concept is correct- the antenna behaves differently if it is driven by a signal or if it is receiving a signal. It is a "directional" device so you can believe it or not. I tire of trying to teach people who follow that idiot Heavyside and his miscarriage of Maxwell's equation which may have single handed set EM theory back 400 years. If you wish to learn pay attention. If you want to believe... then you are already there and therefore no action is necessary.
Well, OK. That is interesting. Does it have other electronic components as part of it? i.e. It's not just all metal and nothing else? Wait, you said "effectively" shorts itself out. How does that work? Can you share some of the details of the design? (I can sort-of imagine it, if it uses directional couplers, or pin diodes, or something. But if not, how?)
I'm really very interested in your point about Heavyside, too. Can you point me toward more information about that, or say a few more words, please?
(Not wanting to argue. Just learn!)
I'm really very interested in your point about Heavyside, too. Can you point me toward more information about that, or say a few more words, please?
(Not wanting to argue. Just learn!)
Well the magnetic converter is a single turn (effective) transformer as part of the antenna elements. This transformer converts any magnetic field around into an electrical signal. Under the driven (transmit) condition it is still doing the conversion of the magnetic field to an electric signal. maybe you can see the problem with that and realize that makes receive and send two different events. No diodes or anything- just that transformer.
As for Oliver Heavyside- in about 1901 he "rewrote" Maxwells equations to a "simplified" version. This simplified version is passed off on us unsuspecting students of EM as Maxwell's equations developed while at the Royal Academy published about 1885. What we are taught is not Maxwell but is Heavyside the idiot.
Ever wonder how a transformer works? No one really seems to know as if there is no current in the secondary then there is no magnetic field outside the core of a typical power transformer. Yet when current flows through the secondary a field appears (by magic!) outside the core produced by the secondary. The point being Heavyside removed all the vector analysis which explained these things. You will find it very common in EM theory books to COMPLETELY IGNORE the cross product of two vectors. Instead, as every book I have seen, shows breaking the two non-coincident vectors into their X, Y, and Z components and adding them together. Of course co-linear vectors don't produce a cross product. On the other hand the rules for vectors and cross products address this specific "cheat" and say it is invalid math and strongly warns against making this grievous error. This method of breaking vectors and reassembling them is fundamental to the present EM theory and invalid. It is also fundamental to quantum theory and equally invalid. If you want another book which explains CLEARLY the make up of matter and will really help with the EM theory stuff... "Vector Particle Physics" by Thomas Lockyer. Now there is a guy I can respect!! There are not many. Once you see how particle waves get tangled in each other to make matter EM theory becomes a whole lot more sensible and intuitive. A few other things- almost all analysis is based on plainer waves where EM are in phase but our world gots lots of spherical waves where EM are not so in phase. Indeed that antenna above- since it detects both it was the "lesson" that showed me beyond any doubt that the incoming wave was almost always elliptical with some rotational polarization unless it was near and line of sight. Big big difference from theory as taught! One more thing- EM waves warp space and change time. Transverse waves only occur when there is a medium of conduction present and are usually not found in EM radiation. Instead, EM waves are much like sound wave causing compression and rarefaction of the space time continuum.
Do you read your private messages here at DIY?
When I was 14 I made the assumption everything I have learned was wrong and started from scratch accepting only language and math as a basis. All conclusions were rejected and theories tossed out in favor of factual discovery. Would not recommend that to many people.
Good luck, =SUM
As for Oliver Heavyside- in about 1901 he "rewrote" Maxwells equations to a "simplified" version. This simplified version is passed off on us unsuspecting students of EM as Maxwell's equations developed while at the Royal Academy published about 1885. What we are taught is not Maxwell but is Heavyside the idiot.
