Help me with my homebrew 800MHz Yagi

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ch40n1k

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Hi folks,
I've used several of the posts on this forum to construct an 800MHz yagi. I'm hoping some of you can help me out by letting me know if everything looks ok. The antenna seems to work fine, I just want to make sure I've constructed it correctly.

1.) I used a 36" wooden boom.
2.) I used 1/8" brass brazing rods for the elements.
3.) The driven element is cut in half, and each half is separated from the other on opposite sides of the boom.
4.) I used hot glue to secure the elements.
5.) Instead of connecting the coax directly to the driven element, I used a PL-259 post from Radio Shack. I soldered 12 gauge copper wire to the center conductor of the connector. I then connected a 12 gauge copper wire to the post itself with a brass bolt and nut. I then connected the center conductor wire to one half of the driven element, and the post connected wire to the other half of the driven element.

Will this method of connecting the coax to the antenna work ok? I've used this method with other antennas I've built in the past, and it seemed to work just fine.

Any help would be greatly appreciated. Thanks!
 

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prcguy

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So Cal - Richardson, TX - Tewksbury, MA
Nice looking antenna but the feed is probably not so great. If the driven element is one solid rod, you might be better off feeding it with a 300ohm TV matching transformer. The center of the 1/2 wave element would be considered 0 ohms and you have probably tapped it in the several hundred ohm area. It would also need to be balanced at that point and the TV matching transformer would accomplish that. It might be better to split the driven element in the center and feed it as a classic dipole with the coax directly attached (no connector) using the shortest leads possible.
prcguy
Hi folks,
I've used several of the posts on this forum to construct an 800MHz yagi. I'm hoping some of you can help me out by letting me know if everything looks ok. The antenna seems to work fine, I just want to make sure I've constructed it correctly.

1.) I used a 36" wooden boom.
2.) I used 1/8" brass brazing rods for the elements.
3.) The driven element is cut in half, and each half is separated from the other on opposite sides of the boom.
4.) I used hot glue to secure the elements.
5.) Instead of connecting the coax directly to the driven element, I used a PL-259 post from Radio Shack. I soldered 12 gauge copper wire to the center conductor of the connector. I then connected a 12 gauge copper wire to the post itself with a brass bolt and nut. I then connected the center conductor wire to one half of the driven element, and the post connected wire to the other half of the driven element.

Will this method of connecting the coax to the antenna work ok? I've used this method with other antennas I've built in the past, and it seemed to work just fine.

Any help would be greatly appreciated. Thanks!
 

prcguy

Member
Joined
Jun 30, 2006
Messages
9,751
Location
So Cal - Richardson, TX - Tewksbury, MA
Aaa, I just read you split the driven element, the leads from the connector are quite long and you would be better off loosing the connector and soldering the coax right to the elements.
prcguy
Nice looking antenna but the feed is probably not so great. If the driven element is one solid rod, you might be better off feeding it with a 300ohm TV matching transformer. The center of the 1/2 wave element would be considered 0 ohms and you have probably tapped it in the several hundred ohm area. It would also need to be balanced at that point and the TV matching transformer would accomplish that. It might be better to split the driven element in the center and feed it as a classic dipole with the coax directly attached (no connector) using the shortest leads possible.
prcguy
 

ch40n1k

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Joined
Sep 29, 2006
Messages
192
Location
Lakewood, Colorado
So, when connecting the coax directly to the driven element, what is the best way to attach the shielding? Do you just twist it up and solder it ?
 

prcguy

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Location
So Cal - Richardson, TX - Tewksbury, MA
For small coax there is a method to keep the shield intact and looking professional. Strip off at least several inches of outer insulation and where the shield meets the outer insulation use a sharp object to wiggle a hole in the braid large enough for the center conductor with insulation to pass through. Bend the coax in half right at the hole you made and hook the center conductor and pull it through the hole in the braid. This will leave you with a pig tail of intact braid running parallel with the exposed center conductor with insulation.
On Teflon coax (RG-142) I like to strip the outrer insulation and tin the braid. You can then score the tinned braid about 1/4" away from the outer insulation junction with a knife and bend the score several times until the majority of the tinned braid comes off in a tube. You can then solder a separate ground wire to the short 1/4" tinned braid and cover the junction with heat shrink. This sometimes works with non Teflon coax with the solid clear dialectic but foam type dialectic will usually melt. Good luck.
prcguy

So, when connecting the coax directly to the driven element, what is the best way to attach the shielding? Do you just twist it up and solder it ?
 
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