The 5/8 and .64 debate!

[Master Chief]

I'll do you one better! I'll change the title AND make it a sticky! I'm all for the discussion, I learn more everyday!

In the beginning, there was CDX-007!.....

I was just thinking about Jay's match and the difference in length between a tuned Maco V5/8 and Jay's...
I bet you cold enlarge that circular match on the Maco and get it to tune correctly to a true .64 in length, (or about 23') instead of that wimpy 19.8' or so it needs to be to tune correctly on Lsb 38 in it's stock form.

Anyone have the correct overall length of the tuned match on the Interceptor 10K from both the feed point to the radiator, and the feed point to the radial?

Then came.....

CDX-007,
Lots of 'no' answers here, be prepared!
Can the matching 'ring' on the Maco be changed to make it work on any particular frequncy? Yes. But that doesn't make the antenna 'resonant' on that particular frequency unless it's length is adjusted also. Then, what does that say about the "true" 0.64 wave length thingy? No idea what it may 'say' to you, but it 'says' several things to me, such as;
A. A resonant length is a nice thing to have but it isn't as critical as it seems sometimes.
B. What a particular antenna is called/named ought to give you at least a little idea of what the thingy is, or is supposed to be, or who made the thing, or something so you don't confuse it with something else.
C. There just ain't no 'perfect' antennas in the 'real world'! Absolutely nothing will do everything that you want it to do, unless what you want to do is very limited. The more extreme that 'limited' is, the closer you can get to a 'perfect' antenna. The key word in that is 'closer', cuz you just will never get there except accidentally, and it depends a lot on your definition of 'perfect'.
D. The more money you can throw at the problem, the easier it gets.
E. The more ~any~ antenna is modified to make it more 'perfect', the more expensive it gets (not just in terms of $$).

So... A strict answer to your question is, 'yes'. Depending on how 'practical' it is, the answer could also be, 'no'. There are five required questions to answer the 'practical' thingy;
Who,
What,
Where,
When,
and
What's it cost.

Being a certified "C & L" Expert, the last one is the 'biggy' for me. Not all of us can be experts.
- 'Doc

[C & L Expert = an expert in cheap and lazy]

Followed by a blantant HYJACK.....

WARNING, Thread HYJACK in PROGRESS!

Can the matching 'ring' on the Maco be changed to make it work on any particular frequncy? Yes. But that doesn't make the antenna 'resonant' on that particular frequency unless it's length is adjusted also.

With the I-10K, you make adjustments for both the vertical element AND the "ring" (tombone) based on your frequency of choice. Oh yea, you also adjust the other trombone (impedance matching) and ground radials too! So I guess the I-10K is really frequency friendly!

Then, what does that say about the "true" 0.64 wave length thingy?

With the I-10K, its ALWAYS at 0.625 wave length (based on x frequency).....if you do the math (included in the TUNING MANUAL) thats provided!

There just ain't no 'perfect' antennas in the 'real world'!

This is true, even for the I-10K, but it still is the BEST!

End of Thread HYJACK!

Then back to 007.....

Hijack? Hmm...

Well, Eddie seems to be among the missing, along with his cool antenna design...bummer... so we may as well go for the longest thread ever seen on planet 38 Lsb...

But my brainfar... uh brainstorm, was simply to add 3' of stinger from a joe-blow mobile antenna, or a piece of aluminum to the top of the Maco V-5/8 to get a total of approx 23'.
One would then simply reset the diameter of the loop match to the correct length / diameter, tuning for the correct impedance feedpoint on the new larger ring.
It seems to me one would then see about a +1 S-Unit increase over the stock Maco due to a lower radiation angle from the true .64, especially at further distances.
I expect a better receive, too, due to greater capture area.

One would basically be making a cheap, light-duty, reasonable facsimilie in performance of the:

INTERCEPTOR
SIGMA-5/8
PENETRATOR
Taylor GLR4
WILSON ALPHA V-5/8,
etc...

