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Posted: 1/26/2011 7:54:06 PM EDT
Hello. My name is KB and I'm a dumpster diver...
Well, only where I work. I see some interesting things get thrown out at the marina. Lots of lawn furniture, old BBQ grills and plenty of TV dishes. The other day I noticed this protruding from the dumpster. 
Now I'm the type that can see a "project" in almost anything, and needing a 2 meter beam, I saw my next project. I removed all the elements except the reflector. 
I ground out the rivets and straightened the aluminum element brackets as they were tweaked. Luckily, one of the insulated brackets survived. This would be the driven element. 
I used the yagi calculator at K7MEM's website to establish the spacing for this 6 element yagi. Gain is about 8.5db. 
The choke balun was made with 5 turns of good quality rg58 around a 7/8 inch OD pvc pipe. 
The choke was mounted in the ever popular CCI .17HMR ammo box. The driven element is coupled to the choke with some brass strapping. So far the only thing I have had to buy is a 6ft section of 3/8 aluminum rod for the last two directors. All else comes from my stash.I'll post the results from my informal testing in the next week or so. I'll add a pic of the entire antenna tomorrow. It's too dark right now for outdoor pics. |
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Posted: 1/26/2011 8:02:00 PM EDT
[#1]
Very nice work there .
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Posted: 1/27/2011 10:31:32 AM EDT
[#2]
Nice work! Let us know how it performs.
Vulcan94 |
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Posted: 1/27/2011 1:48:38 PM EDT
[#3]
My 6m dipole is parts from a broken TV antenna. Classic amateur radio at work in this thread.
One suggestion is to put some anti-oxidant compound at the junction between metal parts on the elements, where those little plates make contact as well as any other metal-to-metal contact points. |
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Posted: 1/27/2011 3:00:13 PM EDT
[#4]
Wow, you are a tinkerer like me. Being that you're local, I have lots of plastic, aluminum, steel etc., a lathe, and a mill if you ever need any custom insulators or whatnot made. The 2m yagi I have up is a 12 element homebrew that still works fine after 12 years.
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Posted: 1/27/2011 3:13:41 PM EDT
[#5]
Thanks guys! Gamma, I have some Eze_ox? or whatever it's called around here somewhere from many years ago..like 20 years ago. I just need to find it.
my65pan, Thanks for offer. I may need a part made in the near future. Let me know if there is anything I can do for you. I work on boats for a living and am Mercury/Mercruiser qualified as well as some Volvo Penta and OMC product. I can also do moderate electronic work on older rigs. I'm going to go outside and see if the match is even close...back in a bit. 
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Posted: 1/27/2011 3:20:25 PM EDT
[#6]
Quoted:
Thanks guys! Gamma, I have some Eze_ox? or whatever it's called around here somewhere from many years ago..like 20 years ago. I just need to find it.
my65pan, Thanks for offer. I may need a part made in the near future. Let me know if there is anything I can do for you. I work on boats for a living and am Mercury/Mercruiser qualified as well as some Volvo Penta and OMC product. I can also do moderate electronic work on older rigs. I'm going to go outside and see if the match is even close...back in a bit. Let me know what you need, I'll be happy to help if I can. Antennas have always been my favorite aspect of ham radio. |
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Posted: 1/27/2011 4:08:18 PM EDT
[#7]
my65pan, Mine too. I have always been fascinated by large antennas and arrays. I recently bought a small chunk of property near Show Low to plant "the farm".
Well, no joy. The SWR was well over 3 at both ends of the band.  It did however favor the high side of 2m. I added a short stub to each end of the driven element but the SWR got higher, not lower as expected. I'm going to try a different matching network. I wasn't thrilled about using the choke to begin with, but it looked easy enough to make and I had the fixins already in view. Off to rustle up some gamma match fixins now.
ETA–– Well now I've done it...should have read some more of K7MEM's website before I made the choke.. 
Driven element construction |
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Posted: 1/27/2011 5:52:31 PM EDT
[#8]
Now this is some very cool and skillful work!
