What dual band antenna has the best performance?

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drbeede

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I was wondering would a dual band yagi be better for distance over a dual band copper J-Pole? Any thoughts or help would be appreciated.
 

mmckenna

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I was wondering would a dual band yagi be better for distance over a dual band copper J-Pole? Any thoughts or help would be appreciated.
Yes, maybe.

Depends on what you are doing. A Yagi is a directional antenna and will easily outperform a J-pole antenna. Drawback is that a Yagi is only going to work best in one direction.
On the other hand, a J-pole is a 1/2 wave omnidirectional antenna and will work in all direction. It's going to have no gain, so not much benefit.

If you are trying to pick up a weak signal from one specific direction, the Yagi will outperform the J-Pole. If you want a base antenna that works well in all directions, the J-pole is going to work better, but isn't going to grab the far off weak signal stuff as well.
 

Ubbe

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If it's a 3 element yagi then it's probably equal to the j-pole. If the yagi have more elements than that then it will have better perfomance, but it will also be more directive and a j-pole are almost omni in coverage, a great plus if you try to receive from different directions.

/Ubbe
 

JoshuaHufford

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More information on what you are trying to do will be much more helpful to us to help you than posting a picture of an antenna.

What frequencies are you trying to receive? Do they all come from the same direction or from multiple directions?
 

drbeede

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More information on what you are trying to do will be much more helpful to us to help you than posting a picture of an antenna.

What frequencies are you trying to receive? Do they all come from the same direction or from multiple directions?
I like to listen to public safety, was thinking of hooking this up to my scanner of which I would be pointing it in one direction at a time to pull in frequencies in the public safety range and some HAM in the 2m and 70cm, also some GMRS which is local chatter. I plan on mounting this to a rotor so I can change the direction if needed.
 

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In my experience a yagi will receive better than an omni, but only in one direction and only for the frequencies that it is tuned for. If the antenna you are considering is tuned for the frequencies you want to monitor and you are willing to rotate it as needed than it will likely work better for you.
 

mmckenna

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here is a pic of the yagi I was looking at.
Using that with a rotor would allow you to search around and receive weak signals that a J-pole may not hear.
J-poles have their place, but I've never been impressed with them. 1/2 wave antenna, no ground plane, so 0dB gain. They are easy to make on your own if you want to give one a try, but I'd not spend money on buying one.

For wider bandwidth, you may want to consider a Log-Periodic antenna. It's directional, like a Yagi, but will cover a much wider bandwidth.

And don't be like the guy that mounted that antenna. Running the coaxial cable straight down along the driven element isn't the way to do it. Run the cable out the back of the antenna along the boom.
 

drbeede

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Using that with a rotor would allow you to search around and receive weak signals that a J-pole may not hear.
J-poles have their place, but I've never been impressed with them. 1/2 wave antenna, no ground plane, so 0dB gain. They are easy to make on your own if you want to give one a try, but I'd not spend money on buying one.

For wider bandwidth, you may want to consider a Log-Periodic antenna. It's directional, like a Yagi, but will cover a much wider bandwidth.

And don't be like the guy that mounted that antenna. Running the coaxial cable straight down along the driven element isn't the way to do it. Run the cable out the back of the antenna along the boom.
Thanks for that tip, also what is the difference between a Log-Periodic and Yagi? I googled them and they seem to look a lot alike in design is it just the bandwidth or frequency coverage that make them different? Sorry for all the questions I been experimenting with different types of antennas on my scanner but it gets expensive after a bit so I'm just trying to figure out what would be the best fit, and btw I live way out in the woods and mountains so there is a lot of stuff that can get in the way of incoming signals.
 

cmdrwill

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And don't be like the guy that mounted that antenna. Running the coaxial cable straight down along the driven element isn't the way to do it.
Exactly, the floping coax de tunes the yagi antenna. Not to mention really fouls up the directivity also.
 

mmckenna

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Thanks for that tip, also what is the difference between a Log-Periodic and Yagi? I googled them and they seem to look a lot alike in design is it just the bandwidth or frequency coverage that make them different? Sorry for all the questions I been experimenting with different types of antennas on my scanner but it gets expensive after a bit so I'm just trying to figure out what would be the best fit, and btw I live way out in the woods and mountains so there is a lot of stuff that can get in the way of incoming signals.
No, that's a good question. In simple terms:

A Yagi antenna is a directional antenna that is usually cut for one specific frequency, although they will often cover several megahertz on either side just fine. They are considered a single band antenna. The dual band one you linked to is just two separate Yagi antennas on the same boom.
A single band Yagi will have a driven element cut for one specific frequency. All the other elements are parasitic.

