Mobile Beam Antennas

[Grump]

Can any one tell me what is the purpose of having a beam antenna on a car. seems to me they are to directional to really do any communicating on. was following on the other day and seen the guy talking but wasn't on his channel so didn't hear nothing then when i got a little in front of him he pegged my meter when i was on 19 and thru searching he was on the bowl so he was using a lot of power.

[jessejamesdallas]

They are directional...That's why guys run them. Usually to get more forward signal in shoot-outs. (competitions)

[linx]

The problem with mobile beams, is they lack the physical SIZE to get any real job done. Are they directional? Sure. Does it really make much difference? No. It's almost just like taking your standard antenna and making it point in one way. I don't think there's any true antenna gain. Take a real base beam like a Moonraker. The element length is 18 ft long...which is 1/2 wave. Each element works together to make it directional. Last I looked, the physical elements on most mobile beams is about 1 ft long. This, to me, is like thd difference in a rubber duck antenna and a 102" or Pred 10k. The rubber duckie just isn't making to make the cut.

[Mr B]

The problem with mobile beams, is they lack the physical SIZE to get any real job done. Are they directional? Sure. Does it really make much difference? No. It's almost just like taking your standard antenna and making it point in one way. I don't think there's any true antenna gain. Take a real base beam like a Moonraker. The element length is 18 ft long...which is 1/2 wave. Each element works together to make it directional. Last I looked, the physical elements on most mobile beams is about 1 ft long. This, to me, is like thd difference in a rubber duck antenna and a 102" or Pred 10k. The rubber duckie just isn't making to make the cut.

If an antenna is directional than there is gain.
One "s" unit can win or lose a key down contest but is not much to your ears.
Most mobile antennas are directional due to the way they are mounted in relation to the ground plane of the vehicle but the gain is low.

[drdx]

Something can be directional and not have gain, but you really need to define what gain is being compared to. Is it a dipole, a coathanger?? Gain is a function of focusing the signal in a direction but not all directional antennas have gain. Would a 2 hot dummy load have gain? No, but it would have a directional pattern and I guess you could say it had a few db gain in one direction over a single dummy load.

I like my stuff slightly directional for skip, so i can block out unwanted signals to a certain degree when it is really crazy out there, but I don't want the pattern too narrow. I want to be loud from georgia up throught the carolinas for example, and not strong in georgia and weaker to the north, not that it is that directional, but you get the picture.

-drdx

['Doc]

The whole point (and the only one) to using a directional antenna is to make the signal tend to go in whatever direction the thing is pointed. So, it's certainly possible. As to why it's done, well, that's up to the one doing it, right?
- 'Doc

[Mr B]

Something can be directional and not have gain, but you really need to define what gain is being compared to. Is it a dipole, a coathanger?? Gain is a function of focusing the signal in a direction but not all directional antennas have gain. Would a 2 hot dummy load have gain? No, but it would have a directional pattern and I guess you could say it had a few db gain in one direction over a single dummy load.

I like my stuff slightly directional for skip, so i can block out unwanted signals to a certain degree when it is really crazy out there, but I don't want the pattern too narrow. I want to be loud from georgia up throught the carolinas for example, and not strong in georgia and weaker to the north, not that it is that directional, but you get the picture.

-drdx

Lets not muddy up the water here.
A dummy load is not an antenna.
It is not intended to radiate RF energy but to displace it as heat.

I dont know how many here are really interested in how this works but I will reply for the benefit of the ones that do

Gain is a technical term. (meaning that it is well defined)
It is a measurement based on a reference that is a known and accepted standard.
A resonant wire in space that radiates RF energy equally in all directions (picture a dot with a ball of energy around it)
is the true standard when measuring antenna gain.
If you wish to confuse or trick someone, you make up your own standard and use that to measure gain.
Many antenna manufactures do just that to make their antenna look better on the spec sheet.

Simply put ...
An Omnidirectional antenna transmits its energy equally in all directions toward the horizon.
Your radio only has X amount of power to send to the antenna ... so ...
If the radiation pattern is altered to project more power in one direction, that power must be taken away from some other direction.
In the favored direction there is a measured amount gain and in the direction it came from there is a measured amount of loss.
Most antennas will exhibit the same pattern for receive as they do for transmit.
This is how a beam antenna works.
It reflects the power from the back side, directs the power from the sides, and projects it forward (transmit) resulting in gain in that direction and loss in the others.
It also attenuates incoming signals (receive) from the back and sides and also reflects it into the driven element because of its design.

A vertical antenna achieves gain by compressing the energy from the top and the bottom (remember the ball in space)
of the pattern and redirecting that energy toward the horizon (now picture a donut).
The more it can compress the ball pattern and shape it into a donut pattern the more energy it will project toward the horizon
and the more gain it will have.
This is what is at work when your vertical, mobile or base antenna exhibits gain.
It is taking the RF energy that normally would be directed toward the ground and up into the air and redirecting it toward the horizon.

Since there is no such thing as a perfect antenna (the reference) all antennas have some gain in some direction.

