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. 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, about 1,5 down from what the manfucturer advertises.
THE PROVIDED SWR :
Besides the phasing coil there is no additional matching device and the antenna is “direct fed”.
A good test to see if the manufacturer and EZNEC provide similair results:
That is pretty much spot on !
1300 KHz 2;1 SWR bandwidth as Grazioli said it would have and resonant at 27.25 MHz.
GAIN IN THE REAL WORLD:
Grazioli provides us another plot with gain figures expressed:
From the plots it clearly shows 4NEC2 is used as software and from the dat 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)
CONCLUSION :
The G-max is indeed a collinear antenna it has the abbility to outperform most of the other vertical omnidirectional antennas with limited exceptions like for example the extended double zepp antenna Key, as often with vertical antennas remains the influence of mast and coax. The use of an RF choke is always advised.
There are 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, but that is comparing appels and peers. It could be considered as 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 !
THERE ARE INSTALLING HINTS AND TIPS !
The antenna still has lots of issues with different mast lengths.
Lengths that NEED TO BE AVOID are 5,5/11/16,5 meters long
(a half wave or multiple of it)
Lengths that are recommended are uneven quaterwave lengths say 2,75, 8,25, 13,75 etc.
(Additional informationn will be added/under construction)