GMRS info request

[jeepers29]

All except dummies like me.

You are not alone. LOL

 

[jeepers29]

For GMRS, you're looking for an antenna that covers 462MHz and 467MHz. The gain of the antenna determines how "pinched" toward the horizon the signal will be - more pinch meaning greater sensitivity to a signal on the horizon and more transmit power pushed toward the horizon. The downside of high gain is if the other station is much higher of lower than yours, they won't be "in the beam" of your antenna. The supplied antenna is 0dBi (omnidirectonal and certainly good enough to start with), 2-3dBi works well in hilly terrain where distance will be limited by line-of-sight anyway, 4-6+dBi is great for flatter areas (including highway).

View attachment 164953

I have a stubby Laird Phantom (AmazonLINK, 3dBi claimed, but perhaps less) and a Midland MXTA26 (AmazonLINK, 6dBi claimed, but it's too short the SWR minimum is well of 470MHz) in addition to the antenna that comes with that radio. I've have a Diamond Luggage rack mount that either the Midland or Laird will screw onto, depending on my plan for the day. (The mounts are cheapest on Gigaparts.com. Roof is 2-3 dB better than hood or trunk as a mounting location, but all work. I suggest buying one with the cable included unless you're proficient at soldering the connectors on. HINT: Buy a good mount, since a crappy one can easily lose you half of your signal power (3dB).)

So, how to visualize how "pinched" the beam is? Here are **ROUGH** estimates of the beam-widths for various antenna gains (mileage varies - a lot).

View attachment 164955

And here is a trick you can use to visualize an angle against the sky or horizon using just your hand at arm's length.

View attachment 164954

So, hang-loose, centered vertically on the horizon is about the height of the 6dBi antenna beam. A 3dBi antenna beam gets a little more than a whole hang-loose above and below the horizon.

A bit over my head, I guess but I really appreciate you taking the time to explain it. I am sure your explanation will make sense as I do some more research. Thanks again.

 

[LostInThought]

A bit over my head, I guess but I really appreciate you taking the time to explain it. I am sure your explanation will make sense as I do some more research. Thanks again.

No problem. It was a head scratcher for me when I started too. We're here to help each other. If you're willing to let me (or one of the others here) take another shot at explaining, I know others here are interested in this too. Tell me where to start, and I'll do my best.

 

[Boppa's Travels]

I know this is a GMRS thread but I guess I'm on my way to having for antennas because I passed on Ham test tonight.

 

[Boppa's Travels]

I am feeling bad about making fun of all y'all with 4 antennas. Forgive me.

 

[LostInThought]

I am feeling bad about making fun of all y'all with 4 antennas. Forgive me.

I've always suspected that if anyone **REALLY** understood how antennas worked, we wouldn't need 4...

 

[Lanlubber In Remembrance]

A bit over my head, I guess but I really appreciate you taking the time to explain it. I am sure your explanation will make sense as I do some more research. Thanks again.

Double ditto, maybe some day it will sink in.

 

[M Rose]

yeah, you don't want your rig to end up looking like mine.

or mine

 

[LostInThought]

Double ditto, maybe some day it will sink in.

My fault. I didnt' do a very good job explaining on the first pass. But I really think this is information that would be helpful to the whole community. Everyone needs a radio in their vehicle. Everyone needs an antenna system that works for what they do. The problem is I'm not sure where to start answering questions and my shotgun approach is obviously not helpful - apologies, I wish I were better at it. Maybe together we can build this into an FAQ with help from M Rose and Prerunner1982 and some of the other hams. Just help us figure out where to start? What are the first few questions we need to answer for someone just starting? Would a set of basic suggestions help? Perhaps you'd bare with me while I take another crack at explaining this. Something like?:

CB, GMRS, or Ham?
CB, GMRS, and Ham are not compatible. Find out what your group/club is using and use THAT. All the other technical goop doesn't matter if your crew is using something else.

How much power does my radio need?
Most mobile radios are basically line of sight. 15W generally works well. Higher power rigs can sometimes help punch through ground clutter better, but nothing gets a signal out of a canyon bottom. Doubling (2x) the radio's (transmit) power improves it's range by ~1.2x when the path between the transmitter and the receiver is unobstructed. Increasing the transmit power doesn't help you "hear" something further away - that's all in the antenna.

What antenna?
For mountainous terrain or terrain where you expect the vehicle to encounter steep ascents/descents, an antenna with 2-3dB gain *rocks*, while an antenna with 6dBi gain may have weird dropouts. On flat terrain, like a highway, an antenna with 6dBi gain will provide greater range. (The issue here is the "shape" of the signal spread from the antenna - gorey details below in "antenna beam")

Where to mount?
Higher on the vehicle is better. Roughly speaking, for typical mobile radios a mount on the ROOF of the vehicle gives you about 1.2x more "reach" than a mount on the hood or trunk, but all will work well for most cases other than trying to reach a distant repeater (repeaters described below).

What mount?
Invest in a GOOD mount (Diamond and Comet are solid brands). A poor mount (poor cable, poor connectors, extra connectors, cable extensions) can reduce your "reach" by ~1.2x.

