The 5/8 and .64 debate!

[freecell]

"resonance is nice but certainly not a necessity.

no, the definition of resonance isn't "nice."

resonance: In an electrical circuit, the condition that exists when the inductive reactance and the capacitive reactance are of equal magnitude, causing electrical energy to oscillate between the magnetic field of the inductor and the electric field of the capacitor. magnitude of the fields are at their maximum in this condition. Note 1: a resonant antenna is a tuned electrical circuit. Note 2: Resonance occurs because the collapsing magnetic field of the inductor generates an electric current in its windings that charges the capacitor and the discharging capacitor provides an electric current that builds the magnetic field in the inductor, and the process is repeated. this is how an antenna works. this is referred to as the "flywheel effect." Note 3: At resonance, the series impedance of the two elements is at a minimum and the parallel impedance is at maximum. Resonance is used for tuning and filtering because resonance occurs at a particular frequency for given values of inductance and capacitance.

"Any length radiator will radiate evey bit of the power that reaches it." the key words there being "every bit of power that reaches it." more power is received and radiated by the antenna when it is resonant as opposed to when it isn't. the further the antenna is from resonance the more power that is wasted simply because impedance, which is by definition the opposition to the flow of current in an ac circuit is greater when unequal vales of capacitance and inductance exist and the resistance is something other than that which is necessary to match the feedpoint to the feedline, after all Z (impedance) consists of both X (reactance) and R (resistance) and again is frequency dependent. how much of a difference can there be? ask the opera singer who shatters glass by utilizing this same effect what happens if the pitch of their voice isn't exactly the same as the resonant frequency of the glass they are attempting to shatter. when the pitch generated coincides with the resonant frequency of the glass and sustained at a given intensity for a definite period of time the glass shatters. any deviation in frequency or reduction in intensity leaves the glass undamaged. the same principle applies to standing wave antennas. is that enough of a difference for you?

 

[Hamin' X]

interestingly enough the "5/8 wave" antenna terminology came into use about the same time that antennas longer than 1/2 wavelength were beginning to be developed while still remaining in compliance with the portion of the FCC antenna height rule dealing with the 20' limitation required when installed on pre-existing structures.

This statement only applies to CB. Broadcast engineers have known since the late 1920's, that the ideal height for best ground wave propagation is a 5/8ths wave electrical length. Not 1/2, or 3/4. We are only talking about the electrical length of the radiator and not the entire antenna circuit. It is the radiator length that is critical to radiation pattern.

I remember talking to the engineer at our local AM broadcast station, when I was a young Ham, in the early 60's. We were discussing the tower and it was then that I first heard about 5/8ths wave antennas. I remember that he said the magic number was 225, as in degrees. Anyway, the point is that 5/8ths gives you the lowest angle of radiation. Feed it with the lowest loss feedline and match it with the lowest loss matching device and minimize the ground losses. Perfect antenna.

Rich

 

[freecell]

"We are only talking about the electrical length of the radiator and not the entire antenna circuit."

that figures.

 

[W5LZ]

Yes, it does 'figure'. Unfortunately, you don't see how it makes any difference. I honestly don't ever expect you to be able to see that 'difference', and that's a shame.
- 'Doc

 

[Hamin' X]

Thanks, Doc. I think that he is missing the whole point.

Who cares about resonance. If you can load into it, with minimum losses, everything radiates. The important factor is, where does it radiate to? If it is not in a useful direction, it does not matter.

Rich

 

[Hamin' X]

On this same subject, I've been designing antennae for over 40 years. I have found that if you design for the radiation pattern that you desire, then figure out how to load the antenna with minimum losses, you have achieved the optimum. Any comments from our new age thinkers?

Rich

 

[freecell]

just explain for the benefit of all here why resonance is a non issue. explain why a non resonant antenna doesn't result in a decrease in the amount of power radiated or intercepted as a result of current and voltage waveforms shifting out of phase with one another as indicated and confirmed by a vector impedance analysis using a network analyzer when applied to any load exhibiting a net value of either capacitive or inductive reactance. (X not equal to 0)

understanding that P=E*I and that when E and I are shifted from their optimum values in a non resonant condition resulting in a decrease in the amount of power delivered to or from the load as the measured values for both E and I result in power cancellation (power factor less than 1.0) tell us why we should simply ignore all of this. please tell us all how we can use antennas with large net values of reactance and not suffer any penalties in the form of energy transfer efficiency. i'm waiting to be enlightened. feel free to be a little more verbose than you have been in your previous posts, i'm all ears.

