Not to start an arguement just some thin s Ive learned over time.

[Grim Reaper]

Antennas: single antennas are great, if your mounting them in the center of a roof , on center of trunk right behind the rear glass;base loads are best.theyll talk ground wave, they talk skip.Old school"bigMommas" new "Wilsons" are both good. A figerglass whip about 4' like the Francise'Firestick' will do nicely.Now for duals on a car; they are awesome,mounted right back of the rear glass and use shaft just tall enough for the center coil to clear the roof. better than a single? yes deffinitly. heres why; the right side will talk left as good as any center mount. the left is the same the other way. and both will equal a center mount talking off the rear. but out front they will kill a center mount hands down. Try this experiment. if you think im wrong. take 2 antennas, 3 watt meters. all meters being equal, the the 1st meter behind the radio. Put the other meters under each antenna. key up all 3 meters will read exactly the same. thus the DB Gain of dual antennas. Feild strength meters will do the same. Dual ground planes, beams its all the same. Next time Ill post bout pickup truck antenna placement. higher is better!!! Thank you for allowing me to join your forum Ken.:bdh:

 

[BOOTY MONSTER]

op:

 

[gamegetter]

I suppose this discussion has been had before.

I have read articles that explain cophase antennas on mobile will put the signal out forward and others that say it will put it out the sides better when mounted side by side.

Below is link to one said article.

The Ultimate Guide to 11 Meter CB Antennas

:sneaky2:op:

 

[eagle1911]

Most of this makes sense to me, although I'm not an expert in antenna theory. From what I understand about phasing with dual (or more) fixed antennas, you can actually change the directionality of the RF field by changing the phase. Many AM and shortwave radio stations have groups of towers or arrays of other types of antennas and use this principle to control their fields for day and nighttime usage, primarily to avoid interfering with other multi-kW stations elsewhere in the world that might use the same frequency.

 

[W5LZ]

Directional antennas work because there are several ways for re-shape radiation patterns to put RF where you'd rather have it. The opposite side of that coin is that you will loose RF going in some other directions. But, if it winds up the way you want it, and if you are familiar with the 'directions' you have an 'advantage' in, why not? There are a lot of misconceptions about all that though. Doing some research about it is a very good idea! It's also possible to 'steer' a signal by phasing (timing). The antennas don't change where they are or the direction they are pointed in, but it get's more 'involved', expensive.
There are always some losses when doing that. They usually aren't much, and the results are worth the loss of a tiny bit of signal. If those losses get to be objectionable, then it's not a good way of doing it, change it.
The biggest problem with directional antennas for mobiles is keeping it pointed in the right direction. As best, you've only got a 50% chance of doing that without a lot of effort. If it satisfies your requirements, do it. If not, why bother?
- 'Doc

 

[RatsoW8]

Grim Reaper...this link will start you on the path to enlightenment.

Antenna Efficiency

 

[Grim Reaper]

Directional antennas work because there are several ways for re-shape radiation patterns to put RF where you'd rather have it. The opposite side of that coin is that you will loose RF going in some other directions. But, if it winds up the way you want it, and if you are familiar with the 'directions' you have an 'advantage' in, why not? There are a lot of misconceptions about all that though. Doing some research about it is a very good idea! It's also possible to 'steer' a signal by phasing (timing). The antennas don't change where they are or the direction they are pointed in, but it get's more 'involved', expensive.
There are always some losses when doing that. They usually aren't much, and the results are worth the loss of a tiny bit of signal. If those losses get to be objectionable, then it's not a good way of doing it, change it.
The biggest problem with directional antennas for mobiles is keeping it pointed in the right direction. As best, you've only got a 50% chance of doing that without a lot of effort. If it satisfies your requirements, do it. If not, why bother?
- 'Doc

I agree with you that phase timing is a great way of making 2 omni directioal antennas directional. but because of space on mobiles it isnt usualy done, my point with the dual antennas on a mobile is you use the autos body to direct your direction of talk. i stated that 1 centered high on the mobile is good. your thinking as if it were a beam, but the addition of the sec antenna gives you a DB gain. the best place to use phase shifting. or as you put it timing is with base stations that have areas large enough to allow 2 or more Ground plane antennas. reread my post. duals will talk any where your single will at the same distances. until the long part of the mobile (front or back) is turned to them , them duals wins. off the sides opposite antenna works to match you with a centered antenna. off the back the 2 together matches your center mount. not 50% at all. Ill talk and hear every thing you do. but when the duals get pointed then single has no chance. thats if on back of mobile. pickups end up diff,

 

[Grim Reaper]

Grim Reaper...this link will start you on the path to enlightenment.