What's a repeater?
A repeater is just a radio station that "repeats" what it hears on a specific frequency. Normally, because of the line-of-sight and the Earth's curvature, you'd be able to send a signal 5-10 miles with an antenna on top of a vehicle to another similar vehicle. But imagine a repeater on a tall mountaintop (where we usually put them when we can). You're 50 miles from the repeater on one side of the mountain, but because it's so high, you can see the mountaintop and thus the repeater can "hear" your signal. From here, the repeater can hear you, but no one on the other side of the mountain can hear you, because the mountain is in the way (line-of-sight). BUT the repeater "repeats" your signal, so anyone who can see the mountaintop can hear your signal. People 50 miles on the other side of the mountain CAN hear the repeater relaying your signal. This means that instead of 5-10 miles of range with your radio, you could have a range of 100 miles. Ham radios can use ham repeaters and some GMRS radios are able to use GMRS repeaters. Repeaters are usually set up by radio clubs or individuals.

What is a "linked repeater"?
Sometimes repeaters are connected (for instance, over the internet). These connected repeaters behave as a single repeater - ALL of them relay any signal heard by one of them. This means that if you can send a signal to ONE of these repeaters, the signal can be heard by anyone who can see a repeater anywhere in the system. Imagine I can see a mountaintop with a repeater on it near Albuquerque and you can see a mountaintop with a repeater on it near Denver. If these repeaters are linked, we can talk over the radios as if we were only a couple miles apart.

What is dBi?
dBi (decibels) is a measure of relative signal strength. Admittedly it's weird, but just remember that each 3dBi difference corresponds to a doubling or halving of signal strength. So a 3dBi increase in signal is a 2x increase in power, and a 6dBi increase (3dBi + 3dBi) is a 4x (2x2) increase in power and 9dBi (3dBi +3dBi + 3dBi) is an 8x (2x2x2) increase in power. Yep, that makes your head hurt. Why not just use the 2x comparison? Because using decibels lets us compare and trade off signal power and losses across a transmission system.

• Example: A 60W transmitter provides 6dBi more signal than a 15W transmitter (60W=15Wx2x2). But it isn't' just the transmitter - we need to consider the radio, the antenna, and the mount.
  • If we pair the 60W transmitter with a 0dBi gain antenna on a mount with 2dBi of loss:
    • 6dBi (transmit power advantage) + 0dBi (antenna) - 2dBi (mount loss) = 4dBi effective transmit power
  • To a 15W transmitter paired with a 5dBi antenna on a mount with 1dBi of loss
    • 0dBi (transmit power advantage) + 5dBi (antenna) - 1dBi (mount loss) = 4dBi effective transmit power
    • (as long as the receiver is "in the beam" of the antenna, next question)
• But on the receive side, the transmit power doesn't matter, just the antenna and mount
  • For the 60W setup:
    • 0dBi (antenna) - 2dBi (mount) = -2dBi effective receive gain
  • For the 15W setup:
    • 5dBi (antenna) - 1dBi (mount) = +4dBi effective receive gain
  • A 6dBi difference.
• Moral of the story? A better antenna/mount improve both transmit and receive and is generally more useful than just more transmit power.

Antenna gain? Shape? Beam?
Hang tight, this is where things got a little harder to understand for me and certainly harder for me to explain. If you want to skip this, just remember: 2dBi antenna for steep terrain, 5+dBi antenna for flat terrain. Let's start by asking, what does the radio wave "look" like? Let's start by imagining slipping a wedding ring over our vertical antenna, so that the center of the wedding ring is at the center of the antenna. This is how a pulse of radio signal starts at the antenna - as a ring around the center of the antenna. The radio signal then propagates away from the antenna at the speed of light, but it generally retains this basic shape of a ring. We talk about "high gain" (5dBi+), "low gain" (2-3dBi), or "omni-directional" (0dBi) antennas - and that tells us something about the shape of the signal ring. For extremely high-gain antennas, the signal ring is squished flat in the vertical direction and spreads out like a circle from the antenna, effectively focusing the power of the signal at the circumference of the circle. For extremely low-gain antennas, there is not squashing and the signal spreads out like sphere from the center of the antenna and much of the signal power is lost to straight up. If we look at the antenna from the side to see the cross section of the signal as it spreads out from the antenna for different gains, they looks something like the following with high gain antennas having a very flat "beam" and low gain antennas having a "taller" beam (the black thing in the middle is supposed to be the antenna, and the gray is supposed to show where the expanding ring of signal would go):



Why does this matter? It goes back to terrain.The antenna beam patterns are shown for vehicle in the center of the diagram below. On the hill, the vehicle on the left and right are "in" the antenna beam of the center vehicle for a 3dBi antenna (they can hear him), and NOT in the beam of a 6dBi antenna (they can't hear him). On flat terrain, the vehicle on the left and right are too far away for 3dBi antenna to reach (they can't hear him because the antenna wastes too much signal power spreading high and low), but the are within the pattern of the 9dBi(left) or 6dBi(right) antenna (they can hear him, because the signal power was more focused and reached further).



Would this work for a start on an FAQ? What needs clarification and what needs to be added? (or should I just stop before I annoy folks?)

 

[M Rose]

My fault. I didnt' do a very good job explaining on the first pass. But I really think this is information that would be helpful to the whole community. Everyone needs a radio in their vehicle. Everyone needs an antenna system that works for what they do. The problem is I'm not sure where to start answering questions and my shotgun approach is obviously not helpful - apologies, I wish I were better at it. Maybe together we can build this into an FAQ with help from M Rose and Prerunner1982 and some of the other hams. Just help us figure out where to start? What are the first few questions we need to answer for someone just starting? Would a set of basic suggestions help? Perhaps you'd bare with me while I take another crack at explaining this. Something like?:

CB, GMRS, or Ham?
CB, GMRS, and Ham are not compatible. Find out what your group/club is using and use THAT. All the other technical goop doesn't matter if your crew is using something else.