 

[Hamin' X]

Power cancelation? Poof, it's gone? Where did this canceled power go? Reflected? SWR? ??

More to come. Where's Kurt, when I need him?

Rich

 

[freecell]

"Poof, it's gone?"

if it really was "gone" that would be a violation of the laws of the conservation of energy. so ALL YOU HAVE TO SAY after my last post is that because you don't know what happened to it then apparently resonance is not an issue? that there's anything missing at all with as little as a 30 degree phase shift and a 15% reduction in power transfer efficiency regardless as to where it went or what it was converted into should be evidence enough to cause you to want to re-evaluate what you think you know. just reply to the points i made in my previous post one at a time and tell me how each one of them is totally wrong. is that all you got?

 

[W5LZ]

Ah, but as was pointed out, if the radiation pattern of the non resonant antenna is such that it puts the signal where you want it, then does it really matter if it isn't the full power, including that which seems to have disapeared, that is possible with a resonant antenna? If the point is that you get the absolute most bestest signal report possible, then that reduced power might be a problem. If the point is to communicate at an understandable level (no matter how much you have to strain to hear it) then less is still good enough. Guess it just depends on what your objective is.
- 'Doc

 

[Hamin' X]

You missed my point. Perhaps I should have been more direct.

I was asking you where your canceled power went to. My position is: In a properly operating antenna system, with proper feedline (parallel conductor) and a properly designed and tuned transmatch at the transmitter, It matters not whether or not the radiating element is resonate. Virtually all of the power will be radiated from that element. Not lost as heat, due to standing waves in the feedline. The trick is to design the radiator to radiate it in a desirable direction.

Rich

 

[freecell]

no, i didn't miss anything. i have no problem with non-resonant radiators.

 

[Toll_Free]

"Poof, it's gone?"

if it really was "gone" that would be a violation of the laws of the conservation of energy. so ALL YOU HAVE TO SAY after my last post is that because you don't know what happened to it then apparently resonance is not an issue? that there's anything missing at all with as little as a 30 degree phase shift and a 15% reduction in power transfer efficiency regardless as to where it went or what it was converted into should be evidence enough to cause you to want to re-evaluate what you think you know. just reply to the points i made in my previous post one at a time and tell me how each one of them is totally wrong. is that all you got?

As Watson's boss would say, it's elementary.

The power is wasted as heat... Heat blowing your over-volted 2879s, heat in the anodes of the tube, and heat in the warm spots every electrical half-wave in your coax!


Anything will radiate power. A dummy load radiates power. Minimal, but it does. What matters is the network that transforms one impedance to another (the transformer). Bottom line.

But, a 5/8ths antenna, 5/8ths above ground, I would bet would kick ass

And, I also say you are all arguing about nothing.... One person may need max power at 35 degrees, another at 18 degrees.... Would one antenna be best for both of them? Would one antenna be that "magic" antenna? Nope. The HAAT for both stations and the differential elevation between the two stations making the comparison have so much more to do with this than the actual power levels transferred from the feedline to the radiator...

Anywho.

--Toll_Free




--Toll_Free


--Toll_Free

 

[Hamin' X]

no, i didn't miss anything. i have no problem with non-resonant radiators.

Then explain your statement in a previous post, please.

just explain for the benefit of all here why resonance is a non issue. explain why a non resonant antenna doesn't result in a decrease in the amount of power radiated...

I did explain why it is a non-issue. All power that is radiated, from any radiator, is in phase. Any out of phase power is reflected back to the ATU and re-reflected back to the antenna, where the same percentage of power is radiated in phase, ad nauseum. If your antenna system is configured properly to minimize ground losses and you are using an efficient feedline, then the amount of radiated power from a non-resonant antenna is virtually the same as a resonant one. Also, a resonant antenna is, only resonant on one frequency. When you change your operating frequency, what do you do? You are not equipping yourself to deal with the real world and severely limiting your capabilities.

