Build 800mhz Yagi

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xwindows2

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trying to build 800mhz yagi not sure which dimensions to use
i have 10 ga copper wire, 3ft yard stick and some rubberbands for a rough draft
and 8ft rg8x for coax,i do have some lmr400 20ft w/connectors
 

k8tmk

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Refer to a Popular Communications magazine article (approx. a year ago) for an excellent article on building an 800 MHZ yagi. I built one from the article and it works great.

Randy
 

AZScanner

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k8tmk said:
Refer to a Popular Communications magazine article (approx. a year ago) for an excellent article on building an 800 MHZ yagi. I built one from the article and it works great.

Randy
Took some digging but I think I found it on PopComm's back issues pages: http://www.popular-communications.com/Feb07Highlightsblank.html - the article is for VHF yagi's but the idea's probably pretty much the same. But unless you're a subscriber you need to order the backissue to read the article.

How about some online resources instead? I've found a few but I'm a bit of a noob when it comes to building antennas so I don't quite "get it" from the sites I've looked at - I've always bought them instead because I'm just not very handy with tools. But $60+ for a used yagi is a bit spendy so I'd like to build one too. Being the antenna noob that I am, I need step by step & fairly idiot proof instructions. Any links out there?

-AZ
 

Airdorn

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800Mhz

Wavelength: .375 meters

5 element yagi:


Element Length

Reflector 7.3 inches

Driven element: 7.0 inches

Director 1: 6.5 inches

Director 2: 6.4 inches

Director 3: 6.3 inches


Element Spacing

Reflector - Driven Element: 1.84 inches

Driven Element - Director 1: 1.845 inches

Director 1 - Director 2: 3.7 inches

Director 2 - Director 3: 3.7 inches

This is output from a program I wrote based on some data gleaned from the internet. I built a 380.075 Mhz yagi using the formulas in the program and it is my best antenna.

For what its worth, those numbers above match pretty closely to a professionally-built 823 - 898 Mhz yagi I have on my roof.

Good luck.
 
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kb9hgi

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slicerwizard said:
Yikes, what are you using - exhaust pipes off a truck? :)
Exhaust pipe? sounds more like sewer pipes...LoL
 

tonsoffun

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Airdorn said:
800Mhz

Wavelength: .375 meters

5 element yagi:


Diameter of elements

Reflector 7.3 inches

Driven element: 7.0 inches

Director 1: 6.5 inches

Director 2: 6.4 inches

Director 3: 6.3 inches


Element Spacing

Reflector - Driven Element: 1.84 inches

Driven Element - Director 1: 1.845 inches

Director 1 - Director 2: 3.7 inches

Director 2 - Director 3: 3.7 inches

This is output from a program I wrote based on some data gleaned from the internet. I built a 380.075 Mhz yagi using the formulas in the program and it is my best antenna.

For what its worth, those numbers above match pretty closely to a professionally-built 823 - 898 Mhz yagi I have on my roof.

Good luck.
Airdorn, I think you should check your program. Something sounds a little off.
Take care
 

Skypilot007

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tonsoffun said:
Airdorn, I think you should check your program. Something sounds a little off.
Take care
I think what is listed as element diameters is supposed to be element lengths.
 

k8tmk

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The Pop Comm article I was referreing to was specifically for an 800 MHz yagi.

There were lengths and spacings for three different configurations (numbers of elements). I built the one with the most number of elements (I think 8 or 10).

Randy, K8TMK
 

Skypilot007

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I've used this site for design help for a few yagi's I have built.

http://www.k7mem.150m.com/Electronic_Notebook/antennas/yagi_vhf.html

I finished a UFH yagi a few months ago. Its mounted in my attic and works great. I building another one more robust to mount outside and I'm finishing up an 11 element 800 MHz yagi now. I had to switch to a metal boom on this one because the PVC boom would sag a little due to its length. Here's a pic of my UHF PVC boom 6 element yagi.



