Imax above beam

[wavrider]

i think the nature of a beam is that the elements are looking for each other to work right and thats why you can use a pole or rotor up the middle and it still works right. the imax isnt the right length to activate like the 1/4 wave element halves and so it might not even make a difference or it might F#C% it all up!

Exactly.

 

[Henry HPSD]

Any object in or near the antenna will have influence.

The amount of this influence cant be explained as is done so far in the thread.
(though i liked the first explination best).

Its just not as simple as "they are looking for each other" ..

Ill give a example:

Take for instance a interlaced mutliband yagi, that will never be as good as a monoband yagi..you could ask yourself why not ? As the elements lengths differ from each other?

Lets look at another strange thing..Its possible to feed one dipole and put another one for a totally different band next to it and the it will work on both bands..
This without a second feed line! ..a example of very good "coupling", were now using it to ouwer bennefit.

Oke, take a 1/4 wave vertical and you "attach" a 3/4 wave vertical next to it..
We have a J-pole..that works.. and it has a almost omni directional pattern.
This opposite to what if been reading here..the Imax will be "directional".
Now, im not saying it is not the case...the imax will probarbly be directional...but im only trying to give insigth its not that straigth forward.

Now, the 5/8 wave vertical or 0,64 wavelenghte or any equal length, can be devided in such a way its just short of a 3/4 wave..
Then were going back to the beam..all additonal elements are either to long or to short for the resonant frequency ..thats the same "thingy" what was going on by our just to short 3/4 wave. So actually we have created a situation where we are certain we will have influcence.

The idea given: that one can just "put the mast and rotator" between a yagi in a vertical polarisation is inaccurate.
The first indication of this is cause the manufacturers who advertise with vertical and horizontal often give different measurments. (If it didnt mather why do they do that?)
Besides you guys aswell as i know the stories of difficult SWR issues with vertical beams.
Again a indication of the problem...
The sad thing beeing most people can "only" measure swr.

Im willing to express it futher:...if you would actually measure the pattern of the (vertical) yagi ,You would be very dissapointed.
The antenna which is capable of producing a good/tigth pattern in a vertical way would be the quad. (of course situation: mast / rotator inside the beam)

It migth be wise to see it slighlty different:
All things close or "in" a antenna will have influence.
There are some situation where this is minor or almost nill (as is the case with a boom)
There are some situation where it will be to our bennefit (as is the case with a well designed additional element or with a imax above a horizontal beam)
All other situations need to be moddeld to get an idea of what is actually going on.
But the odds will most likely always be towards the negative aspect.

Kind regards,

henry
All about antennas

 

[148 Alaska]

are you the 148 out of alaska that we hear on L38 who sounds so much like 625 jack?

dont know 625 jack...
but yes I ran 38 lsb but I have not since this past spring

 

[Needle Bender]

Any object in or near the antenna will have influence.

The amount of this influence cant be explained as is done so far in the thread.
(though i liked the first explination best).

Its just not as simple as "they are looking for each other" ..

Ill give a example:

Take for instance a interlaced mutliband yagi, that will never be as good as a monoband yagi..you could ask yourself why not ? As the elements lengths differ from each other?

Lets look at another strange thing..Its possible to feed one dipole and put another one for a totally different band next to it and the it will work on both bands..
This without a second feed line! ..a example of very good "coupling", were now using it to ouwer bennefit.

Oke, take a 1/4 wave vertical and you "attach" a 3/4 wave vertical next to it..
We have a J-pole..that works.. and it has a almost omni directional pattern.
This opposite to what if been reading here..the Imax will be "directional".
Now, im not saying it is not the case...the imax will probarbly be directional...but im only trying to give insigth its not that straigth forward.

Now, the 5/8 wave vertical or 0,64 wavelenghte or any equal length, can be devided in such a way its just short of a 3/4 wave..
Then were going back to the beam..all additonal elements are either to long or to short for the resonant frequency ..thats the same "thingy" what was going on by our just to short 3/4 wave. So actually we have created a situation where we are certain we will have influcence.

The idea given: that one can just "put the mast and rotator" between a yagi in a vertical polarisation is inaccurate.
The first indication of this is cause the manufacturers who advertise with vertical and horizontal often give different measurments. (If it didnt mather why do they do that?)
Besides you guys aswell as i know the stories of difficult SWR issues with vertical beams.
Again a indication of the problem...
The sad thing beeing most people can "only" measure swr.

