UHF Fan Dipole Antenna Design

http://www.rsgb.org/

Hello Ronz:,

I saw the magic letters 'UHF'............

Good suggestion PWSlack! You cannot find a better place for just about any antenna designs.

I was just a 'listener' and used a 'half-wave 66' straight-wire antenna.

I am interested in your plans. Can you tell me what you want it for and, do you have an Amateur radio?

stay safe

babybear

The ARRL publishes the definitive book on antennas which will tell you more than you ever wanted to Know Just Google ARRL (American Radio Relay League) and pick up a copy of their Antenna Book.

Hello Guest,

yes, the ARRL are the American version of the UK's Radio Society of Great Britain

stay safe

babybear

The woods are alive

http://www.google.com/search?hl=en&safe=off&q=%22bowtie+antenna%22+%2Bcalculator&btnG=Search

with bowtie antenna calculators, or any other type

Hello all,

Thanks for all of the responses, but so far I have been unable to find a difinitive source for the design or construction of a 4-bay bowtie for any of the sources pointed to by your responses or my own research.

I have searched both the ARRL and the RSGB websites with no luck. These two groups specialize more in sharp tuning directional antennas for both transmission and reception, while the bowtie is an Ultra Wide Band type commonly used for reception only.

What I need is the dimensions for something like a Channel Master CM4221A so I can use that as a starting point for constructing a similar array. It would be nice to also find a theoretical discussion of the array itself, but failing that, the construction specifications would be adequate.

As for the application, its just a bit of fooling around on my part. I just moved into an apartment and rather than pay for cable - $17/Mo. for local channels - I felt I had an unusual opportunity to do a bit of antenna experimentation. As an aside, I generally do not watch more than a few hours of TV a week, and I just can't see paying for something I can get for free. Sort of a giant step backwards.

I have built several Yagis and other types, but UWB Fan Dipoles have piqued my interest and I just want to fool around a bit in the evenings. I have managed to find a couple of obscure references to UWB bowties, but what is missing is the distance from the reflector to the array, the spacing of the elements, output impedance, etc. I'm also curious as to the difference between using a solid element as opposed to the pair of wire elements (whiskers).

There are a number of amateur videos and whatnot describing homebuilt designs, but even though they seem to give good performance, there is a lack of solid information relating to the actual design.

Let me know if anyone has a more specific link or solid information on the subject.

Regards,

Ron

well you will find ways to make the single antennas, then make 4 of them, and then you need to find out how to make parallel feed harnesses, and then a rotor, and then methods to stop neighbours from storming the ramparts,

Let me see

http://www.google.ca/search?hl=en&q=%22parallel+feed%22+%2Bantenna&btnG=Search&meta=

and

http://www.google.ca/search?hl=en&q=%22parallel+feed%22+%2B%22uhf+antenna%22&btnG=Google+Search&meta=

Aurizon,

Thanks for the links, but they are about 90%+ useless to the question at hand. Most of the links I followed (I do not have the time to look at all of them) led to discussions relating to feed methods, but the bowtie antenna seems to have been neglected. The theory of the fan dipole is what I am lacking, and most of the feed methods differ in some very basic ways to what is used on several commercial types.

Still in the dark.

Regards,

Ron

Yes, That is typical of searches, so you just prune the search tree with extra + and - terms, you add what you want and remove wasted areas.

"bowtie UHF" +calculator +dogs -cats

will only give you results that mention dogs and say nothing about cats in conjunction with bowtie uhf

http://www.google.ca/search?hl=en&q=%22uhf+antenna%22+%2Bcalculator+%2Bbowtie+-yagi&btnG=Google+Search&meta=

As to feed method.

Antennas at UHF frequencies will all connect to a standard connection of some characteristic impedance, usually 50, 75 or 300 ohms, but not always.

With feeds in parallel you are dealing with the same problem you have with resistors in parallel....but at some high frequency, that means the feeds must be phase coherent, and the antennas must also be broadband. This leads to a contradiction in what you can achieve in terms of VSWR. It is easy to do at one frequency, but how do you change the feed line lengths as you change channels? hard to do, so compromises are made.

I suggest you search these areas, and be prepared to go through many screens of drilling to find one you want.

Hello Ronz,

you know nothing happens without a little work and effort...........

The last site I gave, you had the info' to design any antenna but, you has to do a little math. There is no probs with that is there? And you may well design an antenna you can put your name to and sell?

For the sake of 15 minutes of math you could have the exact antenna to fit the bands you want to receive.

stay safe

babybear

Aurizon,

Thanks again. I use those "pruning" methods from time to time with mixed results, but either way, this particular subject seems to be avoided by most people. I guess it's too easy to simply buy one rather than have the fun and satisfaction of creating something yourself.

I'm going to do some "cut and try" experiments in any event, but I just wanted to get a feel for the design before proceeding. I guess that is one of my failings. I lack the ability to take something that works on face value. I'm always wondering if it could be improved.

Early in my career I found a report on Yagi antenna design by the National Bureau of Standards which presented design nomographs developed through empirical testing at an OATS range. It was good data and I designed several Yagi antennas using the information that performed quite well.

It was years later that I found a treatise on the Yagi that explained the how and why without resorting to pages of laborious equations. The math was there, but the author gave some really excellent explanations in layman's terms. For me, it filled in the missing data quite nicely. I'm always willing to use well-documented empirical data, but solid theory is always more satisfying in the long run.

