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What W8JI says about a 1/4 wave vs. 5/8 wave

bob85 said:
bootie,
w8ji modeled the imax with a worst case mast or feedline length scenario that promotes maximum common mode radiation.
i think you missed his opening statements,

End-fed Vertical and J-pole

when i tested my imax vs the i10k on a short mast the imax was way behind, it was also behind the sirio 827 ( no skip )

i took the imax portable on a 10ft flagpole, performance was reported as been about the same as my 1/4wave whip on the car roof and i could not use the amplifier because of high common mode currents badly screwing up my ssb audio, a choke did not help,

on the other hand i have also had decent results from both the a99 and imax,
on a 1 wavelength pnumatic mast i experienced the old a99 equal my sirio 2012 5/8wave to the majority of my locals.
Click to expand...

If every antenna report could be so honest about results there would be better understanding of the empirical performance of antennas. I have moved an antenna over to a spot 40 feet away and the performance change.
 
HomerBB said:
If every antenna report could be so honest about results there would be better understanding of the empirical performance of antennas. I have moved an antenna over to a spot 40 feet away and the performance change.
Click to expand...

we moved a car about 2 feet during a line of sight contact between scotland and n.ireland, we witnessed 5 s units of signal increase,on a president jackson s meter.

just moving slightly can be the difference between being almost blocked by an obstruction to a line of sight signal or having a clear path, it could also cause a massive change in phase of multi path signals which can either increase or decrease signal strength. in light of what i've seen, 40 feet is a considerable difference and is the reason why people whyo use a/b comparisons on twigs seperated apart can get some surprising results.
 
bob85 said:
bootie,
w8ji modeled the imax with a worst case mast or feedline length scenario that promotes maximum common mode radiation.
i think you missed his opening statements,

End-fed Vertical and J-pole

when i tested my imax vs the i10k on a short mast the imax was way behind, it was also behind the sirio 827 ( no skip )

i took the imax portable on a 10ft flagpole, performance was reported as been about the same as my 1/4wave whip on the car roof and i could not use the amplifier because of high common mode currents badly screwing up my ssb audio, a choke did not help,

on the other hand i have also had decent results from both the a99 and imax,
on a 1 wavelength pnumatic mast i experienced the old a99 equal my sirio 2012 5/8wave to the majority of my locals.
Click to expand...
so could a 1/4 w gp outalk say the sirio 2016,maco mounted on a low pole?
just trying to understand this.and think im starting too
 
ALL antenna test are subjective (and variable) if not done under controlled conditions. All aspects of the testing have to be accounted for, or the results are just not very conclusive, and never will be the exact same for the identical antenna being tested in a different situation. All of this is even more 'subjective', and unbelievably variable, if the testing is done by 'on the air' reports, unless you can account for the conditions on the other end of those reports too.
Standards in terminology/definitions.
'Gain' is a very good example of that! There really are some 'givens', but even those are variable, depend on how 'well' antennas are tuned for use on a particular frequency. One of those 'givens' is that a 1/2 wave dipole is the standard for comparison. That means that a 1/4 wave will have less gain than a 1/2 wave, a 5/8 wave will have slightly more gain than a 1/2 wave. If a 1/4 wave antenna is purported to have more gain than a 1/2 wave antenna, then there's a 'catch' to it somewhere. Either that 1/4 wave isn't a 1/4 wave, or the 1/2 wave isn't tuned properly for where they are being used. The purpose of why any size antenna is used also plays a very big part in it. The 'shape' of the radiation patterns of antennas changes with 'size'. If one particular 'size'/pattern fit's your needs, then it's going to work better. Doesn't make any difference on if the thing has 'gain' or not. There's a lot to all that, it isn't simple at all.
So it amounts to what works best for you in your particular situation. No two situations are ever going to be exactly the same, so the performance of a particular antenna won't either.
- 'Doc

(Nothing 'new' in the above.)
 
i have not tested against the 2016, i have had a wilson version of the maco years ago and it performed better than my starduster up high in a field,
i never tested them on short masts.

hotrod said:
so could a 1/4 w gp outalk say the sirio 2016,maco mounted on a low pole?
just trying to understand this.and think im starting too
Click to expand...
 
hotrod said:
so could a 1/4 w gp outalk say the sirio 2016,maco mounted on a low pole?
just trying to understand this.and think im starting too
Click to expand...

Can it out talk it? depends where you are trying to talk. a 1/4 wave would possibly work better close in where a correct fed 5/8 will work better on the horizon.
 
well i hear that 1/4 w gp has very quiet recirve .a plus in my book
plus i live in a small bit of a hole.been told a 1/4 w will serve me
better.i also think your location plays a part also.
 