Ever wonder how a transformer works? No one really seems to know as if there is no current in the secondary then there is no magnetic field outside the core of a typical power transformer. Yet when current flows through the secondary a field appears (by magic!) outside the core produced by the secondary. The point being Heavyside removed all the vector analysis which explained these things. You will find it very common in EM theory books to COMPLETELY IGNORE the cross product of two vectors. Instead, as every book I have seen, shows breaking the two non-coincident vectors into their X, Y, and Z components and adding them together. Of course co-linear vectors don't produce a cross product. On the other hand the rules for vectors and cross products address this specific "cheat" and say it is invalid math and strongly warns against making this grievous error. This method of breaking vectors and reassembling them is fundamental to the present EM theory and invalid. It is also fundamental to quantum theory and equally invalid. If you want another book which explains CLEARLY the make up of matter and will really help with the EM theory stuff... "Vector Particle Physics" by Thomas Lockyer. Now there is a guy I can respect!! There are not many. Once you see how particle waves get tangled in each other to make matter EM theory becomes a whole lot more sensible and intuitive. A few other things- almost all analysis is based on plainer waves where EM are in phase but our world gots lots of spherical waves where EM are not so in phase. Indeed that antenna above- since it detects both it was the "lesson" that showed me beyond any doubt that the incoming wave was almost always elliptical with some rotational polarization unless it was near and line of sight. Big big difference from theory as taught! One more thing- EM waves warp space and change time. Transverse waves only occur when there is a medium of conduction present and are usually not found in EM radiation. Instead, EM waves are much like sound wave causing compression and rarefaction of the space time continuum.
Do you read your private messages here at DIY?
When I was 14 I made the assumption everything I have learned was wrong and started from scratch accepting only language and math as a basis. All conclusions were rejected and theories tossed out in favor of factual discovery. Would not recommend that to many people.
Good luck, =SUM
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My question now is, if I just use a hunk of wire 1.154 meters long, OR SO, will it need to be straight or can I fold it over a few times to place in a whip style enclosure?
Basically what I gather here from the discussion is, an antenna built to mathematical specs to receive/transmit the set wavelength and matching the impedance of the transmitter/receiver is going to give the most optimal performance in those respects. Then of course the type of design will play a major role in performance as well.
But ultimately, sometimes dumb luck designs or rigging produce solid results as well.
The stock antenna, which was just your generic single pole telescopic, was about 10-15 inches long but broke so I replaced it with a generic of the same design that was about 20-24 inches. Worked great but is a pain in the can even if I don't bother with full extension and will undoubtedly break. Replacing it with a 1.154 meter antenna probably allow me to walk around the neighborhood playing guitar if mounted on the roof but uhhhh I already have enough groupies
Ultimately if the little whip or modifying the little whip doesn't attain the results I desire, I'll just use a hunk of wire which I don't have to worry about snapping in half.
The "typical" thing is to wind it in not very tight spiral at all around the whip so it looks like a very stretched out spring. Maybe a long spring and stretch it out would be good. The spring wire would resist breaking also. So the length of the wire in the spring can be the 1.154 meters but with the winding the spring itself could be half that length. A little bit of the wire spring could be fanned out on the end to make the end of the antenna look longer. Like the aluminum foil trick except with the wire of the spring making circles instead of a helix. Without equipment it will be difficult to know if it is the correct length. Touching the end makes the antenna longer. Putting your hand near the end without touching makes it shorter. This may help tune optimally without any fancy gear.
Is a floppy spring thing cool (acceptable) for your application? I have seen these decorated and be rather hilarious! Fuzzy one eyed puff animals on the end!
For transmitting, the thing is impedance match to free space.
And gain by excluding radiation wasted to unwanted directions.
The antenna can be very small, as long as impedance matches.
Small antenna have little directional gain over isotropic (The
sun radiates isotropic (all directions) for example). Directional
gain will require a big antenna, I don't know any way around.
Transmitting antennas do not care or need capture area, but
are usually big for directionality and easiest impedance match.
A physically too small antenna can still be tuned to match, but
this can be complicated and lossy.
Now for receiving, things are different. You need signal well above
noise including the front end noise of the receiver. Selectivity and
directionality, and capture area are important. Impedance match
is maybe not so important if 1st low noise amplifier is co-located
at the feedpoint of the antenna and there are no cables involved.
A small receiving antenna won't capture as much energy, and this
has to be more than the noise of the front end. A small antenna
also won't exclude interfering radiation from unwanted directions.
