Antenna beamwidth

[Rawkee1]

I have read some specs on antennas and I'm a bit confused why I should know about beamwidth on an antenna. I'm looking at an antenna that's omni direction with 3db gain and a 33 degree beamwidth. Why do I have to know the beamwith if I'm just receiving? Can anyone put this in layman's terms? I understand it's a cone however, why should I have to know this?

 

[prcguy]

For an omni directional antenna the beam width is how far up and down in degrees from the horizon the antenna pattern goes at the half power or -3dB points. For a 33 degree total beamwidth antenna, cut that in half and you have 16.5 degrees above the horizon as the point where the antenna gain is down by 3dB and 16.5 degrees below the horizon will have the same 3dB degradation. As you go closer to the horizon the antenna gain will be higher and eventually up to its rated gain right at the horizon. Go beyond the rated beamwidth and the gain will drop off more. The 33 degree example might be good for an antenna that is on a high hill and you want good coverage at the bottom of the hill where the antenna would be looking down at a steep angle.

A higher gain omni like 10dBd might have a half power or -3dB beamwith of 7 degrees meaning at an angle of 3.5 degrees above and below the horizon the antenna will be at its half power or -3dB points. You have to be careful how high you mount this antenna so the antenna pattern doesn't overshoot the users.

 

[Rawkee1]

so I have a chance to pick up a liard FG1563 because I listen to a lot of Rail Road chatter. It would be installed on a mast above the roof approximately 35-40' above the ground. Back in the old days it didn't seem this complicated to pick an antenna. Do you think this would be a good antenna for my application. Some hot box detectors are 10-15 miles out that I hear on a discone choppy at times and clear on other days. The Laird is tuned more to the frequencies I listen to. I am running LMR400 now as well.

 

[MDScanFan]

You can't go wrong with that antenna. I use the same antenna for rail listening. It replaced a discone. Side by side comparisons showed improvement in signal to noise. It is built like a tank.

Are you trying to receive signals from primarily one direction or multiple directions. If the latter, then the FG1563 would be a great fit. If the former, then consider a directional yagi antenna for even more gain in the direction of interest. You can get them for about the same price as the Laird.

so I have a chance to pick up a liard FG1563 because I listen to a lot of Rail Road chatter. It would be installed on a mast above the roof approximately 35-40' above the ground. Back in the old days it didn't seem this complicated to pick an antenna. Do you think this would be a good antenna for my application. Some hot box detectors are 10-15 miles out that I hear on a discone choppy at times and clear on other days. The Laird is tuned more to the frequencies I listen to. I am running LMR400 now as well.

 

[Rawkee1]

You can't go wrong with that antenna. I use the same antenna for rail listening. It replaced a discone. Side by side comparisons showed improvement in signal to noise. It is built like a tank.

Are you trying to receive signals from primarily one direction or multiple directions. If the latter, then the FG1563 would be a great fit. If the former, then consider a directional yagi antenna for even more gain in the direction of interest. You can get them for about the same price as the Laird.

I am glad to hear it would be a good fit. I am trying to pick up signals more about 270 degrees so you probably would consider that omni. I was thinking two yagi's but was told there is more to installing two yagi;s that are on the same band.

 

[MDScanFan]

A multi-yagi setup pointing in different directions can be tricky unless you plan to dedicate a yagi per radio.

It sounds like an omni is the way to go in your situation.

 

[W8HDU]

Multi-antenna arrays are very tricky, as different frequencies will react differently. The suggestion that you use an omni is good advice. And the 33 degree beam is no problem. The only time it could create a problem is when its very high in the air, and then you lose some effectiveness on the ground below.

Case in point; our ham repeater on 443.625 in Lima used a Decibel Products DB-420. Lots of gain. The signal was great out to 12 miles on a handheld radio, but if I walked around the neighborhood 2 blocks from the tower, I would be in an out of the receiver. The beam was overhead and not at ground level.

So for your antenna to be 3db gain and a 33 degree beam width, and assumed not to be way up high, your antenna will be fine.

