Best Moblie Antenna for OTR Truck

[M0GVZ]

Someplace there would have to be loss or the signal source would have to not transfer the same energy, and we all know (or should know) reactance is by definition lossless.

That loss is in the feeder. It is why many amateurs over the years have had antennas with quite significant faults on them but been completely unaware because they've had a long cable run and the losses in the coax have masked the fault and presented a low SWR at the radio end.

much of the information that is out there is beyond the understanding of most hobbyists, which, lets be clear about this, is who you are talking to here.

Talking beyond not only what someone can understand, but also beyond what they are willing to consider will do them no good, and more often than not will turn them off to listening to what you have to say. You have to remember, most people here are not engineers, talking to someone who doesn't understand what you are trying to say, and doesn't know enough to get from where they are to what you are saying, doesn't help them at all.

Which is why my answers are simplified on this forum. I will admit that sometimes when trying to think of a way of simplifying a concept I'll make a mistake but that is because its not always easy to break down things to a level that someone with little or no theoretical knowledge can understand, especially when you're trying to come up with an analogy because for many people antennas and RF almost work like voodoo magic.

Its unfortunate that people on this and other boards I'm on take the fact that I try to reply in simple layman terms as evidence and ammunition that I don't know what I'm on about. If I didn't know what I was on about I'd not have a wall of first place certificates in worldwide amateur radio contests and consistently be in the top 20% scoring higher than stations running 1.5kW with antenna farms despite only having what is a quite mediocre station running 100W that pretty much anyone could put up.

 

[543_Dallas]

Lol..... nothing like some humor.
I think its best you and i sit back and Listen.

CTR wrote the book on this stuff.
Problem is he has very limited time.
The Db has the knowledge to ask the correct questions , especially for LEARNING.
That should be the Key here.

I don't take much of this too seriously anymore. CRT does seem like a sharp guy. If for some reason your 2.5:1 balun is the only way to get a match I say use it to keep feedline loss down and give the transmitter what it needs. If your purposely detuning a 1/4 wave cb antenna only to use a balun to correct it you are wasting resources. Not saying it won't work but it isn't necessary. Read post #65 paragraph 3 very closely.

 

[CTR]

Does a antenna receive better at resonance ?

First of all, using the word "resonance" is pointless. I'm not sure where that came from, but it is a nebulous parameter. By definition resonance is when voltage and current are in phase, or when reactance is zero. So what do you call "resonant"? Do you mean when the imaginary part of the feed point impedance is zero? When the voltage and current are precisely in phase, or do you still call it "resonance" when they are 10 degrees out? How about 20?

If you are asking if receiver S/N level peaks for receiving weak signals at resonance, the answer is absolutely not. S/N ratio in a typical system operating below UHF is determined by antenna pattern, not even antenna system (including feedline) gain or loss, until system internal noise starts to be a significant part of signal level.

You'll see people who have not thought this through, and there are plenty of them, make claim "reciprocity" means if the TX signal is 1 dB better, so is the receive. While that is true in a lossless system, and mostly true in most systems so far as level changes, it is absolutely not true for signal to noise ratio (or actually copying people) in systems that are limited by external noise or interference. This is especially true on HF and with wide azimuthal patterns in antennas.

Most low-noise high performance HF receiving systems have negative gain, or little regard for "gain". The focus is on reducing unwanted signals and noise through antenna directivity, by placing pattern nulls in the direction of noise and allowing the most response only in the direction of a desired signal or signals.

Like most people who are really "into" weak signal work at HF, my receiving antennas have negative gain and are not resonant. Their primary parameters are to provide enough signal level so propagated noise and QRM comfortably sets noise floor, and the directivity (NOT gain or resonance) focuses response on the desired direction.

If I take a three foot non-resonant whip out in a field thousands of feet from any local noise source and use a good amplifier, the signal-to-noise is not noticeably different from a 130 foot vertical from VLF all the way up to around 5 MHz. Above that the 130 foot antenna's **directive pattern** can influence things by nulling some noise or interference sources though a pattern difference.