Antenna Efficiency

thank you but havent you every had or know anybody that run dual beams? effefancy losses to ground arent as bad on mobiles becuase of the entire vec being grounded .if you think im wrong bout the duals antenna being equal to a single. point to me where it is . ive seen and used ARRL hand books since i was 5 yrs old. one of the besttantenna specailist around if hes still alive is N4UJW. Ive been up 3/4 way of commerial radio towers at 15 replacing bussiness ban repeaters for my uncles.try the dual antennas with meters and prove me wrong.I dont have offical schooling at antennas. but my uncle tom was in the navy as a communicatipons officer and he taught me alot.And my first tour in the Army i was a comminucations field radio operatr for our brigade. Doc surprised with the phase changing to get omni directional antennas made directional. didnt think anybody had read that old of litature any more. please if any of this sounds uppity on my part, Take this as an apology.

 

[Grim Reaper]

In my day we called co phase making duals talk eveninly and maling them directional was refered to as fixed phased. Doc Id like to chat with you sometime, your very sharp. My Dad and I actually used fixed phased CLR 2s back in the early 70s. then he put up a long john 5 element.. beams do as you stated aline through extra directors. at the cost of sides and rear power output. but mobiles use the shape of the vec as ground and through that shape your output is sent. my only point was for someone trying to decide to run duals or single center mount antennas on a mobile to have an idea of what to expect from both types of antennas.

 

[Grim Reaper]

I suppose this discussion has been had before.

I have read articles that explain cophase antennas on mobile will put the signal out forward and others that say it will put it out the sides better when mounted side by side.

Below is link to one said article.

The Ultimate Guide to 11 Meter CB Antennas

:sneaky2:op:

I dont have a problem with what was stated on that page, now take those same duals that they had centered and move them forward or backward on the vechile off center and they become directional. but because as the picture showed you dont lose side to side. an as i stated duals combined output, you lose very little if any in the short direction of the vech. but because you made 1 part more directional. you gain that direction. it aint the ultimate . needs to add like raditional directions for like a pickup. and semi tractor trailer. just to name some. boats also come to mind

 

[W5LZ]

Antennas don't just get more directional without loosing some of that being directional in other directions. There's always a trade-off there. That's because of how an antenna acquires that additional 'directiveness', which is by moving it from some other direction to the desired direction.
- 'Doc

 

[Grim Reaper]

ok my responces go back and forth between base and mobile antennas and after reading what I stated i sound like a flake to myself. thing is, duals give you both sides stronger and if off set on the mobile, front to rear , compared to a center mounted antenna. you dont lose the (my ex was rear area) duals lets you keep the same signal. but gives you an advantage when pointed. you dont lose any thing in the other directions. because of the DB gain gotten from them duals on a mobile. the dont respond like beams, and once again thank you for letting me join you forum, I do enjoy posts that you guys saw fit to respond to my input. Ive been called flaky through the yrs. but yall didnt go there.thank you

 

[mackmobile43]

Your arguments are invalid.

 

[eagle1911]

you dont lose any thing in the other directions. because of the DB gain gotten from them duals on a mobile.

What W5LZ is trying to say is that if you were to compare a perfect omnidirectional antenna with one that is directional (assuming they are both being fed the exact same amount of power) you see that as the directional antenna's pattern gets stronger in one direction, there is a lack of strength in other directions. If that wasn't the case, the antenna wouldn't be directional.

I believe this has to do with basic conservation of energy. If you were to feed a theoretical, perfect, lossless, omnidirectional antenna in free space 100W for example, the field generated consists of that 100W of power spread throughout the field, concentrated strongest at the antenna and growing weaker with distance.

If you take a theoretical, perfect, lossless, directional antenna or array and feed it 100W, the field it produces will also consist of that same 100W, only now it will be concentrated in some particular direction more than others. The only way for more energy to be focused in one direction is to take energy away from the other directions. Anything else violates the laws of physics because it means energy is appearing spontaneously from nothing. There's only so much energy to go around, 100W worth for this discussion, so to put more in one direction means you must take away from the others. This also applies to reception of signals, only then we're talking about sensitivity in a certain direction rather than outgoing energy.

I've spoken previously on this forum about the fact that I work with lasers, and lasers are actually a great example of what we're discussing here.

In a laser, the reason that the beam can be so powerful is because it's concentrated in a very small area and all in one precise direction. In laser terms, 500mW is quite a bit of power, easily capable of burning flesh, setting fire to wood, and engraving plastics and many other solid substances (that's 1/2 of a Watt). If you took the energy from a 60W light bulb and found a way to concentrate it in one precise direction like a laser beam it would burn a hole through steel with no difficulty. This equates to "gain". In order for the energy to be concentrated in one direction, energy must be removed from the other directions and redirected.

 

[BOOTY MONSTER]

Ive been called flaky through the yrs. but yall didnt go there.thank you

don't worry if some faceless person is cyberspace calls you names .

BTW ....... you're kinda flaky .