Best Moblie Antenna for OTR Truck

[543_Dallas]

Here it is 543

Try again. That's the part I didn't like.

 

[HARDROCK]

Db I would like to see your view on the conjugate match and maximum power transfer.
My understanding is the system as a whole is resonant.

This is when matching at the feedpoint of the antenna accomplishes 50 ohms at the
source and at the antenna for maximum power radiated.

This is why Low swr can lead you down the wrong road if the system is not matched.

The maximum power theorem does not have to be resonant.
Understanding the theorem is the key. Start with a resistive load then add some reactance
to the load then add a transmission line. Remember that the source impedance is an
integral part of the theorem. Also note that the conjugate matching theorem assumes
zero losses except in the source and load resistances. What that means is that a system-wide
conjugate match cannot exist in the real world since there are always losses in the
transmission line. We cannot know if we are transferring the maximum available power
to the load (antenna) unless we know the losses at each point in the system. Walter
Maxwell was right about lossless systems but a little off for real world systems. Walt
conjured up a "one-way conjugate match" to try to compensate for the real world
conjugate match but that concept has holes in it. The fact is that in the real world
we can create a conjugate match point anywhere we choose by installing a matching
network at that point, i.e. each conjugate matching point requires a separate matching
network at that point.


Tony

 

[HARDROCK]

In most cases the use of feed-line SWR alone to
indicate antenna efficiency is invalid, because
SWR indicates only the degree of mismatch, not
efficiency.

 

[The DB]

In M. Walter Maxwell's books he addresses this. The first of his Reflections books this is section 19-4, in the second and third of his Reflections books this is section 24.5. This is taken from Reflections 3.

In real transmission lines having attenuation, all power entering the line is absorbed in the load, except for that dissipated as heat and lost due to line attenuation. When the matching is performed at the line input, the loss from line attenuation happens because in addition to the attenuation of the forward power, the reflected is also attenuated in the same proportion on its return to the source.

Should this concern us as amateurs? Probably not, if we are using a typical antenna system at HF. When the matched-line attenuation low, as it is in typical amateur installations, the additional loss because of Z0 mismatch is small, as explained in Chapters 1 and 6. The additional losses are so low that even with moderate to high SWR values, the difference in power radiated compared to that with a 1:1 SWR is too small to be discerned by the receiving station. The additional power lost versus SWR may be determined from Figs 1-1 or 6-1, or may be calculated using equation 6-1.

This is where it ends in Reflections, however in Reflections 2 and 3 there is a reference to Appendix 8 and Appendix 8A which is another way of calculating the same thing as the figures he mentioned above. However, in Reflections 3 there is another section that discusses this further.

Along with the myth that no conjugate match can exist when the source of power is an RF power amplifier, another myth concerning the conjugate match has re-emerged. This myth had it that the conjugate match exists only in theory, because the assertion is that it can occur only in a lossless environment that doesn't exist. The claim is that any resistive loss in a circuit containing real reactive elements introduces additional reactances that destroy the true conjugate match. This is true to a point, but it is only the beginning of the story.

He then continues on for nine and a half pages which I am not going to type up here for several reasons, although it is a good read. I will, however, summarize.

When loss is present in the components this loss will change said component's reactance. This is where the claim comes from that a conjugate match can no longer exist. However, according to Maxwell that is where said claims stop.

Maxwell then goes on and talks about adjusting the reactive elements individually to compensate for their loss resistance, in effect "tuning to resonance". For the record, the method described mirrors how ham radio operators use their antenna tuners. I'll quote another part of it here.

However, we must be careful to understand that during the conditions described above, although the conjugate match exists everywhere in the real network, it exists in only one direction -- forward.

Essentially, the conjugate match becomes directional. As long as the system is tuned to be a conjugate match with the source on one side and the load on the other, the conjugate match still exists. If something changes, say, you stop transmitting and start receiving, effectively reversing the source and the load, the conjugate match doesn't exist, in the case of this example, as long as you are receiving.

I hope this helps.


The DB

 

[HARDROCK]

CTR you mentioned one THING.