How much power does my radio need?
Most mobile radios are basically line of sight. 15W generally works well. Higher power rigs can sometimes help punch through ground clutter better, but nothing gets a signal out of a canyon bottom. Doubling (2x) the radio's (transmit) power improves it's range by ~1.2x when the path between the transmitter and the receiver is unobstructed. Increasing the transmit power doesn't help you "hear" something further away - that's all in the antenna.

What antenna?
For mountainous terrain or terrain where you expect the vehicle to encounter steep ascents/descents, an antenna with 2-3dB gain *rocks*, while an antenna with 6dBi gain may have weird dropouts. On flat terrain, like a highway, an antenna with 6dBi gain will provide greater range. (The issue here is the "shape" of the signal spread from the antenna - gorey details below in "antenna beam")

Where to mount?
Higher on the vehicle is better. Roughly speaking, for typical mobile radios a mount on the ROOF of the vehicle gives you about 1.2x more "reach" than a mount on the hood or trunk, but all will work well for most cases other than trying to reach a distant repeater (repeaters described below).

What mount?
Invest in a GOOD mount (Diamond and Comet are solid brands). A poor mount (poor cable, poor connectors, extra connectors, cable extensions) can reduce your "reach" by ~1.2x.

What's a repeater?
A repeater is just a radio station that "repeats" what it hears on a specific frequency. Normally, because of the line-of-sight and the Earth's curvature, you'd be able to send a signal 5-10 miles with an antenna on top of a vehicle to another similar vehicle. But imagine a repeater on a tall mountaintop (where we usually put them when we can). You're 50 miles from the repeater on one side of the mountain, but because it's so high, you can see the mountaintop and thus the repeater can "hear" your signal. From here, the repeater can hear you, but no one on the other side of the mountain can hear you, because the mountain is in the way (line-of-sight). BUT the repeater "repeats" your signal, so anyone who can see the mountaintop can hear your signal. People 50 miles on the other side of the mountain CAN hear the repeater relaying your signal. This means that instead of 5-10 miles of range with your radio, you could have a range of 100 miles. Ham radios can use ham repeaters and some GMRS radios are able to use GMRS repeaters. Repeaters are usually set up by radio clubs or individuals.

What is a "linked repeater"?
Sometimes repeaters are connected (for instance, over the internet). These connected repeaters behave as a single repeater - ALL of them relay any signal heard by one of them. This means that if you can send a signal to ONE of these repeaters, the signal can be heard by anyone who can see a repeater anywhere in the system. Imagine I can see a mountaintop with a repeater on it near Albuquerque and you can see a mountaintop with a repeater on it near Denver. If these repeaters are linked, we can talk over the radios as if we were only a couple miles apart.

What is dBi?
dBi (decibels) is a measure of relative signal strength. Admittedly it's weird, but just remember that each 3dBi difference corresponds to a doubling or halving of signal strength. So a 3dBi increase in signal is a 2x increase in power, and a 6dBi increase (3dBi + 3dBi) is a 4x (2x2) increase in power and 9dBi (3dBi +3dBi + 3dBi) is an 8x (2x2x2) increase in power. Yep, that makes your head hurt. Why not just use the 2x comparison? Because using decibels lets us compare and trade off signal power and losses across a transmission system.

• Example: A 60W transmitter provides 6dBi more signal than a 15W transmitter (60W=15Wx2x2). But it isn't' just the transmitter - we need to consider the radio, the antenna, and the mount.
  • If we pair the 60W transmitter with a 0dBi gain antenna on a mount with 2dBi of loss:
    • 6dBi (transmit power advantage) + 0dBi (antenna) - 2dBi (mount loss) = 4dBi effective transmit power
  • To a 15W transmitter paired with a 5dBi antenna on a mount with 1dBi of loss
    • 0dBi (transmit power advantage) + 5dBi (antenna) - 1dBi (mount loss) = 4dBi effective transmit power
    • (as long as the receiver is "in the beam" of the antenna, next question)
• But on the receive side, the transmit power doesn't matter, just the antenna and mount
  • For the 60W setup:
    • 0dBi (antenna) - 2dBi (mount) = -2dBi effective receive gain
  • For the 15W setup:
    • 5dBi (antenna) - 1dBi (mount) = +4dBi effective receive gain
  • A 6dBi difference.
• Moral of the story? A better antenna/mount improve both transmit and receive and is generally more useful than just more transmit power.

