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Can anyone tell me if I can run a yagi or stacked yagis on a duplexed UHF repeater as opposed to an omni? Thanks, Bill

Bill Rogers wrote:Can anyone tell me if I can run a yagi or stacked yagis on a duplexed UHF repeater as opposed to an omni? Thanks, Bill

Sure. Just be prepared to expect directional coverage.

You will want to make sure that the yagi's are vertically polarized. Some yagi's have been made for horizonal mounting. Polarization loss can be a killer.

FYI: commercial 2-way radio communication uses vertical polarization in over 99% of cases.

Don't expect for a 4 watt portable on the back side of the beam to hit the repeater very well, either.

If anything, use a omni for input and a Yagi for the transmit IF NEEDED- meaning if the repeater is on one end of the coverage zone area. The more elements you have, the more directional and narrower the signal will be.

General rule: don't do it unless it is properly engineered by a pro...and for a reason.

If you wanted the best of both worlds, you could connect a vertical AND a yagi to the same feedline. This could help to cover an area that has coverage problems. Just keep the antennas vertically seperated, so that the yagi doesn't reduce the omni pattern of the vertical.

Keep in mind, if this is a commercial system, you must keep within the ERP limit of your license. Yagi's can have a lot of gain, usually much more then a vertical.

Stacking Yagis is for noise and a little more gain.

We used one yagi for 12 db gain stacked with the correct harness
only gained to 15 db.Noise was better but only 110 degree
of direction.Great for point to point systems.
The railroad likes to do this.
The phone company on the mts and imts systems
used mostly hort. yagi's for there base radio setups
on 152/157 mhz.
Very narrow bandwidth on this setup.

You people are great!....... They will be vertical for the purpose of covering down 2 main highways. I will be using a phasing harness tuned for the frequency. What about 4 yagis (3 phasing harnesses)? That would be to cover 4 highways in 4 directions.
Thanks, Bill

Bill Rogers wrote:You people are great!....... They will be vertical for the purpose of covering down 2 main highways. I will be using a phasing harness tuned for the frequency. What about 4 yagis (3 phasing harnesses)? That would be to cover 4 highways in 4 directions.
Thanks, Bill

Sounds okay... but I still think you should put an omni vertical up there too. What if they go "off road?" Better to be safe then sorry.

I believe 2-way licensing is based on ERP, and assumes that it is omni. I don't know if there are any FCC technical reviews your license would have to go through.

I suppose the ultimate would be to find some high-gain antennas that have a wide beam-width, and mount a half-dozen of those so that they cover all 360 degrees.....



Mike

A yagi may not necessarely be needed...

If you want mild directivity, then mounting 4 phased folded dipoles on the *same* side of the mast will give you more of an egg shaped radiation pattern, with the long end where the folded dipoles point. (a folded dipole in "free space" is omnidirectional, but as nothing is truly in "free space", the folded dipole is affected by the tower or mast, which creates the directivity, the closer the dipoles are to the mast, the more directivity... within logical limits of course).

As for yagis, they can be designed for many factors, some for more directivity, some for wider bandwith, and some for more or less "front to back" ratio. A short 2-3 elements yagi may be a good idea when mounted on the side of a mountain where there is no point in radiating any signal behind the antenna...

You might want to check out HAM sites for programs like QuickYagi4 or Yagimax that allow you to experiment with designs and see their radiation patterns.

Pat

This gets more complicated. I know that I could use a folded dipole for an elliptical pattern. I am trying to not only max out on the highways but have some 'off the side' yagi rejection, in a specific direction, to cut down on interference to another repeater. Getting crazy?

You didn't mention if this was for a ham repeater or a commercial repeater. Could you please enlighten us?

462 MHz.......

You could get a 4 bay folded dipole antenna.

Point 3 of the dipoles in the direction you want it to work the best in. Take the Fourth dipole and offset it slightly in the direction you'd want some coverage in.

It's not as good as a Yagi, but it might give you that extra bit of coverage you need.

You might also look at getting a corner reflecter. Even a small one will be very directional, so you could use an omni on the tower, with the corner reflecter in the direction you need the extra coverage.


Mike