Comparing vertical antenna signals

[bob85]

henry/shockwave,

heres how ezbob sees it,

current maxima on the no hat endfed 5/8wave element is 1/4wave from the tip of the antenna,
current maxima on a dipole is 1/4wave from the ends and only at the center when it is a 1/2wave dipole or odd multiple 1/4wave legs each side of the feedpoint,

extending the dipole by 1/8wave as seen in the gainmaster creates two current maximas spaced about 1/8wave apart or 1/6wave either side of the feedpoint, each current maxima will be 1/4wave from either end of the gainmaster,
the shift in phase angle at the feedpoint vs 1/2wave dipole gives you higher impedance/higher voltage/lower current feedpoint conditions of the extended gainmaster dipole,
if thats not correct then ezbob needs tweaking

my gut feeling solely based on the reports so far is the gainmaster may have the advantage of not needing an extensive groundplane and/or not suffering so much from mast/feedline radiation allowing it to produce the low takeoff angle most people think the 5/8wave has when mounted at typical cb station heights above ground using typical installation methods,
an imax without radials and isolation could be in some cases similar to using the gainmaster without its choke, i would do neither,

imho there is nothing special or low angle about an endfed 5/8wave when mounted at moderate heights above average-good ground, they talk great short skip if thats your thing,

im not sure how the gainmaster would model when mounted on various length conductive masts and feedlines over average-good ground,
i would be surprised if mast/feedline length had NO effect on mast/feedline currents
i would like to see the models,

 

[bob85]

jazz,
i agree in principle, most folk want to know what works best on the mast they have,
in most cases its simple, vector vs imax vs i10k vs a99 vs penetrator vs gainmaster ect ect, you can bolt your antenna straight to your scaff pole/mast but in other cases you can't,

take your starduster, you need to buy a stub mast to mount it, id say a 9ft-12ft mast is typical and perfectly fair,
take the astroplane, it also needs the mast as its listed as part of the antenna and directly effects radiation angle,
it was also designed for a specific purpose to give a claimed 4 degree takeo off angle from higher up than the original pseudo 5/8waves that were also restricted in length due to height restrictions above your property,

to me its clear from the patent that you should include a stub mast of the correct width as it effects impedance and the correct length to put the tip at the same height as whatever 5/8wave you are comparing it to,
you can't just remove your imax and slap the astro on your scaff pole and expect it to work as claimed in the patent,
i would put it at the same tip height and isolate it 1/4wave below the hoop,

now eddie could argue that his starduster was also designed back in the days when we had height restrictions and as such he has every right to mount his starduster at equal tip height to his 5/8wave

does the relaxation of height restrictions mean that you should now mount your duster and astroplane at the same feedpoint height as the longer 5/8wave to compare them

would it be fairer to allow the true 5/8 and sigma/vectors their height advantage over the 20ft or so height restricted antennas, there are several ways to look at the situation,

at the end of the day what matters is which works best for each of us at the height we feel comfortable/safe having each style antenna in our back yards

 

[jazzsinger]

jazz,
i agree in principle, most folk want to know what works best on the mast they have,
in most cases its simple, vector vs imax vs i10k vs a99 vs penetrator vs gainmaster ect ect, you can bolt your antenna straight to your scaff pole/mast but in other cases you can't,

thats my take on things, if you have to change anything other than the antenna then realistically your not comparing antennas but antenna + whatever you have to change to create so called equality. which to all intents and purposes isn't what your average joe buying a new antenna is going to do.

if i gave you two joints, one with good hashish and another with not so good hashish, if you were comparing them you'd put the same amount in each, not put more of the shit stuff in to level the playing field.not the best analogy i know but it makes the point, and i'm gasping for one, so thats whats on my mind,lol. on that note i truly envy you Henry living in the netherlands, lol.

on the matter of ezbob needing a tweak i'm sure your ok there mate, i see things the same as you there, but mel tells me lazybob could be doing with a few tweaks, lol.

by the same school of thought, if comparing two antennas, you should compare what comes in the box, not what should be in the box.

 

[W5LZ]

It's amazing to me how shadows can change with a shift in light. How much they can shorten when the 'light bulb' over your head turns on. Gives me a new 'slant' on things. I think I've just realized who 'ezbob' and 'lazybob' are, or should I say, who they aren't? Anthropomorphically speaking of course.
- 'Doc

 

[bob85]

jazz,
if you ever find yourself in the position of trying to install an astroplane to your scaff pole without the stub mast and after you smoked a lazybob,
give me a call, i will bring the analyser and video cam,
it would be perfect for youtube:blink:

 

[Marconi]

For me the added discussion is fine.

Most of you comment how guys would place their antenna on what they have and I agree, but that is not exactly what I was getting at within the topic. Maybe I wasn't clear, but that is what the typical radio guy would likely do who wanted to talk on his radio not compare antennas. This is probably how most of us started off.

My idea for the topic was as though we wanted to have a shoot-out between antennas, comparing antennas, and how do we set them up in order to have as fair a comparison as possible.

