Antenna Enhancement free power-passive elements???

[drdx]

I wonder. In the big world of antennas and radiation, elements receive and radiate signals. On a yagi, the director(s) receive the signal and re-radiate them to the driven element. The reflector, being a little long, receives and “bounces back” the signal to the driven element as I understand it, thus the term “bounce back” used in some arrangements. Nothing is free in the antenna world but grabbing what is otherwise wasted can result in positive results.

Now I’m not going to carry out this experiment due to a lack of resources and urge but if you had a big enough piece of land, plenty of time, and were utterly bored, this is a cool question. Let’s say you had a big patch of land with an antenna in the middle, a vertical omni-directional antenna of some sort. Surrounding that antenna are other vertical antennas maybe in a circle around the antenna, evenly dispersed around it. I don’t know the distance but not right on top of the antenna as to effect feed quality. These antennas are not fed with coax or connected to anything. Going with theory, could these antennas be beneficial in receiving and re-emitting signals to a point that they would enhance the performance of the fed antenna? Would they be of benefit? Would they act as passive enhancers, pulling signals in due to their length, possibly enhancing weak horizontal signals that would otherwise fall prey to a 20db+ cross polarization drop and not be heard?

Signal conducting structures of the right length constantly receive signals and re-radiate them to some extent. Could this be a source of signal benefit? Would the antennas be grounded or would the vertical element be isolated. Would grounded verticals radiate enough to reduce ground loss?

I’d bet that if you carried out this experiment that when transmitting from the fed antenna that you’d be able to walk around with a field strength meter and sense signal on the surrounding “elements” .

Any thoughts on this?

I'm fully prepared for ridicule but I still believe that there are great discoveries left out there for signal improvement from the antenna perspective.

-drdx

[721HACKSAW]

Lets say you had access to a large metal structure, a bridge, cell tower, or perhaps the St.Louis Arch, could you use that permanate structure to "help" your strategically located antenna in this same fashion? You've got me thinking again DRDX!

[Double D]

Sounds interesting, i'll have to try modeling that with my software.

[drdx]

I didn't think about trying to model it. I have the new arrl antenna book and cd, I'll have to see what it has on it or try to grab one on the web. I'd be really curious if it did have an effect and if so of the elements needed to be 1/4 wave grounded ones, isolated, or if half would be better wavelength wise. I'm visualizing a situation where you're enriching the entire antenna range with signal, using the elements as mirrors of a sort, mirrors that pull signal and make the area a signal magnet so to speak.

I know it may sound a little wacky but I think there has to be something there. Once on a fox hunt I was on a guy took a 2 meter beam and aimed it at a water tower, scattering his signal all over town, making him really difficult to track, even with a doppler setup. Structures to radiate and I'm wondering how well an INTENDED, finely tuned one would. I have my home ground based tree vertical still. I may ground mount a couple of 1/4 wave steel whips out away from it, transmit, and see if I can get handheld readings from the whips. I do know that on my mobile director setup the director lights up a bulb but that's a finely spaced deal in a yagi config so I expect it to there.

-drdx

[Slim Pickins]

I have looked at my groundplane antenna a few times and thought "I wonder if I had more ground radials and supported directors on the ends of them parallel to the vertical what would happen?" I kind of visualized about a dozen radials each supporting a director 9' from the driven element They could be isolated from the radials with pvc and supported at the top with a second ring of pvc radials.

Glad I am not the only one who has thought of this.

Paul

[drdx]

I did read around the web a little while ago after starting this post and there are articles on "passive repeaters" and such that are interesting. One article mentioned using 2 antennas connected with coax and in the example it mentioned using 2 tv antennas, pointed in opposite directions, up on a hill to help the reception for someone down in a valley. The beam aimed at the tv station would receive the signal and it would be retransmitted into the other beam, very interesting. I wonder how that could be employed in our hobby or if it would even be worth the effort. I was just thinking vertical omni stuff.


-drdx

[Double D]

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This is the pattern i generated by placing 8 passive half wave elements 3.56 meters from the center active element. The 8 elements are placed to the north, south, east, west, NW, NE, SW, SE. The system is 11 meters above average ground.