 

[Rawkee1]

I appreciate all you guys input on my situation. There are so many different avenues to travel down to get the best signal for the radio listening you choose. There are many configurations one can try, but it gets expensive to travel down the road of "trial & error" along with a waste of time of climbing up and down a two story house. The Laird's center frequency would be 159 Mhz. I don't believe it's tunable

 

[W8HDU]

Tuning the antenna would buy you fractions of additional receive signal, unless you're trying to receive VHF High/Low on a UHF antenna. I'm not sure you would notice much tuning it.

 

[Rawkee1]

This Laird will be used mainly for Rail Road chatter and some other listening at between 155-158Mhz. I've read some good posts with this antenna and it's 1/2 wave instead of 1/4. I'm not sure with everything being equal on a system, if you put the 1/2 wave against the 1/4 wave, should the difference be noticeable on the distant faint signals?

 

[Ubbe]

if you put the 1/2 wave against the 1/4 wave, should the difference be noticeable on the distant faint signals?

It should almost double the signal, Picking up the electromagnetic radio waves with one 1/4 element compared to a 1/2 wave antenna that consist of two 1/4 elements.

/Ubbe

 

[prcguy]

I've never used a Laird FG1563 but the specs look ok for what you are doing and the price is fair. Not great but fair. However more gain is better. How are you at following instructions and using hand tools? Here is a project that is very cheap and this will give you 3dB more gain over the Laird or 6dBd gain and wide band width. The instructions are in post #5 in this thread.

4-bay VHF dipole array project

This project was inspired by someone wanting a better antenna for VHF RR and this is about the best you can get. It will cover 2m through RR and can be custom tweaked if you have an antenna analyzer. The pdf instructions are a first draft, but it took longer to document the project than it did...

forums.radioreference.com

 

[paulears]

I'm a bit confused? You mention 270 degrees. So you want a directional antenna for a specific direction and NOT an omni where it's performance is spread around the full 360 degrees? Which is it? If you do need that one specific direction, you then can select how far away each side from the 270 degrees you want to go, but I guess you could also mean you want 270 degrees of coverage - so there's 90 degrees you don't want.

 

[Rawkee1]

Sorry about the confusion, I didn't explain it correctly. There is 90 degrees that I don't need coverage for so I need an omni directional antenna I wasn't understanding what beamwidth meant or why I needed to know, but from what other listener's told me, the Laird FG 1563 would be a good antenna for listening to Railroad chatter in my area.

 

[prcguy]

You might look at a dipole array with all dipoles lined up on the same side. This will give you good coverage over about 180 degrees or a little more and not waste gain where you don't need it. The project mentioned a few posts up would be great for this.

Sorry about the confusion, I didn't explain it correctly. There is 90 degrees that I don't need coverage for so I need an omni directional antenna I wasn't understanding what beamwidth meant or why I needed to know, but from what other listener's told me, the Laird FG 1563 would be a good antenna for listening to Railroad chatter in my area.

 

[Rawkee1]

i am going to look into that project. It might be worth my while. Thanks for that info prcguy!

 

[paulears]

I live on the east coast of the UK, so here, 180 degrees of the compass is water. Two and four stack dipoles, as mentioned above are very popular on VHF and UHF to try to not waste the power output. The marine users have theirs on the east side of the masts, and the land users have their antennas on the west. For higher bands there are designs that have large grid type reflectors behind a dipole, these two work well, but are massive and very heavy.

 

[Ubbe]

i am going to look into that project. It might be worth my while. Thanks for that info prcguy!

I'm a bit worried about your RF location. You had that Diamond F23 that consists of 3 stacked 5/8 verticals. I cut mine to 155MHz instead of 144MHz and the reception of AIS signals at 160Mhz got a big improvement compared to a 155MHz 5/8 GP. Diamond says it does 7.8dB gain. I don't know what that means, as they don't refer the dB to something, but I guess its 5dBi as it seems logical being three stacked 5/8.

But you had no luck with that higher gain omni antenna.

/Ubbe

 

[Rawkee1]

I am wondering myself about the diamond F23. Is there a way to test the antenna? Maybe it’s defective? im in a pretty decent location on a medium size hI’ll about 750’ above sea level.

 

[W8HDU]

Older Diamond antennas had a problem with corrosion due to environment and dissimilar metals. Depending on the amount of degradation, it could detune or provide a less than acceptable load at the antenna, (which also affects receive). Before taking it all apart, check the input and make sure there is no corrosion on the threads or pins. It's also good to look at the dielectric between the center pin and ground side.