That said however, so far only one person has voted to do what most of you are suggesting as what most will do. I voted to do what I think is the fairest way to really compare antennas, where they are both elevated to the center of the maximum current node.

I really figured most would vote to mount the antenna at the same height with the mount provided.

So, what should we do to compare a 30' foot Vector to a 12' AstroPlane, what height arrangements should be used in order to be as fair as possible?

How about the same comparison with an A99 or an 18' foot Starduster?

An I-10K, Imax, Penetrator vs. the Vector?

How about the Sirio Gain Master with the feed point in the middle of the antenna up against the Vector 4000 at about 30' feet? Is mount to mount really fair in this case...with the Vector towering over the GM about 8' feet?

I think SW used a similar setup and the GM showed him better results than the taller Sigma4, but all of my comparisons show when the base of the antenna's are the same height...the taller antenna always shows a better signal, and maybe even 100% of the time.

So the topic question is, "...what is fair, not what is practical."

 

[Shockwave]

I just thought I would mention that my GM was mounted at about the same tip height as my Vector was. The Vector was mounted on a 15 foot pole on my chimney with about 5 feet of mast attached with four chimney straps. I noticed the top U-bolt was tightened to the point where it kinked the mast. Out came the hack saw and I chopped off the bottom 5 feet before installing the GM. I still can't tell the antennas apart other then reduced power handling and added bandwidth. In all fairness, my chimney is over 40 feet above ground level and clears all surrounding buildings. I don't think the extra 5 feet in my case makes much difference.

 

[bob85]

eddie,
in this area a cber and many hams typically use aluminum scaffold pole for a mast, its very close to 2" diameter and about 1/4" wall,
most cb antennas mount straight to the scaff pole and thats what locals would do when comparing any endfed or antennas such as the gainmaster and vector,

with the starduster style antennas locals including me buy a stub mast 9ft-12ft long that fits the antenna and fastens inside the scaff pole,
you can't mount the starduster or astroplane without the thin stub mast,
nobody cuts down their pole or winds down their tower because their new antenna needs a stub mast to mount it.

 

[hotrod]

i choose at the antenna mount. or the base of antenna.now i
dont know as much as some of you out here and my way probaly is
wrong but its what ive used and seems to work.i mount antenna on
10-15 foot mast and test the antenna.way i see it any antenna should
work great at 100 feet in air. but what about 10 feet?now like i said
this isnt the most accurate but it works for me. id like to see the SGM
against the imax and maco done with 10foot mast.seeing how thier close
in overall lenth the imax i think maybe the longest. but id give it last place..lol

 

[BOOTY MONSTER]

i guess it depends on what type of results you want . if you want results that the typical user can make use of id just put them as high as they will go on the same length/height of mast and compare them that way . i dont think most users are going to add 5 or 10 or 15 feet of mast to get one antenna to do as good or better than one mounted lower if that lower antenna will do better than the higher one when mounted at the same mast height/feed-point .


just my opinion........

 

[itx]

I'd hate to butt in to a conversation, but, if you are going to try to do an exhaustive comparison of antennas, why not test both heights to see if it is design or height providing the advantage? Test a 12 footer and 30 footer at the same mounting point, then add 18ft of mast to the 12ft antenna....

 

[Marconi]

I'd hate to butt in to a conversation, but, if you are going to try to do an exhaustive comparison of antennas, why not test both heights to see if it is design or height providing the advantage? Test a 12 footer and 30 footer at the same mounting point, then add 18ft of mast to the 12ft antenna....

Welcome itx, you're not buttin' in. Pull up a chair.

Messin' with antennas is basically what I like to do. In this case I was trying to check the range in height where the shorter antenna compared well with the new Gain Master I just got...which is basically what you suggest. I was checking my AstroPlane with a 4' foot radiator vs. the GM that is 21' feet tall, just trying to see how effective it is to the longer antenna. It's exhaustive work for me, and now I've taken the AP down, so I'll start doing the antennas on the same mast, coax, and location...just like Hotrod suggested. I figure with conditions changing all the time and my contacts changing gear from time to time...will present additional and new problems, but I'll try and be careful and take that into consideration on my reports.

Seems, no matter what we do in CB...somebody will raise some viable counter-points regarding how we do it, and that's fine too...that's how we learn.

 

[Henry HPSD]

Oke, guys a thougth...

Say our testing mast (receiving site and test site) is a 10 meter pole (approx 30 feet)

Say the difference in antenna length for the antennas under test is upto about 3 meters

Were setting the receiving antenna at 10..15 wl distance.

Now, that (for example) 3 meters difference in heigth represents a very small change at our receiving antenna.. would it really be of issue?

Ofcoures if we are testing with someone far away as the higher the more the antenna can see.. and would represent something to bare in mind.

Just thougth...

Regards,

Henry
11 meter Dx antenna systemx

PS Jazzsinger...its no fun when things are legal m8 ..

