What can we expect from the stock G-MAX ?
An analyse with EZNEC PRO 4 using NEC4&NEC5 engines.
Lets start with something that need to be said:
The manufacturer claims G-Max is the first and only vertical antenna in the world for the bands of 10 or 11m in a collinear configuration 5/8λ over 1/4λ with high gain.
Im afraid that is not entirly true, the HAM international BIG MAC, an icon from the past was the first and at that time the only one. But also other companies like DUORO, BIG HAIR and HPSD have made collinears antennas for 27 MHz.
(The HAM international BIG MAC from our own collection)
And there are a couple other things that are questionable, for example: Is it actually a 5/8 wave over a 1/4 wave with these dimensions ?, We also find statements like “performance is better than a 2el yagi”… then after our findings, we must conclude the reference 2el yagi must have been really bad. And a couple other things..but on the other hand: For sure we have seen worse advertisment claims from others, not need to investigate it all… It is better to just go to the facts !
So, although the concept isnt new, it certainly gets the hart pomping to to see a company producing a “true” collinear for 11 meters !
Actually excited to run the antenna through EZNEC.
THE DIMENSIONS IN EZNEC :
We used the sizes provided for 27,2 MHz. Most of the sizes can be found in the manual provided by Grazioli, except the coil lenght which was provided by “BOB85” on the “Worldwidedx.com“ forum. (Thank you Bob !)
The average gain factor is 1 which indicates the model does not have any problems and is accurate.
THE FREESPACE GAIN:
First we will have a look at the gain provided, the manufacturer claims 5,65 dBI.
Eznec indicates the following:
In freespace the antenna produces 4,24 dBi gain, which is about 1,5 dB less from what the manfucturer advertises.
THE PROVIDED SWR :
Besides the phasing coil, there is no additional matching device. The antenna is “direct fed”.
That provides a good test to see if the manufacturer and EZNEC provide similair results:
That is pretty much spot on !
It has 1300 KHz as its 2;1 SWR bandwidth exactly what Grazioli said it would have and resonant at 27.25 MHz.
GAIN IN THE REAL WORLD:
Grazioli provides us an antenna plot with the following gain figures expressed:
From the plots it clearly shows 4NEC2 is used as software and from the data we can conclude two things: The first the plot was provided with the antenna at a height of 11 meters. And secondly, it should produce 6,48 dBi of gain.
On the Worldwidedx.com forum I actually mentioned: I was impressed with that gain if it was above “average ground” conditions. As 6,48 dBi gain is a hugh number for a vertical antenna. However, another keen modeler enthusiast “the DB” on that forum discovered that 4NEC2, when data is inserted in the “new editor” the 4NEC2 program uses “moderate ground” by default, instead of the commonly used and adapted standard the “average ground” conditions. This is unexpected.
For anyone with no modelling experience it is logical the above perhaps makes no sence at all. In short: “The modelling world” has adapted “average ground” as the standard for modeling antennas above real ground. The mentioned “moderate ground” is a step-up from that, the ground has better “electrical” values and will show higher gain numbers. For anyone with keen modeling interest, it perhaps is considered odd that 4NEC2 uses “moderate ground” for that single specific editor.
What will happend if we place the EZNEC model at the given height above the most likely used “moderate ground” :
Here we find 6,43 dBi gain a difference of only 0,05dB with the manufacturer.
Im guessing it is fair to conclude they did use the “new editor” in 4NEC2 and the “moderate ground”
to provide the antenna plot.
Which brings us to the questions: What gain can we expect if we set the antenna 11 meters from ground, above the standarised “average ground” conditions:
The 5,13 dBi might not be as high as the (perhaps not so wrong advertised) 6,48 dBi.
But…..it still is almost 2 dB higher then a vertical halve wave at the same mast heigth
or almost 1 dB at the same tip height. (it also beats a 5/8 wave)
ABOVE GROUND WITH A MAST
As often is the case with vertical antennas, they are highly influenced by the mast and the coax cable. Although the G-max has 4 radials which help to prevent currents going down the mast, there still is significant secundary radiation in “worst case” senarios.