This idea that an antenna must be resonant has only been in vogue for the last 30 years or so, since the takeover of solid state PAs. The consensus thinking is that you have to have a resonant antenna to keep the finals happy. It's a bunch of hooey. Prior to this, every good ham shack had an efficient transmatch and low loss feedline. Nowadays, nobody wants to fiddle with them. They want instant gratification---Plug-And-Play. And don't even get me started on these automatic tuners that the charlatans are peddling these days. Have you looked at the low-Q coils that these lossy things are using. You have to have high-Q in the ATU, in order to have as close to a perfect miss-match to reflect the reflected signal back to the antenna.

Stop worrying about resonance and SWR. Throw up two wires as high as you can and as long as you can. Make, or buy the highest Q ATU that you can. Make, or buy the best parallel feedline that you can(not ladder line) and load-er-up.

Have fun and talk to the world, on all bands, on the cheap.

Rich

 

[freecell]

"All power that is radiated, from any radiator, is in phase."*
in phase with what? itself? Power = Voltage X Current.

all current (electric field ie. capacitance, capacitive reactance) and voltage (magnetic field, ie. inductance, inductive reactance) that is radiated, from any radiator, is in phase. no, that's not correct either.

phased 1/4 wave verticals fed with a transformer in which one of the two legs either leads or lags the other leg by any number of degrees constitutes and out-of-phase (current/voltage) relationship in and between the two radiators when compared to the same two verticals fed in phase. that's just one example.

*no it isn't. in one of my previous posts i demonstrated that quite clearly. power may be radiated but that doesn't necessarily constitute the proper phase relationships for both voltage and current, the stuff that power is made of. furthermore cb and 10 meter rigs don't have atu's and are fixed at 50 ohms output. as long as the real part of impedance is composed of resistance and reactance the resistances have to be matched and something has to be done with any imbalance in reactance. i noticed that some of you like to throw terms around like impedance matching and load matching while claiming that resonance is just some fad but if impedance is comprised of a combination of resistance and reactance then just what is happening with the reactance present in the system if you're not paying any attention to it? part of impedance matching dictates that reactance is present and yet for you maybe it is of no importance. i think otherwise, particularly in the case of the designs that are or were originally the topic of this thread.

"When you change your operating frequency, what do you do?"

re-establish resonance in the antenna CIRCUIT so that X = 0.

"This idea that an antenna must be resonant has only been in vogue for the last 30 years or so, since the takeover of solid state PAs. The consensus thinking is that you have to have a resonant antenna to keep the finals happy."

i'm not a participant in the concensus and i don't use balanced feedlines. keeping the finals happy has nothing to do with my preference for resonant antenna systems.

the antennas under discussion originally in this thread are not all band antennas and they're designed to be used with 50 ohm feedline.

and i have never disputed the fact that most RADIATORS are not resonant based solely on their physical dimensions. i don't care about that and it's not important, it's the ELECTRICAL resonance of the antenna circuit that's important. the fact that the physical properties of the radiator alone don't constitute a resonant condition don't concern me. if you're not able to measure reactances present in the system then you're certainly in no position to comment on it.

the antennas that are the subject of this discussion are designed to operate in or near a condition of electrical resonance. while so-called 5/8 wave radiators for cb radio run the gamut in lengths anywhere from 11.5 - 27 feet (which clearly indicates that resonance is not derived from the physical dimensions) they are all electrically resonant 3/4 wavelength operationally when the entire antenna circuit is given proper consideration. let's get back on track here. this thread was closed once before because someone wandered off from the topic. let's redefine everything.

the antennas under discussion are described as 5/8 wave and .64 wavelength and designed to be operated in at or near resonant condition in the cb band. by virtue of that the feedline predominantly used is 50 ohm coaxial cable. the radio equipment used is designed to operate optimumly into a 50 ohm purely resistive load and doesn't include atu's as standard equipment, much less as an option.

if you want to talk about radiation patterns, 80 meter dipoles that can operate multiple amateur bands when used with a transmatch, amateur rigs with atu's or am broadcast stations then start another thread. the introduction of these unrelated items is only adding to the confusion.