 

[HomerBB]

Hopefully bringing this over here is OK. I thought this information ought to be here as well given some folks might not read through the other thread to discover it:

On a center-fed, HALFWAVE DIPOLE, maximum current and therefore maximum radiation occurs at the feedpoint. On an end-fed, halfwave antenna, maximum current and maximum radiation does NOT occur at the feedpoint, rather, in the CENTER of the antenna (same as a halfwave dipole).

With a 1/4 wave end-fed vertical, (regardless of type, style, absence or presence of radial elements), maximum current & therefore maximum radiation occurs at the feedpoint.

With a 5/8 (.625) or a .64 wavelength antenna, maximum current & therefore maximum radiation occurs at 1/4 wavelength from the top TIP (end) of the antenna. Even the venerable Sigma IV has it's MAXIMA approx 1/4 lambda from the TOP TIP of the antenna.

Having stated the obvious, the SGM (Sigma GainMaster) is slightly 'different' because of the capacitor in the radiating element; just as an inductor makes an antenna appear electrically 'longer' to an rf signal, the addition of a capacitor makes an antenna appear electrically 'shorter' to rf (i.e.: CCR Antennas); therefore the current maxima is somewhat S-T-R-E-T-C-H-E-D along the radiator. I'm no electrical engineer by any means, but I believe this is called: capacitive reactance.

Knowing 'WHERE' antennas radiate from makes field antenna testing somewhat more difficult because you CANNOT compare apples-to-oranges; meaning, you cannot compare a 1/2 wave to a 5/8 wave; or a 5/8 wave to a 1/4 wave, or a 1/4 wave to a 1/2 wave. You can only compare APPLES-TO-APPLES. The reason I state this is because if I was mounting all my different antennas on the same 20' mast, they all would be providing maximum radiation from different heights, thereby giving maximum LOS near field advantage to the LONGEST antenna (in most cases). For example, let's look at the height of maximum radiation / current node on the following antennas, all mounted with their BASES on a 20' pole:

- .64 wavelength (24') antenna: (i.e.: Imax 2000): Max rad @ 35' approx
- .625 wave (21-22') antenna: Max rad @ 32' approx
- Vertically Oriented 1/2 wave center fed dipole: Max rad @ 28' approx
- 1/2 Wave End-Fed Vertical (i.e.: Ringo): Max rad @ 28' approx
- 1/4 Wave Vertical (i.e.: Top One, M-400, etc): Max rad @ 20' approx

So, as you can see, there is a 12 - 15 foot advantage in HEIGHT OF CURRENT MAXIMA / POINT OF MAXIMUM ANTENNA RADIATION, with the LONGER antennas to begin with. Mounted on the same pole (at the same height) one would expect them to BOTH hear and talk better (an S Unit(s) advantages in the near field / LOS-Line Of Sight.)

Now, if we adjust the height(s) of antennas in an attempt to "normalize" the readings, for example, raise a 1/4 wave vertical to a height of 32 - 35' to compare it to a .625 or .64 antenna mounted at 20'..... what are we accomplishing??? In reality, if a person could get a 5/8 wave antenna's base up to 35' rather than 20' wouldn't we do that?..... & vice-versa.... if we could get the 1/4 wave up to 35' for the purposes of testing, wouldn't we leave it there to take advantage of it??? Remember.......... ANTENNAS DON'T CREATE POWER, they merely couple it to the ether. The advantage of a .625, or a .64, or a Vector (Sigma IV, Saluit, or LW-150) is that their EXTENDED LENGTH creates a current maxima HIGHER UP THE PHYSICAL MOUNTING POINT. Any 'GAIN' offered in such designs only comes from concentrating the RF 'beam' closer to the horizon.

For LOS (local) work, THE HIGHER THE BETTER IN ALL CIRCUMSTANCES.

For DX (long-haul) work, ANY HEIGHT OF 5/8 WAVELENGTH OR MORE ABOVE GROUND WILL SUFFICE TO PROVIDE ADEQUATE LOW ANGLE CHARACTERISTICS FOR ANY ANTENNA, VERTICALLY OR HORIZONTALLY POLARIZED.

For any VERTICAL antenna mounted BELOW 5/8 lambda from ground, providing adequate ground-loss isolation (decoupling coaxial cable common mode currents notwithstanding) in the form of either ground screens, ground planes, tuned or un-tuned radials, etc., will reduce ground losses and make the antenna more effective. Even if the antenna is mounted at ground level (as many backyard Amateur (Ham) Radio installations are, the DX won't know how high your antenna is. It's getting your lobe where you want it that counts; that's why on the LOW bands, Verticals are superior to horizontal dipoles for DX'ing; because they concentrate their maximum radiation TOA's (take off angles) MUCH lower than horizontal antennas.
http://www.worldwidedx.com/cb-antennas/76970-new-antenna-sirio-gain-master-32.html#post248519

 

[Marconi]

Very good Homer, it truly applies here also. CTStallions explanation says it pretty clearly and I have always been challenged on how is the best way to compare different antennas. If you consider the design and structure, it is not just a simple matter of putting them up and compare.