A log periodic antenna has all the elements driven (connected to the coaxial cable). There will be many different length elements, longer ones for lower frequencies, shorter ones for higher frequencies. The antenna is still directional, like a Yagi, but won't have as much gain.

For single band use, a Yagi will outperform a log periodic in most cases. For wide band use, like scanner listening, a log periodic antenna will cover more than one band.

For your application, a log periodic antenna fed with the best coaxial cable you can afford and a rotor will give you a lot of options. In fact, our county radio shop has one mounted on top of a tower at their shop for listening in on various systems, as well as narrowing down interference.
 

drbeede

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No, that's a good question. In simple terms:

A Yagi antenna is a directional antenna that is usually cut for one specific frequency, although they will often cover several megahertz on either side just fine. They are considered a single band antenna. The dual band one you linked to is just two separate Yagi antennas on the same boom.
A single band Yagi will have a driven element cut for one specific frequency. All the other elements are parasitic.

A log periodic antenna has all the elements driven (connected to the coaxial cable). There will be many different length elements, longer ones for lower frequencies, shorter ones for higher frequencies. The antenna is still directional, like a Yagi, but won't have as much gain.

For single band use, a Yagi will outperform a log periodic in most cases. For wide band use, like scanner listening, a log periodic antenna will cover more than one band.

For your application, a log periodic antenna fed with the best coaxial cable you can afford and a rotor will give you a lot of options. In fact, our county radio shop has one mounted on top of a tower at their shop for listening in on various systems, as well as narrowing down interference.
Thanks for the info, I learn something new every day, of course that is what the hobby of radio is suppose to be about anyways, learning and experimenting along the way,thanks again for all the input I really appreciate it.
 

mmckenna

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Thanks for the info, I learn something new every day, of course that is what the hobby of radio is suppose to be about anyways, learning and experimenting along the way,thanks again for all the input I really appreciate it.
No problem. Building your own antennas can be enjoyable, plus you can build it for the specific frequencies you want.
 

Ubbe

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And don't be like the guy that mounted that antenna. Running the coaxial cable straight down along the driven element isn't the way to do it. Run the cable out the back of the antenna along the boom.
Check if that antenna has a balun where the coax connects. In the picture it looks as if the impedance matching are done by short elements in parallell with the dipole element. It will not work as a balun and the coax will be an antenna element to the yagi independent of how you route the coax.

You probably need to get a 1:1 balun or a choke balun which is lots of ferrite rings on the coax where it attach to the antenna. At least make 5 turns of the coax next to the antenna to get some isolation between antenna and coax.

/Ubbe
 

drbeede

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Check if that antenna has a balun where the coax connects. In the picture it looks as if the impedance matching are done by short elements in parallell with the dipole element. It will not work as a balun and the coax will be an antenna element to the yagi independent of how you route the coax.

You probably need to get a 1:1 balun or a choke balun which is lots of ferrite rings on the coax where it attach to the antenna. At least make 5 turns of the coax next to the antenna to get some isolation between antenna and coax.

/Ubbe
if i go with ferrite rings how many and what size?
 

Ubbe

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There are different ferrite material for different frequency ranges. They are supposed to stop any radiosignals or interferencies riding on the outside of the coax. The maximum signal level will be at 1/4 wavelenghts so to be sure that the rings are effective you could use enough of them to cover a 1/4 wavelenght. You could also measure a 1/4 from the antenna and use only 4-5 ferrite rings at that position, the middle one on the 1/4 wavelenght.

The hole in the middle of the ring should fit snuggle enough on the coax to have the best effect but a little loose fit are probably what will be available. It could look something like this:


/Ubbe
 

drbeede

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There are different ferrite material for different frequency ranges. They are supposed to stop any radiosignals or interferencies riding on the outside of the coax. The maximum signal level will be at 1/4 wavelenghts so to be sure that the rings are effective you could use enough of them to cover a 1/4 wavelenght. You could also measure a 1/4 from the antenna and use only 4-5 ferrite rings at that position, the middle one on the 1/4 wavelenght.

The hole in the middle of the ring should fit snuggle enough on the coax to have the best effect but a little loose fit are probably what will be available. It could look something like this:


/Ubbe
yeah I seen some similar to that on ebay, I just thought I needed to clarify on those before I actually buy any. Thanks for the help.
 
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