Since nobody now makes one for under $300, which is out of the price range of more than a few CB'rs, I figure someone with a bit more time than money could spend a couple of hours & a couple 10 spots, and be rather pleased with himself after successfully modding the only sub-$100 metal GP available today into a real .64 GP.

Just a far... uh, thought :idea:

Then me again.....

Since nobody now makes one for under $300, which is out of the price range of more than a few CB'rs, I figure someone with a bit more time than money could spend a couple of hours & a couple 10 spots, and be rather pleased with himself after successfully modding the only sub-$100 metal GP available today into a real .64 GP.

Yet, those with a CB mentality (not a good thing) are more than ready to spend BIG bucks on overpriced "export" radios, a 2x4 to (over)drive their 8 pill, a 10-tube nightmare, or even a 6 X 3-500Z box, yet go cheap cheap cheap on an antenna and coax and wonder why it doesn't work.

I just installed another I-10K for a local and EVERYONE except a couple of us are surprised how well he is getting out. We have been telling people for YEARS and yet they still don't believe.

I rebuilt a Maco V58 for a local. He could never get better than a 1.5:1 with it. I got a 1:1 SWR (sorry, only one SWR today, so I can't say SWR's). The antenna is working better than ever.

I tell people ALL THE TIME, "If you can't afford an I-10K, get the Maco V58."

The difference between a .625 wave and a .640 wave is almost not worth measuring. .625 = 5/8 BTW. If you think about it, .64 is the maximum length before your radiation pattern begins to degrade. If your antenna is tuned to channel 20, all channels above channel 20 suffer because the antenna is longer than .64 wave. Oh GOD, where will this thread go now?! :twisted:

Lastly , read my signature, yet again!!!!

007.....

Yep, I have to agree, and you mentioned the difference between a .625 & .64 not being much of a difference, but I'm referring to the difference from a 19.8' to a 23' antenna.
For the price of a couple pieces of 3/8" tubing from the local hardware store, a person could conceiveably build their own nice little true .64 from that light-duty $100 Maco V-.55 wave.

By the way, I pulled off the radials from a buddies brand spankin' new Maco V-5/8 last fall, (that he loaned to me while I was cleaning up the Penetrator) and saw ZER0 difference in performance or SWR without the radials.
The ONLY difference I saw was a little more TVI without them.

After I cleaned up the Hy-Gain Penetrator and put it back up where the Maco had been for testing, EVERYONE noticed at least an S-unit better signal strength and I noticed more like 2 S-units increase on receive, especially with those a little farther away.

If someone enjoys chatting CB or 10m and needs a cost effective .64 which would still handle full legal limit on 10m, I can't imagine one could do better for the $110 or so it would cost to buy & mod a Maco V-5/8 (.55) to a full .64.

Now, anyone got the measurements of the Interceptor match for all those reading this who already own a Maco and want to upgrade their performance?
I'll wager it would be dang close to perfect for a 23' modded Maco, and you could keep it a ring rather than having to mimic the trombone of the I-10K.
Strange, the Avanti Sigma 5/8 is basically the same antenna, but it's match is fed at the beginning of the bottom of the ring, not near the center like the I-10K.

Now I have to decide which amp I want to keep, Drake L-4B, Drake L-7, Kenwood TL-922A, or Swan MarkII...???
Decisions, decisions.

me..... (I'm almost caught up)

You keep saying ".55" That would only be slightly longer than a 1/2 wave. Do you mean .625? The Maco is a V58 and probably best not to confuse everyone out here.

The Maco could NEVER be modified like the I-10K. Neither could the Penetrator. They are designed completely different, most notably is the elevated feed of the I-10K.

The Avanti Sigma 5/8 is no way near identical to any of the above mentioned antennas (Maco, Penetrator, Sigma).

If you could make any changes to the Avanti or the Maco, it would be to add a top-hat and re-adjust for best length. But, all these antennas work fine as designed so I wouldn't bother.

Any changes I make to the antennas are more about mechanical upgrades than electrical.

Then C2!

What he is saying about the .55?

