• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

dipole on a big rig swrs

@Marconi I wondered if you had the SWR plot, too.
I think it might be an answer for a big rig that has otherwise poor antenna performance, but I am not a fan of antennas on the back corner of a vehicle so I didn't run it long.
I still think of trying the roof mounted dipole in the U shape once made for RVs. I have materials for it except the 8" standoffs (the distance the original was above the roof), but I can easily enough make them. I'm way too busy with too little time. . .

You are right Homer. I can appreciate the idea that my model may not be very useful in the setup presented. It might have more utility mounted on the mirror mount as noted by Rabbiporkchop, and for sure if he runs a big rig dump truck.

I showed the antenna mounted on the rear, because it shows a lot more gain. It is also no higher at the radiator tip than the Bronco with a radiator mounted in the center of the roof.

Does your U shaped setup produce a horizontal pattern?
 
You are right Homer. I can appreciate the idea that my model may not be very useful in the setup presented. It might have more utility mounted on the mirror mount as noted by Rabbiporkchop, and for sure if he runs a big rig dump truck.
I was actually referring to the original post about using it on the big rigs needing a better antenna. I actually think your model is useful to demonstrate the feasibility of a dipole setup on a truck. I just like my antennas on the top near center of the vehicle which, of course is a different discussion.

Does your U shaped setup produce a horizontal pattern? I showed the antenna mounted on the rear, because it shows a lot more gain. It is also no higher at the radiator tip than the Bronco with a radiator mounted in the center of the roof.
I have tried it, yet. When it was manufactured it was claimed to be a vertical polarity setup, which I tend to doubt. I was considering it as an experiment, and a possible DX antenna. A 20db reduction in local communications could be overcome with the puck mounted vertical antenna and an antenna switch in the vehicle, or, because I don't do much local it would be inconsequential.
 
I have heard guys describe that U shaped antenna as working horizontal and others saying it was vertical. I'm just curious, but it looks to me to be horizontal.
 
With the dipole, one side is the HOT side and the other is the RF ground side. Obviously you would use the HOT side as the top vertical section of the dipole. You can use MFJ -347 dipole mount or make your own as long as the HOT antenna uses the insulator bushing and the RF ground does not.

I doesn't actually matter. An RF ground is just as hot as the "hot" side of the connection. I would agree that the convention would be to put the center conductor as the upper section of the dipole, but that isn't to say the antenna wouldn't also work the other way as well.

You SHOULD use equal lengths antennas to do this correctly.

I love that word "SHOULD". Its among my favorite words. It is entirely possible and feasable to tune a vertical dipole by just tuning a single element. A dipole also doesn't have to be fed in the exact center to work well, and being slightly off center electrically won't affect it enough to be noticed. There is actually something called an off-center fed dipole. While the principles aren't seen often on the CB side, they are still valid.

Most fiberglass antennas these days are 5/8 wave but that doesn't really matter.

It would be correct to say claim to be 5/8, they are not electrically 5/8 wavelength antennas, and they don't act like 5/8 wavelength antennas. Its nothing more than using 5/8 physical wavelength of material in a 1/4 electrical wavelength configuration so they can claim the antenna is something it is not.

There is one point to consider, Since a dipole is a balanced antenna, it is not 50 ohms. Even using 2 full size 1/4/ wave whips in this manner will have an feed-point impedance around 75 ohms, not 50 ohms, so the SWR will not be flat if that's what you were hoping for.

When it comes to balanced antennas, it is impossible for a vertical dipole to be in perfect balance, especially that close to an earth. However, you won't notice that much of a difference. The top element will be the "dominant" element if you will.

Correct (or very close) impedance, assuming you are using two full 1/4 wavelength antennas in freespace you can expect 72 ohms of impedance. Using shortened loaded antennas instead will lower that to some point depending on how much the antenna was shortened and where the loads are. However, being so close to an imperfect ground will raise that impedance as well. In this case, because of said proximity to the ground below, using top loaded antennas will be better than base loaded antennas for this type of situation.

This is a easy fix using a 2:1 balun. A balun is a transformer device used to balance an unbalanced feed-line for feeding a balanced antenna, Hence the name BAL-UN. At a 2:1 ratio, this means it will cut the feed-point impedance down at 100 ohms in half to 50 ohms which should give you a nice flat SWR match. 50 ohm coax cable is an unbalanced feed-line.

