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

[Marconi]

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.

I agree with eagle's perfect idea. However, the co-phase setup that Grim is talking about, is typically far from perfect at best. For one thing, if you had a co-phase setup installed with everything as perfect as possible, you would still have some increased loss...due to transformation by the harness, and a very low starting impedance at the antennas. IMO, this would tend to minimize any improved gain advantage that others have noted.

I didn't fully understand Grim's analogy earlier using three meters, but if I had understood, I would probably disagree...even without my having tested such a setup myself. Maybe Grim would describe for us what he did with a little more detail?

IMO, theoretically a well designed and installed co-phase setup should produce similar results, as some described here. There may be some improved gain in one direction, but the process also adds more loss with the co-phase type system. This tends to equalize results...as compared to a single antenna that is also designed and installed well.

 

[eagle1911]

I used the theoretical "perfect" model because it takes environmental influence and losses from small mismatches out of the equation which simplified my point a little, but I agree with you that real-world conditions will be different due to outside influences.

 

[Grim Reaper]

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

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

btw just kinda? damnn i was trying so hard too

 

[Grim Reaper]

I agree with eagle's perfect idea. However, the co-phase setup that Grim is talking about, is typically far from perfect at best. For one thing, if you had a co-phase setup installed with everything as perfect as possible, you would still have some increased loss...due to transformation by the harness, and a very low starting impedance at the antennas. IMO, this would tend to minimize any improved gain advantage that others have noted.

I didn't fully understand Grim's analogy earlier using three meters, but if I had understood, I would probably disagree...even without my having tested such a setup myself. Maybe Grim would describe for us what he did with a little more detail?

IMO, theoretically a well designed and installed co-phase setup should produce similar results, as some described here. There may be some improved gain in one direction, but the process also adds more loss with the co-phase type system. This tends to equalize results...as compared to a single antenna that is also designed and installed well.

what losses? you arent running 100' of coaxe. my meters anology was presented by nu tronics in the early 70s. also the mannufactures of clr2 s also posted litature about time and fixed phased antenneas they didnt find any losses that would be sigificate enough to stop from using them. rf isnt lasers or like water where things get divided in half. its a magnetic field. buy 2 cheapo antenneas stick them 6' apart cophase them. using 72 omn coax for 12' then finish the run to the radio with 52 omn then use any watt meter or field strength meter you want youll find that totall output has dbl. and use any type meter you want and use 100 watts or higher you wont have coflicting signals.. no higher SWR , you will have if your right and all the manufactures from 40 yrs and on up are wrong. theory and opions are nice but bottom line. they are still opions and ive told you where to and how to find the facts i based my post on, thank you again for your time and considerations , and most definitly thank you for responding to my posts here

 

[BOOTY MONSTER]

i read running 100 ft of coax will make your audio louder ... so does running two 100 ft runs to a pair of antennas make the audio even more louder ?

 

[AudioShockwav]

Twin center loaded hustler antennas were good but you still get a directional pattern off of the car.
To see this all you need to do is walk around the car with a field strength meter and note the readings.
Placing the field strength under the antenna will not show you the pattern. You have to move away from the car and then walk around it in a full circle.
Give it a try.
73
Jeff

 

[psycho]

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:

Ths only way dual antennas will significantly increase gain is if one is hot and the other is used as a grounded reflector. Side by side cophased duals have to be at least 10 ft apart to have a chance of working properly. Cophased or 1 hot/1 reflector duals gain in one direction at the expense of the other directions.

 

[DIRTYWHITEBOY]

UOTE=Grim Reaper;319395]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:[/QUOTE]

 

[rabbiporkchop]

co phase

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:

This is nothing new for those in the know, but there are many people out there who have preconceived ideas that it is a bogus way to go. Whenever I setup a tractor trailer, I almost always choose to go that route for the very benefits you mentioned. Not to mention it wipes out receive from the sides which I like.

 

[Needle Bender]

Two Wilson5000s 9' apart, one behind the other, on the roof of a '92 Suburban got a perfect omni pattern as good off the sides as one in the middle of the roof was off the front and back.
Tom wasn't looking for gain just uniform performance in all directions and he got it.
He could do a full circle and the s meter wouldn't move more than a needle width.
He made a phasing harness from two 1/4 wave x vf, pieces of 75 ohm RG-11 to a T connector.

 

[BOOTY MONSTER]

Two Wilson5000s 9' apart, one behind the other, on the roof of a '92 Suburban got a perfect omni pattern as good off the sides as one in the middle of the roof was off the front and back.
Tom wasn't looking for gain just uniform performance in all directions and he got it.
He could do a full circle and the s meter wouldn't move more than a needle width.
He made a phasing harness from two 1/4 wave x vf, pieces of 75 ohm RG-11 to a T connector.

did "tom" ever compare those "Two Wilson5000s 9' apart, one behind the other, on the roof of a '92 Suburban" to a single 5000 in the middle of the roof ? if he did , what were the results ?

 

[nav2010]

Marconi wrote

I didn't fully understand Grim's analogy earlier using three meters, but if I had understood, I would probably disagree

This statement has me pondering Eddie. You didn't understand what he was doing with the three meters but if you did understand you would disagree? How can you conclude that you are going to disagree with someone without actually understanding what they are talking about.
That's like saying 'i've just read Einstein's theory of relativity and I don't understand it at all from start to finish but I think Einstein was wrong'.
I think I'm putting that one in the top 20 dumbest statements of the 21th century.

 

[Needle Bender]

did "tom" ever compare those "Two Wilson5000s 9' apart, one behind the other, on the roof of a '92 Suburban" to a single 5000 in the middle of the roof ? if he did , what were the results ?

Same off to the sides as one in the middle, and a near perfect omni. Front to back about the same, all he gained was side performance to match.

Thing I don't see is how the watt meter shows the same power at each antenna as at the rig when the load is split between 2 antennas. Should drop to 1/2 power at each antenna, but I've never tried that trick.

 

[ab4d]

Same off to the sides as one in the middle, and a near perfect omni. Front to back about the same, all he gained was side performance to match.

Thing I don't see is how the watt meter shows the same power at each antenna as at the rig when the load is split between 2 antennas. Should drop to 1/2 power at each antenna, but I've never tried that trick.

All the watt meters are reading is the same RF signal from the transmitter going through the entire system. I believe this is where the misconception from the original poster is coming into play. From reading Grim Reaper's synopsis, it appears there is a misconception that because each meter is reading the same power at the base of both antennas, the power output is doubling (left antenna 4 watts, right antenna 4 watts = double the power).

The meters are reading the voltage going up to the antennas and returning through the entire system. Just because someone is using two antennas, you are still dealing with the same 4 watts from the transmitter. Because the system is phased, the 4 watts of power is alternating between the two antennas, you just can't see it with a simple RF meter, because it is happening too fast at a cycle rate of 27 mhz.

As Doc pointed out, the dual radiating elements help direct the RF and receive in the desired direction which is "gain." There is no free lunch or magic power secrets when it comes to antennas or gain. Gain is not an increase in power, you are stuck with whatever power is coming from the transmitter, minus the losses. Gain is the ability to concentrate the transmit power and the area of receive, in the direction you want.

73

 

[hookedon6]

All the watt meters are reading is the same RF signal from the transmitter ... because someone is using two antennas, you are still dealing with the same 4 watts from the transmitter..

'zactly correct
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