He is talking about the length from the tip of the maco to the lower bolt of the groundplane, which is specified as something like 240 inches by the instruction sheet. Whatever the length is that they do specify, it is somewhere between 1/2 wave and 5/8 wave, IIRC.

Now, if you take a wavelenght of 234/F for a 1/4 wave element and apply some simple math, you get ~413 inches for a full wave element, then divide by Maco's 240 and take the reciprocal, you get a figure of 0.58.

Could that be why they call it a V58? It's 0.58 wave long?

And then I always wondered about the lenght being less than 5/8 wave...I finally guessed that the rest of the lenght was in the matching coil....the path from the coax feed point, along the ****** wire, around the aluminum ring, and up the mast would be linearly close to 5/8 wave.

:idea:

and finally, Corn Hollio.....

1 full wave at 27.205 = 36.1'
That means a 5/8 = 22.5' long
That means the .64 antenna = 23.1 feet long.

Now, what NONE of this takes into account is the VELOCITY FACTOR!!! These measurements are all in free space.

Take velocity factor into account and you get:
(and this is theoretical at this point, since I don't have the vF sheet in front of me, nor can I get it atm)

Anywho, vF of .75 to .95 are common... Take your 5/8 antenna and see it jump down to:
22.5'x.9 (sake of argument) = 20.25 feet long.


The difference that most of you see is the velocity factor. Nobody takes that into account.



You saw no difference with the Maco when the radials where pulled off because at that point, you created an untuned dipole, a la ringo ranger. Without the tuned counterpoise and decoupling from the mast / tower / etc., you where doing nothing but using your mast as a counterpoise. See elsewhere where I talked of isolating the ground section (plane) of the antenna from the supporting structure. Try that, and remove the ground plane assembly. Your match just went to shit. Again, not isolating your antenna from the supporting structure skews the polar plot of the antenna....... And causes tvi and all sorts of nastiness.

If your going to use your S Meter as the component to measure your antenna improvements, make sure your getting s meter readings from people < S5 on your end... Otherwise your AGC will skew any and all readings. And AGC usually works log.... Meaning its non-linear in it's clamping ability.. The stronger the signal, the more its going to clobber it by varying the gain of the incoming signal. Don't use the RF gain to take a S8 to a S1 either... Won't work, since the RF gain usually varies the AGC voltage. S1 to S3 signals work best, with a DMM on the s meter to make finite adjustments.

Want the best antenna, forget the match. Tune your antenna for the maximum recieved signal (small signal)... Then adjust your feedpoint for minimum reflected power. NOW your where your antenna is RESONANT.

As others have said, the distance to the other station makes a difference as well.

Bottom line, your not going to notice the difference talking between a .6 anything wave antenna. CB meters JUST don't have the ability to do so.

YOUR GOING TO NOTICE THE DIFFERENCE IN THE FEEDPOINT, THE AMOUNT OF LOSS FROM THE FEEDPOINT DESIGN AND THE INSERTION LOSS OF ANY METERS more than you will from going from .55 to .64... SERIOUSLY!

You saw an increase in the signal before because you took a simple resistive bridge (which is what the Maco feedpoint is, taking and tapping a coil for the maximum power transfer, OR for minimum reflected power... Which don't always coincide) to an antenna that used a tuned input.

What works better on a linear... Tuned input or swamped input?

Nuff said, put it to rest.

--Toll_Free

 

[bob85]

hey 007, modify your v5/8 and post your results

to me this is exactly what the radio hobby is all about and imho there is just not enough of it nowadays unless you consider clipping limiters and running a shit sounding 200%+ modulation a worthwhile mod,

if i could not experiment and modify i would have zero interest in cb, ham radio, hifi or cars.

 

[freecell]

a 5/8 wl antenna, (.625) .64 (whatever) CANNOT BE RESONANT since it IS NOT A MULTIPLE of a ¼ wave length. (.25, .50, .75, etc.) the antennas mentioned in the locked thread are all 5/8 wavelength with a NET CAPACITIVE REACTANCE, in other words THEY'RE PHYSICALLY TOO DAMN SHORT TO BE RESONANT. ALL 5/8 WAVE ANTENNAS have an inductance fitted somewhere along the length of the antenna to cancel out the capacitive reactance and RESONATE the antenna. the 5/8 wave antenna is commonly tuned using A LOADING COIL, HAIRPIN MATCH OR GAMMA MATCH DEVICE TO RESONATE IT AS A 3/4 WAVELENGTH ANTENNA.

electrically speaking there IS NO SUCH THING AS A RESONANT 5/8 WAVE ANTENNA.

