Antenna project ??

[Skypilot007]

I found a fairly large quantity of copper wire in my attic this evening. Two spools, both solid copper wire, at least 150 feet of each. One spool the bare wire is .100 diameter and the other is .160 diameter. See attached images. I was thinking of building a couple of yagi antennae since I know I have everything here I need to build one now. I was re-reading some threads on these, this one in particular. http://www.radioreference.com/forums/showthread.php?t=45999&highlight=yagi

I was wondering with this wire if I should strip it bare or can I leave the insulation on it. My plan is to use a PVC boom, drill holes for the elements so the fit snug and secure with something I'll think of later. Strip the ends of the drivin elements and solider 50ohm coax to either side of the split drivin element. Other than that its basically the same plan as the thread I referenced above. This will be for receiving for now, maybe transmit in the future. Let me know about this insulation, should I strip it or leave it.

 

[Northe]

I'd leave the insulation on, if possible, to help prevent corrosion. There won't be any measureable difference in performance, _however_ the insulation will change the _velocity factor_ of the elements a bit, which means that if you want to cut the lengths precisely you'll have to take it into consideration.

Take a look here:

<<http://www.qsl.net/wa3yxk/jpole.html>>

Northe
N6KO
Green Valley, AZ

 

[Skypilot007]

That's what I was thinking. I'm going to leave it on and test it like that. I could not find the calculations used for the antenna in the thread I referenced because I wanted to up the resonate frequency to around 500MHz so I used the K7MEM web site and punched in all my info in there and I will go by that and see how it goes.

 

[jonny290]

antenna elements will be about 3-5% shorter with the insulation on, but otherwise you'll be fine. many vhf/uhf yagis are built out of house wiring.

 

[hoser147]

Check out the WIKI there is a wealth of information on there..........Good Scannin Hoser

 

[Skypilot007]

Had some time today to smack something together. Its not that pretty but it is performing quite well, better than expected and its mounted in my attic. I can't wait to add a few more elements and put it outside. Here are a few pics of it. I used some 5 minute epoxy to hold the drivin elements in place, the others are very snug thru the holes in the in the boom and do not require anything at this time to hold them in place. I also positioned the drivin elements directly in line with eachother since there was room inside the boom for this. I'm getting some good signal readings so far. More testing to come.

 

[Highlander_821]

That's great!

 

[N_Jay]

Looks like fun, but don't worry about the "Velocity Factor" changing due to the insulation.

We are dealing with antenna elements in air, not a transmission line. The insulation is insignificant!

 

[mancow]

With copper prices today you could probably sell those rolls and buy all kinds of antennas.

 

[Kfred]

matching transformer

Glad to hear the antenna works better than expected. Maybe someone who knows more about antenna's could answer questions I have about this antenna? Are the elements spaced to provide an adequate match for the coaxial cable? Would a matching transformer like the kind on a television antenna transfer more or less signal to the cable and to the radio? Keep building antenna's and letting us know how well they work. Read the article mentioned above and answered some of these questions. does any one have info on using toroid cores for matching antenna to cable?

 

[jonny290]

It looks to be an OWA style design, using the first director as a secondary driven element to increase bandwidth and provide a direct 50 ohm match.

non-folded dipole Yagis have _low_ feedpoint impedance if you direct feed, unless you specifically design for 50 ohms. Many are designed for 12.5 ohm or 28 ohm feed.

The problem is that the yagi is an inherently narrowband antenna and the mismatch and pattern is absolutely terrible off-frequency. So, using a balun to match impedance in one specific frequency range may help if you are focusing on that, but you may incur massive signal losses _off_ frequency. And besides, the antenna won't do that hot off-tune anyways.


Broadband baluns for RX antennas do exist but it's tricky at VHF/UHF due to losses and need to select the proper toroid material. Still, http://www.rason.org/Projects/balun/balun.htm shows how to construct 4:1 toroid baluns. A much more popular option is to use narrowband antennas and transmission line transformers, check this page out for more. http://www.qsl.net/w4sat/qtrwavtr.htm

 

[Kfred]

thank you

Thank you jonny290 for the information and links to those sites, you have answered my questions.

 

[CBFD]

nevermind... figured it out...