Yet mobile situations lack of directionality is sometimes required.
Longwire antennas are under-appreciated almost forgotten tech.
They have huge capture area. And in certain arrays, very good
directionality. Broadband impedance match is all over the place,
but like I said earlier, not really important if all we do is receiving.
And not really a problem to transmit specifically tuned frequencies.
I abuse 7 foot rabbit ears in narrow 30deg V for HDTV. Horizontally
polarized with the open V end pointed at the station towers. I got
string of lossy snubber resistors on the open ends to kill reflections
that originate from the backside, and stop antenna from misbehaving
as-if a resonant dipole that favors only certain harmonics.
Tilted rhombic array even more potent, if you have space in your
attic. Its not really that big when we are talking only UHF.
Arie Voors' 4NEC2X is the best of free simulators. Forget all others.
And gain by excluding radiation wasted to unwanted directions.
The antenna can be very small, as long as impedance matches.
Small antenna have little directional gain over isotropic (The
sun radiates isotropic (all directions) for example). Directional
gain will require a big antenna, I don't know any way around.
Transmitting antennas do not care or need capture area, but
are usually big for directionality and easiest impedance match.
A physically too small antenna can still be tuned to match, but
this can be complicated and lossy.
Now for receiving, things are different. You need signal well above
noise including the front end noise of the receiver. Selectivity and
directionality, and capture area are important. Impedance match
is maybe not so important if 1st low noise amplifier is co-located
at the feedpoint of the antenna and there are no cables involved.
A small receiving antenna won't capture as much energy, and this
has to be more than the noise of the front end. A small antenna
also won't exclude interfering radiation from unwanted directions.
Yet mobile situations lack of directionality is sometimes required.
Longwire antennas are under-appreciated almost forgotten tech.
They have huge capture area. And in certain arrays, very good
directionality. Broadband impedance match is all over the place,
but like I said earlier, not really important if all we do is receiving.
And not really a problem to transmit specifically tuned frequencies.
I abuse 7 foot rabbit ears in narrow 30deg V for HDTV. Horizontally
polarized with the open V end pointed at the station towers. I got
string of lossy snubber resistors on the open ends to kill reflections
that originate from the backside, and stop antenna from misbehaving
as-if a resonant dipole that favors only certain harmonics.
Tilted rhombic array even more potent, if you have space in your
attic. Its not really that big when we are talking only UHF.
Arie Voors' 4NEC2X is the best of free simulators. Forget all others.
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Heaviside rewrote Maxwell's equations using modern vector notation. He did not change their meaning; they still describe exactly the same physics. That is why we still call them Maxwell's equations, not Heaviside's equations. They are intimately related to the structure of modern physics, and can be derived as the classical limit of the necessary spin-1 gauge particle arising from the quantum field theory of electrons (quantum electrodynamics, or QED). Engineers are not taught this, as it is graduate-level physics, so they sometimes feel free to criticise what they do not understand.
There are always people who want to make physics more "sensible and intuitive". The trouble is, they are almost always wrong. We have to accept the universe as God made it, not as we would wish it to be. There are aspects of EM and quantum theory which are counter-intuitive. That does not mean they are wrong, just that we are not smart enough to fully understand them. Note that intuition is merely a set of (classical) prejudices laid down in early childhood. If the speed of light was much smaller, and Planck's constant was much larger, then our intuition would be a better guide to accurate modern physics because we would be accustomed to seeing non-classical effects in daily life.
Reciprocity tells us that most passive antennas (e.g. metallic, dielectric - but not necessarily those using biassed ferrites?) behave in exactly the same way for reception and transmission, as others have said. Their operation in a system obviously depends on the related equipment.
Small antennas usually have a dipole-like radiation pattern - about 1.5-2dB over isotropic.
No, you can get good gain from a small antenna but it will have narrow bandwidth or low efficiency (see supergain antennas, and Chu-Wheeler limit). Making the antenna with superconducting elements is a possibility which some have explored.
So, to return to the original question, and based on my experience of designing and building antennas:
As of yet I haven't seen a reply that has improved on this, although many have obfuscated the issues, in some cases with a prolixity that has to be observed to be believed.
