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4 square array for comp antenna???

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4 square array for comp antenna???

Post by Hypo » Sunday, 15 November 2009, 22:03 PM

Has anyone ever tried a 4 square phased array on a comp vehicle? 4 1/4 wave verticals in a square a 1/4 wave on each side? It would put 2 mounted out to the side of the vehicle a little ways. If it was only for a single direction it wouldn't need any switching circuit just the phasing harness. It would be cool to have a vehicle with an electrically steerable array. If you used a coil loaded antenna it would be possible to keep the total height below 13.5 feet. Switching in another phasing harness and it could also be used for DF work as well. 8 elements would work better for DF though, but would be difficult to keep from interfering with the 4 square for transmit. Any thoughts? There is lots of info on beam forming arrays on the internet. I found this interesting facility that GA Tech runs.

GTRI http://www.gtri.gatech.edu/gtri75/innov ... erformance" onclick="window.open(this.href);return false;
That looks like a T-72 tank mounted on the turntable.
For radar signature collection to program mm wave radar warhead seekers for use in conditions where infrared might be occluded. Think heavy rainstorm.

Keydowns fascinate me since I believe it is the closest thing to EW that we civilians can engage in. It is Electronic Warfare in a way.

GTRI also has a high power lab where they can create up to 10 megawatt pulses just to simulate EW and is effect on electronics.

One Day......got to make it through Calc IV first.

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Re: 4 square array for comp antenna???

Post by drdx » Monday, 16 November 2009, 6:33 AM

I love the 4 square, but the spacing and good grounding that array needs to work well I believe make it a tough to do mobile. I wonder if, due to grounding and metal mass of a vehicle, that it would have a weird pattern? I'm assuming it would. I think you'd be just as well or better off with a parasitic or phased array in a single line. I have a topic on my isolated L director deal and many others have 2 hots and more with parasitic elements on that. That said, you never know when a new approach may be the next best thing.

-drdx


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Re: 4 square array for comp antenna???

Post by Hypo » Monday, 16 November 2009, 9:07 AM

I found some antenna simulation software on the internet for free that I am trying to get to run on my Linux computer. Even if it is a crippled demo version with a limited number of segments in the model it would at least be able to show the skewing effects of an offset ground plane on a vertical. Still trying to learn my way around Linux with all its "sudu apt get" commands and all. Like going back to DOS in a way. I am too cheap right now to give any more money to Microsoft.
I zoomed in on the picture of the test range and it looks more like an M1 on the test stand. I am really considering the 4 square for my home station since I am on a lot with tons of trees that make it impossible to erect a tower without clearing them away. Long wires are no problem though but swinging a long boom just isn't in the picture.



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Re: 4 square array for comp antenna???

Post by drdx » Monday, 16 November 2009, 10:00 AM

Well, you mention long wires and that usually applies to the lower hf bands, and this is a cb crowd, but I would think you could easily erect a wire based fixed directional system for cb with relative ease. For the lower bands, it could be a little more difficult to do a fixed directional array. If you have the space and the trees a loop skywire is a good performer for multi band use. For cb, other possibilities may be deparate wire yagis, a remotely switched sloper array, or a central reflector based multi directional array, via a remote switch, where you have one reflector in the middle, and 4 or more fixed wire yagi arrays in the vertical plane hubbed out like spokes on a bicycle wheel. Maybe a set of cloud burning beverages?? V beams? Rhomic,Sterba?? The possibilities are endless, but even if you do a serious directional array, make sure you have at least one antenna in the opposite plane to switch to. In other words, if you have a vertical array, have a horizontal dipole or something to switch to as the signal reduction when cross polarized is around 20db, probably more than any beam array's gain you will cook up. Skip is random while local signals are a little more definite in polarization so it is nice to have that as a choice. And, it is always nice to have a point of reference, such as a 5/8 vertical that is 1 wavelength high, to base your findings on.

