Home |
Search |
Today's Posts |
#21
![]() |
|||
|
|||
![]()
On Apr 2, 10:37 pm, wrote:
On Apr 2, 1:41 pm, Art Unwin wrote: Pray tell me then why I am incorrect. You can salvage the answer from your own mind or even from a book. When the air breaks down around an antenna it is because the antenna is not in a state of equilibrium. Define equilibrium as it pertains to an antenna. Until you do, it's fairly hard to comment on the first statement. I don't think I can do that for you, it would take to long. If you have corona discharge from an antenna, it's usually due to sharp points when using wire or a whip with a pointed tip. Thats why they stick round balls on whips, flagpoles, etc.. When you have a discharge it is a loss of energy When a dipole is replaced by a quad ala a series circuit is replaced by a tank circuit it clearly shows that the latter is more efficient. What clearly shows this? Well there is no discharge. This is becaquse that there is a route of a lesser impedance available This is the statement which drew my comment. The efficiency of a 1/2 WL dipole and a 1 WL loop are so close as to be almost unmeasurable in the real world. Almost doesn't count when measuring efficiency and in the real world many CAN tell the difference But you can take this even farther. Almost *any* size dipole or loop will radiate most all of what is fed to it. Again you are admitting to lower efficiency when you use the word "most" A 1/10 WL whip radiates almost all of the power applied to it, same as a 1/4 WL, 1/2 WL, or whatever you want to try. This not not conjecture. This is pretty much written in stone after many years of testing. Again you use the word "most" which is admitting less efficiency Why you continue to ignore this simple fact boggles my mind. So your statement is so far from reality I would be amiss in my "talking head" duties if I did not comment. Don't take my word for it. Ask anyone you can think of that has a clue. They will tell you the same thing. What it going to spoil your "full size performance from a dinky radiator" picnic is not the radiator and it's abilities to be an efficient radiator. It's going to be actually feeding the power to such a small radiator and not turning a large amount of RF to heat in the process. No cheating letting the feed line be the antenna.. I think you are missing the point here. My antenna has a full wave length of wire not a fraction there of. So the radiator has the same inductance and capacitance that one would expect from a full wave antenna spread out in a straight line where the wire surface is exposed to the atmosphere, so there is no reason for the energy to circumvent the wire circuit as it must do for a fractional wavelength. Look at "small" HF transmitting loops. Do you see any using 22 gauge wire? I doubt it. They will be using the fattest or widest strip of material they can get their hands on. What you are seeing as representing a loop antenna is a fractional wave length Often it comes with a HV variable capacitor for tuning. The loop that I made was a plastic loop with a full wave length of wire wound upon it. No high voltage capacitor needed as it coveres the whole band. As far as 22 gauge wire being used this is because there is no mechanical stresses imposed on it as would be for a stretched out radiator. So the main consideration is to supply enough skin depth since the diameter itself is not a factor in terms of fusing.current There are other issues involved also in feeding such an antenna. Never do these small loops equal the performance of a full size antenna. They radiate enough to maybe let you operate, and thats about it. If the scource impedance is one that you can match efficiently then you have at hand a efficient radiator of a wavelength where the normal loop you are refering to uses a metal loop as the radiator which is much shorter than a wavelength of wire wound on a plastic loop. The loop is now a small full wave radiator not a small fractional small wave antenna This was firmly proven in Quito.Maximum radiation efficiency requires equilibrium. Period Again, the change to quad loops at HCJB was to avoid the sharp points of the dipoles, yagi's, or whatever they were using. In the high alitudes of Quito, HV breakdown at the tips was a serious problem. The change had absolutely nothing to do with antenna efficiency. If the impedance is to high on the antenna compared to discharging through air to the transmitter ground then that is a very inefficient antenna Not to mention that the whole idea of a loop being more efficient than a dipole is totally wrong. The energy travels easily along the wire circuit without encountering a high impedance that it is forced to take a circuitous route thru ground to the transmitter ground. When the energy is passing thru ground it becomes a loss. And I don't see how equilibrium has anything to do with it, whatever you might mean by that silly "E" word. If a circuit is not balanced and a fractional wave length long it is not in equilibrium!. The energy supplied to the radiator will always encounter a energy wasting impedance in the wire itself if is not at least a wavelength long, and of the right material (diamagnetic) otherwise the energy will seek a route outside the wired circuit which can only lead to losses. Think of it this way, a fractional wave length radiator cannot avoid the energy taking a route thru ground and the ground is a loss. Hopefully you now see antennas in a different light. I do urge you to look up the tank circuit since it is quite an interesting circuit with its phase changes and effective resistances apparently changing without being diverted from the circuit wire confines. Another place where the books are in error is their association with the iron filing magnet experiment at HS which forms a magnetic field very different from that formed from aluminum, copper and other diamagnetic materials. When you pass a time varying current thru copper the magnetic field turns at right angles to the radiator axis and in fact compliments the electrical field vector ( they are not at right angles) Now you can see what lifts or ejects the static particles resting on the surface because they are repelled instead of bing magnetically atracted ( Static: nearly devoid of energy and of small mass) .. So the EH antennas which supposedly combines the EH fields just didn't understand that with a radiator the combination of vectors is already a given! I think you also are making a mistake that many books make when referring to small antennas instead of referring to ELECTRICALLY small antennas Anything else you are curious about? BTW, no grabbing of books were needed to form this response. Art Best regards, no offence intended Art Unwin ......KB9MZ..(uk) |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
what size antenna? | Shortwave | |||
what size antenna? | Shortwave | |||
Recomend Size of Aux Antenna for use with MFJ-1025/6 or ANC-4 | Antenna | |||
Question of Antenna Size? | Shortwave | |||
Physical size of radiating element? | Antenna |