A good eye for junk, too! Congrats, guy! |
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Posted: 1/27/2011 6:01:30 PM EDT
[#9]
This is the feed arrangement I've used on several 2m yagis, somewhere I have a program to model yagis.
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Posted: 1/27/2011 6:17:11 PM EDT
[#10]
Quoted:
Wow, you are a tinkerer like me. Being that you're local, I have lots of plastic, aluminum, steel etc., a lathe, and a mill if you ever need any custom insulators or whatnot made. The 2m yagi I have up is a 12 element homebrew that still works fine after 12 years. You willing to help a non-local?  I have an antenna I am trying to rebuild and I need a couple of plastic insulators made for it. No particular hurry other than I'd kinda like to have it operational by the June VHF contest. They should be very simple to make if you have a lathe, I don't have a lathe though.
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Posted: 1/27/2011 6:19:15 PM EDT
[#11]
Quoted:
Quoted:
Wow, you are a tinkerer like me. Being that you're local, I have lots of plastic, aluminum, steel etc., a lathe, and a mill if you ever need any custom insulators or whatnot made. The 2m yagi I have up is a 12 element homebrew that still works fine after 12 years. You willing to help a non-local? I have an antenna I am trying to rebuild and I need a couple of plastic insulators made for it. No particular hurry other than I'd kinda like to have it operational by the June VHF contest. They should be very simple to make if you have a lathe, I don't have a lathe though.Sure, send me a PM, we'll go from there. |
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Posted: 1/27/2011 7:06:34 PM EDT
[#12]
Cool beans, bro. I've got one of those in my garage.
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Posted: 1/27/2011 7:15:00 PM EDT
[#13]
Thanks AFM and my65pan, I have that drawing in my antenna book. I'm going to go ahead and make the folded dipole driven element. All my elements lengths and spacing are within 1/16 of an inch for the folded dipole arrangement. I just need to match the 300 ohm feedpoint to 50 ohm coax. Repositioning the plastic box will be a snap and I should be able to make a small balun to go inside the box.
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Posted: 1/27/2011 7:19:32 PM EDT
[#14]
Quoted:
my65pan, Mine too. I have always been fascinated by large antennas and arrays. I recently bought a small chunk of property near Show Low to plant "the farm".
Well, no joy. The SWR was well over 3 at both ends of the band. It did however favor the high side of 2m. I added a short stub to each end of the driven element but the SWR got higher, not lower as expected. I'm going to try a different matching network. I wasn't thrilled about using the choke to begin with, but it looked easy enough to make and I had the fixins already in view. Off to rustle up some gamma match fixins now.
ETA–– Well now I've done it...should have read some more of K7MEM's website before I made the choke..
Driven element construction Yagis will alter the driven element impedence quite a bit, usually by lowering the impedance. If you have material for a folded dipole for the driven element, try using a simple 1/2 wave 4:1 balun to connect to it - that's a common yagi drive arrangement and usually works well. The impedance drop brings the nominal 300Ω for a folded dipole down to closer to 200Ω so it matches well. 
All the shields connect together, the "loop" is 1/2 wavelength at the frequency of use (take into account the velocity factor). |
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Posted: 1/28/2011 6:15:20 AM EDT
[#15]
Gamma, thats the scheme I plan to use but I'm not going to ground the folded dipole in the middle. K7MEM's site recommends to insulate it from the boom. Theoretically, there should be no current in the center, but he suggests that any stray current on the boom is bad and I don't need any more stumbling blocks.
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Posted: 1/28/2011 5:09:28 PM EDT
[#16]
In keeping with the "one mans junk" theme, after posting that scan from the ARRL antenna book I went out in the garage and sorted through my old antenna junk. I have some leftover insulators and SO-239 brackets that I made from those plans if anyone needs them. I think I have some shorting bars to tune the folded driven element around here somewhere also.
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Posted: 1/29/2011 5:57:04 AM EDT
[#17]
Looks like you have some antenna building to do! Kinda like finding a FCG and then needing everything elst for the rifle build.
