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Mobile End Fired Phased Array Antenna
- Thread starter LeapFrog
- Start date
CB Mobile Beam Antenna - End Fired Phased Array Antenna (Amazon)
Is this application snake-oil, or can I really learn how to build a "key-down" style van for $3.99 and have more gain than an Antron 99?
This must work, why else would the "key-down" competition guys build these antenna setups?
Please share some thoughts, ideas, & an opinion on the topic.
I have not looked into the theory behind this setup, but this link tells me I might be onto something here!?
The description on Amazon goes on to describe how the idea was taken from the "radio handbook"? (ARRL?)
My real question is how is this not just a co-phased antenna setup if "both elements are driven" as the description reads?
And more importantly how can I learn to build something like this:
Where do I find the formula(s) for the spacing... And yes you can just tell me to go read an ARRL antenna book if you like.
Maybe i'm waisting my time trying understand and recreate these style of rigs, but it is part of CB radio that I want to learn more about.
Thank You
73
I didn't notice the pics this morning. Have you saw the undertaker hearse with the maco m105s and the tower raised? He tubbed out the rear fenders and put a rear end out of a dually pick up under it to hold the weight.
This bad boy right here?
Just found the video searching for a hearse with maco!
Cool Idea, the undertaker 71 Olds with tower and m105!
What a bad @ss machine, a "mobile hammer".
I think my little QRM issue would "work itself out" if I had one of these bod boys!
Also I think the "Jesus is coming" theme suits my needs as well.
I would hate to "copy his idea" but dang I think I can find an old hearse for cheap.
If anyone would like to see more footage of this beast-mode hearse, UndertakerInTX is on YouTube.
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He had 2 m105s on it at one time. Last I heard of him he bought an AC suburban. I hear him on ch15 every now and then but no idea what he's talking on. He always has the cuckoo clock key up toy.
They didn't read any real radio book on the subject, if they did they would have worded this very differently.
Which book? "The radio handbook" isn't very descriptive, and can refer to any number of books. Seriously though, what they would have read, if they read anything, would be an antenna book of some sort.
This is a warning sign. A low SWR is not necessarily a good thing, and a low SWR over a huge bandwidth is more often the sign of a problem than a good antenna.
This isn't necessarily the case. If you get the spacing correct, the parasitic "reflector" element will generally add more forward gain, but the front to back ratio will be slightly worse. In other words, for key-downs this would be second to another very similar looking setup.
That depends on how high the Antron 99 is. If it is mounted at ground level, sure, however if it is on a tower 30 feet off the ground and this setup outperforms it you need to figure out what is wrong with your Antron 99. It may seem like it outperforms it for a short distance, but the phrase "height is might" really does mean something when it comes to antennas, and really is far more important than anything else when it comes to performance.
This isn't the only setup used in key downs, and is really more a sales pitch than anything.
A "cophased" antenna array generally refers to a 0 degree phased array, which is another way of saying that both antennas get the same signal at the same time. An end fire array like this is not a 0 degree phased array, one of the antennas gets the signal a little later than the other. The two setups will have very different results, including different directions for whatever gain they may have.
Assuming these setups were done with the same type of phasing, setting these up would simply be adding more antennas in line with the same distance between them. If you master getting the first two working, adding more in is just following the same directions again.
Here is a more complete and more readable version of the chart Captain Kilowatt posted above. It is larger than the forum will show so if you need it to be larger right click to see the whole thing.
The columns denote the antennas separation, so everything in the second column are two antennas 1/4 wavelength apart.
The rows are the phase differential between antennas. The first row, for example, are what people in the CB world like to call "cophasing" and the term is limited to this row. As you can see, their really isn't much gain to be had with cophasing, at least with the distances used on vehicles, however, if you can get the antennas further apart you can get some real gain from such a setup..
The phasing commonly used for end fire arrays are in the third and fourth rows. Actually, the setups I have seen used in the CB world are row three, 90 degree separation, and the distance apart is about halfway between the first and second columns. This is used more for the easy setup than anything, their is more gain to be had with other setups, but getting the antenna system tuned really gets to be a pain, and you can't easily direct feed it without some form of matching, which is not desirable when used in key downs, which is where this type of setup is generally used.
If you want forward gain and rear rejection, and have enough area on the roof for this type of setup, this is one way of achieving it.
If you really want help setting up such an antenna system, don't buy this, their is plenty of information available for free on-line.
The DB
Old post but This is awesome.
Anyone sill here? Brake brake...
The chart is for horizontal? How much difference would the vertical look like?
Is there a good, free, easy antenna pattern program to see the patterns of different possible setups? Like if You take this 180 degree out of phase array and add a reflector or director or both. How would the pattern change? That would be kool to play around with.
Is there a way to see the pattern for my actual antenna setup?
or will an analyser, app, or other devise show my actual pattern?
How do I know what my setup is real world doing rather than what a computer calculates the pattern to be? I might have a unwanted null? That's different than an unwanted station which is where we want the null. lol
180 degrees out of phase is half electrical wavelength is that right?
Which is approximately 12 ft with vf .66 on 27.205? is this correct?
Thanks for all the great info!
72's Ala"Bama" in Colorado
I'm still here, and thanks for liking my older post.
The chart is actually for vertical antennas.
I use the 4nec2 modeling program for things like this. It is free and pretty powerful. If you have any questions about 4nec2 or modeling, just ask.
I've been known to use a field strength meter to confirm the basic pattern of the antenna. Its not precise, but you can see where the peaks and nulls are.
It will be a little under 12 feet in length.
The DB
the guy posting / selling this info on amazon is not the original source for the document. I have acquired it else where 3 years ago. For the sake of the hobby and public knowledge, here's the info. Enjoy and hope to hear you on the air.
That book has been out for over 10 Years now and free. If he’s selling it , that’s like people selling air in a bottle .
Hogie electrically yes you can use multiple of 1/2 wl but the longer the length the more critical the measurements will be due to nature of the capacitance in the coax,
Cut it a little long and trim to what you need
Cut it a little long and trim to what you need
Thank you very much! I didn't want to get stuck using 11 feet 11inch when i actually need 30 feet to get to transmitter. I totally understand 90degrees phase feeding the 2nd antenna! Going to try this in a stealth location. It would be perfect for what i have in mind. See im in south Florida. On the ocean. I want to transmit west nortwest! This would be perfect! Also going to try a moxon... horizontally polarized it should quiet the noise floor a bit to. Going to put both up at 20 feet. Thats as high as i can go Hoa crap! Any higher they will see it..