The subject is field strength.
You had mentioned earlier that applied power and FS was certainly a better way to test for efficiency.

Will you explain the proper way of tuning a mobile antenna via FS. ?

Tony

 

[StrangeBrew]

One thing to keep in mind is that all this discussion is only relevant if efficiency is priority one, for many less serious operators priority one is to present the radio with a match that won't cause damage when you key it up. In these cases good enough really is good enough as far as getting out is concerned and for these people a simple SWR meter is more than adequate for the job at hand.

I only mention this because a couple comments here seem to be bordering on putting down users of SWR meters, they may not be the best way to tune an antenna out there but the best isn't always needed.

 

[The DB]

One thing to keep in mind is that all this discussion is only relevant if efficiency is priority one, for many less serious operators priority one is to present the radio with a match that won't cause damage when you key it up. In these cases good enough really is good enough as far as getting out is concerned and for these people a simple SWR meter is more than adequate for the job at hand.

No argument here.

I only mention this because a couple comments here seem to be bordering on putting down users of SWR meters, they may not be the best way to tune an antenna out there but the best isn't always needed.

With all due respect, you got it backwards. It isn't people who use SWR that is being put down, its people who use "resonance". At least as far as my posts are concerned, if you picked up that I was talking down to or about people that use SWR, you should consider re-reading them.

Let me break it down for you. There are two methods of tuning an antenna, lets call them method1 and method2. CTR and I agree that you won't notice the difference between using the two different methods. However, CTR says you should use only one of those methods and that he doesn't get why anyone would ever use the other method, and is almost to the point of talking down to the person who defends using said other method. My point is what does it matter which method you use if you won't notice the difference anyway?

In my posts, SWR was not talked down at all, and if you got that impression you either misread, misunderstood, or read into said posts. I have asked over and over what difference does it make if you won't notice the difference anyway, but have yet to get a good answer to this. All I get is CTR making fun of people who tune with resonance, and some comments that sound technical, but are really not relevant to the question at hand, and really make no difference in the end. If I need to I can go get a bunch of quotes to demonstrate this, they are all there in this thread.

All I want is a good answer from CTR, but all he has done is talk around the issue, as well as talk down about people who disagree with him.

Now if it is other people's posts you are referring to I have no comment.


The DB

 

[StrangeBrew]

Not really calling anyone out in particular, and it definitely wouldn't be anything you said. It's just the "if it's not the way I prefer it's wrong" thing that has a way of creeping into threads like this one. Just wanted to put up a reminder that we don't all have the same goals in this hobby, what doesn't work for one purpose may be just fine for another.

Sorry if I offended anyone, I certainly didn't mean to.

 

[543_Dallas]

CTR is one of those gurus that should stick to blogs with commentary disabled. He wants to preach but doesn't do well when asked too many questions.

 

[The DB]

Sorry if I offended anyone, I certainly didn't mean to.

No offence taken.


The DB

 

[HARDROCK]

Db that helps. Thanks.

Is the grid dip meter a better way for finding resonance ?

 

[HARDROCK]

Db that helped Thanks.


\\

All I want is a good answer from CTR, but all he has done is talk around the issue, as well as talk down about people who disagree with him.

Yes that is how we benifit and Learn. Maybe he will answer.


Tony

 

[543_Dallas]

Db that helped Thanks.


\\


Yes that is how we benifit and Learn. Maybe he will answer.


Tony

We benefit and learn from him dodging questions and talking down to people? Do you even read the things you respond to?

 

[HARDROCK]

We benefit and learn from him dodging questions and talking down to people? Do you even read the things you respond to?

If you look above what i wrote you will see that i am agreeing with The DB.
Yes means he should answer the question and stop going around the questions
with irrelevant answers.

So to answer your question Yes.

 

[543_Dallas]

If you look above what i wrote you will see that i am agreeing with The DB.
Yes means he should answer the question and stop going around the questions
with irrelevant answers.

So to answer your question Yes.

Sorry about that, I misunderstood you. Might have had something to do with all the CTR cheerleading you've done in the past. I couldn't imagine you ever questioning the integrity of the prophet.