Here is the thread about the construction.

http://www.radioreference.com/forums/showthread.php?t=91317
 

AZScanner

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Hey... by golly I think I'm getting the idea finally! Thanks to this post: http://www.radioreference.com/forums/showpost.php?p=344796&postcount=17 I now understand how you build one of these things (I didn't understand where you hook the coax up and that post answered it). That thread also contains a PDF file that details the parts and construction.

Hmmm, we just happen to have a home depot down the street AND a radio shack down the other way, and Mrs. Scanner is going to be visiting friends all day tomorrow...yup, I sense a weekend project coming on. :D

-AZ
 

Airdorn

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There's a better way to hook it up than that, imho. I'll draw a picture later and post it.
 

railfanjjf

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x windows 2----from railfanjjf, nokewsville, va.--i am an antenna collector and keep all antenna info from magazines in 3 ring binders.....these "cheap yagi's" do a good job. i have built th 800 mhz/military air/462.975 to listen to the medivacs in the d.c. area.etc. the cost is minimal. due to the fact i have all the articles from popcom in my binder i'll list below so that we will have a record on the antenna forum if kanyone else wants to build on.
1-air band 108/136=======march 2008
2-840-890 mhz i built the 10 element model,caution: the article has incorrect dimention info and there is a correction in the following month issue=======start with may 2007
3-325-400 mhz mil-air......3 element======june 2006
4-family radio service 465 mhz.=======nov. 2007
5-vhf high-155 mhz----february 2007
6-450-470 mhz uhf========november 2006

hope this helps you. be sure you aim the antenna directly toward the anatenna you are trying to listen to. these antenna's are real tight on coverage. someone mentioned earlier about interpolating dimentions to design to an exact frequency. all info must bve adjusted including the antenna length, element lengths and the spacing. if you have any further questions i'll watch this thread for a while.
 

Airdorn

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Here's a quick picture of the coax hookup to the driven element of a yagi. I used this on my own yagi I built recently and it works beautifully.
 

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Skypilot007

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Airdorn said:
Here's a quick picture of the coax hookup to the driven element of a yagi. I used this on my own yagi I built recently and it works beautifully.
I wonder why this way is better. I too just connected the coax directly to each isolated 1/2 wave element. I've had great results this way for receiving only.

I like to try and experiment with different designs, maybe I'll modify one of my home brewed yagi's to feed it like this and see what happens.
 

Airdorn

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Skypilot007 said:
I wonder why this way is better. I too just connected the coax directly to each isolated 1/2 wave element. I've had great results this way for receiving only.

I like to try and experiment with different designs, maybe I'll modify one of my home brewed yagi's to feed it like this and see what happens.

I think because it looks cooler.
 

xwindows2

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thanks for every ones input,i used K7mem yagi calc prog
I am still playing around with different spacings
cut DE for 870mhz, #10 bare copper wire, 1-flat wooden yard stick and rubber bands
for a rough prototype Trying to pick up mpls ,mn from new brighton
not too far as the crow flys, bottom floor in apartment
Airdorn i like your antenna design i will give that a try when more time is available
 

xwindows2

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Fridley MN.
thanks for every ones input,i used K7mem yagi calc prog
I am still playing around with different spacings
cut DE for 870mhz, #10 bare copper wire, 1-flat wooden yard stick and rubber bands
for a rough prototype Trying to pick up mpls ,mn from new brighton
not too far as the crow flys, bottom floor in apartment
Airdorn i like your antenna design i will give that a try when more time is available
what's the impedance on that one?
 

Mikey54

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Airdorn said:
I think because it looks cooler.
Actually with the coaxial balun, you have a balanced feed pattern, and the antenna is also at ground potential, so it would tend to be quieter noise wise. A Gamma match is also a fairly easy to make feed system if you are at all handy. Again, the antenna is at ground potential with a gamma match system as well.

Bottom line is whatever works for you, and what your construction skill set can handle.

Mike VE3MKY
 
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