Antenna gain? Shape? Beam?
Hang tight, this is where things got a little harder to understand for me and certainly harder for me to explain. If you want to skip this, just remember: 2dBi antenna for steep terrain, 5+dBi antenna for flat terrain. Let's start by asking, what does the radio wave "look" like? Let's start by imagining slipping a wedding ring over our vertical antenna, so that the center of the wedding ring is at the center of the antenna. This is how a pulse of radio signal starts at the antenna - as a ring around the center of the antenna. The radio signal then propagates away from the antenna at the speed of light, but it generally retains this basic shape of a ring. We talk about "high gain" (5dBi+), "low gain" (2-3dBi), or "omni-directional" (0dBi) antennas - and that tells us something about the shape of the signal ring. For extremely high-gain antennas, the signal ring is squished flat in the vertical direction and spreads out like a circle from the antenna, effectively focusing the power of the signal at the circumference of the circle. For extremely low-gain antennas, there is not squashing and the signal spreads out like sphere from the center of the antenna and much of the signal power is lost to straight up. If we look at the antenna from the side to see the cross section of the signal as it spreads out from the antenna for different gains, they looks something like the following with high gain antennas having a very flat "beam" and low gain antennas having a "taller" beam (the black thing in the middle is supposed to be the antenna, and the gray is supposed to show where the expanding ring of signal would go):

View attachment 165000

Why does this matter? It goes back to terrain.The antenna beam patterns are shown for vehicle in the center of the diagram below. On the hill, the vehicle on the left and right are "in" the antenna beam of the center vehicle for a 3dBi antenna (they can hear him), and NOT in the beam of a 6dBi antenna (they can't hear him). On flat terrain, the vehicle on the left and right are too far away for 3dBi antenna to reach (they can't hear him because the antenna wastes too much signal power spreading high and low), but the are within the pattern of the 9dBi(left) or 6dBi(right) antenna (they can hear him, because the signal power was more focused and reached further).

View attachment 165001

Would this work for a start on an FAQ? What needs clarification and what needs to be added? (or should I just stop before I annoy folks?)

I think you are doing an excellent job. I’m fallowing very well, but then again I’ve been studying and experimenting with different antennas and power settings. I really don’t have anything to add yet in hopes of not confusing others...

I’ll keep watching this thread though.

 

[LostInThought]

I think you are doing an excellent job. I’m fallowing very well, but then again I’ve been studying and experimenting with different antennas and power settings. I really don’t have anything to add yet in hopes of not confusing others...

I’ll keep watching this thread though.

Thanks Mike. The antenna stuff is probably the weirdest aspect of radio to get a handle on, but getting it right can make a huge difference in communication performance. I'm still learning, but if we can accumulate some of our collective knowledge and share it here...

 

[Boppa's Travels]

My fault. I didnt' do a very good job explaining on the first pass. But I really think this is information that would be helpful to the whole community. Everyone needs a radio in their vehicle. Everyone needs an antenna system that works for what they do. The problem is I'm not sure where to start answering questions and my shotgun approach is obviously not helpful - apologies, I wish I were better at it. Maybe together we can build this into an FAQ with help from M Rose and Prerunner1982 and some of the other hams. Just help us figure out where to start? What are the first few questions we need to answer for someone just starting? Would a set of basic suggestions help? Perhaps you'd bare with me while I take another crack at explaining this. Something like?:

CB, GMRS, or Ham?
CB, GMRS, and Ham are not compatible. Find out what your group/club is using and use THAT. All the other technical goop doesn't matter if your crew is using something else.

How much power does my radio need?
Most mobile radios are basically line of sight. 15W generally works well. Higher power rigs can sometimes help punch through ground clutter better, but nothing gets a signal out of a canyon bottom. Doubling (2x) the radio's (transmit) power improves it's range by ~1.2x when the path between the transmitter and the receiver is unobstructed. Increasing the transmit power doesn't help you "hear" something further away - that's all in the antenna.

What antenna?
For mountainous terrain or terrain where you expect the vehicle to encounter steep ascents/descents, an antenna with 2-3dB gain *rocks*, while an antenna with 6dBi gain may have weird dropouts. On flat terrain, like a highway, an antenna with 6dBi gain will provide greater range. (The issue here is the "shape" of the signal spread from the antenna - gorey details below in "antenna beam")

Where to mount?
Higher on the vehicle is better. Roughly speaking, for typical mobile radios a mount on the ROOF of the vehicle gives you about 1.2x more "reach" than a mount on the hood or trunk, but all will work well for most cases other than trying to reach a distant repeater (repeaters described below).

What mount?
Invest in a GOOD mount (Diamond and Comet are solid brands). A poor mount (poor cable, poor connectors, extra connectors, cable extensions) can reduce your "reach" by ~1.2x.

What's a repeater?
A repeater is just a radio station that "repeats" what it hears on a specific frequency. Normally, because of the line-of-sight and the Earth's curvature, you'd be able to send a signal 5-10 miles with an antenna on top of a vehicle to another similar vehicle. But imagine a repeater on a tall mountaintop (where we usually put them when we can). You're 50 miles from the repeater on one side of the mountain, but because it's so high, you can see the mountaintop and thus the repeater can "hear" your signal. From here, the repeater can hear you, but no one on the other side of the mountain can hear you, because the mountain is in the way (line-of-sight). BUT the repeater "repeats" your signal, so anyone who can see the mountaintop can hear your signal. People 50 miles on the other side of the mountain CAN hear the repeater relaying your signal. This means that instead of 5-10 miles of range with your radio, you could have a range of 100 miles. Ham radios can use ham repeaters and some GMRS radios are able to use GMRS repeaters. Repeaters are usually set up by radio clubs or individuals.

What is a "linked repeater"?
Sometimes repeaters are connected (for instance, over the internet). These connected repeaters behave as a single repeater - ALL of them relay any signal heard by one of them. This means that if you can send a signal to ONE of these repeaters, the signal can be heard by anyone who can see a repeater anywhere in the system. Imagine I can see a mountaintop with a repeater on it near Albuquerque and you can see a mountaintop with a repeater on it near Denver. If these repeaters are linked, we can talk over the radios as if we were only a couple miles apart.