['Doc]

Would there be any benefit? There certainly can be, this isn't exactly a new idea, broadcast stations have been doing it for a very long time. Implementing it is the problem, it does take space and additional 'structures'. Would it be worth it? I don't think it would be for me, your milage may vary.

Oh, the 'passive repeaters' thingy. It works, but there are only a few instances where it would be of any appreciable benefit. It depends a lot of the distance between the two antennas used, and the type of antennas. There will always be more loss in that 'passive repeater' than in just running a low loss feed line to that distant antenna. That low loss feed line definitely won't be coax!
You still see a lot of those passive repeaters used with cellphones in a car. They are not very effective, and in most cases not worth the trouble.
- 'Doc

[drdx]

Interesting. I wonder what the optimum range away from my home based ground mounted vertical would be good. Since my antenna is on the ground, the house blocks a large chunk of its open exposure to the northeast. I have trees on about every corner of the property. I wonder if a few "passive antennas" would get me around the structure. It would be free to try but probably impossible to measure to any real degree. Would a grounded vertical antenna be ok I wonder, or an isolated quarter wave above ground, just a simple vertical element work better?

On the program image above, it appears that more elements would be needed for uniform pattern. How does that pattern compare if you overlayed the same vertical on it but without the added elements? I know that no antenna will have a perfect pattern in the real world but reducing the dimples would be a goal to achieve. I see that the program takes into account elevated elements. That would get expensive and ugly fast but we're just dreaming here.

-drdx

[Double D]

On the program image above, it appears that more elements would be needed for uniform pattern. How does that pattern compare if you overlayed the same vertical on it but without the added elements?

-drdx

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[drdx]

Interesting. It looks like the shapes differ but the area of intensity is similar. It reminds me of a spirograph pattern from my childhood. I wonder how a simple all vertical half wave element would work. Looking around my house, over on public property are a couple of tall trees at a slightly better elevation that I could put passive radiators in. I wonder how a shortened one would work, as in a pair of 5 foot fiberglass mobile antennas joined at the threads with allthread and hung vertically in a tree? I've got about 100 of those in various lengths. I've also got a bunch of wire, that would work, be cheaper, and invisible.

-drdx

[Red Warrior]

At the risk of misintreperting your intention let me add this.

All the power ever radiated from a transmitter is present at the output of the final stage. Everything beyond that point absorbs some of the power. The transmission cable, the antenna, free space. A vertical dipole will radiate but the sum of all energy radiated is a net loss compared to the output of the transmitter. The concept of "gain" from an antenna is a misnomer. There is never any "gain" from an antenna. One can direct the radiated energy in a certain direction resulting in a received signal that is equivalent to a vertical antenna radiating at a higher power. We often refer to this as "gain" but it really is not a gain in power.

Place any other metal object, near in length to the radiated wavelength, in the aperture of the antenna and you will change the radiated pattern but you will also absorb some of the radiated power. The result will be a perceived signal gain in a certain direction based on the spacing and relationship of the radiator and passive element. Every time you add a passive element (as in a director in a yagi) you absorb some of the radiated power which is dissipated as heat in each element. You are trading power for directionality.

[drdx]

Great point. I totally agree on the not "adding" any power. I always think of the example in the old antenna books where it kinda describes a beam antenna in terms of being like a flashlight reflector. I was originally wondering in my first post about the possible benefits of cleaning up or making a certain area more rich in vertical signal. Then, I read on about some passive repeaters and saw that for total other applications the topic of even putting an amp on them comes up, but I was more thinking passive for my fun.

I realize we're not going to pull power out of thin air but do wonder that in a situation where the elements were vertical that if there were enough of them that they'd contribute to the reception as they would be also pulling to come extent signals that aren't vertical? That brings up a whole other thought. Would a dual polarized passive element offer anything?

-drdx

[Red Warrior]

passive repeaters

Every vertical metal object close in length to the resonance of the transmitted frequency will react to the transmitted signal. Some of the energy will be absorbed and dissipate as heat and other will be reradiated ( looks like a reflection). I believe this is a very inefficient way to propogate a signal.

dual polarized passive element

Dual polarity can add up to 3dB of received signal using a diversity combiner.