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Whats The Difference Between A Yagi Antenna And A Omnidirectional Antenna

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Good evening I wanted to ask whats the difference between a Yagi antenna and a Omnidirectional antenna. I was thinking about buying a base antenna in October. I wanted to get a UHF base antenna. Could someone explain the difference to me please.


Thank you
 

wtp

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the difference

a yagi is directional, it will pickup better in one direction at the sacrifice of the others.
an omni-directional picks up in all directions. it might sound good unless the target you want is out of range,
think of the pattern of reception as a balloon the omni is just the circle as seen from the top. a yagi is like when you push in the sides, the lobes streach out in two directions, the better the antenna the father out they go. like the old tv antenas would say 200 mile reception , but if you had omni it might get 25.

so if your target is in only one direction and far away go with yagi for that band.
if you are just interested in everything all around get an omni
not to push RS but they have a good "christmas tree" dis-cone that is omni for around $80.
hope this helps
 

zz0468

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An omnidirectional antenna functions equally well in all directions. A yagi antenna's performance favors one direction over all others.
 
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a yagi is directional, it will pickup better in one direction at the sacrifice of the others.
an omni-directional picks up in all directions. it might sound good unless the target you want is out of range,
think of the pattern of reception as a balloon the omni is just the circle as seen from the top. a yagi is like when you push in the sides, the lobes streach out in two directions, the better the antenna the father out they go. like the old tv antenas would say 200 mile reception , but if you had omni it might get 25.

so if your target is in only one direction and far away go with yagi for that band.
if you are just interested in everything all around get an omni
not to push RS but they have a good "christmas tree" dis-cone that is omni for around $80.
hope this helps
Thank you for the info. I was trying to get in one direction. I was trying to get Des Moines PD.
 

n5ims

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So do you think the Omnidirectional Antenna be better?
Please correct me if I'm wrong. You're trying to pick up Des Moines Iowa from Peoria Illinois (250 miles give or take as the crow flies)? At that distance, the difference in tower locations won't make any difference with a directional antenna. If you're quite close (especially if you're located where they're in several different directions) an Omni may be better (unless you're trying to eliminate one or more towers by using the yagi).

If you're trying to get signals from 250 miles away, you'll need a very tall tower (think TV broadcast tower height instead of TV receiver antenna height), a very directional antenna, loads of gain, and lots of luck. Chances are very good that even then it won't be possible. The horizon will block the signal (hence the very tall tower). Also it's quite likely that someone between you and your distant station will use the same frequencies you're trying to pick up and will block the desired signal.
 
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Please correct me if I'm wrong. You're trying to pick up Des Moines Iowa from Peoria Illinois (250 miles give or take as the crow flies)? At that distance, the difference in tower locations won't make any difference with a directional antenna. If you're quite close (especially if you're located where they're in several different directions) an Omni may be better (unless you're trying to eliminate one or more towers by using the yagi).

If you're trying to get signals from 250 miles away, you'll need a very tall tower (think TV broadcast tower height instead of TV receiver antenna height), a very directional antenna, loads of gain, and lots of luck. Chances are very good that even then it won't be possible. The horizon will block the signal (hence the very tall tower). Also it's quite likely that someone between you and your distant station will use the same frequencies you're trying to pick up and will block the desired signal.
Do you think if I got the omni it would pick it up on skip?
 

jhal94

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Do you think if I got the omni it would pick it up on skip?
Very little skip is on UHF frequencies though you may be able to get the VHF link on a very excellent and lucky day.

You're going to need more than a very tall tower. I was once flying in a cessna at 6500ft listening to UHF cutting in and out on a XTS2500 from 150 miles away in flat florida. Now this was a rubber duck and not a full wave antenna but the station was just barely receivable from that altitude. You probably wont get squat even on a tower 250 miles away on UHF.

You could buy an AWACS if you have the money though.

Distance to horizon is measured as: D=3.57√h (h being the height in meters) (d being the distance in kilometers)

so at 250 miles (402km) use the calculation 402/3.57=√h or (402/3.57)²=h

So the altitude required is: 12679m or 41597ft

Now this isn't absolute as this does not account for atmospheric refraction. It also does not factor in the height of the transmitter. The actual distance to horizon is going to be farther than this, so the height required is going to be less than what the math tells you, but it's still going to be more than likely out of reach even on a good day. This formula is also intended for light waves and not Radio but the principles are the same.
 
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zz0468

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Do you think if I got the omni it would pick it up on skip?
No. An omni is for receiving in all directions. If you're trying to get something in one direction, then you use a directional antenna. A yagi is what you'd want for that, not an omni.

Trying to receive public safety transmissions from over 200 miles away is usually an exercise if futility, unless there is some sort of mitigating circumstance that would make it possible.

Out here in California, it's possible to hear such things from 200 miles... by sitting atop an 8000 foot mountain. This is what I mean by a mitigating circumstance. If you pursue this, there is an excellent chance you would be wasting your time and your money.
 
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timkilbride

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Des Moines PD runs several voted receive sites with 1 TX location. Before your even out of the county, flutter starts to occur. It seems they run just enough power to cover the city or are utilizing some down tilt.

Tim
 

wtp

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skip vs computer

with all they have said i would go with computer reception as skip is not too common.
it would be great to just turn on a radio and get to hear them, but that would not be the case..
 
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with all they have said i would go with computer reception as skip is not too common.
it would be great to just turn on a radio and get to hear them, but that would not be the case..
Maybe I will just stay with the computer. I still might buy one of the antennas for the fun of it and see what else I get with it compared to my mobile antenna.
 

ab5r

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Hi, it might be helpful to read: Line-of-sight propagation - Wikipedia, the free encyclopedia

It might be helpful in learning about antennas and their performances. I personally wished that someone MUCH more intelligent that me (not hard at all) would write a "basic antenna: article for RR that could be a reference to many people that do not a good understanding of antennas. We very frequently see it asked, "Which is best" type questions, and that it not easily answered! Which car is best, who's girl friend is prettiest, and other open ended questions.

Your situation may differ in a multitude of reasons due to geography, frequencies interested in, weather, antenna height and many more.

The preceding answers were excellent. Hope the article above will help.
Regards,
Jerry
 

kayn1n32008

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...as skip is not too common...

Minor point, VHF/UHF/700/800MHz does not tend to skip(bouncing of ionosphere & ground) like HF does, rather enhanced propagation on VHF-Hi and above is caused, most likely, by tropospheric ducting.


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Very little skip is on UHF frequencies though you may be able to get the VHF link on a very excellent and lucky day.

You're going to need more than a very tall tower. I was once flying in a cessna at 6500ft listening to UHF cutting in and out on a XTS2500 from 150 miles away in flat florida. Now this was a rubber duck and not a full wave antenna but the station was just barely receivable from that altitude. You probably wont get squat even on a tower 250 miles away on UHF.

You could buy an AWACS if you have the money though.

Distance to horizon is measured as: D=3.57√h (h being the height in meters) (d being the distance in kilometers)

so at 250 miles (402km) use the calculation 402/3.57=√h or (402/3.57)²=h

So the altitude required is: 12679m or 41597ft

Now this isn't absolute as this does not account for atmospheric refraction. It also does not factor in the height of the transmitter. The actual distance to horizon is going to be farther than this, so the height required is going to be less than what the math tells you, but it's still going to be more than likely out of reach even on a good day. This formula is also intended for light waves and not Radio but the principles are the same.
I tried the VHF link freq and I got anther police on it. It had a 203.5 PL on it.
 
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