What is dBi?
dBi (decibels) is a measure of relative signal strength. Admittedly it's weird, but just remember that each 3dBi difference corresponds to a doubling or halving of signal strength. So a 3dBi increase in signal is a 2x increase in power, and a 6dBi increase (3dBi + 3dBi) is a 4x (2x2) increase in power and 9dBi (3dBi +3dBi + 3dBi) is an 8x (2x2x2) increase in power. Yep, that makes your head hurt. Why not just use the 2x comparison? Because using decibels lets us compare and trade off signal power and losses across a transmission system.

• Example: A 60W transmitter provides 6dBi more signal than a 15W transmitter (60W=15Wx2x2). But it isn't' just the transmitter - we need to consider the radio, the antenna, and the mount.
  • If we pair the 60W transmitter with a 0dBi gain antenna on a mount with 2dBi of loss:
    • 6dBi (transmit power advantage) + 0dBi (antenna) - 2dBi (mount loss) = 4dBi effective transmit power
  • To a 15W transmitter paired with a 5dBi antenna on a mount with 1dBi of loss
    • 0dBi (transmit power advantage) + 5dBi (antenna) - 1dBi (mount loss) = 4dBi effective transmit power
    • (as long as the receiver is "in the beam" of the antenna, next question)
• But on the receive side, the transmit power doesn't matter, just the antenna and mount
  • For the 60W setup:
    • 0dBi (antenna) - 2dBi (mount) = -2dBi effective receive gain
  • For the 15W setup:
    • 5dBi (antenna) - 1dBi (mount) = +4dBi effective receive gain
  • A 6dBi difference.
• Moral of the story? A better antenna/mount improve both transmit and receive and is generally more useful than just more transmit power.

Antenna gain? Shape? Beam?
Hang tight, this is where things got a little harder to understand for me and certainly harder for me to explain. If you want to skip this, just remember: 2dBi antenna for steep terrain, 5+dBi antenna for flat terrain. Let's start by asking, what does the radio wave "look" like? Let's start by imagining slipping a wedding ring over our vertical antenna, so that the center of the wedding ring is at the center of the antenna. This is how a pulse of radio signal starts at the antenna - as a ring around the center of the antenna. The radio signal then propagates away from the antenna at the speed of light, but it generally retains this basic shape of a ring. We talk about "high gain" (5dBi+), "low gain" (2-3dBi), or "omni-directional" (0dBi) antennas - and that tells us something about the shape of the signal ring. For extremely high-gain antennas, the signal ring is squished flat in the vertical direction and spreads out like a circle from the antenna, effectively focusing the power of the signal at the circumference of the circle. For extremely low-gain antennas, there is not squashing and the signal spreads out like sphere from the center of the antenna and much of the signal power is lost to straight up. If we look at the antenna from the side to see the cross section of the signal as it spreads out from the antenna for different gains, they looks something like the following with high gain antennas having a very flat "beam" and low gain antennas having a "taller" beam (the black thing in the middle is supposed to be the antenna, and the gray is supposed to show where the expanding ring of signal would go):

View attachment 165000

Why does this matter? It goes back to terrain.The antenna beam patterns are shown for vehicle in the center of the diagram below. On the hill, the vehicle on the left and right are "in" the antenna beam of the center vehicle for a 3dBi antenna (they can hear him), and NOT in the beam of a 6dBi antenna (they can't hear him). On flat terrain, the vehicle on the left and right are too far away for 3dBi antenna to reach (they can't hear him because the antenna wastes too much signal power spreading high and low), but the are within the pattern of the 9dBi(left) or 6dBi(right) antenna (they can hear him, because the signal power was more focused and reached further).

View attachment 165001

Would this work for a start on an FAQ? What needs clarification and what needs to be added? (or should I just stop before I annoy folks?)

After reading that post looks like if your traveling in various terrains then you would need 3 antennas per type of radio if you wanted 100% coverage 100% of the time. So CB 1, GMRS 2, Ham 3. 3 radios X 3 antennas each = 9 antennas. Right?

 

[Sparksalot]

Y’all are talking about antends farms like they’re a bad thing!

this is for hf/vhf/uhf ham, plus gmrs, plus CB.

 

[Boppa's Travels]

Y’all are talking about antends farms like they’re a bad thing!

this is for hf/vhf/uhf ham, plus gmrs, plus CB.

View attachment 165014

Hate to be the bearer of bad news but I think one of your antennas is crooked

 

[Sparksalot]

Wid

Hate to be the bearer of bad news but I think one of your antennas is crooked

Wide angle lens. Plus a bit of roof curve on the side. I usually have a 4 inch dual band stubby there.

 

[Prerunner1982]

After reading that post looks like if your traveling in various terrains then you would need 3 antennas per type of radio if you wanted 100% coverage 100% of the time. So CB 1, GMRS 2, Ham 3. 3 radios X 3 antennas each = 9 antennas. Right?

