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Custom CB Antenna: Pointless or Potential?

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Blenderite

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I just got my CB setup installed and working properly, with a Firestik. I am perfectly happy with the antenna, but curiosity has gotten me thinking.

Is there a better shape than a straight up and down rod?

Yes I know that I am probably over thinking this (Don't fix what ain't broke, right?). But coming from an RC background and using all kinds of different antenna types, I can't help but be curious. I asked Google and didn't find anything about it on there. I have heard that a coat hanger would receive, but not transmit hardly at all, due to the length. I am guessing that has to do with the length.
 

mmckenna

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Radio waves tend to travel in straight lines unless the bounce off something. "Polarization" of the antenna plays into this. RF energy radiated by a vertically polarized antenna (what you have) will be picked up better by another antenna that is in the same orientation, in most cases.
So, since most CB'ers tend to use vertical antennas, you'd want yours to be vertical too, at least if you want the best performance.

There are those that will use antennas mounted horizontally, as that tends to follow terrain better, especially on lower frequencies, but again, depends on what it bounces off of.

So, ideally you want a vertical antenna. Pretty much any other shape is going to distort the polarization and result in less signal being picked up by other users. Also, a horizontally polarized antennas at CB frequencies gets to be a bit cumbersome. Actually a lot cumbersome.

As for length, the antenna length decides what frequencies it works best at. Sort of like a musical instruments. A ukulele with short strings makes a high note. A big ol' bass with long strings makes a lower note. Same goes for antennas. Short antennas work on higher frequencies. Long antennas work on lower frequencies.

There are "tricks" you can use to shorten antennas, but it comes at a cost of lower performance. What you'll see in the RC world, and even consumer two way radios, is that shorter antennas are preferred for convenience, with the known drawback of shorter communications range. Unfortunately most consumer don't understand this and base their decisions solely off looks rather than technology/science.

Good questions though.
 

Blenderite

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Radio waves tend to travel in straight lines unless the bounce off something. "Polarization" of the antenna plays into this. RF energy radiated by a vertically polarized antenna (what you have) will be picked up better by another antenna that is in the same orientation, in most cases.
So, since most CB'ers tend to use vertical antennas, you'd want yours to be vertical too, at least if you want the best performance.

There are those that will use antennas mounted horizontally, as that tends to follow terrain better, especially on lower frequencies, but again, depends on what it bounces off of.

So, ideally you want a vertical antenna. Pretty much any other shape is going to distort the polarization and result in less signal being picked up by other users. Also, a horizontally polarized antennas at CB frequencies gets to be a bit cumbersome. Actually a lot cumbersome.

As for length, the antenna length decides what frequencies it works best at. Sort of like a musical instruments. A ukulele with short strings makes a high note. A big ol' bass with long strings makes a lower note. Same goes for antennas. Short antennas work on higher frequencies. Long antennas work on lower frequencies.

There are "tricks" you can use to shorten antennas, but it comes at a cost of lower performance. What you'll see in the RC world, and even consumer two way radios, is that shorter antennas are preferred for convenience, with the known drawback of shorter communications range. Unfortunately most consumer don't understand this and base their decisions solely off looks rather than technology/science.

Good questions though.
Thanks!

What I was thinking is copying this style over to cb.



It would give the vertical as well as other angles. Based off what you said, I'm assume that there would be no benefit to the extra angles correct, even if you managed to give each one a proper ground plane consistent with its angle?


Here is another thing I thought of. What would happen if I connected multiple antennas together, say five? Have I gone off the rails?

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movinon

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Would catch ice well in winter...

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KC3ECJ

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A horizontal V 1/4 wave dipole over the bed of a pickup worked fine for me.
 

mmckenna

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Thanks!

What I was thinking is copying this style over to cb.

That looks like a circular polarization antenna commonly used for GPS and other satellite communications modes. It's designed to send most of the signal upwards. One designed for CB would be pretty large and likely not fit on a pickup.

It would give the vertical as well as other angles. Based off what you said, I'm assume that there would be no benefit to the extra angles correct, even if you managed to give each one a proper ground plane consistent with its angle?
Like I said, it would send the power mostly upwards. Wouldn't work so well for mobile use. What you can do with an antenna that sends power mostly upwards towards the sky is do what they call Near Vertical Incidence Skywave (NVIS). That's where you bounce your signal off the atmosphere directly above you so it reflect back down. It's great when you need to cover an area directly around you without sending power off towards the horizon where it tends to ricochet off the atmosphere and "skip".
When I was in the USCG they had a large radio station on Kodiak Island. They could talk all over the North Pacific ocean easily, however coverage a few hundred miles away was crappy since it was not in direct line of site of the antenna, but not far enough away to catch the skip bouncing off the ionosphere. To help with coverage closer in around the island, there was another transmitter a few hundred miles away with a NVIS HF antenna that filled in the dead areas.

Problem is, a 4 watt CB radio isn't going to have enough power to really make it work well. Also FCC still has a rule on the books about how far you are allowed to communicate with a CB. An odd rule, but at one point it made sense to someone.


Here is another thing I thought of. What would happen if I connected multiple antennas together, say five? Have I gone off the rails?
Depends on how they are positioned and how they are fed. AM broadcast stations do this to make their signal directional. Usually you'll see 3 tall towers in a row. This is done to send their signal in a figure 8 like pattern. It takes a lot of engineering to do right. Antennas need to be fed in phase using tuned lengths of coax.

Used to be a guy near where I worked a long time ago. He had 3 CB base verticals in his backyard. I don't know for sure what he was doing, but I suspect it was a directional array.

Feed them out of the correct phase or in a funny pattern and all bets are off.
 

JayMojave

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Hello B+10: you said

"Is there a better shape than a straight up and down rod?"

No straight up and down is vertically polarized, just like all the rest of the CB world. If you used such a antennas as shown you will lose -3 dB and then some as it appears circular polarized as said by others here. If you used a horizontal antenna you would be down -20 to -30 dB from the vertical CB crowd.

If you installed a linear amplifier that would increase your transmitting range somewhat, but even at ten times the original power is only +10 dB which would more than double your transmitting range. Good luck.

Jay in the Great Mojave Desert
 

wa1nic

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For local work you definitely want vertical.

For DX, maybe you want both. When skip bounces it's polarity gets messed with. It may or may not come back down the same way that it went it. Circular polarization might have some advantages at times. Selectable polarization might have an advantage sometimes as well.
 

JayMojave

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Yeah what NIC said: I use to run a Moonraker 4 element yagi beam antenna that used a quad reflector and yagi type elements for both vertical and horizontal polarities.

Monitoring the incoming skip switching from the two different polarities (vert and Horiz) I could see significant increase in received signal strength or decrease in received signal strength when switching between the polarities.

So now modifying a modern design 5 Yagi element beam to have both Vertical and Horizontal elements, the trick will to use a Haipin Matching system for both polarities.

Jay in the Great Mojave Desert
 

mm

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That's a quadrahelix antenna.

It's hard to tell the frequency but most likely gps 1575.4 MHZ.

For cb that antenna would be 58 times larger.

Also the radiation pattern is off the top of the antenna as it is designed for overhead satellite use.
 
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