Weekend Yagi Antenna Project (pics)

[Airdorn]

Hey all.

Recently, the US Dept. of Defense brought a P25 system online near me, but I had had a hard time receiving it with the Scantenna. The control channel is 380.075.

So... I built a Yagi antenna! I dug around on the net and found some rough plans and theories. I drew it out and then went to Lowe's to get the equipment.

What I ended up buying is a 3 foot section of "channel configuration" aluminum... its basically a squared 'C' shape. I got a handful of nylon spacers, some grommets, and some 3/16 steel cylindrical rod.

I used a tiny welding rod soldered to one of the rods for the driven element. I attached it all together with an 8 foot section of RG-58, and used a tiny piece of it for the little RF choke thingy up near the driven element connection. I figured that was simpler than messing around with baluns and what not.

Anyway, the following pictures show the end result.

The first picture is just what my roof looked like BEFORE I made and installed the new home brew yagi. The yagi in the first picture is tuned to the 823 - 868 Mhz range and is attached to a nice little Channel Master rotator. The other little antenna on the first picture is a simple mag mount 800Mhz antenna I use for general purposes.

The Second and third pictures are of the home brew yagi I made. I sealed it all up with Silicone rubber. It turned out very well, IMHO.

The last picture is what my roof looks like now, after installing the new home brew Yagi to my Channel Master rotator.

Thanks all for a great site and all the help figuring out this radio stuff!

[tonsoffun]

Good job, well how is it performing for you. Are you receiving your system any better?
Take care

[kd5dga]

Yes, do point out the performance inprovement. The end results look excellent, and the choice of materials are good for a budget.

[Airdorn]

Woops, completely forgot about that part

Yes.

Before, best I could receive that system with the Scantenna was 1 bar. Occasionally, 2 bars. I have a BCD996T. Unitrunker wouldn't even lock onto it.

Now, I get a full 5 bars. Strong and consistent. Unitrunker reports between 70% and 90%.

I rotated it toward another system that is a UHF Motorola trunked system and I pick it up much better too!

All-in-all, I had a lot of fun figuring it out and putting it together. Now I just hope the US Government gets on the ball and gets some activity on there.

[Airdorn]

By the way, could someone explain in simple terms (for my simple brain) how that little loop thingy works, up there at the connection point to the driven element?

It's a short piece of coax that is bent-over into a U-shape. The shields of the coax are all soldered together, and the cores of 2 of the ends solder to one side of the driven element "loop", while the core of the other coax piece solders to ther other end of the driven element.

What function does that U-shaped piece serve?

Thanks!

[Skypilot007]

Nice antenna! Gota love the home brewed antenna. Especially when they work so well. I built a yagi for 506MHz and hung it in my attic and it works much better than expected. I'm building an 11 element 866 MHz yagi now. Its almost done.

[Airdorn]

Originally Posted by Skypilot007

Nice antenna! Gota love the home brewed antenna. Especially when they work so well. I built a yagi for 506MHz and hung it in my attic and it works much better than expected. I'm building an 11 element 866 MHz yagi now. Its almost done.

Thanks for the kind words. Be sure to take pics of your new yagi! Btw, how did you decide to hook-up the driven element?

Thanks

[nd5y]

Originally Posted by Airdorn

By the way, could someone explain in simple terms (for my simple brain) how that little loop thingy works, up there at the connection point to the driven element?

It's a short piece of coax that is bent-over into a U-shape. The shields of the coax are all soldered together, and the cores of 2 of the ends solder to one side of the driven element "loop", while the core of the other coax piece solders to ther other end of the driven element.

What function does that U-shaped piece serve?

Thanks!

It is a 4:1 balun. The coax is an electrical 1/2 wavelength at the design frequency. It does the same thing as a TV type matching transformer, but only over a narrow frequency range.

[N8DRC]

Nice antenna and pics, gotta love the home brew stuff it's always fun to built your own..

[Mikey54]

Excellent job. Thanks for sharing the pictures. And good explanation of the coaxial balun, ND5Y. Coax cable is not a balanced feed, so the little balun that you made helps your feedpoint.

Mike
VE3MKY

[cb360t]

Whoops. Didn't mean to hijack this thread.