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Posted: 2/2/2011 6:11:09 PM EDT
[#18]
After some deliberation, I decided to go with a gamma match. I changed the layout slightly to duplicate this design. (6 element version) 
The Gamma is made from the center conductor/insulator from RG213 and a scrap piece of TV antenna element. 1/2 inch copper pipe straps were straightened out and formed for the gamma tube mount. 
I have been able to tune the SWR down to 1.1 to 1 anywhere in the band by adjusting the gamma tube and mounting strap. I can't wait to get it outside and tuned up properly. I'm also curious about the pattern.
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Posted: 2/3/2011 12:47:40 PM EDT
[#19]
Very nice work KB
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Posted: 2/3/2011 1:28:19 PM EDT
[#20]
If you're going to install that antenna outdoors, you need to replace that copper shorting bar with aluminum. Bare copper will create significant galvanic corrosion to aluminum. A strip cut from an aluminum can even would probably work.
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Posted: 2/3/2011 1:40:52 PM EDT
[#21]
If you need any special insulators you can't fabricate... I have a minilathe and a supply of Delrin rod. Perhaps I can turn something for you?
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Posted: 2/3/2011 3:22:56 PM EDT
[#22]
You're right Gamma. It didn't even cross my mind..and I'm a boat mechanic! Meaning I see galvanic corrosion on a daily basis.
I'll pick up some AL strap soon. All I have here and at work is 1/4 inch thick.
AFM, Thanks for the offer! Local my65pan has offered his services also. Thanks to both of you! Once it's tuned up, I'm going to coat the PL259 (solder side) with Liquid Tape and glue a plastic cap on the end of the gamma tube and elements. Good 'ol butyl tape (windshield sealer tape) will be applied to the connector side. Next is a UHF yagi. Then I can put up my homebrew az-el rotator. az-el rotator video
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Posted: 2/3/2011 4:34:48 PM EDT
[#23]
Quoted:
You're right Gamma. It didn't even cross my mind..and I'm a boat mechanic! Meaning I see galvanic corrosion on a daily basis. I'll pick up some AL strap soon. All I have here and at work is 1/4 inch thick.
AFM, Thanks for the offer! Local my65pan has offered his services also. Thanks to both of you! Once it's tuned up, I'm going to coat the PL259 (solder side) with Liquid Tape and glue a plastic cap on the end of the gamma tube and elements. Good 'ol butyl tape (windshield sealer tape) will be applied to the connector side. Next is a UHF yagi. Then I can put up my homebrew az-el rotator. az-el rotator videoI have aluminum strap if you need it. Gamma762, shoot me some dimensions for the insulators you need. I'm off work tomorrow so I'll have time to turn them. |
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Posted: 2/3/2011 7:45:02 PM EDT
[#24]
Quoted:
Gamma762, shoot me some dimensions for the insulators you need. I'm off work tomorrow so I'll have time to turn them. I'll try to measure them tonight. Had SHTF to deal with the last few days
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Posted: 2/4/2011 1:40:15 AM EDT
[#25]
Quoted: Quoted: Gamma762, shoot me some dimensions for the insulators you need. I'm off work tomorrow so I'll have time to turn them. I'll try to measure them tonight. Had SHTF to deal with the last few days was that Snow HTF?  |
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Posted: 2/4/2011 8:24:01 AM EDT
[#26]
Quoted:
Quoted:
Quoted:
Gamma762, shoot me some dimensions for the insulators you need. I'm off work tomorrow so I'll have time to turn them. I'll try to measure them tonight. Had SHTF to deal with the last few days was that Snow HTF?
Ice storm, power outages, etc etc. |
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Posted: 2/4/2011 3:24:56 PM EDT
[#27]
Thanks my65pan. I have to go to the hardware store tomorrow and I'll pick up a strap then. Thank you though. I'm also going to pick up some boom material for a 440 yagi while I'm there. I'm on a roll with the antenna building (bench is a wreck) and want to build a UHF yagi befor I clean up.
Speaking of cold...my water pipe froze yesterday morning and this morning. I know thats common up north, but I'm 30 miles East of Phoenix! RING RING..calling Al Gore......
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Posted: 2/4/2011 4:18:32 PM EDT
[#28]
He is hiding in his mansion...lol
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