Be careful with the word "balun". Many people use it interchangeably with "unun". Also, it is possible to find 2:1 baluns, but 4:1 baluns are far easier to find. Its not nearly as easy to make a 2:1 balun as it is a 4:1 balun. For this size of mismatch, should it occur at resonance, I would recommend using a 1/4 electrical length of 75 ohm coax immediately before the antenna instead, if you can find someone with the proper gear to make one of the proper electrical length for you.

You could also use a mobile antenna tuner which will be easier. But antennas tuners don't really tune an antenna, they just match your radio to a mismatched antenna.Your antenna will still have a higher SWR from the impedance mismatch, but at least your radio will see a near perfect match.

With respect, you seem to misunderstand what an antenna tuner actually does. It actually tunes the entire antenna system as a whole, creating a conjugate match. A conjugate match is still a match, even if it isn't the "Z0" match that most people are uses to seeing now days. Most people aren't even aware that it actually has a name... In fact, the "Z0" match is a special case conjugate match. Yes, there is still high SWR with an antenna tuner, but SWR in and of itself is not a problem as far as the the antenna system ic concerned. Its only real issue is an additional amount of loss as the signal travels back and froth on the coax between the tuner and antenna. Use a shorter and/or higher quality low loss coax to minimize this. In fact, before the advent of coax, SWR was seen as nothing more than a curiosity... Still, using an antenna tuner is as much tuning an antenna as the matching system found on many base antennas, if you discredit one you must discredit both as they are exactly the same thing.

Good luck with your project!

I agree, keep us informed, and pictures are a plus, or shall I say pics or it never happened? ;)


The DB
 
I doesn't actually matter. An RF ground is just as hot as the "hot" side of the connection. I would agree that the convention would be to put the center conductor as the upper section of the dipole, but that isn't to say the antenna wouldn't also work the other way as well.

Since you pick me apart I will do the same.
Here you said absolutely nothing to the contrary since you agree it is better to put the "hot" side on top. I used simple terms in my posts to avoid any confusion. That's why I used those terms that the HOT side would be the element with the plastic insulator bushing and the RF ground side element wouldn't use one and mount direct.

I love that word "SHOULD". Its among my favorite words. It is entirely possible and feasable to tune a vertical dipole by just tuning a single element. A dipole also doesn't have to be fed in the exact center to work well, and being slightly off center electrically won't affect it enough to be noticed. There is actually something called an off-center fed dipole. While the principles aren't seen often on the CB side, they are still valid.

Yes I know that, but we are talking on a CB forum here and I'm keeping it simple. If you ever noticed my sig you will see I use a Carolina Windom antenna which is a variant of off-centered fed dipoles. Problem with off centering the elements causes un-equal currents to each side and usually causes feed-line radiation. This is acceptable for us amateurs since we use antennas like these and the feedline radiating becomes part of the antenna for multi-band work. We then use 1:1 isolator baluns to stop the RF currents from coming into the shack usually at specific points on the feed-line depending on antenna type. This is hardly the thing a CBer wants for a mono-band dipole in a mobile unit. So in this case I used the word "should" because it is relative to this thread and to what the OP was interested in. Once again you added nothing to the contrary relative to this thread.

It would be correct to say claim to be 5/8, they are not electrically 5/8 wavelength antennas, and they don't act like 5/8 wavelength antennas. Its nothing more than using 5/8 physical wavelength of material in a 1/4 electrical wavelength configuration so they can claim the antenna is something it is not.

That's true, that's why I said it doesn't matter to the OP if he uses 5/8 antennas. The fiberglass antennas like the Wilsons, K40's, and Firesticks that I'm familiar with are all marketed as 5/8 wave antennas so that's why I suggested Francis antennas since they are the only fiberglass antennas I know of that are currently marketed as 1/4 wave antennas. I don't get why you are challenging me on this one.

When it comes to balanced antennas, it is impossible for a vertical dipole to be in perfect balance, especially that close to an earth. However, you won't notice that much of a difference. The top element will be the "dominant" element if you will.

