Imax above beam

[fisjr]

How about a imax 2000? A little more than 5/8.

 

[Needle Bender]

the imax is what this thread is about, see the topic. and its not a 64. the imax is 23 feet long not including a foot on the bottom of mounting bracket which has nothing but coax inside going to the matching network which uses about 6-7 inches of the remaining 23 feet leaving right at a 5/8 of wire above the match

 

[Henry HPSD]

Guys,

There seems to be some miss understanding or explaining.

Again:

You can place above a horizontal beam any vertical without radials.
The effect the vertical will have on the horizontal beam is nill.
This is due to the different polarisation. (the EM fields are 90 degrees from each other).

We have to make sure the "hot" side of the vertical is isolated as would be the case with most verticals.
If we connect a 1/4 wave in a vertical position above a beam not using the standard isolation..(so we get a gizmochty antenna) it will have affect.

If you place a vertical with radials above a beam you either need to model the entire system in order to get a good impression what is going on...
Or you need to dismantel the radials and let the horizontal yagi be its "radials".
That can only be done if all the radials are "grounded" to the boom.

Some manufacturers have isolated radials for a good reason.
If the elments are grounded to the boom one need to consider a thing called "boom correction". the boom can make the elements electrically slightly shorter.
The problem given...often the 'grounded" connection is made by U bolts.
Since those are not made of aluminum tubing it is fair to say the connection will have corrosion after a while (different metals will have corrosion) which will make the "electrical" connection worse after time has set in.
This will change the boomcorrection and on its turn will change the electrical element length. That will change antenna pattern.
Now, on 11 meter thats a effect where one can argue if it is noticable or not.
However, one manufacturer who does has made sure it is prevented anyway.

Hope it made helped.

Kind regards,

Henry HPSD
All about antennas

 

[Needle Bender]

one reason i stick to a quad

 

[Grim Reaper]

why 9 feet ?
Thats not needed...i would prefer to place it directly above the beam.
In that case the Imax will have maximum bennefit of the yagi acting as a groundplane.

The distance for interaction in this case is of no interest.
otherwise those dual polarity yagi's wouldnt work.
neither would stacked beams etc etc etc.
Its the difference in polarisation that is enough.

It would have been different if the vertical had radials.
in that case i would loose the radials and let the yagi take over that job.
(at least if the elements are grounded to the boom).

Kind regards,

Henry HPSD 19SD348
All about antennas

i thought the bean had verticle as well as horizonal cross fire, i used 9' because thats 1/4 wave when using 11 meters. thatll give the imax its own radiation pattern with out the yagi knowin its there. and vice versa. i looked at the picture and I stand corrected your horizonal and Imax is vertical .sit right on top and let the yagi be its ground plane, if you dont mind the beam acting as the ground plane making the imax directional. if so why not crossfire the beam

 

[Grim Reaper]

introducing a 1/4 wave 9' mast element into the center of the beam will most certainly SKEW the pattern and negatively affect performance. a 5/8 isnt a resonant length and will go all but unoticed by the beam

if he puts right on top of the beam. the beam is the ground plane. and what ever direction the beam is point say east and west the Imax is no longer omni directional . thats why ground plane kits made are 360* and if your worried bout squeing the beam what about the tower. or isnt it vertical and horizon. if horizonal the beam wont care bout the mast. if vertical why is the tower invisible to the beam

 

[Grim Reaper]

the imax is what this thread is about, see the topic. and its not a 64. the imax is 23 feet long not including a foot on the bottom of mounting bracket which has nothing but coax inside going to the matching network which uses about 6-7 inches of the remaining 23 feet leaving right at a 5/8 of wire above the match

the matching net work is a capiter that is like you said in the bottom half. and thats where the antenna transmission starts. the Imax is a .64 wave length antenna makes it almost perfect for groundwave as well as DX talking. good choice on antenna N.B.

 

[Needle Bender]

once the rf leaves the matching network it begins radiating and it doesn't include the matching network to say 5/8. its the length of the aluminum or wire that designates the type of antenna. 1/4 or 1/2 or 5/8 or 64 all depends on the length of the element then you build a matching network acordingly. the reviewer who started the rumor of the imax being a 64 mistakenly included the matching network as part of the bottom 1/8 wave. if you remove the match and the mounting plate on the bottom you have 22 1/2 feet which is a 5/8 on cb