I urge anyone that is interested in antenna theory to seek information and study this subject.
A good place to start would be the ARRL dot ORG site.
Hams have been experimenting with antennas for many years and what they have learned applies to CB as well.

[Grump]

I just wondered why they use them in mobiles. When you want to talk to someone you almost have to stop and finish your conversation cause unless it is on a mount that you can rotate you will loose signal when you make a turn. Thats what I was wondering I guess you guys answered that. Mostly for compitition

[drdx]

I am a ham, and believe me, it means nothing in reference to my technical ability. There are a bunch of hf operating hams out there that can't calculate simple theory or even make a dipole without a buddy. All the ham license means is that you studied and retained information long enough to pass a test at one time. I've dogeared my arrl antenna handbook in America's favorite reading room, lots of good information there. Most of the time, gain is expressed in either dbd(dipole) or dbi(over an isotropic), which is imaginary and 2.1 less than dbi, so a dipole has a said 2.1 dbi.

I guess in the most common application, gain is expressed in what you get over a single element, or antenna, for a given application. For a mobile, if you had a 102 inch whip and wanted to phase some coax and spacing with another radiator, say another 1/4 wave, 1/8 apart, with say 135 degrees of coax delay phasing(derrived from the true velocity factor of the coax, not from a tech sheet, but from an anlyzer), you could get some gain, not the 4.1 textbook perfect deal, but some.

That said, yeah, the directional deal is primarily for competition, but I use it because I'm a little out of town, and for skip. Here in North TX, nothing spoils skip worse than a full meter of southern based spanish pepperbellies filling your receive.

-drdx

[PONY EXPRESS]

Something can be directional and not have gain, but you really need to define what gain is being compared to. Is it a dipole, a coathanger?? Gain is a function of focusing the signal in a direction but not all directional antennas have gain. Would a 2 hot dummy load have gain? No, but it would have a directional pattern and I guess you could say it had a few db gain in one direction over a single dummy load.

I like my stuff slightly directional for skip, so i can block out unwanted signals to a certain degree when it is really crazy out there, but I don't want the pattern too narrow. I want to be loud from georgia up throught the carolinas for example, and not strong in georgia and weaker to the north, not that it is that directional, but you get the picture.

-drdx

If you phase 2 Dummy Loads together in proper phasing you can have approx 3 db gain over a dummy load less loss in the coax
phase 8 of the rascals together and you have 9 db gain over a Dummy load minus coax losses .

But no actual gain as DRDX said over a dipole DBD or DBI

[drdx]

Well, a dummy load plugs into a transmitter, offers an acceptable load, and although it doesn't radiate far, it does radiate, so I'd call it an antenna. In fact, some of the short fiberglass antennas are so inefficient that I'd almost call them partial dummy antennas. Way back, I used to have a local by me that could hear me talking into my dummy load if his beam was pointed my way, and he was several blocks over. I consider anything that I transmit into an antenna, and in my case it may be a mobile antenna, my tree wire, or my favorite, the big 120 foot long metal fence that borders my yard.

If I was on my dummy load and someone in my front yard hears me, and says "what kinda antenna are you running?" I wouldn't say I don't have an antenna, or otherwise he wouldn't hear me.

It would be funny to get a field strength meter and phase delay a couple of dummy loads just to see if you saw a pattern or if they would just radiate due to lack of ground.

-drdx

[North Texas Mudduck]

let me narrow down the search here

are we talking about a stargun beam
you can say it S T A R G U N

if this is what your refering to lke said before it lacks the size.

now if we talking about a hot 10k on the back of the suburban and then another one up front that hot
sure we can see around a 3 to 5 s-uints differnece than from just one antenna

now a bounce back where the rear is grounded either with cap or solid ground
then the front hot also you can see gain from 3 to 5 s-unit increase

what did this antenna look like

[Grump]

let me narrow down the search here

are we talking about a stargun beam
you can say it S T A R G U N

if this is what your refering to lke said before it lacks the size.

now if we talking about a hot 10k on the back of the suburban and then another one up front that hot
sure we can see around a 3 to 5 s-uints differnece than from just one antenna

now a bounce back where the rear is grounded either with cap or solid ground
then the front hot also you can see gain from 3 to 5 s-unit increase

what did this antenna look like

It looked similar to the stargun single antenna beam was close to the base of the antenna

[North Texas Mudduck]

did it have a shaft coming from antenna mount then like 3 or 4 elements then a coil sitting on top

[Grump]

to me it was weird looked like a normal coil type antenna (10k or mm) but had a four element beam on it

[North Texas Mudduck]

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is this the tinkertroy you be referring

[Grump]

close but the elemnts were lowerer and coil was higher but yeah

[North Texas Mudduck]

Well then i got one word for it

Crap

not trying to sell another antenna or hate the guy building them

but Crap

i have been there done it and worked over 1 1/2 years trying to get it to work
even drove from lubbock texas to longview texas
just because troy said he would help me with it
i got there and he didnt even want to lift a finger
i lifted my finger to him and introduced stargun antenna to mr tree on the northwest side of the raddison hotel

im going to stop my soapbox on this subject is alot taller than im going to step up on today

but to answer you question it does not work

swr my be 1.1 or 1.2 it may look cool and neat and parts can change out
but for it being a beam design and it trying to be a directional beam
its not working in that department

did i mention what one word explains it

[drdx]

I actually spotted one of those Starguns in New York City while on vacation, on a big truck.