 

[Master Chief]

Yep! I agree with everything freecell said above!

When speaking of velocity factor, we are usually talking about coax, but it applies to the flow of energy through antennas too.

Another item not discussed is the tapered element. This also changes the length of the element. An electrically resonant (or non resonant) element of 14ga wire will be physically LONGER than the same resonant element made of 1" tubing.

I was working on an older Maco V58 the other week that used a 3/8 diameter tubing for the top section. Using a recent downloaded copy of the manual direct from Maco, it was clear that the stepping of this older antenna was different than the current versions. The main element had to be made LONGER than the newer antennas to make it work correctly.

The Maco manual, when speaking of over all length, says, "...the chart length is not sacred and may be changed to allow for variations in construction." This is when you use the "Bob Method" and keep working it until it's right! Why not, it will be up for years if you build it right! Maco also says there are only 2 adjustments when tuning their antenna; the main radiator length and the tap point on the ring. This ring is also of a fixed size, limiting your range of frequency it can tune to.

The Avanti Sigma 5/8 is not tuneable at all unless you cut down the top section or buy a new piece to make it longer. You don't tap the ring n the Sigma. Then again, the Sigma 5/8 was designed in the middle of the CB band.

As I pointed out before, this is where the I-10K differs. The I-10K give a specific equation to set the length of the main radiator AND the ground plane radials based on your desired frequency. Once these are set, you don't need to touch them again (which is why I pop-rivet them in place and call it a day). Then you tune the antenna using the pair of trombones. I don't know where Jay came up with the equation for setting the 5/8 radiator or if he took the element stepping into account, but I do know it works!

I asked Jay about changing the math from "xxx/Mhz X .625 =" to "xxx/Mhz X .640 =" The difference was just over 6", not 3' like 007 example above. Why mess with a good thing anyway?

 

[Toll_Free]

Yep! I agree with everything freecell said above!

When speaking of velocity factor, we are usually talking about coax, but it applies to the flow of energy through antennas too.

Not to be condescending, but that's the difference between talking engineer and cb..... An Engineer knows that EVERYTHING has a VF.. Even air! Since the VF is measured against the theoretical "free space", you BETTER believe your antenna has VF based mathematics as well!

Another item not discussed is the tapered element. This also changes the length of the element. An electrically resonant (or non resonant) element of 14ga wire will be physically LONGER than the same resonant element made of 1" tubing.

And in somewhat the reverse, that 1" tubing will be GREATLY more widebanded than that 14 ga. wire, even tho the 14 ga. is LONGER! This is the skin effect at work. The tapered element is completely different animal, but your right to bring it into the equation here.

<<<<<<SNIP>>>>>
I asked Jay about changing the math from "xxx/Mhz X .625 =" to "xxx/Mhz X .640 =" The difference was just over 6", not 3' like 007 example above. Why mess with a good thing anyway?

Your talking a difference of 15 thousanths. Is it really worth all this arguing about?

What makes an antenna an antenna is the matching network. That's the reason ladder line fed antennas are better.

VOA uses ladder line on it's BIG stuff, why do you think? coax... 50 ohms.. It's not what's best, it's what was available surplus after WWII. Your matching network is matching an antenna that is WILDLY different than the impedance of the transmitter and the coaxial cable... So, eliminate the losses there, and you MORE than make up for the capture area of 3 inches or even a foot!

--Toll_Free

 

[C2]

VOA?

 

[Hamin' X]

VOA?

Voice Of America radio.

The main reason that VOA uses ladder line is, they use tremendous power and feed balanced antennas. It has nothing to do with impedance.