A RF-CHOKE is a MUST and there are critical mast lenghts which need to be avoid.
Below you wil find for each heigth 3 different situations. The first plot indicates the antenna and mast grounded to earth the second if the mast is isolated from the ground and the third if a non-conductive mast is used.
For all these situations “average ground” has been used and the mast was connected to “mininec” ground.
(click to enlarge)
At 2,75 meters height, an ideal situation for the grounded mast exist. Almost no currents on the mast. If on the other hand the mast is isolated from the ground the mast will become part of the antenna and large currents are present and will have effect on the pattern.
(click to enlarge)
At 5,5 meters we see the pattern is disturbed and currents on the mast are significant for the grounded mast and the opposite is true for the isolated version.
(click to enlarge)
At 8,25 meters height, we see again that the grounded mast holds minimal current and a nice pattern is created, the isolated version is disturbed.
(click to enlarge)
At 11 meters height the pattern of the grounded mast isdistrubed by the “in phase’ mast length, and the opposite for the isolated version.
(click to enlarge)
At 13,75 meters the ideal situation repeats again for the grounded version and the skewed pattern for the isolated mast
(click to enlarge)
And at 16,5 meter the pattern is highly disturbed again for the grounded mast and the isolated mast is the winner.
From the above we find these results:
Height MAST GROUNDED MAST ISOLATED
2,75 meter 2,64 dBi 10 degrees 1,27 dBi 10 degrees
5,50 meter 3,29 dBi 9 degrees 3,66 dBi 9 degrees
8,25 meter 4,54 dBi 8 degrees 4,53 dBi 8 degrees
11,00 meter 4,08 dBi 7 degrees 5,14 dBi 7 degrees
13,75 meter 5,97 dBi 7 degrees 4,66 dBi 7 degrees
16,50 meter 5,55 dBi 6 degrees 6,37 dBi 6 degrees
The mast lenght always has influence, sometimes that influence is negative and very significant ! Resulting in heavily reduced performance. This is the case at each halve wave lenght or any multiply of that for the grounded mast. It then actually is sometimes better to leave the antenna at a lower preferred height while the opposite findings are true for the isolated mast.
(Just to have it said, this is not something that only is true for the G-max antenna. The mast and coax influence can be just as bad, or worse for other vertical antennas and contributes to the reason why people experience different results while comparing antennas.)
CONCLUSION :
The G-max is indeed a collinear antenna. It has the abbility to outperform most of the other vertical omnidirectional antennas, with limited exception. (for example the extended double zepp antenna)
The antenna produces 4,24 dBi (freespace) gain.
Basiclly the antenna has two main advantages :
The first being its height, the antenna is simply higher then most of the commonly used CB antennas, when an antenna is higher… it can “see” further and that gives the potential to produce a better signal at the horizon. (an advantage well known from the Avanti Sigma 4).
And secondly it actually does have more gain then the most commonly used vertical antennas.
For DXing a horizontal high placed antenna will seriously outperform the G-max, though that is comparing appels and peers.
It could be considered a nice DX monitor antenna.
As it is omnidirectional and the main lob is rather low.
From an electrical point of view, not bad at all !
Key, as often with vertical antennas remains the influence of mast and coax.
There are situations where the G-max will under-perform.
Mast lenght (and coax length) is something to consider, and the use of a RF-choke is must.
This antenna (as many other vertical antennas) has lots of issues with different mast lengths.
For a grounded mast: Lengths that NEED TO BE AVOID are 5,5/11/16,5 meters height. (a half wave or multiple of it) Lengths that are recommended are uneven quaterwave lengths say 2,75, 8,25, 13,75 etc. In case of an isolated mast the exact opposite is true, The difference of those configurations can easily add 1 dB or more.