This whole thing about trying to make "resonance" an important parameter is ridiculous. In over 50 years of being in radio, this "adjust for resonance" question is a first for me. It is a real puzzlement why anyone who knows anything about how radio and antenna systems work would focus on that. Perhaps somewhere someone made a true statement that was misconstrued, and it took off with a life of its own to where it means nothing like the original statement.

 

[CTR]

Loss in a given feedline is determined by SWR, and if the feedline is real short (less than 1/2 wave or so) by the direction of mismatch.

On receiving, the receiver sets the feedline SWR and resulting feedline loss from mismatch. But it is largely unimportant.

On transmitting, the antenna is the termination and sets the feedline SWR for a given feedline.

Stop the resonance nonsense.

 

[The DB]

First of all, using the word "resonance" is pointless. I'm not sure where that came from, but it is a nebulous parameter. By definition resonance is when voltage and current are in phase, or when reactance is zero. So what do you call "resonant"? Do you mean when the imaginary part of the feed point impedance is zero? When the voltage and current are precisely in phase, or do you still call it "resonance" when they are 10 degrees out? How about 20?

This goes along with what many people say about resonance, but it is at best incomplete. I would expect someone who understands what noise temperature is to know this.

You'll see people who have not thought this through, and there are plenty of them, make claim "reciprocity" means if the TX signal is 1 dB better, so is the receive. While that is true in a lossless system, and mostly true in most systems so far as level changes, it is absolutely not true for signal to noise ratio (or actually copying people) in systems that are limited by external noise or interference. This is especially true on HF and with wide azimuthal patterns in antennas.

No one here, and as far as I am aware no one ever said reciprocity had anything to do with the noise floor. Did you read this in to what someone said?

Most low-noise high performance HF receiving systems have negative gain, or little regard for "gain". The focus is on reducing unwanted signals and noise through antenna directivity, by placing pattern nulls in the direction of noise and allowing the most response only in the direction of a desired signal or signals.

This is true, I have worked with some myself. I don't see how your point relates to what people are actually talking about however.

Loss in a given feedline is determined by SWR, and if the feedline is real short (less than 1/2 wave or so) by the direction of mismatch.

This is assuming that everyone uses the right feed line for the job, which in this world is not always the case. You are also assuming that the feed line isn't damaged by a door closing on it all the time, water intrusion, ect. All of these can cause the system to present an even lower SWR than what it would normally present. You also have people that will get the cheapest chinese coax that can find and run 200 feet of that to their first base antenna. All of these things can, and often will, show a lower SWR than what the antenna has, sometimes significantly lower.

On receiving, the receiver sets the feedline SWR and resulting feedline loss from mismatch. But it is largely unimportant.

On transmitting, the antenna is the termination and sets the feedline SWR for a given feedline.

What you are saying here is absolutely true, but is also completely irrelevant to this conversation. As I mentioned above, the two SWR readings will, by definition, be the same. You who understand that the receiver sets the feed line SWR should also understand this as this is based on principles that are more basic than what it takes to realize that when receiving the receiver sets the SWR. Something else to note, and make this point that you are harping on even less relevant, when receiving, SWR is far less important than when you are transmitting (because you don't have to worry about damaging a radio), and makes almost no difference. Look, for example, at scanners, or shortwave receivers. The antennas used for these devices have nothing even resembling a good SWR for at least most of the bandwidth they are used on, and they still work fine. If you are going to harp on something like this, please at least make sure it is relevant to the discussion at hand...

Stop the resonance nonsense.

In paraphrasing what you just said, stop this SWR nonsense. By your own words, (not me twisting your words but how you chose to word it) it is just as irrelevant.