Rich

 

[Master Chief]

VOA actually uses parallel feeders and not ladder line, but I understand what you are saying.

While they do transmit a large amount of power, the main reason for using a parallel feed system is the long distance from the transmitters to the antennas. There is very little loss when using a parallel feed line. You still have to have a matching network at the transmitter however.

I've fed standard yagi beams using ladderline and a tuner. It works great!

We have a local who is running upwards of 500' of Heliax to feed his I-10K. I've wanted to use ladderline as a test, but he isn't interested. I'd eliminate the trombones completely and extend the radials to 5/8. Someday.....

What makes an antenna an antenna is the matching network. Your matching network is matching an antenna that is WILDLY different than the impedance of the transmitter and the coaxial cable... So, eliminate the losses there, and you MORE than make up for the capture area of 3 inches or even a foot!

And as I've said here before, "A 5/8 is a 5/8 is a 5/8. What makes the I-10K the best antenna currently available is the reduction of losses in the matching network!

 

[Toll_Free]

VOA actually uses parallel feeders and not ladder line, but I understand what you are saying.

I based my entry on a PopComm article on the closing of one of the midwest VOA stations. It was a mid to early 90s article, and the last tx from them was an amateur station using their rhombic... They described it as ladder line. Doing a small bit of research I couldn't find a difference between parallel feeders and ladder line, except ladder line was referred to mostly as homebrew and parallel line was referred to as the "window" line you can pick up most anywhere.

http://www.qsl.net/ng3p/haminfo/ham-tutor/antennas_and_feedline.htm

Ladder line IS parallel feedline. Please explain the difference. I'm not talking about that crappy stuff radio shack sells, I'm talking about REAL ladder line.... Not receiving 22 ga. wire.

While they do transmit a large amount of power, the main reason for using a parallel feed system is the long distance from the transmitters to the antennas. There is very little loss when using a parallel feed line. You still have to have a matching network at the transmitter however.

Not necessarily. If your amplifier is set up to talk 600 ohms impedance, your rhombic is 600 ohms, and your feedline is 600 ohms, then your already "matched"

Ladder line will handle a mismatch TONS better than coaxial cable. It is balanced, and an all around better monster than coax for "us".

I've fed standard yagi beams using ladderline and a tuner. It works great!

Yes, but unless your "tuning" at the feedpoint, again, your only fooling your TX to deliver full power to the feedline.

We have a local who is running upwards of 500' of Heliax to feed his I-10K. I've wanted to use ladderline as a test, but he isn't interested. I'd eliminate the trombones completely and extend the radials to 5/8. Someday.....

The problem with that is that heliax is just about lossless, for all intents and purposes. I <<doubt>> you'd see any difference, a nd if you did, it would probably be in bandwith and not "performance".

We both talking about Apples here, or having a conversation based upon semantics? Methinks that might be the case, and we are arguing EACH OTHERS points!

You bring some ladder line up, we'll try it. Could be the fix to everyone's TVI problems.

With coaxial cable, I could run 3 to 3.5 kw with Jay's antenna without tearing up a neighbor. Wonder what ladder line could accomplish?

--Eye uh Toll Uh Ass Uh Hole Uh

 

[Master Chief]

Hey Toll!

I should have used the term "window line" as you did. When I hear "ladder line" I think of the 300 ohm or 450 ohm INSULATED stuff you get from HRO.

A true parallel feed line is NOT insulated. Putting insulation on a wire adds to the velocity factor of that wire! This is why those high power lines behind everyones houses are uninsulated and high in the air. Those neighborhoods with underground power have to run a larger diameter cable to carry the same amount of power the same distance. But yes, we are saying the same thing!

600 into 600 into 600 does not equire a tuner. I agree. Parrallel feeders are better than coax! We could get into a whole discussion on how a true balanced feedline does not radiate, putting almost all of the energy into the antenna, but that would raise some hackles and is best left to a different thread.

Feeding the beam with laddeline and using a tuner is more about converting from 50 ohms to 450 ohms(or 300 or 600). It all depends on how the beam is designed and if it will accept a 450 ohm feedline (like a LPDA). Everything else being wrong, then you are correct.