The easy part about a yagi is that it almost "wants" to work. As long as you can simulate some sort of reflector that is 5% or so longer than a half wavelength in the same plane, or a director that is shorter by that much, or a combo of those and/or more directors, you will easily achive directional antenna behavior in the desired direction. It is the fine tuning that brings in the really good front to back and fwd gain, or the best compromise between the two that is harder to dial in, but it can be done by putting in enough time. The only real drawback to the fixed directional array that I see would be that you would want at least 8 directions of signal concentration to cover it all, but then again, years ago the Super Scanner vertical fixed array only had three and did fine, and had an omni mode, so you could do that too.

To save on coax, roll with an ameritron remote coax switch or something equivalent so you can experiment cheaply. Depending on your location, you may want do erect dedicated high gain arrays in strategic directions so you can null out the unwanted areas and concentrate both receive and transmit.

Software that does modeling is out there all over and works well but when you throw other variables in there such as trees, it gets messy fast. Sometimes it is just more practical to get an ARRL or Orr handbook, some wire and hardware, and start building and testing. The materials you use, their thickness, hardware, etc., also plays into the length that it truly needs to be in order to radiate where you want. Get yourself an antenna analyzer. I use a palstar zm30 but the mfj is good to, and others make them. I use a home based junk radio to transmit and receive and record my results from my mobile from various locations to gather data, a basic but workable method in the real world. RF is weird, and often what looks great on a screen is greatly skewed due to proximity related interference. In the vehicle scenario, I'd be curious how it sees it. It would vary based on vehicle and mounting arrangement but in reality the 4 square is usually thought of as a solution to having a fixed electrically rotatable array where on a vehicle all you have to do is move it around, kind of negating the purpose of the 4 square.

I apologize for getting techy and formal sounding this early on a Monday, so at this time, please resume General Lee talk, Predator 10k praising, and the usual, and always essential "watts per pill" bragging. :lol:

-drdx


Yes it's me, Dollar-98, drdx, the original all *Censored*, shot cawla on workin this no-fade technology.

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Re: 4 square array for comp antenna???

Post by Hypo » Monday, 16 November 2009, 12:17 PM

LOL at the "cloud burning beverage" Our lot is 1 acre wide by 4 acres deep on an East-West axis. I could run some beverages pointing due west for listening to Prime Minista out on the coast or maybe even Kangaroo Land. I did the free equidistant projection off of a website to get my bearings. I am thinking I could do a small self support no more than 50 feet high for the 5/8 and then to V beams radiating off of that towards the Northeast and Europe. 60 feet would be better but then guy wires start to be needed. I found a surplus dealer that has some Rohn sections but finances are a little tight now so a roof mount about 20 feet up or wires in the trees will be my short term options. Looked at the Army MARS site for great info on the loop skywire. Only runing a FT-1500 2M, a HR2510 for 10M and a switched crystal Messenger 23 radio , the 25 and 29 are sitting around right now but I hope to pick up an older Ten Tec or Kenwood for the low bands. I wouldn't walk away from a deal on a 716 though. I need to dig up my 1999 antenna handbook. Lots of stuff still in boxes from moving 4 years ago and running OTR the whole time since. I might sell some of my older music equipment to swing the analyzer deal. Anyone want an older Yamaha TX-816 synth? I have 3 to sell.
A comp vehicle wouldn't need the switching gear like you mentioned and would be really simplified. Just the 4 way splitter into the phasing lines. Perhaps use a shortened balanced dipole for the outer elements off of the center line of the vehicle. I actually ran such an antenna on the International in my Avatar picture for a year. I made a Balun in a cast aluminum box drilled and mounted 2 4 foot Francis antennas on it, one up one down then mounted it in the middle of the mirror mount trying to keep an equal amount of metal near each element. I was trying to see if I could build an antenna that didn't need the truck for a ground. I'm sure the pattern was biased to the drivers side but it was almost too sensitive. I could really hear the difference in static from wet to dry pavement and even the stripes in the road. It wasn't the antenna waving around like you can hear when the nylon insulator is wearing out or is cracked. In one really quiet location I picked up auto ignition noise from over 100 yards away when I was shut down waiting for a load in a nearly abandoned industrial park.
Interesting forums on CBRT. Primarily ideas here are geared toward increasing the signal to noise ratio by jacking up the power in the signal but reducing background noise can be a really dramatic difference as well.

