Hi Seyit,
You are asking questions that everyone ponders when they get involved with radio. Even though I am no expert I have been a licensed ham since 1965 and I'm still learning but will throw in my 2c worth anyway.
What is an antenna? It's a means to couple radio waves into the atmosphere. Some forms of antennas work better than others for some jobs, like a 1/4 wave vertical radiator above a ground plane works great when you have a moving mass of metal to use as a ground reference, like a truck. Or consider a dipole which is a half wave fed in the middle and not requiring a ground (even though the real ground highly effects it). Now add umpteen other shapes and forms of antennas to the list, all having unique characteristics. It gets complicated. Let's stay simple here.
Since most interest here is antennas on vehicles, and a ground plane antenna lends itself to vehicle mount, lets start there.
Your AB-15 mount and length of elements is a good example. The goal is to provide best coupling into the antenna at the frequency (or narrow frequency range) of interest.
The difference between operating on one frequency, and desiring to operate on multiple frequencies becomes the complication. The antenna can be resonant on one frequency (and odd multiples) but it cannot be resonant on all frequencies. The result is deviation from a usable feed point impedance.
For operation on one frequency (or narrow band like CB) the 1/4 wave antenna can simply be tuned for resonance. We want to have the radio "see" about 50 Ohm's resistance (non-reactive) at the frequency we operate. Why 50 Ohms? Check this out:
http://www.belden.com/blog/broadcastav/50-ohms-the-forgotten-impedance.cfm
So our radio is mounted to the truck (mechanically grounded to it, but does not have to be), we run a piece of coax to the base of the AB-15 and its whip, hook it up and apply RF power. We don't ground the antenna end of the coax shield. What radiates and what does not? The part of the antenna 'system' that radiates the most to the atmosphere is the part above the metal surface of the truck. But there's also radiation from the coax outer conductor inside the truck.
By grounding the far end of the coax shield we allow the coax to do it's job by defining "where the antenna begins" with that ground. Everything before that grounded point is now forced to be non-radiating 50 Ohm transmission line. That's why a complete AB-15, or any other antenna base (with exceptions, later) has to have a ground. Any CB whip antenna will also be grounded at the fender, unless thwarted by heavy paint.
With the correct ground at the antenna, the antenna performance can be tuned. But, the meter we use has to be installed at the base of the antenna for best results! Why? because the Forward power and reflected power, SWR, (standing wave ratio), or Return Loss, whatever we measure, will vary all along the length of the coax, and the length of the coax is critical to what the radio sees. I'll just call the measurements the SWR.
So, how do we handle that coax stuff? Most of us just cut whatever length we need, install the antenna, install the radio, and cut the antenna so the radio likes what it sees. An SWR meter installed at the output of the radio will tell us that. We have tuned not only the antenna but the coax, too. We might have tuned the coax to operate at a different impedance and losses might have gone up, but we really do not care. The radio will work and nothing will smoke.
Ideally we would cut the coax to a length such that there is an odd multiple of half waves at the frequency of interest, inside the coax. That's a mouthful. Couple of important words there: The "frequency", and "inside". Most of you have heard the term 'velocity factor'. That's the fudge factor we have to multiply by to calculate the actual length of a wavelength of a specific frequency, inside the coax. That number varies from around .5 to about .8. Specifications on the coax will tell us a number that's usually close enough if we want to trim our coax length for perfection.
Ever wonder why a standard CB antenna usually came with about 17 ft of coax? At least they used to come that way before "economy" of coax overtook engineering. 17 ft is roughly the length of a multiple 1/4 wave at about 27 MHz (trust me, or ask me LOL). The manufacturers wanted you to see the SWR at the radio that is presented at the antenna.
That sort of covers the "one operating frequency" scenario. What if we want to operate across a whole band, or even many different bands? First, the whip cannot be tuned to multiple frequencies at the same time, the impedance at the base of the antenna will not be 50 Ohms, and there is no resonance of the antenna.
This is where a coupler comes in. Call it a coupler, antenna tuner, antenna matcher, whatever the name, the purpose is to transform the impedance seen at the base of the non-resonant antenna into something close to the radio's 50 Ohms. With such a miracle device we can theoretically operate that whip antenna on multiple frequencies.
Seyit, you mentioned TUAAM, and other names for antenna matchers. That term is common with the British Clansman radios and means 'Tuning unit automatic antenna matching'. We might know of the more common matcher in the base of many USA VHF radio antennas like the AS-1729, AS-3900, and others. Note that "automatic" in most cases does not mean the tuner actually does anything on it's own. It has to be pre-tuned by a human then the suitable band is switched by the radio. Some, like the AS-3900 are fixed tuned and do not switch. They work like ^%$# too.
Earlier I said that an antenna base does not have to be grounded and may not be at 50 Ohms. Some radio installations do not force the radio to output 50 Ohms, or for the antenna to present a 50 Ohm load. A good example would be an old RF-302 antenna coupler that connects directly to the base of a whip antenna and actually does a good job of matching it across a wide range of frequencies. No '50 Ohms" applies in this case, and the feedpoint of the antenna is not grounded.
To specifically answer your questions, by number:
1) To use an AB-15 and it's whip on CB you do not need a balun. The antenna system is unbalanced end to end and no conversion to 'balanced' is needed. If you want to put a dipole on your CB, as in camp, where ever, then a balun at the feedpoint of the dipole is a great idea.
2) That is correct. If you want to operate an antenna as a non-resonant antenna on multiple frequencies, then the tuner can allow you to move around in frequency and still have a reasonable match to the antenna.
3) Great question. In most of those cases of antenna paraphernalia, you can use those on any antenna system, military, ham, or commercial. Just analyze what the military device does and use it instead of the commercial/ham counterpart. You will find, though, that many military devices have unique mounts, unique shapes, or require specific connection types. Weight and cost are not insignificant either. Military parts can get expensive when they are in short supply.
Bob WB4ETT
Sorry all for my questions,but ; I come accross with " Baluns " and " Tuners" while I'm going through this issue.
1.How necessary is a balun while adopting a military antenna(MS-116,117,118 and base (AB-15) to a CB?
2. So far as I understand some tuners are used only to adjust the SWR and then put aside while some others are installed handy in the system to apply to the changing conditions,right?
So I am thinking to dissmiss my present VHF CB and buy a HF/VHF/UHF one.
In that case do I have to install (or had better)one of them in the system ?
3.Will I be able to use some military type baluns and tuners such as VHF Automatic Antenna Tuning Unit " TUAAM ", "ARFAT" RF Antenna Tuning Box,Clansman Initiate Box,Center Junction Dipole Balun,Clansman PRC-319 Dipole Balun,Clansman PRC-320 Dipole Balun etc?
Are these for some specific military radio models or for general use? If specific ,do I have to go for some civillian models? ( If all necessary of course)
and base (AB-15) to a CB?