Heliax is NOT lossless! He is running 1/2" Superflex (not designed for outdoors anyway) through no less than 6 connectors! The specs on the 1/2" Superflex is only slightly better than LMR-400! Heliax is aweome, but it is still only coax!

(I feel like I'm giving away some secrets here!)

Are you settled yet? Ready for your tower? No luck on a replacement I-10K yet. I need to buy another one also!

I'm almost ready for a road trip!

 

[freecell]

"Not to be condescending, but that's the difference between talking engineer and cb..... An Engineer knows that EVERYTHING has a VF.. Even air! Since the VF is measured against the theoretical "free space", you BETTER believe your antenna has VF based mathematics as well!"

every engineer should know that the antenna length correction for VF in terms of the percentage of the speed of light (radio waves) in free space is automatically compensated for when reactance in the antenna is balanced so that X equals 0 at the intended or desired operating frequency. this should come as no surprise because the whole reason for length correction for the VF in the first place is to establish resonance.

without exception, every so-called 5/8 wave base antenna since the Avanti Astro Plane (11.5') and the HyGain CLR-2 with a total length of 19' 10 3/4" to present models as long a 27' have shared a few common characteristics.

one of them is that regardless of the measured physical length, ALL OF THEM are ELECTRICALLY 3/4 WAVELENGTH IN OPERATION. in almost every example without exception the electrical length IS NOT solely a function of the PHYSICAL LENGTH OR DIMENSIONS.

so now why was it again that manufacturers referred to them as 5/8 wave antennas? more importantly, WHY DO YOU CONTINUE TO REFER TO THEM AS 5/8 WAVE ANTENNAS? i'll tell you why, BECAUSE THE MANUFACTURERS SAID SO. guess what, the manufacturers are WRONG. it (THE 5/8 WAVE REFERENCE) certainly has nothing to do with either the electrical length (measured in degrees) or physical length of the radiators..

using either formula that you like to determine a physical 5/8 wavelength at 27.185 you're left with 21.5' - 22.6'. it doesn't matter because it's incapable of resonance and can't be fed directly with 50 ohm feedline unless the capacitively reactive load is cancelled, at which point the antenna becomes 3/4 wavelengths electrically, X = 0 and all that is left at the feedpoint is a pure resistance. at the target frequency, once X = 0 VF is corrected and no longer an issue.

quit trying to make it one. element taper, varying diameter to length ratios and all the other related physical inequities or variables that you could possibly worry about are all neatly reconciled when X = 0.

 

[Master Chief]

I was with you in the beginning, but when you got to the part about "beacuse the manufacturers said so", you lost me.

As you well know and as we have agreed, in order to match a feed point of ANY antenna to a 50 ohm coaxial feedline, you need to have an antenna that is in 1/4 wave increments.

As has been stated by me and proved way back in the 1930's, the LONGEST single element radiator giving the lowest angle of radiation (gain) is .640 wave long. Anything beyond that length is wasted energy!.

Speaking specifically about the Avanti antenna, the main radiator is 5/8 wave long; electrically 5/8 wave long! In order to feed this radiator with coax, the engineers needed to bring it up to the next 1/4 wave; in this case, 3/4 wave. They did this buy using a 1/8 wave loop, positioned in the HORIZONTAL plane so as not to interfere with the 5/8 radiated signal.

This antenna IS a 5/8 wave antenna. This antenna IS electrically 3/4 wave long, but the main radiating element is still only 5/8 and encompasses all of the advantages associated with it.

Believe me, if Avanti or anyone else could sell you a 3/4 wave antenna (remember, bigger is better) than they would. As it is, they tried to sell the Sigma IV as a 3/4 wave antenna and most people bought it not realizing that it actually isn't.

A 5/8 antenna is a 5/8 antenna. Some people like to push it to .64 wave, but its still just a 5/8 antenna.

I do agree that the physical length of different 5/8 wave antennas will vary based on the design, but it is still a 5/8 antenna. Calling it a 3/4 wave antenna due to it's need of a matching network is only a play on words.