In over 50 years of being in radio

Fifty years? Good for you. Twenty five myself, not that how long people have been in radio is actually relevant here. I know people that have been around longer than even you and know really not much more than many beginners. I also know people that have been around for less than five years that know a surprising amount of information. Often when someone makes a claim like this they are using time in the field as a stop gap in place of putting out actual knowledge. It is a cop out. If you can't stand on and explain your own knowledge and have to rely on such crutches as years of experience with radio, is your knowledge really any good? If you really need a crutch, quote a relevant source that backs up what you are saying. How about this as an example...

THIRD, we should become more familiar with the universally known, predictable behavior of off-resonance antenna-terminal impedance and its correlation with SWR. This knowledge provides a scientific basis for evaluating SWR-indicator readings in determining whether the behavior of our system is normal or abnormal, instead of blindly accepting low SWR as good, or rejecting high SWR as bad.

-Another Look at Reflections, a freely available .pdf file, page 6.

Now I will take a step back from what I just said for a second, but only for one specific reason. Dating yourself to that time frame tells me quite a bit about your likely early experiences with radio, and I can tell you with absolute certainty that what you did and what people getting into CB, and even the radio hobby in general today are doing is very different. What you did then and what they are doing now aren't even similar, the equipment as well. Apples and oranges if you will. The experiences you had to build from are very different than the experiences (and for that matter generally accepted information) available today. If I could give everyone experience like that before they try and set up their first mobile CB antenna, forums like this would not be necessary.

Also, do you expect people to change what they have heard, and in many cases really want to believe, simply because you are you? What do I, a person you are talking to, know about you other than what you type here in this thread? You are not a regular on this forum, so I have no past information to go on, you have harped on something that is a fact, but irrelevant to the discussion at hand and have yet to even try to explain why it is relevant, and you use a fact to tell people to stop doing something, when the fact on its own as you have chosen to word it states that the results one way or the other makes no noticeable difference. If you are trying to persuade or teach something, with all due respect, you are doing a very poor job.


The DB

 

[HARDROCK]

CTR said: ↑
First of all, using the word "resonance" is pointless. I'm not sure where that came from, but it is a nebulous parameter. By definition resonance is when voltage and current are in phase, or when reactance is zero. So what do you call "resonant"? Do you mean when the imaginary part of the feed point impedance is zero? When the voltage and current are precisely in phase, or do you still call it "resonance" when they are 10 degrees out? How about 20?

So if resonance is when voltage and current are in phase or when reactance is zero.

Is this not when maximum power and effieciency is achieved ?

As a system whole , antenna amp coax etc... ?

I think Db is correct your on too high of a level which confuses rather than being of benifit.

Below you quoted ,


There are cases where efficiency peaks near or at resonance, and there are cases where it peaks off resonance. There are cases where lowest SWR might be best, and cases where resonance is best, and cases where efficiency peaks between the two.

So which is it this contradicts what you say about resonance being nonsense ?

 

[HARDROCK]

The reason efficiency peaks is because SWR is also lowest around resonance.

We have to be careful how we word this stuff. It is not resonance that causes the peak, it is also NOT SWR that causes it.

It is a system issue, and SWR cannot be low if the antenna system is not resonant.

BUT, a system can have terrible SWR and poor efficiency when resonant. It can also have terrible efficiency with a low SWR.

 

[HARDROCK]

AA4PB
Member

Posts: 14006


Notice the last paragraph. This explains my case best.



MFJ-259 measuring antenna resonance
« Reply #3 on: December 27, 2006, 07:36:00 PM »

To adjust an antenna to resonance, you adjust it until the reactance is zero. The value of the remaining load resistance is not important as far as resonance is concerned. If you want to have it resonant and a low SWR then you have to provide something to convert the impedance to 50 ohms.

Take a look at a gamma match on a VHF yagi driven element for an example. The length of the element is adjusted to resonance and then the gamma match is adjusted to provide a 50 ohm load.

A short mobile HF whip is another example. If the loading coil is adjusted to tune the antenna to resonance, the load impedance will often be very low (20 ohms or less). A matching transformer at the base is often used to convert this low impedance to 50 ohms in order to provide a low SWR on the 50 ohm feed line.

