| Author |
Message |
    
Foxracing
Intermediate Member
Username: Foxracing
Post Number: 106
Registered: 11-2003
| | Posted on Friday, April 23, 2004 - 11:10 pm: | 
|
A-99 and BIGSTICK
I have a tree where my antenna is in now and my 3 section A-99 is up there in the tree by at least 60-65ft and i have another tree about 50ft away from the one where my antenna is if i were to put up a big stick instead of another A-99 and co-phased them both together would this help my recieve or transmitt.I would like to know if you guys or gals explan the possitive and negative points to this.
THANKS
(GREG)
FOX--CEF 234 |
ELCO Guy. (Unregistered Guest)
Unregistered guest
| | Posted on Saturday, April 24, 2004 - 7:21 am: |
|
It is possible to cophase antennas.
However your trees are unfortunately too far appart for good linkage/radiation pattern. One wave length (depending on the frequency) for CB is an average of 32 feet. In order to link efficiently two antennas they must be within one wave length of each other, one quarter wavelength being the best possible case.
A second problem you may have in this case would be your antenna. Every Antenna Book in my library, which is many, state that the antenna should be a quarter wave length antenna. Your antenna is a 5/8 wave if I remember correctly. As I stated this may or may not have an adverse effect even if you were to bring both into proper proximity to each other. If you can bring two antennas close together you will have to cross your fingers. But what the heck, experimentation is half the fun. Is it not?
At any rate here is a brief summary of cophasing of verticals. Per the books the vertical must be a quarter wave antenna. If you space them one quarter wave length appart and feed each side with equal lengths of quarter wave coax you will get a broad side effect (draw a line between the two antennas and the signal will be bi directional and broadside to the plane of the antennas). If you feed one antenna with a quarter wave feeder and the other with a half wave feeder (keeping the distance between the two antennas at a quarter wave) you will make a mini beam with one big signal lobe favoring one direction IN LINE with the plane of the two antennas.
However your trees are just too far appart for vertical cophasing.
But on the bright side, if you ever get your ham license you could easily fit a 40 meter dipole between the two and even snug in a dandy 80 meter dipole.
On the topic of tree care. First do not wrap the tree trunk with rope, wire or cable. A tree is a growing thing. Wrapping with rope or worse, cable/wire) will eventually girdle the tree trunk causing a reduction of nutrients and kill the tree.
In general use caution when using trees for support. Use them only for temporary support and not for permanent support. The best permanent support is a good tower. |
Ozzie
Intermediate Member
Username: Ozzie
Post Number: 180
Registered: 11-2003
| | Posted on Saturday, April 24, 2004 - 9:09 am: |
|
I dont belive you'd get much in the way of benefit. To co-phase antennas they should be either a quarter or a halfwave length apart - depends on required radiation pattern. The 50ft mentioned is too large a space to give much in the way of iomprovement. Tech 833 mignt be able to give you a better idea, as I havent played with phased antennas in a few years. |
Tech833
Moderator
Username: Tech833
Post Number: 649
Registered: 8-2002
| | Posted on Saturday, April 24, 2004 - 12:50 pm: |
|
Co-phasing antennas means feeding them in phase with equal amounts of power.
If you co-phase antennas, then change their spacing from one another (assuming equal height), then the pattern changes. As you get them further than 1/2 wave apart, you begin to create minimas and nulls which cancel the signal radiated in various directions from the array. At 50 feet apart, you are at 1.39 wave of seperation, or 500.4 degrees. Your pattern will look unusual at best. A lot like a dandylion flower.
I would urge you to reconsider. |
Tech833
Moderator
Username: Tech833
Post Number: 650
Registered: 8-2002
| | Posted on Saturday, April 24, 2004 - 12:51 pm: |
|
Another thing,
You can co-phase any kind of antenna, 1/2 wave, 1/4 wave, 5/8 wave, etc. It does not matter as long as you can match the impedance and reactance. |
Foxracing
Intermediate Member
Username: Foxracing
Post Number: 108
Registered: 11-2003
| | Posted on Saturday, April 24, 2004 - 11:46 pm: |
|
I measured it today before i was guessing.. The tree and the second tree are 32ft away from each other.. THIS WILL NOT WORK FROM WHAT YOU ARE ALL TALKING ABOUT RIGHT..
FOX |
Tech833
Moderator
Username: Tech833
Post Number: 653
Registered: 8-2002
| | Posted on Sunday, April 25, 2004 - 11:28 am: |
|
It will 'work', depending on what your definition of 'work' is. If you mean making your signal stronger in all directions, then it will not 'work'. |
Creator
Member
Username: Creator
Post Number: 73
Registered: 1-2004
| | Posted on Sunday, April 25, 2004 - 1:30 pm: |
|
How would one go about co-phasing 2 Imax 2000's, what would be the length the two antennas would have to be separated from each other? I was thinking of doing this.. |
Dindin
Member
Username: Dindin
Post Number: 72
Registered: 2-2004
| | Posted on Sunday, April 25, 2004 - 2:40 pm: |
|
Creator ,the simplest way is to mount antennas equal heights 9 feet apart,use a mobile co-phase harness to connect them together,if one antenna is mounted north of the other then your signal will concentrate in a east/west pattern with major lobes roughly forming a figure 8.radiating pattern could be changed by the addition of a switchbox and delay lines,but that could be another thread
|
Bullet
Intermediate Member
Username: Bullet
Post Number: 322
Registered: 7-2003
| | Posted on Monday, April 26, 2004 - 6:26 pm: |
|
my 2 cents
id never cophase two verticals side by side like mobile antennas.
just for the fact its to much trouble to go through for little effect.
much easier to use a PDL2 for this purpose.
now mounting them one over the other "OH YEA" works great for an omni directional.
otherwise use a dipole or a beam.unless your just doing it for fun. |
