Homebrew a 850mhz Yagi!

[bagged2000]

Yesterday i built a 850mhz Yagi and I am still really impressed on how well it performs. This was my very first antenna i've ever made. Here are the directions on how i assembled the antenna. I used 1/8" brass tubing and a 5.8" wooden dowel from Home Depot. The cost was about 16 dollars ($2.00 for dowell, $5.00~ each for brass rod, and $4.00 for spray paint). Quality is excellent. The main problem I had was the direction the antenna was facing. Good luck. Any questions feel free to ask! This antenna is mounted in my attic and is ran to my scanner with a 50' RG cable with 256-258? connectors. I can get pictures tomorrow if you need them!

[hoser147]

It would be cool to see some pic's Hoser

[bagged2000]

Well, the pictures didnt turn out as well as I had hoped. But here are two quick ones i took this morning. I plan on building another for the 160mhz range. When i do that one i will be sure to take step by step pics.





Drew

[kg4ivt]

Looks good! I always had fun trying new and different antenna projects in the attic when I was younger.

Not trying to hijack this thread but has anyone made one of these using a panel or bulkhead mount BNC/SO-239/whichever instead of just soldering coax to it?

If so, how did you do it and how did it work out?

[digitalanalog]

Good job, Love the Home Brew's.

[k9rzz]

Yes, props on the homebrew !!

[bagged2000]

Thanks all, I still am not 100% that i made the driven elements correctly I believe i did but can someone explain it to me a little better. When i have the total measurement for the driven i add the diameter of the boom to it and them cut in half? is that right. and then also since the drivenis 2 pieces when i measure the holes from the reflector i basically cented the 2 elements on both sides of that mark. It gets good signal but since this is my first one, i really dont know if the signal im getting is as good as it gets. I went from the RS 800mhz antenna with static in the house to this which has very little static only on very few transmissions.

[hoser147]

Looks Good, let us know if you decide to make another one or revamp it........

[Skypilot007]

Are those elements pictured 1/2 wavelengths for 850MHz? They look a little long. Your demensions look close in on the data sheet. The reflector element at 6 3/4" total, it almost looks like you have 6 3/4" above and below the boom. Maybe its just the pic play games with my eyes. Also most of the plans I've seens or design calculators make the reflector the longest element, drivin element is cut to the center frequency and then the director elements get shorter as they go on down the boom. I have a home brewed 500MHz yagi now outside and it works awesome. Can't beat the performance for the money spent on it.

[bagged2000]

Yeah i see it, The measurements i used are right on whats in that chart, atleast i think. I could of made a measuring error. But being my first one i know its not perfect, and to be honest, the quality i am getting from it is really good and i really cant see the reception getting much better(that might be beacuse i havent heard any better). Ive been listening for the past hour and a half and havent heard but one person in static and dispatch said they couldnt hear either.

Drew

EDIT: I just looked at the calculator i used and i did mess up the first director. it is actually supposed to be a little less than 6 1/4 (6.208in) total and i made it 7 for some UNKNOWN reason and that would make them all largest to smallest. Will this make a big difference in my reception, because like i said its pretty darn good right now.

[mtindor]

It _should_ make a difference in the reception and directivity with that longer director. The bright side is that it's too long rather than too short - Just clip that SOB down to size and you'll be good to go.

Very nice job on that btw. It's been years since I built one, but I built a 900 mhz yagi about 12 years ago and had a helluva lot of fun doing it. I think this makes me want to do it again. You have inspired me !

Mike

[blueangel-eric]

i'm curious how the SWR's are without a matching device. All the real beams i've seen has gamma matches. Also with the boom wood, how does that affect the length of the elements? do you measure the length for the elements from outside of the boom or do you count the measurement from exact center of the boom/ elements? i'd be leary of using wood because if you mount it outdoors then it could warp from the weather.

[Skypilot007]

I used this web page to to get my dimensions when I made mine.

http://www.k7mem.150m.com/Electronic.../yagi_vhf.html

You can design lower gain yagi's that work fine with this site also. I have not tried transmitting with one of them yet. I'm curious too about what it would take to get it to match up. Mine is feed with 50ohm 9913 and the pigtail is 50ohm RG8X. One photo shows how I attached the pigtail directly to the driven elements. If some sort of matching device was used I suppose it would attach to the drivin elements and then to the feed line. Sound right? It receives very well and much better now that its been weather sealed and put up on the roof.

[bagged2000]

Originally Posted by blueangel-eric

i'm curious how the SWR's are without a matching device. All the real beams i've seen has gamma matches. Also with the boom wood, how does that affect the length of the elements? do you measure the length for the elements from outside of the boom or do you count the measurement from exact center of the boom/ elements? i'd be leary of using wood because if you mount it outdoors then it could warp from the weather.

Good question. Like i said this was my first. and i really dont know if I should of added the Diameter of the wood to each of the elements. All i know is that this was my first and it exceeded my expectations about 100 times. I went from reading all these numbers and not knowing a thing, to putting this thing together for about 15 bucks, and hearing some very good quality transmissions.

Drew

[cassidy1190]

wow this is really great! Im gonna build one of my own pretty soon, it will be my first homebrew as well. Im wondering though, what is the reason for separating the shielding and inner coax and connecting them to the different sides of the dipole? Im a little confused on how to do this. Also what are some good yagi calculators you've used before?

[nickcarr]

Originally Posted by bagged2000

I used 1/8" brass tubing and a 5.8" wooden dowel from Home Depot.

Why did you use brass? It's not a good conductor of electricity. You can try to find "electrical brass" but it seems harder to find these days.

Aluminum or Copper is a good choice. Yes it is more expensive, but you'll likely get better performance with them.

[digitalanalog]

I use brass connections in high DC voltage[i.e. from 400 to over 3,000 amps]applications on a daily basis.
Its a very good conductor, where as aluminum is NOT.

Copper is the best.

[ermin]

That is great. I made a 2m beam with 4 elements and put the two driven element pieces together as close as possible without touching. I got into a repeater 25 miles away with only 1.5 watts almost full quieting. It was in the atic with a tile roof. Home made antenna's are a blast.
73 de Ermin

[nickcarr]

Originally Posted by digitalanalog

Copper is the best.

No actually silver is best, but I'm not going to quibble over it.

[cassidy1190]

do the two halfs of the driven elements have to be offset from eachother? also, tell me if im right...the driven element is split at the middle but all the others go striagth through the boom...right?