What am I looking for...

gcopter1

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I'd like to combine the signal from three different antennas, all from the same band, into a single output.

What should I be searching for?

Would there be a problem taking that output and feeding it to a duplexer?
 

ka3aaa

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a single antenna for the frequencies you want should do what you want with nothing else required.
 

gcopter1

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Not for Yagi's...

I monitor P25 Simulcast systems, all on the 800 Mhz band.

3 Different sites. 3 different locations, thus, my want to find something where I can combine those antennas into one.

One of those locations is more distant than the others so, by necessity, I have to have one Yagi pointed in that direction.

If, all of the sites I wanted to monitor were in the same direction, I could do the job with just one antenna.

Before the Yagi I now use, I was getting high decode errors. The Yagi, helped that, being able to zero in to just one site, helps a lot with simulcast and decoding errors.
 

majoco

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Are you thinking of three yagis pointing in different directions picking up different frequencies? Providing that one yagi picks up it's designated frequency well and very little signal on that frequency is picked up by the other two yagis then you may get away with it but there will be some degree of signal cancellation. The perfect yagi hasn't been invented yet - it doesn't pick up signal from only one direction, there are sidelobes all around too but hopefully the main forward lobe is much bigger than all the rest - you might have to erect a screen behind each yagi so that a signal from behind may not be received - but that may also affect the polar diagram too. IMHO I would think about it from another direction - three antennas, three receivers and combine the audio from each. That's been done for years, even three different frequencies with the same audio - called diversity reception.
 

prcguy

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You can combine two or more identical Yagi antennas all pointed in the same direction and when properly spaced and phased you will get more gain. If the same Yagi antennas are pointed different directions you will get at least 3dB loss through a 2-way splitter and about 5dB loss for a 3-way splitter. Plus whatever nulling of unwanted stations you might get with one Yagi, improving decoding, more Yagi's pointed in different directions will probably pick up unwanted signals which might contribute to decode errors.


Not for Yagi's...

I monitor P25 Simulcast systems, all on the 800 Mhz band.

3 Different sites. 3 different locations, thus, my want to find something where I can combine those antennas into one.

One of those locations is more distant than the others so, by necessity, I have to have one Yagi pointed in that direction.

If, all of the sites I wanted to monitor were in the same direction, I could do the job with just one antenna.

Before the Yagi I now use, I was getting high decode errors. The Yagi, helped that, being able to zero in to just one site, helps a lot with simulcast and decoding errors.
 

ScubaJungle

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I wanted to do the same thing with dipoles, and I tried, but I found the loss was not worth the convenience. If you have string signals, you might get away with it.
 

gcopter1

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You can combine two or more identical Yagi antennas all pointed in the same direction and when properly spaced and phased you will get more gain. If the same Yagi antennas are pointed different directions you will get at least 3dB loss through a 2-way splitter and about 5dB loss for a 3-way splitter. Plus whatever nulling of unwanted stations you might get with one Yagi, improving decoding, more Yagi's pointed in different directions will probably pick up unwanted signals which might contribute to decode errors.
So that's the trick, still, that's three antennas for a splitter I cannot find that handles 800Mhz with an N connector or at the very least, an SO239 or BNC.

Most everything I've found so far, and my Google Fu is weak, is for different bands, not for a single band.
 

prcguy

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Ubbe

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Now you use one antenna at the time, or have each antenna to its own scanner. If you combine antennas pointing in different directions, wouldn't that receive sites in the same system from different directions, defeating the purpose of having directional antennas to improve reception of simulcast systems by only receiving one of the sites?

You'll have to wait for a scanner with three antenna jacks that can be configured to switch between them depending of the system scanned.

/Ubbe
 

gcopter1

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Now you use one antenna at the time, or have each antenna to its own scanner. If you combine antennas pointing in different directions, wouldn't that receive sites in the same system from different directions, defeating the purpose of having directional antennas to improve reception of simulcast systems by only receiving one of the sites?

You'll have to wait for a scanner with three antenna jacks that can be configured to switch between them depending of the system scanned.

/Ubbe
No, I'm looking to monitor 3 different systems on the same scanner.
 

prcguy

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I think the extra Yagi's pointing at different directions may pick up interfering signals that caused you to go with a Yagi in the first place. Yagi antennas are not like Laser beams, even a 10 element model may only be 3dB down at +/- 20 degrees from center and they can pick up ok off the sides and back. If a single Yagi is working for you then that single Yagi on a rotor might be the only way to hear what you want without simulcast problems.

The only time I've seen more that one Yagi in a system pointing different directions is 180 degrees apart back to back to cover a very narrow corridor. Or all pointed the same direction and phased together for more gain and a tighter pattern. Not multiple directions and connected to the same feedline.


No, I'm looking to monitor 3 different systems on the same scanner.
 

bobruzzo

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You can combine two or more identical Yagi antennas all pointed in the same direction and when properly spaced and phased you will get more gain. If the same Yagi antennas are pointed different directions you will get at least 3dB loss through a 2-way splitter and about 5dB loss for a 3-way splitter. Plus whatever nulling of unwanted stations you might get with one Yagi, improving decoding, more Yagi's pointed in different directions will probably pick up unwanted signals which might contribute to decode errors.
This sounds interesting to me. I have a 6 element yagi (see picture) which works well. But I could use a bit more gain and stacking a pair of these might help. I like to monitor the Mass State PD on 800mhz Motorola trunked system (not P25). But I have a stupid obstructing hill right in the way. Currently (on a good day) I can hear them with some static. I can hear the voice frequencies a little better. Anyway how can I stack a set of these yagis? How do you figure out the distance between the 2 on the mast? This yagi has a female "N" connector on pigtail. So I would need a jumper cable with male "N" connectors on each end. These yagi's are VERY well made and at a reasonable price ($69). What happens when you stack 2 vertically polarized yagis side by side as opposed to top and bottom? I would think side by side would give a wider beamwidth. Top and bottom would give a narrow beamwidth.
 

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Ubbe

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I would think side by side would give a wider beamwidth. Top and bottom would give a narrow beamwidth.
The beamwidth gets more narrow in the same plane that you stack. Side by side stacked horizontally it will get a more narrow beam sideways as the antennas gets out of phase with each other and starts to cancel out the signal when it doesn't come diectly from where the antennas point. Thats why you see vertical dipoles stacked on top of each other to still get an omni coverage but the beam are compressed in height and only points parallell to the ground and not up in the sky. The more distance between antennas the more directive it will be. Having antennas too close to each other will, as with any metal, throw of it's tuning and impedance.

When you stack you loose a little in the stacking cabling, you have to transform two 50 ohm antennas to a single 50 ohm coax and it might be a 2dB or 2,5dB gain improvement depending of the quality of the installation. The lenght of the coaxes to stacked antennas needs to have the exact same lenght. Usually when you stack and the beam loob are focused more at the horizon, and less from the electronics in the building below it, will make the reception better due to less interference. So it is a double gain with both increased signal level and less interference.

/Ubbe
 
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