Funny stargun story time: There is also one here local to me, on a mag mount this guy made, that is 2 magnets and a big flat piece of metal, the mags situated front and rear, what an idiot. He runs an old 4 pill 455( a hurricane or something from the early 80's) box and thinks he's on top of the world. I by chance ran across him one day in traffic by accident. I turned on my radio really quick and rattled his relays as I passed and he got a little irritated, but it was funny. He can't be doing too much because he never rattled my relays and on a tx star, they rattle easily in close proximity to serious RF.

-drdx

[linx]

LOL, what did I get started.

The reason to "two hot" setups work, and have so high of S-unit gain is due to them being almost, or at full 1/4 wave antennas. So, I can see where the "two hot" setup could be considered a simple 2 element beam and would be directional.

The stargun is directional, as is other mobile antennas, but I don't believe them to have any real gain just b/c they are directional. The directional part works just fine. I've seen them on the road, and talked to users that run them on the road....but that doesn't mean my single omnidirectional can't walk all over them with running the same power. I mean, a 4" element on something like a stargun vs a 9 ft element on a real base beam like a Shooting Star or Moonraker. It just lacks the physical properties to make any sense at all.

Run what ya wanna run.

I think this convo started out asking what the purpose of running them is, and I got it side tracked saying it was smoke and mirrors and it has got to the point of where it is now. I appologize for hijacking this thread, lol.

I think we need a drdx fan club.

[Mr B]

I actually spotted one of those Starguns in New York City while on vacation, on a big truck.

Funny stargun story time: There is also one here local to me, on a mag mount this guy made, that is 2 magnets and a big flat piece of metal, the mags situated front and rear, what an idiot. He runs an old 4 pill 455( a hurricane or something from the early 80's) box and thinks he's on top of the world. I by chance ran across him one day in traffic by accident. I turned on my radio really quick and rattled his relays as I passed and he got a little irritated, but it was funny. He can't be doing too much because he never rattled my relays and on a tx star, they rattle easily in close proximity to serious RF.

-drdx

Rattling relays ... that sounds interesting ... please tell me more about how that works.

[North Texas Mudduck]

rf from radio causes the relay to close causing the amp to key up

well when a high power source like another mobile can key up and make the relay open and close or chattering

[drdx]

Yeah, with just a few hundred watts you can roll up on a mobile with an amp on and really chatter them, and "rattle someone's cage" so to speak, fun fun. When I was a teenager we'd constantly operate car to car and would have to roll several hundred feet apart if we were running power or we'd be chattering away. The same went for the local hangouts, where the rule was barefoot, to avoid chattering and TVI.

We also used to do that to irritating base stations just to keep them in line. Nothing says I love you right under someones antenna with a kilowatt on an odd channel like 3a so they don't know what hit them. Then, you roll around their neighborhood, say their handle a few times over all of the neighbor's televisions, and BAM, problem base station solved. Irritate me once, shame on you, irritate me twice, STRIKE 3. -drdx

['Doc]

Some general thingys...

All directional antennas have 'gain'. May not be much, but some. That's because they redirect signal from one direction to another, like a reflector behind a light bulb, sort of. You end up with more light/signal in some direction, but you don't have any/much in another direction. Antennas can not generate/make signal, they just radiate it, direct it.
The size of an antenna is determined by the frequency it's used on. The lower the frequency, the bigger the antenna. Sure, you can 'load' an antenna and make it shorter, but that also reduces it's efficiency so at some point it just isn't worth it anymore. Same for directional antennas or beams. You might make the length of it's elements shorter, but reducing the space between those elements means it isn't going to be -as- directional as the 'full sized' ones. Think in terms of light again. The elements behind the driven element (light bulb) are reflectors. The elements in front are directors or lens. For a lens to work, it has to be at the right distance (focal point) from the light bulb. Same for RF, just a different kind of 'lens'.
It's all frequency dependent! At 2.5 Ghz, you're talking a couple of inches. At 400 Mhz, several inches to a foot. At 144 Mhz a couple of feet. At 27 Mhz, about 8-9 feet. And at 1.8 Mhz, something like at least 120 feet. You can reduce those lengths a bit, but not a huge amount, just ain't practical.
An unbelievable number of 'depends' in all that. They are sort of like the 'depends' you find at Wal-Mart, eventually they get full of '$_._+' and you need to change them. The 'trick' is knowing when to change them, and they sure beat the mess you'd make if you didn't use them...
'Doc

[MUDDUCK MOBILE]

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is this the tinkertroy you be referring

I do not have a MFJ to test what i have heard from several techs in the houston. But i have been told the beam by itself loads up @ 1.0:1 @ 220 megahertz.