Correct (or very close) impedance, assuming you are using two full 1/4 wavelength antennas in freespace you can expect 72 ohms of impedance. Using shortened loaded antennas instead will lower that to some point depending on how much the antenna was shortened and where the loads are. However, being so close to an imperfect ground will raise that impedance as well. In this case, because of said proximity to the ground below, using top loaded antennas will be better than base loaded antennas for this type of situation.

I already stated that two 1/4 wave whips will have an impedance "near 75 ohms", actually it is closer to 74 ohms last time I measured one not 72 if you need to be more precise . So thanks for trying to contradict me.

Yes height above ground, metal proximity, terrain all play into affect. But when installing a mobile antenna system, a lot of these things can't always be avoided so a compromise is what we settle for. The only piece of new advice you have given in respect to this thread is, "because of said proximity to the ground below, using top loaded antennas will be better than base loaded antennas for this type of situation"

Be careful with the word "balun". Many people use it interchangeably with "unun". Also, it is possible to find 2:1 baluns, but 4:1 baluns are far easier to find. Its not nearly as easy to make a 2:1 balun as it is a 4:1 balun. For this size of mismatch, should it occur at resonance, I would recommend using a 1/4 electrical length of 75 ohm coax immediately before the antenna instead, if you can find someone with the proper gear to make one of the proper electrical length for you

I explained that easy enough already about baluns and what they would do in this situation, but it wasn't easy enough for you. A BALUN and UNUN are 2 different words I would think most people would see that and get it. If a UNUN was needed I would have specified it and defined what a UNUN is. I use an UNUN on my mobile HF screwdriver antenna since I'm using an unbalanced antenna being fed with unbalanced feedline, but my UNUN is also a matching transformer type so I can effectively match the different feed-point impedance's of different bands. I just gave clues to what an UNUN is right there.

I mentioned 2:1 baluns since I'm assuming what the feed-point impedance will be using two 50 ohm loaded antennas with 50 ohm coax. I also mentioned using an analyzer to verify this since I haven't used one to check a mobile dipole before. Maybe someone could chime in that has in fact measured the feed-point of an antenna like this so we may all know for sure. If it is indeed close to 100 ohms, then a 2:1 balun would be the better choice in this situation. Yes you can find them commercially made or make one yourself but you didn't offer advice on how to, you just said make a 1/4 wave piece of 75 ohm coax to have someone make one up. Anyhow, 75 ohm coax to a 50 ohm transmitter still has an impedance mismatch, just it"s a little closer. So I see nothing constructive by quoting my posts as though I'm wrong or misinformed.


With respect, you seem to misunderstand what an antenna tuner actually does. It actually tunes the entire antenna system as a whole, creating a conjugate match. A conjugate match is still a match, even if it isn't the "Z0" match that most people are uses to seeing now days. Most people aren't even aware that it actually has a name... In fact, the "Z0" match is a special case conjugate match. Yes, there is still high SWR with an antenna tuner, but SWR in and of itself is not a problem as far as the the antenna system ic concerned. Its only real issue is an additional amount of loss as the signal travels back and froth on the coax between the tuner and antenna. Use a shorter and/or higher quality low loss coax to minimize this. In fact, before the advent of coax, SWR was seen as nothing more than a curiosity... Still, using an antenna tuner is as much tuning an antenna as the matching system found on many base antennas, if you discredit one you must discredit both as they are exactly the same thing.

Wrong! That would be somewhat true IF you used a remote tuner at the antenna feed point therefore the tuner will be part of the antenna itself sort of speak. This is common knowledge I thought every Amateur radio operator knew assuming you are one.

Here is a quick search that I copied from the ARRL Q&A about this very subject.

How Do I Use an Antenna Tuner?

I'm a little confused about how antenna tuners function in terms of reducing antenna system SWR. Is it true that an antenna tuner does not really 'tune' the antenna?

Yes, it's true-an antenna tuner doesn't really tune your antenna in the strict sense of the word. It does not, for example, adjust the lengths of your antenna elements, their heights above ground and so on. What an antenna tuner or transmatch does do, however, is transform the impedance at the feed line input to a value that your transceiver can handle (typically 50 Ohm-see Figure 1). When thinking about antenna tuners and SWR, it's important to remember that the tuner has no effect whatsoever on the SWR between itself and the antenna. It's the SWR between the tuner and the transceiver that changes.