You can take CB off that list. A 1/4 wave CB antenna is about 102" long and has little to no gain and they really only make mobile CB antennas that are shorter which will also have little to no gain.
If you are running a dual band ham radio you won't find an antenna that is 1/4 wave on both bands so you will end up with a 1/4 wave on 2m and 1/2 wave on 70cm or 1/2 wave on 2m and 5/8 wave on 70cm.
So sometimes you have to compromise... either carry one extra antenna or use GMRS with a 1/4 wave antenna for up close comms and ham with a longer antenna for more distant comms.... if your buddies are running both of course..
Even antenna placement is a compromise if you are running more than one antenna as they all can't be in the middle of the roof or on the roof at all if you have a removable top vehicle.

 

[jeepers29]

My fault. I didnt' do a very good job explaining on the first pass. But I really think this is information that would be helpful to the whole community. Everyone needs a radio in their vehicle. Everyone needs an antenna system that works for what they do. The problem is I'm not sure where to start answering questions and my shotgun approach is obviously not helpful - apologies, I wish I were better at it. Maybe together we can build this into an FAQ with help from M Rose and Prerunner1982 and some of the other hams. Just help us figure out where to start? What are the first few questions we need to answer for someone just starting? Would a set of basic suggestions help? Perhaps you'd bare with me while I take another crack at explaining this. Something like?:

CB, GMRS, or Ham?
CB, GMRS, and Ham are not compatible. Find out what your group/club is using and use THAT. All the other technical goop doesn't matter if your crew is using something else.

How much power does my radio need?
Most mobile radios are basically line of sight. 15W generally works well. Higher power rigs can sometimes help punch through ground clutter better, but nothing gets a signal out of a canyon bottom. Doubling (2x) the radio's (transmit) power improves it's range by ~1.2x when the path between the transmitter and the receiver is unobstructed. Increasing the transmit power doesn't help you "hear" something further away - that's all in the antenna.

What antenna?
For mountainous terrain or terrain where you expect the vehicle to encounter steep ascents/descents, an antenna with 2-3dB gain *rocks*, while an antenna with 6dBi gain may have weird dropouts. On flat terrain, like a highway, an antenna with 6dBi gain will provide greater range. (The issue here is the "shape" of the signal spread from the antenna - gorey details below in "antenna beam")

Where to mount?
Higher on the vehicle is better. Roughly speaking, for typical mobile radios a mount on the ROOF of the vehicle gives you about 1.2x more "reach" than a mount on the hood or trunk, but all will work well for most cases other than trying to reach a distant repeater (repeaters described below).

What mount?
Invest in a GOOD mount (Diamond and Comet are solid brands). A poor mount (poor cable, poor connectors, extra connectors, cable extensions) can reduce your "reach" by ~1.2x.

What's a repeater?
A repeater is just a radio station that "repeats" what it hears on a specific frequency. Normally, because of the line-of-sight and the Earth's curvature, you'd be able to send a signal 5-10 miles with an antenna on top of a vehicle to another similar vehicle. But imagine a repeater on a tall mountaintop (where we usually put them when we can). You're 50 miles from the repeater on one side of the mountain, but because it's so high, you can see the mountaintop and thus the repeater can "hear" your signal. From here, the repeater can hear you, but no one on the other side of the mountain can hear you, because the mountain is in the way (line-of-sight). BUT the repeater "repeats" your signal, so anyone who can see the mountaintop can hear your signal. People 50 miles on the other side of the mountain CAN hear the repeater relaying your signal. This means that instead of 5-10 miles of range with your radio, you could have a range of 100 miles. Ham radios can use ham repeaters and some GMRS radios are able to use GMRS repeaters. Repeaters are usually set up by radio clubs or individuals.

What is a "linked repeater"?
Sometimes repeaters are connected (for instance, over the internet). These connected repeaters behave as a single repeater - ALL of them relay any signal heard by one of them. This means that if you can send a signal to ONE of these repeaters, the signal can be heard by anyone who can see a repeater anywhere in the system. Imagine I can see a mountaintop with a repeater on it near Albuquerque and you can see a mountaintop with a repeater on it near Denver. If these repeaters are linked, we can talk over the radios as if we were only a couple miles apart.

What is dBi?
dBi (decibels) is a measure of relative signal strength. Admittedly it's weird, but just remember that each 3dBi difference corresponds to a doubling or halving of signal strength. So a 3dBi increase in signal is a 2x increase in power, and a 6dBi increase (3dBi + 3dBi) is a 4x (2x2) increase in power and 9dBi (3dBi +3dBi + 3dBi) is an 8x (2x2x2) increase in power. Yep, that makes your head hurt. Why not just use the 2x comparison? Because using decibels lets us compare and trade off signal power and losses across a transmission system.

• Example: A 60W transmitter provides 6dBi more signal than a 15W transmitter (60W=15Wx2x2). But it isn't' just the transmitter - we need to consider the radio, the antenna, and the mount.
  • If we pair the 60W transmitter with a 0dBi gain antenna on a mount with 2dBi of loss:
    • 6dBi (transmit power advantage) + 0dBi (antenna) - 2dBi (mount loss) = 4dBi effective transmit power
  • To a 15W transmitter paired with a 5dBi antenna on a mount with 1dBi of loss
    • 0dBi (transmit power advantage) + 5dBi (antenna) - 1dBi (mount loss) = 4dBi effective transmit power
    • (as long as the receiver is "in the beam" of the antenna, next question)
• But on the receive side, the transmit power doesn't matter, just the antenna and mount
  • For the 60W setup:
    • 0dBi (antenna) - 2dBi (mount) = -2dBi effective receive gain
  • For the 15W setup:
    • 5dBi (antenna) - 1dBi (mount) = +4dBi effective receive gain
  • A 6dBi difference.
• Moral of the story? A better antenna/mount improve both transmit and receive and is generally more useful than just more transmit power.