Note that some of the wound fiberglass whips are pretty close to 50 ohms at resonance. That is because the high losses in the wire and ground system add to the feed impedance. Lets say the impedance at resonance is 25 ohms. If the loss is also 25 ohms then the total impedance is 50 ohms and the SWR is 1:1. Nice match, but half the power is being radiated and the other half is being converted to heat.

 

[The DB]

Hardrock, I have a question for you. Are you talking about HF antennas in general, or are you taking general HF knowledge as ham would need it and trying to apply it to a CB antenna?

In the real world, if you are using something like a 40 meter ham radio antenna in a mobile environment, the data you like to quote is fine. However, if you are trying to apply it to CB specifically, you are reading to much into it. If you have a CB antenna of reasonable length and you get an R of "20 or less", then you have a problem with the CB antenna.

In one case you are shortening a CB antenna to, lets say for comparison purposes, about 50% of its optimal (resonant) length, and in the other, to get an antenna of the same physical length and tune it to the 40 meter ham radio band (a frequency band in the ham radio spectrum commonly used for mobile work) you are looking at closer to 15% of its optimal length.

Which of these antenna is going to have more of an effect on R at resonance than the other? Which antenna will take a much bigger hit to coil efficiency?

Also, do you think coil efficiency is the only loss you have to worry about in a mobile environment that adds to the R variable? Set up a full length CB antenna that has no loading coil on a car and see what R is, it will be higher than you expect. You can take a magnet mount antenna and move it around the vehicle and see changes in R, and that will happen weather or not there is a loading coil on the antenna. Thinking that a loading coil is the only thing that will raise R on your antenna analyzer is a dangerous and incorrect assumption.

Also, as far as a vast majority of CB antennas are concerned, if you have more than one or two ohms of loss on an antenna that is five feet long or longer, then you have a problem, much less 25 ohms. To make this determination, however, you would have to separate said loading coil from the antenna and measure such things separately, as when it is on the antenna, as I mentioned above, it isn't the only thing that affects R in that way.

And for information purposes, the more you shorten a given antenna, comparatively speaking, the more additional losses you will see. To explain that, lets use an example. Lets say you have a full length resonant antenna (no loading coil) and decide to shorten it by 10%. There will be some loss in the loading based on that 10% of shortening. Then you decide to shorten it again taking another 10% of its original size off. The total losses in the antenna will increase yet again, but this time, even though you took the same length away again, the loading will add even more losses. Do this a third time and you have even more losses added than the second time. Each time you take away a given percent of antenna length losses go up more than the last time. Another way of saying this is as you physically shorten an antenna losses increases exponentially.

What does this mean in the real world? There is an effective limit to efficiently shortening your antenna, and depending on how it is shortened, that limit is between 40% and 50% of original length. You get beyond those numbers and performance significantly drops off due to the exponential growth of losses in efficiency.

Now lets add this to the CB/40 meter comparison above. In one case we are at 50% of the resonant length, it is on the edge, but still relatively efficient, and its effects on R, both the lowering of R due to antenna length, and raising R due to losses in the coil, will be visible but minor.

In the other case the antenna is near 15% of its resonant length, you will have a much larger effect on R from both shortening the antenna and additional losses, and the antenna will be far less efficient.

One thing to note in both of these situations, you will see far more of an effect on R from shortening the antenna than you will see from the added loading losses, but like I said above, coil losses are not the only thing in a mobile environment that will increase R.


The DB

 

[w9cll]

http://www.k0bg.com/eff.html

 

[HARDROCK]

Hardrock, I have a question for you. Are you talking about HF antennas in general, or are you taking general HF knowledge as ham would need it and trying to apply it to a CB antenna?

Yes , as bob aa4pb stated above . It is a 5ft firestik cb antenna, it makes no differnce it depends on the antenna system.