Mr. DB, you are a very knowledgeable person on a lot of things pertaining to radio as I have read on other threads, but in this case, you seem quick to disparage a person who may not have the years of experience as you, but has gained knowledge from personal experience first hand and with research and asking knowledgeable people directly with mobile installs particularly on semi trucks and to some degree on base antennas.
 
Last edited:
Since you pick me apart I will do the same. Here you said absolutely nothing to the contrary since you agree it is better to put the "hot" side on top. I used simple terms in my posts to avoid any confusion. That's why I used those terms that the HOT side would be the element with the plastic insulator bushing and the RF ground side element wouldn't use one and mount direct.

I didn't say it was better, I said it was convention.

Yes I know that, but we are talking on a CB forum here and I'm keeping it simple. If you ever noticed my sig you will see I use a Carolina Windom antenna which is a variant of off-centered fed dipoles. Problem with off centering the elements causes un-equal currents to each side and usually causes feed-line radiation. This is acceptable for us amateurs since we use antennas like these and the feedline radiating becomes part of the antenna for multi-band work. We then use 1:1 isolator baluns to stop the RF currents from coming into the shack usually at specific points on the feed-line depending on antenna type. This is hardly the thing a CBer wants for a mono-band dipole in a mobile unit. So in this case I used the word "should" because it is relative to this thread and to what the OP was interested in. Once again you added nothing to the contrary relative to this thread.

I don't particularly pay attention to signatures.

Also, in this case of tuning a single whip of the two in the dipole situation, its not like you are going to push the feedpoint to an approximate 1/3 - 2/3 situation. Honestly, their closeness to the earth will have more of an effect than this minor displacement in feedpoint location. As the earth will add more capacitance to the lower element, if you tune the two in such a way that the lower element will be electrically longer, this should (didn't I say I love that word?) minimize the small amount of CMC's present even further. That being said, I can't think if an easy way off the top of my head to be sure you found that electrical center point, so "closer" is all said technique can do. In any case, I would mirror your point of an isolater you brought up later in said post, but I don't think anything more than a choke is needed. A few appropriately chosen snap on ferrite beads should more than do the job.

I am curious though, nearly every OCF design I played with and made work had a 4:1 balun to get acceptable readings, yet you used a 1:1 balun? Given my experience working with similar antennas, R is generally pretty close to 200 ohms at resonance at the feed point. Is your antenna using a different impedance feed line (many use window or ladder line for this) as part of the matching system? I'm sorry, getting a bit far off topic here.

That's true, that's why I said it doesn't matter to the OP if he uses 5/8 antennas. The fiberglass antennas like the Wilsons, K40's, and Firesticks that I'm familiar with are all marketed as 5/8 wave antennas so that's why I suggested Francis antennas since they are the only fiberglass antennas I know of that are currently marketed as 1/4 wave antennas. I don't get why you are challenging me on this one.

I simply get nervous when I hear someone call a mobile CB antenna a 5/8 as they really aren't 5/8 wavelength antennas. I wasn't calling you on this, but was simply trying to make sure the OP and others that may be searching for additional info on this type of setup were aware of this. Based on your previous posts I'm actually surprised you mentioned it the first place.

I already stated that two 1/4 wave whips will have an impedance "near 75 ohms", actually it is closer to 74 ohms last time I measured one not 72 if you need to be more precise . So thanks for trying to contradict me.

You have an anionic chamber available to accurately measure a center fed dipole in the simulated free space environment that I mentioned that 72 ohm figure for? Sweet...

My statements here were meant to be simply informational for those working with shortened dipoles near an earth, meant more to explain any differences one might see from the numbers typically given, which your numbers lined up the usual part. I did say "correct (or very close)" for this didn't I? It did not contradict your numbers, but explained why someone using such an antenna might see variations. 72 ohms was simply a known theoretical starting point, then that was modified to take into account the real world elements of shorting the elements with an inductive load, which will have varying effects based on where and how large said load was. Then that was modified again by the real world presence of an earth, which didn't exist in the original number figure, and will vary based on the properties of said earth, and even though I didn't mention it, will change based on ones movement over said earth as well, and especially in the case of this antenna as they drive near other metal objects such as cars. It wouldn't surprise me if the antenna's feedpoint impedance wasn't close to, if not even higher than, you later number of 100 ohms in some cases.