I take a pride in explaining things without needless complication, and I haven't got a lot of time for people who indulge in nit-picking for the gratification of their egos, particularly when their points are not well taken, their attitude ungracious and their tenacity beyond good taste.
w
As of yet I haven't seen a reply that has improved on this, although many have obfuscated the issues, in some cases with a prolixity that has to be observed to be believed.
I take a pride in explaining things without needless complication, and I haven't got a lot of time for people who indulge in nit-picking for the gratification of their egos, particularly when their points are not well taken, their attitude ungracious and their tenacity beyond good taste.
w
DF96- well there is this history repeated over and over where so many thought what was right was really wrong. See you have fallen into the Heavyside trap and missed the point. Being a physicist is it possible then what I wrote is true? EM theory and the ridiculous exclusion of the cross product is fundamental to the Heavyside error and the QED errors. As for the "intuitive and more simple" part, nature loves simplicity and it is man that makes things complicated. Can tell from your somewhat "I know the facts" statement that you do not know the facts and have not read the writings of Thomas Lockyer and are still caught in the folly of "modern" theories. I actually figure if it was not for Heavyside we would be floating about on anti-gravity machines by now. But then you have taken up the Heavyside flag and the errors that go with it. "Ignorance is bliss" and closed mindedness leads to a lot of bliss so enjoy your happiness. People are not interested in facts, they are interested in feeling good about what they believe. You are there DF96.
Whenever I was in school I said "This class... is not science because it can easily be shown what is taught is not correct. Call it a mathematical exercise or religion but don't call it science because it is not." Apparently you, as many others have, overlooked the breaking and summing of vectors to prevent the cross product as a convenience as so many other also have and is the basis of the Heavyside simplification.
These are the facts and will not argue about them. Have never seen a text or modern theory which did not commit this cross product violation. If you wish to "believe" those results that is your prerogative. Don't call it science though, it is not.
Whenever I was in school I said "This class... is not science because it can easily be shown what is taught is not correct. Call it a mathematical exercise or religion but don't call it science because it is not." Apparently you, as many others have, overlooked the breaking and summing of vectors to prevent the cross product as a convenience as so many other also have and is the basis of the Heavyside simplification.
These are the facts and will not argue about them. Have never seen a text or modern theory which did not commit this cross product violation. If you wish to "believe" those results that is your prerogative. Don't call it science though, it is not.
I think violenceontheradio is working on a spring version of the antenna anyway. I await his results.
Rather than wasting time with stuff that does not work, read that book I mentioned.
This is how we get fooled in the copies of text. Make the X,Y,Z breakdown. Seems valid enough... Then proceed to do the math only using the co-linear vectors. This eliminates the cross product. Easy as π, except I did not get fooled by this trickery as my method to pass physics, instead of recalling formula, was to derive the formula on the spot. I saw this one as invalid as soon as it was postulated. The stench of the lie expands endlessly from here! The Heavyside method. He is not the only one to blame. Simply the leader of false and misrepresentation.
Rather than wasting time with stuff that does not work, read that book I mentioned.
This is how we get fooled in the copies of text. Make the X,Y,Z breakdown. Seems valid enough... Then proceed to do the math only using the co-linear vectors. This eliminates the cross product. Easy as π, except I did not get fooled by this trickery as my method to pass physics, instead of recalling formula, was to derive the formula on the spot. I saw this one as invalid as soon as it was postulated. The stench of the lie expands endlessly from here! The Heavyside method. He is not the only one to blame. Simply the leader of false and misrepresentation.
Attachments
You still haven't told me where the alleged cross-product arises. I don't see what the Coulomb force has to do with it. Just referring me to a book I don't have is not very helpful.
So, what is it about the two pages you have shown which illustrates the issue you are raising? All it seems to say is that the Coulomb force is directed along the direction vector (true) and the strength follows an inverse-square law (true). What is wrong with that?
So, what is it about the two pages you have shown which illustrates the issue you are raising? All it seems to say is that the Coulomb force is directed along the direction vector (true) and the strength follows an inverse-square law (true). What is wrong with that?
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