 

[fatdude1]

wow

very well put dude

 

[W5LZ]

As I vauguely remember someone saying, resonance is nice but certainly not a necessity. Any length radiator will radiate evey bit of the power that reaches it. If that radiator's length is such that it happens to have a nice radiation pattern, who cares if it's resonant?
The matching system's only purpose is to make the feed line's impedance and the impedance at the antenna's feed point at least reasonably close to being the same. Same thing holds true for a tuner (impedance matching device) used between the transmitter and the feed line.
A feed line's only purpose is to provide a path from the transmitter's ouput to the antenna's input. That's all it's meant to do. Using it as an impedance matching device is about like under inflating a larger tire to compensate for a smaller tire on the other end of the axle. Sure, it can be made to work, but it certainly isn't the best way of doing it, now is it?
Open-wire, ladder line, parallel conductor feed lines. What's the difference, they all do the same thing, and in my opinion, much better than coaxial feed lines. Not necessarily harder to use, just different. A @#$$ of'a lot less losses to boot (also don't much care what the probable mismatch is at the antenna end, won't amount to much anyway, and certainly not enough to destroy the feed line as can/does happen with coax). Besides, the typical ladder line's price sure beats that of any reasonable quality coax's!
- 'Doc

 

[freecell]

how the antenna performs electrically is the only thing that's important. resonance and reactance are "electrical properties" of an antenna. since the matching system is an integral component of any resonant antenna it can not be viewed otherwise. since resonance is the goal in any standing wave type antenna the physical length is irrelative. a 5/8 wave length of tubing or whatever has no "advantages". a capacitively reactive antenna is of no use to anyone. the electric and ensuing magnetic fields generated to create the electromagnetic field are a direct result of the antennas "electrical properties," not physical properties. regardless of the physical length of the main radiator the only thing that counts when determining the electrical length of the antenna is the number of degrees transitioned by the applied voltage and current from one end to the other. 270 degrees is 3/4 of a single wavelength at the operating frequency.

and just in case i haven't repeated it enough times already, the revolutionary design of the Sigma 4 more than compensated for the deleterious effects of the rising take off angle of the radiated wavefront that limits performance in the previously mentioned .64 wave design. not only is all of that thoroughly explained in the patent but it has been confirmed by the many operators who use it. the old limitations have been exceeded with this design. the only difference between a .625 and a .64 wave physical radiator is that the latter of the two requires less inductive reactance to achieve resonance than the former. whoopedoo. in the final analysis where the "electrical properties" (reactance, resistance and resonance) that we look for to determine the proper operating parameters of any antenna they're all 3/4 wavelength in operation. those three "electrical properties" aren't determined by the physical length in these antennas nor can they be for obvious reasons. it's the same reason that you can get away with directly feeding many antennas with 50 ohm line like a 1/2 wave dipole or a 1/4 wave end fed vertical or monopole but it'll never happen in any instance where the radiator is not electrically corrected for resonance to occur at the required 1/4 wave intervals. resonance of any standing wave antenna can only be achieved when the electrical length is exactly equal to any number of 1/4 wavelengths. a pure resistance can only be represented when reactance is balanced and X = 0. when this occurs the antenna is resonant at the target frequency. none of this occurs in a radiator alone that is physically 5/8 of a wavelength and furthermore you don't need a radiator that is anywhere near 5/8 of a wavelength physically to have the "antenna" operate electrically at 3/4 wavelength.

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. in that light it's no surprise that one of the early entries to the market in the form of the HyGain CLR/CLR2 came in under 20' while still being labelled as a 5/8 wave antenna. the only way the electrical length could be extended to improve performance beyond 1/2 wave was to go to the next electrical 1/4 wavelength and use a radiator that would come up under the 20' limitation in overall height. to do this the radiator would have to be much more capacitively reactive than it would have been if it could have been "physically longer". the 5/8 wave antenna was born. the term to this day is still used inaccurately and as it speaks to the electrical properties of a resonant antenna is little more than a name or a label.