Yes height above ground, metal proximity, terrain all play into affect. But when installing a mobile antenna system, a lot of these things can't always be avoided so a compromise is what we settle for. The only piece of new advice you have given in respect to this thread is, "because of said proximity to the ground below, using top loaded antennas will be better than base loaded antennas for this type of situation"

Seriously? Hmm... Most of what I said was actually meant to expand on what you said... There is at least one other suggestion that has nothing to do with what you said as well.

I explained that easy enough already about baluns and what they would do in this situation, but it wasn't easy enough for you. If a UNUN was needed I would have specified it and defined what a UNUN is. I use an UNUN on my mobile HF screwdriver antenna since I'm using an unbalanced antenna being fed with unbalanced feedline, but my UNUN is also a matching transformer type so I can effectively match the different feed-point impedance's of different bands. I just gave clues to what an UNUN is right there.

I mentioned 2:1 baluns since I'm assuming what the feed-point impedance will be using two 50 ohm loaded antennas with 50 ohm coax. I also mentioned using an analyzer to verify this since I haven't used one to check a mobile dipole before. Maybe someone could chime in that has in fact measured the feed-point of an antenna like this so we may all know for sure. If it is indeed close to 100 ohms, then a 2:1 balun would be the better choice in this situation. Yes you can make one yourself but you didn't offer advice on how to, you just said to have someone make one up. So I see nothing constructive by quoting my posts as though I'm wrong or misinformed.

Again, additional information based on your original comments. I, again, didn't say anything that disagreed with what you said. Not everyone is aware of the things I mentioned. For the record, I haven't measured a vertical near center fed dipole on a vehicle, but I have measured a near center fed dipole with a feedpoint a little higher than this, it was a T2LT mounted just above ground level. If memory serves R was somewhere between 85 and 90 in that case. That will go up as you approach the earth, but as I mentioned above, the quality of earth will also have an effect, so your measurements may vary.

Wrong! That would be somewhat true IF you used a remote tuner at the antenna feed point therefore the tuner will be part of the antenna itself sort of speak. This is common knowledge I thought every Amateur radio operator knew assuming you are one.

Here is a quick search that I copied from the ARRL Q&A about this very subject.

How Do I Use an Antenna Tuner?

I'm a little confused about how antenna tuners function in terms of reducing antenna system SWR. Is it true that an antenna tuner does not really 'tune' the antenna?

Yes, it's true-an antenna tuner doesn't really tune your antenna in the strict sense of the word. It does not, for example, adjust the lengths of your antenna elements, their heights above ground and so on. What an antenna tuner or transmatch does do, however, is transform the impedance at the feed line input to a value that your transceiver can handle (typically 50 Ohm-see Figure 1). When thinking about antenna tuners and SWR, it's important to remember that the tuner has no effect whatsoever on the SWR between itself and the antenna. It's the SWR between the tuner and the transceiver that changes.

This is one of the few areas I actually disagreed with you. I will also state that you can find very knowledge people on both sides of this discussion, as well as official ARRL documents that takes both sides. I am happy to refer you to an ARRL document that disagrees with this if you wish, a document written by an RF engineer that worked for various organisations such as NASA. Its actually highly recommended reading, and is a source that opened my eyes to what was really happening with antenna systems, and really even the concept of "antenna system".

If you look at what I said, I specifically said "antenna system". There are specific, yet large, differences between the concepts of "antenna" and "antenna system", which in my experience is also a rather large divider on this discussion point. I don't know how far I can go here without you taking this the wrong way, again, so I'll hold off here as, believe it or not, it wasn't my goal to be argumentative through most of your post. I will say that the person in the quote you used above is actually half way to figuring it all out, he just needs to take that next step in understanding...

Mr. DB, you are a very knowledgeable person on a lot of things pertaining to radio as I have read on other threads, but in this case, you seem quick to disparage a person who may not have the years of experience as you, but has gained knowledge from personal experience first hand and with research and asking knowledgeable people directly with mobile installs particularly on semi trucks and to some degree on base antennas.

Thank you for the complement. I apologize for not being more careful with my wording of things as you clearly took them differently than I intended. It was much later at night than I was used to being up and I may not have been firing on all cylinders. Although that is just an excuse, I should have waited till morning.