BOOTY MONSTER said:
"Most of the radiation is up in the sky at a high angle. The angle is so high, it is even useless for skywave.

This is a NEGATIVE gain antenna at low angles. A 1/4wl groundplane would seriously outperform the I-MAX 2000 or any other 1/2 or 5/8th wl antenna that does not have a large groundplane.

This pattern is over real earth, where a conventional dipole has about 8 to 8.5 dBi gain. This antenna about -2 dBd gain maximum. It has negative gain over a dipole. The gain over a dipole at most useful angles for DX is about -10 dB....significant negative gain."

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

im no imax or 99 fanboy , but there are tons of folks that use them and have compared them to maco and other 5/8 antennas with 1/4 wl ground elements and the imax excelled both locally and skip wise for them . and theres others that had the exact opposite results with the imax loosing .

seems to be a contradiction between w8ji's post and the real word results of a lot a folks . or im misunderstanding something .
Click to expand...

BM I'm not sure in reading your post who is saying what in quotes, so I'm just addressing your final statement. In my opinion you may be assuming what others are saying regarding what W8JI means is correct. What if these words from others are wrong, take their word anyway? Sometimes I have a different opinion. See attached: http://www.worldwidedx.com/cb-anten...-about-1-4-wave-vs-5-8-wave-3.html#post281745 and BM within this linked post, I think I directly address the issues for your concerns.

Example going on in this thread: It has been suggested to me that free space models are of little value since our antennas are always mounted over real Earth. In these terms it is hard to argue such a statement, but then an argument was made that the mistaken free space model with a mast connected to Earth resulting in a funky antenna pattern, demonstrates just what both W8JI and Cebik tell us will happen when we don't include the mast and feed line in our models...create a mess where the models are not correct. Such an argument is illogical and has nothing to do with the specific issue raised by W8JI or Cebik in their discussions on modeling without including the mast and feed line.

In my opinion a free space model should only be generated with the model set to ZERO losses for soil conditions and material resistance, which would certainly include a conductive mast attached to Earth.

I knew better than to run a free space model with a mast attached, but at the time I was only considering for my discussion the Avanti Patent and what I take to be a free space model exhibited therein. I had just modeled the New Top One over real Earth, and it included the mast. When the idea I had came to mind I ran the free space model for my NTO and I forgot to delete the line of code representing the mast from the model, and the pattern did look funky. I did set all other loss features to zero however, but forgot about the mast.

Maybe I'm wrong...that the modeled pattern presented in the AstroPlane Patent is a free space model, but it sure looks like one to me. What caught my eye when I printed the pattern view to the screen for my model...was that the pattern showed a -5* degree maximum gain below the horizon, similar to what is shown in the Patent...where a slight tilt is to be noted. I posted this model hopefully to add a little creditability to my own model...since the patterns looked similar to me. I just made a mistake in my zeal to post the idea with an error included when I wasn't thinking.

Now ask yourself, if you're convinced by any argument that is base on any contention...using a known mistake or an error? Do you think this is what W8JI and Cebik meant...when they talked about the problems associated with modeling results? I don't think so! I just made a mistake, which I acknowledge, but common sense should tell us all, among other things, free space models should not include the mast or the feed line in the model...else IMO the antenna is not in free space.

This will be all I have to say regarding modeling.
 
Last edited:
marconi , the quote was from w8ji .
End-fed Vertical and J-pole

others have had a different experience comparing their imax to other 5/8s' with ground elements than the results w8ji got . but as bob pointed out , i did miss something .


bob85 said:
bootie,
w8ji modeled the imax with a worst case mast or feedline length scenario that promotes maximum common mode radiation.
i think you missed his opening statements,

End-fed Vertical and J-pole
Click to expand...

i still can't makes heads or tails of modeling programs . :headbang:headbang:headbang
 
BOOTY MONSTER said:
marconi , the quote was from w8ji .
End-fed Vertical and J-pole

others have had a different experience comparing their imax to other 5/8s' with ground elements than the results w8ji got . but as bob pointed out , i did miss something .




i still can't makes heads or tails of modeling programs . :headbang:headbang:headbang
Click to expand...

Believe me BM, you're better off, cause nobody around here wants to risk their showing a little human frailty, ignorance...even in the process of learning.
 
i rather like it when someone is wrong once in a while , particularly if they admit it . (y)

i make mistakes all the time . just a few weeks ago i found out i didn't understand a simple swr meter . :redface:
 

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