Yagi directional antennas?

[wv_mountaineer]

Could someone make this simple for a guy that seems to make things more difficult than they need to be?

I live in Pa. just about 15-20 miles from a few 800 mhz towers that I would like to listen to in Ohio. My thoughts are a Yagi directional antenna. But I don't really understand a couple things about buying one.

Like why do they range from 3 to 12 elements?

How would I know what Gain (db's) would work best for me without buying one first and trying it?

Here is the page I am looking at with a few choices:

800 MHz Yagi Antennas : The Antenna Farm :: , Your Two Way Radio Source!

 

[K9WG]

Put simply, a Yagi is like placing a candle in front of a mirror. Instead of the light going in all directions it is reflected and therefore intensified in a smaller area. The Yagi antenna does the same with the signal being reflected off the reflector element. The director element(s) define how narrow the beam will be. (This theory works for both transmit and receive). The more elements the narrower the beam width. Now if you are handy it would be easy to built a simple Yagi using copper wire. I build a simple 800MHz one and would be glad to share it with you. Just give me a PM

 

[n5ims]

K9WG is correct on the element counts and why more may be needed. One additional point is that with a narrow beam width you also get more gain so more elements also helps there as well.

More elements are necessary to provide two things, more gain and narrower beam. Why would you want a narrow beam you ask? There may be an interfering signal on the side of where you need to go. If you can get your beam narrow enough to eliminate it you may get a good signal from what you want and little or no signal from where you don't want.

On your gain question, you can make an easy correlation between gain and distance. The greater distance you need to cover the more gain you'll need to cover it. It's much more complex than than, but the complexities are easy to ignore here. If the desired site is close by, little gain is required. If it's real far away, lots of gain is required. Somewhere inbetween, you need some gain, but not lots of it. It's often better to have more gain than needed than not enough so error on the side of more.

Just remember that more gain also indicates a narrower beam so your aim will need to be more accurate. The aim isn't as hard as you may think though. Just bring a handheld and connect it to the antenna with a short jumper. Move it until you get maximum signal and you're there. Change the jumper to your normal feedline and done!

 

[wv_mountaineer]

Cable end?

What kind of hook-up to a coax do these antennas have? Wow, I don't think that really makes sense. Anyways, what kind of connector do I need on the end of my coax so I can use a Yagi antenna?

 

[W2NJS]

Antenna connections, at the antenna, are usually an SO239/PL259 or, preferably, type N connectors.

 

[mike_s104]

Could someone make this simple for a guy that seems to make things more difficult than they need to be?

I live in Pa. just about 15-20 miles from a few 800 mhz towers that I would like to listen to in Ohio. My thoughts are a Yagi directional antenna. But I don't really understand a couple things about buying one.

Like why do they range from 3 to 12 elements?

How would I know what Gain (db's) would work best for me without buying one first and trying it?

Here is the page I am looking at with a few choices:

800 MHz Yagi Antennas : The Antenna Farm :: , Your Two Way Radio Source!

I bought one of these a few months ago and it works great.

Amazon.com: Wilson Electronics 301111 Single Band (800 MHz) Yagi Antenna Model Y8009EL with N Female Connector: Cell Phones & Accessories

 

[n5ims]

What kind of hook-up to a coax do these antennas have? Wow, I don't think that really makes sense. Anyways, what kind of connector do I need on the end of my coax so I can use a Yagi antenna?

There is no real majic to this, the antenna maker puts on whatever type of connector they think will work (or sell) best, at times they make similar models that only differ in what connector they use. What you'll need to do is check what connector is used on the antenna you buy and get your coax made with the connector that mates with the one used on the antenna you get. As was stated earlier, most scanner or ham/commercial antennas are made with "N" connector or the UHF series (PL-259 plug matting with the SO-238 socket), but some use BNC, "F", SMA, or various other types.

Please be aware that you can (and it's often best to) order your cable with different connectors on each end so you can without adapters use an antenna with an "N" connector and a scanner that has BNC connectors. There's nothing forcing you to chain many adapters on both the antenna end and the scanner end because the coax came with other types of connectors. While you may still need to use adapters (some connectors simply aren't made for some types of coax), you can easily specify ones that minimize their use if you order carefully from a supplier that does more than pull some pre-made cables out of the overseas maker's box to send to you.

 

[WA1ATA]

I live in Pa. just about 15-20 miles from a few 800 mhz towers that I would like to listen to in Ohio. My thoughts are a Yagi directional antenna. But I don't really understand a couple things about buying one.

Like why do they range from 3 to 12 elements?

How would I know what Gain (db's) would work best for me without buying one first and trying it?

Are the towers that you want to receive in the same direction from you? Or at least close?

If you are trying to receive just one tower, then higher gain is better, but if you want to monitor towers that are not in the same direction, then the highest gain antenna might not be the best.

Think of the beam antennas as the equivalent to reflectors or lenses focusing light. The very narrow, concentrated beam from a spotlight is good if you want to light up just one thing. But if you want to light up several things that are at different angles, then a broader beam flood light is better.

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Can you receive the desired towers using a handheld receiver and the standard rubber ducky antenna? If you can go up on the roof or wherever you intend to mount your yagi and receive a hint of signal with your rubbery ducky antenna, then the 10 dB or so of gain from the yagi will probably get you a good useable signal.

If other the other hand, you don't hear anything at all when using a small antenna from the proposed yagi antenna location, there is a good chance that the tower is over the horizon and blocked by hills and even with a yagi antenna you won't receive the tower.

 

[WA1ATA]

If you want to build your own, it is pretty simple for 800MHz since the antennas small.

It might even be worth your while to slap together one and try it out while standing on your roof just to see if it is worth the trouble and expense of buying a more permanent, more rugged commercial one to mount permanently.

See http://forums.radioreference.com/antennas-coax-forum/45999-yagi-antennas-under-5-a.html
Post #16 has a link to a pdf file that has dimensions for an 8 element yagi for 850MHz. All you need is some coathangers and a broomstick.

I used this to build the 6 element 460MHz version yesterday. It took less than an hour and performance is pretty good (I'm spending much more time checking out the performance than it took to build it).

 

[KC4RAF]

Something you may want to add

is a rotation device. This will allow you to point the Yagi in different directions for other RF signals.

 

[Violation]

Straight antenna elements

For those of you making homebrew VHF-UHF antennas, try this little trick. Clamp one end of your wire in a bench vise, and the other end into the chuck of a 1/4 or 3/8 drill. A few quick spins will make a straight wire out of a crooked one. I generally start out with an element a couple inches longer than the planned finished legnth. This gives you room to trim the flattened ends from the clamping of the wire, and plenty of room for "trimming" for the final legnth. Keep in mind the twisting of the wire does diminish the diameter of the wire somewhat. I keep the twisting at a minium, only enough to do the job, and size my drill bit after this is done. I've used this on #12 galvanized as well as up to #6 copper wire. Experiment with a scrap piece first. It works and makes nice clean, straight elements. I read about this in Popular Science too many years ago...PW