The DB
 
We are getting too cerebral here, but here goes...

I am curious though, nearly every OCF design I played with and made work had a 4:1 balun to get acceptable readings, yet you used a 1:1 balun? Given my experience working with similar antennas

If you played with nearly every OCF type of antenna, surely you have to come across a Carolina Windom before. Yes it uses a 4:1 balun at the top, but if you read what I wrote, the 1:1 balun is used to stop feedline radiation from entering the shack at a specific point on the feedline due to radiation from having two unequal dipole elements. This is what happens when 2 dipole elements are unequal and was the only point useful to this thread.

It wasn't necessary to explain my whole antenna system but maybe I need to for you. The Windom antenna has two lengths of wire, one is 90ft. and the other is 43 ft. and uses 50 ohm coax fed to the 4:1 balun that divides the 2 different wire lengths creating an off center formation, but the coax is broken up towards the top and that section is used as a vertical radiator. The specific point where the 1:1 balun is placed stops the vertical radiator from radiating below it and creates a 1/2 wave 15 meter vertical radiator above it and becomes part of the antenna system for different bands. This antenna can work effectively on 10 thru 80 meters and on many portions of those bands, without using a tuner. Does that make sense now?

windom-antenna.gif


I simply get nervous when I hear someone call a mobile CB antenna a 5/8 as they really aren't 5/8 wavelength antennas. I wasn't calling you on this, but was simply trying to make sure the OP and others that may be searching for additional info on this type of setup were aware of this. Based on your previous posts I'm actually surprised you mentioned it the first place

Fair enough, I only mentioned it because the OP mentioned it as a concern when it isn't.

You have an anionic chamber available to accurately measure a center fed dipole in the simulated free space environment that I mentioned that 72 ohm figure for? Sweet...

Of course not, and neither do you to get such an scientific absolute measurement. I only have a RIG Expert antenna analyzer. Free space doesn't mean much in the real world since were not in free space as it's usually a starting point, the velocity factor is more real world applicable, so that's being over geek-y-ness.
You were compelled to pick me apart and had to correct me of 1 ohm like it's going to make a difference, so I did the same to you.

As for antenna tuners, we will agree to disagree.
 
Last edited:
...with respect, you seem to misunderstand what an antenna tuner actually does. It actually tunes the entire antenna system as a whole, creating a conjugate match. A conjugate match is still a match, ..., there is still high SWR with an antenna tuner, but SWR in and of itself is not a problem as far as the the antenna system ic concerned... ;)


The DB


allow me to jump into this pizzin contest.:D


the issue here is not "as far as the the antenna system ic concerned", it is about "as far as the transmitter is concerned".

a typical antenna tuner (there are certain specific exceptions) does NOT "tune" anything in line after the tuner, it does not tune the "antenna system".... and the discussion of conjugate match theory with out in depth reference to transmission line length Vs wavelength is "cherry picking" at best..

a fixed impedance device (transmitter) looking into an antenna "system", using the conjugate matching theory WILL decrease power transfer efficiency by up to 50% as compared to "conventional" matching theory.

bottom line: applying conjugate matching theory to 27 MHz is non productive at best.
 
  • Like
Reactions: fourstringburn
allow me to jump into this pizzin contest.:D

No pizzin contest... Just a misunderstanding... But you are welcome to join the conversation...

the issue here is not "as far as the the antenna system ic concerned", it is about "as far as the transmitter is concerned".

Hmm point of view vs point of view. One of these points of views is a goal oriented, namely the goal of making the radio happy, and the other is understanding oriented. Both are valid points of view from their own perspective.

a typical antenna tuner (there are certain specific exceptions) does NOT "tune" anything in line after the tuner, it does not tune the "antenna system".... and the discussion of conjugate match theory with out in depth reference to transmission line length Vs wavelength is "cherry picking" at best..

