Using a yagi ?

[OldskoolPirate]

Thinking about using a 3 element yagi to push the signal from a high area into a lower area because my area is almost fully flat for miles. but does the signal get wider the further into the distance it gets or does it stay the same beam size like a microwave link for example ? (But wider)

The area the antenna will be in I have little to no interest in covering, I’m solely using it for the height. And my broadcast location I want to cover would be right in the distance. Would this actually work or be no good with all the power going in a narrow’ish straight line ?

[Albert H]

The beam width of a 3-element Yagi is about 100°, and you'll get about 4½dB more than a dipole in the beam direction. This assumes that it's properly built, and matched, of course. You can tilt it up or down a bit to better aim at your target, but try not to waste energy into the ground! You'll have little signal going backwards off the aerial (the "front to back ratio" should be around 20dB).

The best way to align its position is with a mate in the target area equipped with a portable receiver with a signal strength meter. You get him to report the received signal strength by phone, then alter the direction and tilt of the aerial for the best signal.

Getting Yagis to match can be a major pain, and there's little point in going to B&Q and buying a receive one, since it just won't match (and they're usually 75Ω anyway). You're going to have to either buy or build one yourself:

Yagi-Antenna-formula.jpg

[OldskoolPirate]

So the 100 degree would be wider in the distance than it would be closer to the antenna then?

And yes im building it with that formula.

[Albert H]

Yes it would - the further away, the wider the beam.

You're probably going to have to use a Gamma Match to get your 50Ω unbalanced feedline to match the antenna.

[tokingmenace]

Or another option would be a moxon.

Great front to back and direct feed point.

They have a shorter boom, so take up less space, which may help when setting up.

[Albert H]

That's not a bad idea, but unfortunately the Moxon gain is much less than the 3-element Yagi, and the radiation pattern is virtually hemispherical, just like a 2-element Yagi. It's easy to match a Moxon if you use a Pawsey Stub, because it has a balanced feedpoint, and you have to get the dimensions exactly right, but it's really just a broadened folded dipole.

The original poster wants to "throw" his signal at a distant town, with a tilted boom to maximise the signal in the target area. Depending on the distance to the target area, the size of the target area, and the difference in heights, it might even be worth going for a 4-element Yagi. Four elements is going to further narrow the beam width (to about 75°) and give another 2dB of antenna gain if built correctly. The dimensions are more critical, and getting it to match accurately is harder work, but it might be a worthwhile trade-off....

As ever, electronic design is a set of compromises!

[OldskoolPirate]

I’m using a pawsey stub on the feed line for it. Iv read it’s more critical to have a balun on a yagi than it is on just a standard dipole

[Albert H]

That's the way to go! The Pawsey Stub is a great way of driving a balanced antenna.