Get as techy as you want. I am here to learn from all perspectives. I got started with CB and just got bitten by the radio bug. There are guys in here that have been professionals in various RF related fields that are great resources of information. Only thing I ever did outside of trucking was climb Cell towers for one summer and do sweep testing on the antenna and cable installs with a HP 8714. It was fun but $12.00 an hour wasn't enough for the risks involved and no benefits.
Thanks for the reply.
Tom




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Re: 4 square array for comp antenna???

Post by drdx » Monday, 16 November 2009, 13:59 PM

I don't know, anytime you start talking about shortening anything it starts to suck the wind out of the performance but I am a firm believer that in a mobile directional array that if you can use isolated tuned elements over making the car half of the system you're moving ahead of the game. My director uses my rear roof mounted puck antenna and the director is an L, the horizontal part aiming forward, the vertical vertical, so the element itself being an L is directional by itself a little, and it brings in a horizontal radiator. I've ran L antennas mobile and had great luck testing but had no skip at the time to really test it on. For competition that horizontal element would be meaningless but for skip I think having a horizontal radiating part in addition to the rest of it is bound to help a little.

Get on the web and look up L antennas. There is an article on one for 10m that has the plotting and everything and it follows that same logic. It is said to be good in both horiz and vert performance. I've said it before, but I do think that polarization diversity in a mobile holds the key to unlocking performance in skipland. Directional and polarization diversity? That's got to be a good thing. Cover both polarization extremes, as that random signal reaches you, no matter what the angle, the most polarity related fade would be 3db, at the 45 degree cross, and not the 20db that you see having an antenna that is singularly polarized and encounters a cross signal.

Maybe you could use non loaded elements, incorporate some type of L arrangement in your square, but I looked in my book and it shows 4 square layouts with half wave spacing, way too big for a vehicle. How about a 3 or 4 hot phase delayed array?

Am I making any sense here?

Also, look up that single element V beam the guy made from some hamsticks. I made one and played with it, but again had no conditions, still a cool concept if it works like that guy says it does. It basically goes on the theory that a dipole with forward tilted legs is directional.

How about a mobile moxon? Not for comp, as it would be flat.

How about a flat side comp class? Now that would speed up the evolution of mobile antennas for sure.

-drdx


Yes it's me, Dollar-98, drdx, the original all *Censored*, shot cawla on workin this no-fade technology.

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Re: 4 square array for comp antenna???

Post by 5pills » Wednesday, 09 December 2009, 14:57 PM

i run 4 antennas on my 2002 f150 once...4 1/2 '' aluminum tubing 1/2 wave ...the 2 hot was 70'' away from the 2 blockers .......one hot and blocker was on the left side and the other two was on the other side....they where co-phased like 2 hots with their own blockers......this setup had serious rejection but i really didn't notice a whole bunch of gain......i played with it a few times and matched it out with analyzer .......then gave up...my subervan...(lol). with one director beat this setup and i finally played with it a lil longer till I beat my suburban... i made it a bit more directional...i believe yielding more gain...i used 50 ohms throughout....i also used 75 ohms and got a match with both ......one thing that was weird was i was standing in the middle between all 4 antennas...(in like a box) and the field strenght meter never would register....as i moved to the outside of the antennas it would peg........i dont know the technical terminology ....but i know what values to look for on the MFJ........im going to do this setup again when it warms up here


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Re: 4 square array for comp antenna???

Post by Hypo » Wednesday, 09 December 2009, 23:30 PM

Cool.
Nice to hear someone has tried it.
When you couldn't get a reading on the field strength meter, you were standing right in the middle of the interference pattern null.
This is where all the incoming signals cancel each other out.




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