Learning about antennas

[TheDude1969]

I have read so many articles from CB sites, I can't stand to see another re-post from 'Firestik'
I've searched and don't find many articles on antenna theory.

I'm a truck driver and get the basics, top loaded is better than bottom, good ground, low SWR, etc

examples of questions:
Why a large center helical design on high dollar antennas?
Why some trucks aim antennas at 45 degrees forward, way beyond wind blown upright angle?
Why doesn't a vertical antenna become horizontal with winding/load?

I hope you get the idea... If you answer these questions, I'd have a hundred more lol. Just point me in right direction to read and learn more pls.

 

[AC9BX]

(27Mhz CB)
The ARRL antenna book is a great resource, although intended for hams and not CB and the topics get quite advanced. You can poke around at wikipedia as well. You may want to try more generic web searches to avoid CB sites. Most of them are either just ads or misinformation. Search for the antenna type. For example a ham may be using a 10M vertical ground plane. Aside from slight changes in measurements this is the same as for CB.
Many commercial antennas, for CB, TV, FM, and more, are hybrids. There is a helical antenna. Then there's using a helical section as part of some other design. Finding information on these are difficult. A common roof-top TV antenna for example is a blend of Yagi and log-periodic and sometimes corner reflector. This is done to get the most out of the least space and metal. They don't follow any basic antenna design.
A big truck is perhaps the worst vehicle to set up a CB in. Clamping to a mirror, with all that trailer behind you and the cab makes for a horrible radiation pattern and can make it difficult to match to the radio. So various attempts are made to correct this such as slanting the thing forward or using 2 antennas with a phasing line to try to create a pattern that projects more forward. Most of those ideas do not work very well, if at all. A better place for the antenna would be in the middle of the roof of the cab. But then it can be too tall to get under many overpasses and of course a trucking company may not be happy about drilling a hole to mount it.

To answer one of your questions, a vertical antenna is only exactly vertical when it is oriented that way. If it bends down in the wind it does begin to become horizontal. However, it really isn't bending very far. It's still mostly vertical. A few degrees doesn't matter much. It will change the impedance match a bit but the polarity won't change much. But there's more, when you're talking about a ground plane or similar antenna used this way if it were laid down horizontally it wouldn't work at all because it's parallel to the counterpoise. It doesn't become horizontally polarized it becomes not an antenna.

 

[sdeeter19555]

examples of questions:
Why a large center helical design on high dollar antennas?
Why some trucks aim antennas at 45 degrees forward, way beyond wind blown upright angle?
Why doesn't a vertical antenna become horizontal with winding/load?

The big coils are looks/marketing (assuming you are talking about something like a Predator 10k or Monkey-Made)...they offer no more performance to the average user than a standard Wilson 1000 or Wilson 5000.

They tilt the antennas forward for height clearance, and looks...nothing more.

WJYSTV62 answered the last one better than I could have...

 

[TheDude1969]

Thank you both!

 

[shortride]

I have read so many articles from CB sites, I can't stand to see another re-post from 'Firestik'
I've searched and don't find many articles on antenna theory.

I'm a truck driver and get the basics, top loaded is better than bottom, good ground, low SWR, etc

examples of questions:
Why a large center helical design on high dollar antennas?
Why some trucks aim antennas at 45 degrees forward, way beyond wind blown upright angle?
Why doesn't a vertical antenna become horizontal with winding/load?

I hope you get the idea... If you answer these questions, I'd have a hundred more lol. Just point me in right direction to read and learn more pls.

1. The helical antenna is designed primarily for a wide banded radio like a Export Galaxy radio. Most of them will handle more power as well.
2. The idea for the angled antenna is because the forward motion of a truck is supposed to keep the antenna straight. I'm not convinced that it make much difference.
3. With an antenna that has smaller diameter more flexible element some people think that those antennas are prone to cause the transmitted signal to change its polarity. If you will notice sometimes a mobile radio signal will fluctuate when your listening. A lot of the reason for that is the mobile unit is going between buildings, trees and other things that affect their signal while they are talking.

Note: Most of what you see people do with their CB radio and antenna usually will not do a lot for performance. The most important is to keep the SWR's down, keep the coax tight and maintain a well tuned radio.

 

[prcguy]

A helical wound antenna has nothing to do with wide band radios and if anything it has less bandwidth than some other antennas. Antenna BW is measured and displayed as a "Q" factor. Antennas that are closer to a 1/4 wavelength without any loading will have wider BW than a loaded antenna. Larger diameter conductors and coils can help increase BW. Placing the loading coil near the middle of the antenna is best and base loading incurs a bit more loss since most of the RF current is in the base of the antenna and the coil is lossy.

You can be line of sight and looking at a transmitter and still have fluctuations while driving. This is not because the direct signals are getting weaker and fading, its because the reflected signals (multipath) are causing a phase cancellation with the direct signals.
prcguy

1. The helical antenna is designed primarily for a wide banded radio like a Export Galaxy radio. Most of them will handle more power as well.
2. The idea for the angled antenna is because the forward motion of a truck is supposed to keep the antenna straight. I'm not convinced that it make much difference.
3. With an antenna that has smaller diameter more flexible element some people think that those antennas are prone to cause the transmitted signal to change its polarity. If you will notice sometimes a mobile radio signal will fluctuate when your listening. A lot of the reason for that is the mobile unit is going between buildings, trees and other things that affect their signal while they are talking.

Note: Most of what you see people do with their CB radio and antenna usually will not do a lot for performance. The most important is to keep the SWR's down, keep the coax tight and maintain a well tuned radio.

 

[Sportster77]

Howard Sams published a book called Citizens Band Radio handbook by David E. Hicks. It is an older book and I don't know if it is still available, my copy is a 4th edition 6th printing from 1975. It may answer alot of your questions.