Im willing to express it futher:...if you would actually measure the pattern of the (vertical) yagi ,You would be very dissapointed.
The antenna which is capable of producing a good/tigth pattern in a vertical way would be the quad. (of course situation: mast / rotator inside the beam)

It migth be wise to see it slighlty different:
All things close or "in" a antenna will have influence.
There are some situation where this is minor or almost nill (as is the case with a boom)
There are some situation where it will be to our bennefit (as is the case with a well designed additional element or with a imax above a horizontal beam)
All other situations need to be moddeld to get an idea of what is actually going on.
But the odds will most likely always be towards the negative aspect.

Kind regards,

henry
All about antennas

you make it sound like all the beams ever made with a verticle side dont work anywhere near as well as they could without the rotor or mast going up the center. now i know theres allways a little bit more you can get to be better and better but splitting hairs isnt as important as having a couple godd antennas up to use

 

[Henry HPSD]

That was not my intention.
They will work, but not to the abillity they can.

It was my intention to make clear your "ideas" are not accurate.

However, i am confident that in most cases: the odds a vertical beams with a rotator and mast and a coax cable running through the elements are by far not performing as they can do in reference to one where the mast (etc) is at a 90 degree angle.

There will always be guys explaining the vertical beam they have up is great, and that there good rigth.
Its the effort one has put into it to put the antenna up together with the (some) directivity (that doesnt mean efficiency) that makes people think the systems performance.

Its the "mobilitiy" thingy:
If your used to walking,then driving any old car would be a improvement.
though its by far not a ferrari.

Kind regards,

Henry
All about antennas

 

[Needle Bender]

ok, so in the end you have a beam and a stick and they both work well even though there not perfection. i have heard alot of guys with beams and sticks up the middle that love there performance even though its not perfection but im sure theres allways room to improve but maybe just having a good working antenna system is 100 times better then not having one and only 1.2 times worse then not having perfection. sounds like a stacked pair of verticals would be the hot setup

 

[wavrider]

ok, so in the end you have a beam and a stick and they both work well even though there not perfection. i have heard alot of guys with beams and sticks up the middle that love there performance even though its not perfection but im sure theres allways room to improve but maybe just having a good working antenna system is 100 times better then not having one and only 1.2 times worse then not having perfection. sounds like a stacked pair of verticals would be the hot setup

Needle Bender, now I like the way you are thinking, It seems like you are looking outside the box as far as antennas are concerned, but not really.

Term used is phased verticals, or vertical arrays, and so many different ways to fed them there verts. In phase, out of phase, delayed phase, all depends on how you want the pattern to be as far as the lobe them there "stacked" verts will produce.

But that is a topic for another thread. Hammies have been "stacking" verticals for a long time, some even have four, six or more in an array and cover the globe with direction just by flipping a switch. Oh and most of them are ground mounted.

 

[Needle Bender]

im talking about mounting a imax on top of the rotor mast up through a beam

 

[wavrider]

I thought I read it as stacked verticals?

 

[Needle Bender]

sorry, your right, i was just thinking at the end about how to support and run coax at 90 degrees from a vertical beam to avoid what henry was warning about and the obnly thing that came to mind was stacked vertical beams

 

[wavrider]

High Performance CB Antennas

Actually there is stacked verticals on 11 meters.

Check out the link using IMAX 2000.

Yes beams can be stacked vertically, with enough space between the yagi's they do have more gain.

Easier to stack them side by side.
for the higher bands.

 

[Grim Reaper]

you wuill probably see more effect on the imax then the yquad. the imax will have more strength in the forwrd bean direction and a little less to the back. the yquad is looking for a resonent 1/4 wave above the boom not a 5/8. it will have an effect on the vertical beam but nothing to worrry about and almost nothing on horiz

if the Imax is put about 9' above the beam unless both are powered together the Imax will be invisible to the beam, the reason is theres nothing for the beam to reflect off of, power into both at the same time causes the rf fields to intermesh and sque, but one with remain invisible to the other,\ otherwise, thats how they varios agancicies like the poluice, emergymangent , bussiness band, military can run so many atennas right on top of each other, frequency diff, doesnt matter,

 

[Henry HPSD]

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

 

[Robb]

So Henry, what you are saying is that you can put an Imax above a horizontal beam - but it will affect the beam.

Are the effects strong - or weak?

I was under the impression that because of the polarization were different that it wouldn't matter.

 

[Needle Bender]

if the Imax is put about 9' above the beam unless both are powered together the Imax will be invisible to the beam, the reason is theres nothing for the beam to reflect off of, power into both at the same time causes the rf fields to intermesh and sque, but one with remain invisible to the other,\ otherwise, thats how they varios agancicies like the poluice, emergymangent , bussiness band, military can run so many atennas right on top of each other, frequency diff, doesnt matter,

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