Thanks again.

Regards,

Ron

Hello Ronz,

Is this any help? Have you tried googling?

Are thinking of a half-wavelength dipole. UHF bow-tie antennas usually use a full-wavelength dipole, with a fat element diameter for wide bandwidth. This configuration, which is sometimes called a collinear pair or 2-element collinear or two half-waves in phase, has a number of advantages. First, you get 1.6 dB more gain. Second, by selecting the proper shape and thickness of the elements you can achieve good bandwidth and a good match to the half-wavelength phasing lines that connect the dipoles together in the 4-bay array, at maximum possible gain.
For example: A 1-wavelength dipole with a total length of 16 inches (8" each side) and 1-1/2 inch diameter elements (L/D=approx 10) will have a BW of 130% and a feed point impedance of 330 ohms. (The feed point impedance with a thin diameter would be much higher.) A 2-bay using whiskers or triangles for CH 13, would have elements and phasing lines about 26 inches long.

stay safe

babybear

Hello Ronz

I paste this pic of a four bay dipole. The size is listed as 40" x 18". which means if you count the wires going up and across you can work out the size of the 'bows'.

Let us know if it is of any help please? And, is this the type of antenna you want designs of? I have seen much simpler models using just the 'bow-tie' bit spaced and screwed to a 2" by 4". I can post them but there is no sizes.

stay safe

babybear

This is a stacked dipole reflector antenna. It has a fan-shaped beam: very broad horizontally, very narrow vertically. An excellent antenna in the 20-30 mile range, a rotor is usually not needed. It is a bad choice where multi-path occurs. (Multi-path and ghosting result when the direct signal path is blocked.) 4-Bays are made by Channel Master, Winegard, Antennacraft, Wade-antennas.com, and Antennasdirect.com. This UHF only antenna is roughly 40"x18".

Hello Ronz

try this site: http://www.hdtvprimer.com/ISSUES/erecting_antenna.html

Go down to 'antenna basics'. It gives all you need to know between the antenna element and the radiated signal received.

stay safe

babybear

BabyBear,

Thanks for all of the information. In truth, I had found most of it during my searches, but the comments you posted in your next to last post reinforced other information.

A friend of mine, who is a Mechanical Engineer I work with made the 2X4 & coat hanger version of the stacked bowtie which I tried out last night in my apartment. There was so much multipath distortion that performance was poor at best. So far the base performance has been obtained from a set of rabbit ears I made using 25" lengths of 1/4" aluminum rod elevated to a heigth of 6' above the apartment floor. Since I live on the second floor, this is not surprising. Another problem is that most of the stations I want to receive are located on the opposite side of the building, so the signal has to pass through the structure to get to my receiving antenna. This presents an interesting problem, and I'm having a bit of fun trying to come up with ways to address it.

What I will do next is construct a Yagi cut for the center of the UHF band using fairly large elements to increase the bandwidth and see if the performance improves. The directionality of the Yagi should cure the multipath problem to some degree. I am also using an 18db amp (booster) to increast the gain which is a considerable help.

Please remember that all this is for the pure, unadulterated heluvit and is nothing more than an engineering sabbatical of sorts.

Thanks for all of the help, but the original issue is still unresolved. The design theory and construction of an actual quad bowtie still eludes me. I have managed to uncover quite a few details from several different sources and a bit of guess work and empirical test will probably reveal the rest, but I'm astounded that this most common and one of the best performing Ultra Wide Band antennas does not have design information and construction details readily availably on the internet.

Regards to all,

Ron

Hello Ronz,

it is a shame you were not able to find a design description for what you want.

However, I feel the site 'hdtvprimer' does give enough detailed info' of how to make an antenna. It may be that a yagi is better suited as you can adjust the elements to receive the bands you want. And it might be the bow-tie can't do the job in your situation?

Take care and good luck

babybear

Try this forum for some detailed drawings and dimensions on UHF bowties and others http://www.avsforum.com/avs-vb/showthread.php?t=798265&page=27

Are you familiar with the Haverman design? Go here for discussion, schematics and diagrams. Even a couple photos of finished units.

http://www.google.com/url?sa=t&source=web&ct=res&cd=3&url=http%3A%2F%2Fwww.digitalhome.ca%2Fota%2Fsuperantenna%2F&ei=Fv0CSofyHKK0tAPN3pyCAg&usg=AFQjCNGGi7PubeabFlLm0Ke8WgIVirxlDw

Good Luck!

CC

Hi Ron

I just viewed a program on PBS dealing with Fractal Geometry, the program title escapes me. In the program it mentions how fractal geometry has miniturized antennae for cell phones. If you were to find a design program for this you could have a VERY small antenna say 4"x6" that could set on bookshelf, could also incorporate a signal amp for weaker stations also.

1Foxtrot70

Foxtrot,

I'm not sure a miniaturized version of a broadcast band TV antenna would be worth the effort. You still need a TV converter in any event, and I finally found that a simple pair of home-brew rabbit ears performed as well as any other antenna design in my apartment. It was an interesting project, but one that had results that were in inverse proportion to effort.

I'll be vacating the apartment at the end of the month in any event. The current job contract is ending and I'll be looking for another job in the near future which will more than likely involve a move.

I also found more than enough free media on the internet, so my laptop is my entertainment center for all intents and purposes.

Thanks for the comment.

Regards,

Ron