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Author Topic: An Easy Yagi for 2m.  (Read 4645 times)

gil

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An Easy Yagi for 2m.
« on: October 01, 2013, 01:05:03 AM »
First, let's give credit where it is due: A "Yagi" is actually a "Yagi-Uda." Uda was the main guy, as I understand, and Yagi did the promotion.. So maybe it should be called a "Uda."  :o
Second, I got the design here: http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12570

My issue was the length of most driven elements. As you may know, a Yagi antenna has one reflector, the longest element, in the back, followed by the driven element, fed from the radio, and a number of director elements. There are a few ways to feed a Yagi, but none that simple, except a folded dipole or a quad. Problem is, my 1/4" aluminum rods were 60 inches long... After some research I found the design linked above which uses a half folded dipole; kind of like feeding your Yagi with a J-Pole.. Or not quite, but you get the picture.

A quick trip to Home Depot yielded a 3/4x1-1/2" by 8ft. long piece of select pine for the boom. Maybe not quite rigid enough, but it was cheap. I bought two just in case. All these materials were easily found in convenient sizes, hence the title of this post.

I can't stretch enough how much easier life is when you use a dual system tape measure, standard and metric! I don't know why we haven't switched to Metric here, the Australians did it a while ago, it would be so much simpler  ::)

I cut all the elements and made sure to mark them at the center point as well. My Dremel died two cuts from completion, so I finished with a hacksaw. The boom was drilled using a drill press and a 1/4" drill bit. It all went very quickly.

I haven't epoxied the elements to the boom yet, so they are 3/4in off-center on the photo. The driven element hasn't been built yet. I plan on using aluminum solder to attach the coax wire to the driven element. I am waiting for my antenna analyser to arrive (should be shipped around the 15th) so that I can do a good job at impedance matching on that element.

Now Elecraft, please finish testing your KX3 2m module, I'll be ready! I hope the bandwidth will be wide enough to test it vertically with my UV-5R. If it spends any time outside I would have to varnish it to prevent the boom from warping. Not that I want to mount it permanently with a rotor anyway.. Not anytime soon. This is just a quick experiment in building a Yagi. Altough it could come handy if repeaters around went dead after running a while on generators...

Stay tuned for more...

Gil.

« Last Edit: October 01, 2013, 01:27:57 AM by gil »

mdmc

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Re: An Easy Yagi for 2m.
« Reply #1 on: October 01, 2013, 01:30:09 PM »
Gil, I would really like to know how the aluminum solder works out. I am familiar with heli-arc but not aluminum solder. I have heard that with some alloys there can be galvanic action problems. Maybe rumor though.

If you had not planned on it, I would strongly consider a good spar varnish on the wood. I assume spar varnish has no problem electrical properties, but don't know that for sure either.

Anxious to know how this all works out


IZ2UUF

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Re: An Easy Yagi for 2m.
« Reply #2 on: October 01, 2013, 07:41:47 PM »
I plan on using aluminum solder to attach the coax wire to the driven element.

Instead of soldering aluminum, consider also rivets. Simple and mechanically very strong.


gil

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Re: An Easy Yagi for 2m.
« Reply #3 on: October 01, 2013, 09:58:46 PM »
Not sure how I will make the electrical connection.. The aluminum solder is Uniweld UNI-4300, found on Ebay...

Gil.

gil

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Re: An Easy Yagi for 2m.
« Reply #4 on: October 01, 2013, 11:44:41 PM »
It only took a few minutes tonight to bend the driven element and epoxy all of them in place. I won't touch it until tomorrow night.. A pair of alligator clips will suffice for some preliminary testing. I bent the aluminum rod on a steel pipe. it is maybe three inches too long, but I will only trim it after I receive my antenna analyser, though I suspect it won't make any difference. Until then, the antenna should do well to search for VHF signals using my TV dongle. That was a smart suggestion from Ray.

The antenna is a bit unwieldy to move around now. Definitely the maximum size you'd want to handle inside a house. Spar varnish will definitely be on my shopping list for this one.

Left to do is the connection of the coax, securing the driven element a bit better, probably with a little block of wood, and adjusting the element length and impedance. I also will have to think of some way to attach a mast to it, allowing it to be used vertically or horizontally..

Gil.
« Last Edit: October 01, 2013, 11:48:04 PM by gil »

KK0G

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Re: An Easy Yagi for 2m.
« Reply #5 on: October 02, 2013, 12:14:05 AM »
Cool project. I'd tend to agree with Davide, rivets would be my preferred method of attaching a feed point. I didn't look up the Uniweld product you mentioned but I'm guessing it's something similar to the gimmicky stuff I've seen demonstrated by a guy wearing a boom mic at gun shows, the state fair, etc. as he "welds" (actually he's either soldering or brazing depending on the temperature) everything from beer cans, to transmission cases, to tree bark, to the kitchen sink and everything in between. If there was an easy way to solder or braze aluminum the industry would be clamoring all over it............... I don't see that happening.
"Those who would give up essential liberty to purchase temporary safety, deserve neither liberty nor safety" - Benjamin Franklin

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gil

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Re: An Easy Yagi for 2m.
« Reply #6 on: October 02, 2013, 12:17:07 AM »
Quote
I'm guessing it's something similar to the gimmicky stuff I've seen demonstrated by a guy wearing a boom mic at gun shows, the state fair, etc.

Probably.. More like hot glue.. Certainly NOT welding  ::)

Gil.

IZ2UUF

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Re: An Easy Yagi for 2m.
« Reply #7 on: October 02, 2013, 03:14:25 AM »
Probably.. More like hot glue.. Certainly NOT welding  ::)

Rivets are made of aluminum and offer a optimal electric connection, thanks also to the great pressure they apply once in place. I have used them on several antennae.
Make sure that the "hot glue" you are using is a good conductor: although it welds aluminum, it must be itself full of other chemical stuff.

Davide

gil

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Re: An Easy Yagi for 2m.
« Reply #8 on: October 02, 2013, 08:55:52 PM »
Hello,

I tried the antenna vertically tonight on a stool in my bedroom.. The local repeater is not very far, so not surprisingly (gain is supposedly 11.62 dBi) they heard me full blast. SWR is 1.6:1 on 146MHz and seems to go up from there.. More testing is required and I am waiting for my antenna analyser.. I am happy however that I can use it a little above mid-band if needed..

Gil.