Antenna gain? Shape? Beam?
Hang tight, this is where things got a little harder to understand for me and certainly harder for me to explain. If you want to skip this, just remember: 2dBi antenna for steep terrain, 5+dBi antenna for flat terrain. Let's start by asking, what does the radio wave "look" like? Let's start by imagining slipping a wedding ring over our vertical antenna, so that the center of the wedding ring is at the center of the antenna. This is how a pulse of radio signal starts at the antenna - as a ring around the center of the antenna. The radio signal then propagates away from the antenna at the speed of light, but it generally retains this basic shape of a ring. We talk about "high gain" (5dBi+), "low gain" (2-3dBi), or "omni-directional" (0dBi) antennas - and that tells us something about the shape of the signal ring. For extremely high-gain antennas, the signal ring is squished flat in the vertical direction and spreads out like a circle from the antenna, effectively focusing the power of the signal at the circumference of the circle. For extremely low-gain antennas, there is not squashing and the signal spreads out like sphere from the center of the antenna and much of the signal power is lost to straight up. If we look at the antenna from the side to see the cross section of the signal as it spreads out from the antenna for different gains, they looks something like the following with high gain antennas having a very flat "beam" and low gain antennas having a "taller" beam (the black thing in the middle is supposed to be the antenna, and the gray is supposed to show where the expanding ring of signal would go):

View attachment 165000

Why does this matter? It goes back to terrain.The antenna beam patterns are shown for vehicle in the center of the diagram below. On the hill, the vehicle on the left and right are "in" the antenna beam of the center vehicle for a 3dBi antenna (they can hear him), and NOT in the beam of a 6dBi antenna (they can't hear him). On flat terrain, the vehicle on the left and right are too far away for 3dBi antenna to reach (they can't hear him because the antenna wastes too much signal power spreading high and low), but the are within the pattern of the 9dBi(left) or 6dBi(right) antenna (they can hear him, because the signal power was more focused and reached further).

View attachment 165001

Would this work for a start on an FAQ? What needs clarification and what needs to be added? (or should I just stop before I annoy folks?)

No need to apologies, as you have been very helpful. The bottom pic helped a lot as did your post that I quoted. Breaks it down much better for us that are not in the know. Thank you.

 

[Lanlubber In Remembrance]

You did a very good job

My fault. I didnt' do a very good job explaining on the first pass. But I really think this is information that would be helpful to the whole community. Everyone needs a radio in their vehicle. Everyone needs an antenna system that works for what they do. The problem is I'm not sure where to start answering questions and my shotgun approach is obviously not helpful - apologies, I wish I were better at it. Maybe together we can build this into an FAQ with help from M Rose and Prerunner1982 and some of the other hams. Just help us figure out where to start? What are the first few questions we need to answer for someone just starting? Would a set of basic suggestions help? Perhaps you'd bare with me while I take another crack at explaining this. Something like?:

CB, GMRS, or Ham?
CB, GMRS, and Ham are not compatible. Find out what your group/club is using and use THAT. All the other technical goop doesn't matter if your crew is using something else.

How much power does my radio need?
Most mobile radios are basically line of sight. 15W generally works well. Higher power rigs can sometimes help punch through ground clutter better, but nothing gets a signal out of a canyon bottom. Doubling (2x) the radio's (transmit) power improves it's range by ~1.2x when the path between the transmitter and the receiver is unobstructed. Increasing the transmit power doesn't help you "hear" something further away - that's all in the antenna.

What antenna?
For mountainous terrain or terrain where you expect the vehicle to encounter steep ascents/descents, an antenna with 2-3dB gain *rocks*, while an antenna with 6dBi gain may have weird dropouts. On flat terrain, like a highway, an antenna with 6dBi gain will provide greater range. (The issue here is the "shape" of the signal spread from the antenna - gorey details below in "antenna beam")

Where to mount?
Higher on the vehicle is better. Roughly speaking, for typical mobile radios a mount on the ROOF of the vehicle gives you about 1.2x more "reach" than a mount on the hood or trunk, but all will work well for most cases other than trying to reach a distant repeater (repeaters described below).

What mount?
Invest in a GOOD mount (Diamond and Comet are solid brands). A poor mount (poor cable, poor connectors, extra connectors, cable extensions) can reduce your "reach" by ~1.2x.

What's a repeater?
A repeater is just a radio station that "repeats" what it hears on a specific frequency. Normally, because of the line-of-sight and the Earth's curvature, you'd be able to send a signal 5-10 miles with an antenna on top of a vehicle to another similar vehicle. But imagine a repeater on a tall mountaintop (where we usually put them when we can). You're 50 miles from the repeater on one side of the mountain, but because it's so high, you can see the mountaintop and thus the repeater can "hear" your signal. From here, the repeater can hear you, but no one on the other side of the mountain can hear you, because the mountain is in the way (line-of-sight). BUT the repeater "repeats" your signal, so anyone who can see the mountaintop can hear your signal. People 50 miles on the other side of the mountain CAN hear the repeater relaying your signal. This means that instead of 5-10 miles of range with your radio, you could have a range of 100 miles. Ham radios can use ham repeaters and some GMRS radios are able to use GMRS repeaters. Repeaters are usually set up by radio clubs or individuals.