There are a lot of people here making silly pie in the sky claims. They probably get away with it in CB forums because some people like to argue nonsense, and other just don't know when it is nonsense.

CTR hit the nail on the head with this statement.

This is a waste of time.

I think its best if we go to CTR website and Learn . He is the best.
W8JI.COM



Tony 73

 

[HARDROCK]

http://w8ji.com/mfj-259b_calibration.htm

This is cool.

 

[543_Dallas]

Yes , as bob aa4pb stated above . It is a 5ft firestik cb antenna, it makes no differnce it depends on the antenna system.



CTR hit the nail on the head with this statement.

This is a waste of time.

I think its best if we go to CTR website and Learn . He is the best.
W8JI.COM



Tony 73

He is almost as good as Mark Sherman at Fine Tune CB Shop. You and rabbiporkchop should go to lunch and talk physics.

 

[HARDROCK]

Lol. .. that is funny.
Just cut the rug out from under neath us.
Nothing like the good ole boys from Texas.
The truth hurts some times.
Every one Have a Great Thanksgiving.


Tony 73

 

[The DB]

It is a 5ft firestik cb antenna, it makes no differnce it depends on the antenna system.

It makes no difference? Really? There lies your problem. In theory, they are conceptually the same, however in the real world... Shortening a 40 meter ham radio antenna to work on a vehicle, and getting it to tune and shortening a CB antenna to 5 feet long is only the same in concept. One will have far more loss in play than the other. One may need a shunt, while if the other needs a shunt it is a sign that something is wrong.

When it comes to a mobile environment, HF covers a lot of territory. On one side of the band you can have full length antennas mounted on vehicles with no shortening added, and if you choose to shorten the antenna, you can do so easily and relatively efficiently. At the other you have frequencies that no matter what you do, in a mobile environment will never be more than 15% of the full 1/4 wavelength that you are resonating the antenna to, and almost always even shorter than that. These antennas are shortened to the point that you often cannot find a low SWR point when tuning for them without additional help.

The problem is you are taking things that you *might* have to do with antenna systems that work though out the entire HF spectrum (if not a majority of it) and saying that you must apply them to what is a very narrow single bandwidth that happens to be in a region of the HF spectrum that doesn't require anything more than mounting an antenna in a good spot on a vehicle to get a good tune.

I know this has been stated above by another, but the fact is, if you take an antenna of a reasonable length that was designed to be used on the CB band and mount that in the middle of the metal roof of a car and you cannot get it to tune then you have a problem with the antenna. You don't need to worry about shunts that were discussed above as if the antenna will need a shunt it will have been added into its design to begin with, and this frequency range won't have such a need. You don't need to worry about losses as unless the antenna is excessively short, the losses from the loading will not be particularly high, if noticeable at all. All this because of where in the HF spectrum the CB band happens to be.

Now if the CB band happened at closer to 10 MHz, or god forbid 3 MHz said discussions might be more relevant, however, you have to factor in that single band antennas can be designed to take even these requirements into account, and even then, with the lack of knowledge of many (most) on the CB side, they would still build antennas like the Firestik in question that requires nothing more than mounting an antenna and tuning it for SWR/resonance, and it would still work fine. A vast majority of CB antennas would be made that way.

If all of this is over a discussion of 5 foot antenna as you say it is, you are taking this way to far, and reading far to much into it.

I think its best if we go to CTR website and Learn . He is the best.
W8JI.COM

You are trying to say that CTR is W8JI? I'm not buying it.

There is nothing even similar in how CTR says things compared to how topics are stated on the W8JI site. Also, I have seen W8JI post on other forums under W8JI, again, not even close to what and how CTR is saying things. And to take that one step further, why did he not use W8JI as a name here as well, a forum that includes a ham radio section, he would have been instantly recognized and respected, especially by those of us who have quoted from his site often enough.

I'm sorry, but CTR being W8JI just doesn't add up.

For what it's worth, I agree that you need to read W8JI's site more, there is much there for you to learn.


The DB