What is a "linked repeater"?
Sometimes repeaters are connected (for instance, over the internet). These connected repeaters behave as a single repeater - ALL of them relay any signal heard by one of them. This means that if you can send a signal to ONE of these repeaters, the signal can be heard by anyone who can see a repeater anywhere in the system. Imagine I can see a mountaintop with a repeater on it near Albuquerque and you can see a mountaintop with a repeater on it near Denver. If these repeaters are linked, we can talk over the radios as if we were only a couple miles apart.

What is dBi?
dBi (decibels) is a measure of relative signal strength. Admittedly it's weird, but just remember that each 3dBi difference corresponds to a doubling or halving of signal strength. So a 3dBi increase in signal is a 2x increase in power, and a 6dBi increase (3dBi + 3dBi) is a 4x (2x2) increase in power and 9dBi (3dBi +3dBi + 3dBi) is an 8x (2x2x2) increase in power. Yep, that makes your head hurt. Why not just use the 2x comparison? Because using decibels lets us compare and trade off signal power and losses across a transmission system.

• Example: A 60W transmitter provides 6dBi more signal than a 15W transmitter (60W=15Wx2x2). But it isn't' just the transmitter - we need to consider the radio, the antenna, and the mount.
  • If we pair the 60W transmitter with a 0dBi gain antenna on a mount with 2dBi of loss:
    • 6dBi (transmit power advantage) + 0dBi (antenna) - 2dBi (mount loss) = 4dBi effective transmit power
  • To a 15W transmitter paired with a 5dBi antenna on a mount with 1dBi of loss
    • 0dBi (transmit power advantage) + 5dBi (antenna) - 1dBi (mount loss) = 4dBi effective transmit power
    • (as long as the receiver is "in the beam" of the antenna, next question)
• But on the receive side, the transmit power doesn't matter, just the antenna and mount
  • For the 60W setup:
    • 0dBi (antenna) - 2dBi (mount) = -2dBi effective receive gain
  • For the 15W setup:
    • 5dBi (antenna) - 1dBi (mount) = +4dBi effective receive gain
  • A 6dBi difference.
• Moral of the story? A better antenna/mount improve both transmit and receive and is generally more useful than just more transmit power.

Antenna gain? Shape? Beam?
Hang tight, this is where things got a little harder to understand for me and certainly harder for me to explain. If you want to skip this, just remember: 2dBi antenna for steep terrain, 5+dBi antenna for flat terrain. Let's start by asking, what does the radio wave "look" like? Let's start by imagining slipping a wedding ring over our vertical antenna, so that the center of the wedding ring is at the center of the antenna. This is how a pulse of radio signal starts at the antenna - as a ring around the center of the antenna. The radio signal then propagates away from the antenna at the speed of light, but it generally retains this basic shape of a ring. We talk about "high gain" (5dBi+), "low gain" (2-3dBi), or "omni-directional" (0dBi) antennas - and that tells us something about the shape of the signal ring. For extremely high-gain antennas, the signal ring is squished flat in the vertical direction and spreads out like a circle from the antenna, effectively focusing the power of the signal at the circumference of the circle. For extremely low-gain antennas, there is not squashing and the signal spreads out like sphere from the center of the antenna and much of the signal power is lost to straight up. If we look at the antenna from the side to see the cross section of the signal as it spreads out from the antenna for different gains, they looks something like the following with high gain antennas having a very flat "beam" and low gain antennas having a "taller" beam (the black thing in the middle is supposed to be the antenna, and the gray is supposed to show where the expanding ring of signal would go):

View attachment 165000

Why does this matter? It goes back to terrain.The antenna beam patterns are shown for vehicle in the center of the diagram below. On the hill, the vehicle on the left and right are "in" the antenna beam of the center vehicle for a 3dBi antenna (they can hear him), and NOT in the beam of a 6dBi antenna (they can't hear him). On flat terrain, the vehicle on the left and right are too far away for 3dBi antenna to reach (they can't hear him because the antenna wastes too much signal power spreading high and low), but the are within the pattern of the 9dBi(left) or 6dBi(right) antenna (they can hear him, because the signal power was more focused and reached further).

View attachment 165001

Would this work for a start on an FAQ? What needs clarification and what needs to be added? (or should I just stop before I annoy folks?)

Thank you for this far reaching explanation of this issue (antennas). The problem was not as much with your explanation as it is with plain old stupid on my part. All hobbies have terminology that has to be learned. It reminds me of the time I said something about the rear end in my car to my wife and she thought I was joking. I knew she wouldn't know what a differential was for sure or the Butt of a rifle stock. It's all in the terminology to me and when I see an abbreviation I'm instantly lost not knowing what is common knowledge to those familiar with their hobby or trade. It will never be a hobby to me, it's more like a trail travelers necessity and just a handy means of communication.

Thank you again, you do know your stuff and all of us in OB need your knowledge and patience. I sure hope we camp together sometime so I can learn from you.

 

[Lanlubber In Remembrance]

Y’all are talking about antends farms like they’re a bad thing!

this is for hf/vhf/uhf ham, plus gmrs, plus CB.

View attachment 165014

No comment other than your rig looks like the CIA in the boonies checking us out.

 

[Sasquatch SC]

No comment other than your rig looks like the CIA in the boonies checking us out.

He's really playing up the ex-police vehicle. I bet you see more brake lights on the highway than the rest of us!