OK, then if said device doesn't tune the antenna system as a whole behind it, how exactly does it present a match condition to the radio/feedline before it? There is one and only one way for such a device to do that, and that is to provide a match. Essentially, at that point in the system, matching whatever the impedance is on the antenna side with the desired impedance on the radio side. This can actually be described either way, as once a match is made in one direction you have an equivalent match in the other. It doesn't matter how this is achieved, be it a T matching network found in most manual antenna tuners, relay based switching L networks found in most relay based automatic tuner, or a stub, or tuning device that is part of an antenna, or whatever, they all do the exact same thing in the exact same way. Anything other than that, (with one exception I can think of that would also have seriously undesirable side effects) the appearance of the match you are trying to present to the radio will not, and in fact can not happen. If you are seriously telling me that there is another way aside from providing a match, please explain.

I'll save the conjugate match specifics for the next part which is also related to such.

a fixed impedance device (transmitter) looking into an antenna "system", using the conjugate matching theory WILL decrease power transfer efficiency by up to 50% as compared to "conventional" matching theory.

By definition, with a conjugate match, the radio will see whatever impedance it is supposed to see. If the radio is supposed to see an R = 50 X = 0 output to a feed line and doesn't you don't have a conjugate match. As an extension, if your radio lowers its power because of it (or such happens automatically due to the phase mismatch presented in the radio's matching circuit), you did it wrong.

It doesn't matter how long the feed line is in line length, wavelength, or whatever. If a conjugate match is properly applied at any point in the system then you have a system match, even if some parts of the system are operating with a high SWR.

bottom line: applying conjugate matching theory to 27 MHz is non productive at best.

There are very few uses for an antenna tuner for such a narrow single band. In most cases, a properly tuned single band antenna will work at least as well, and will be far easier to set up. This applies to any small set of frequencies. Where an antenna tuner really benefits someone is when they have multiple bands over a wide range of frequencies to cover, like the HF bands in ham radio. In that case, running a multi band antenna vs a single wire antenna and antenna tuner fed will feed line that has a low enough loss (ladder line and such) will work very well. I guess in that case it also comes down to personal preference over anything else.

Also a note on the conjugate match, the so called "regular" match that people usually try and achieve is also, by definition, a conjugate match. It is a special case that fits within the principles of the conjugate match, and because of that, it actually has a name of its own, not that anyone actually uses it, or even knows what it is...


The DB
 
well, now I am really interested, could you tell me where to get the parts to build a real world conjugate matching device?

... and some design criteria would help too.

I keep reading chapter 19(a) (not chapter 19) of reflections and I get a different perspective about conjugate matches.
 
  • Like
Reactions: rabbiporkchop
well, now I am really interested, could you tell me where to get the parts to build a real world conjugate matching device?

There are plenty of examples of this, just look at (insert random antenna that includes a matching circuit here). You can also loot at (insert random antenna tuner model here). As for devices, anything that can act as inductors and/or capacitors, including lengths of feed line (which can be used in the form of a stub to match a circuit).

... and some design criteria would help too.

The book you mentioned has all the information in it that you need. If you can't get that information from the book, which is clearly spelled out within, why do you think it would be any different if I try and explain it to you?

I keep reading chapter 19(a) (not chapter 19) of reflections and I get a different perspective about conjugate matches.

Question 1, what version of the book do you have as the chapters don't all line up across Reflections, Reflections II, and Reflections III. Based on the question, I would guess you have a copy of Reflections, and are not referring to eighter of the newer revisions...

Question 2, in all of the versions of the books there is no "Chapter #(a)" for any chapter. I do know that there is a disk that the books refer to, but I haven't gotten that as I haven't needed it, are you referring to information on this disk that the books mention? If so I'm happy to locate said disk...

Question 3, Are you sure you read and understand Chapter 4 "A View Into The Conjugate Mirror" and Chapter 7 "My Transmatch Really Does Tune My Antenna" at least beforehand? There are other chapters that really should be read and understood first as well...

Question 4, You ignored my initial question while asking another that really looks like it may have been designed to trap me. Are you unable to answer my initial question?

Question 5, The name of Chapter 7 written in Question 3 above is very descriptive. As a matter of fact it is hard to miss. Because of this, I have to ask, are you in disagreement with the author that you are asking me to help explain what he is saying?

The book you referred to is a good book, it is honestly the starting point that helped me break through the ceiling of knowledge that I didn't know was limiting me, but it took several times reading through it, as well as quite a bit of though about what was written and its applications before I truly understood it. With that understanding came a complete shift in how I look at antennas and matching. Anyone reading this book, I implore you, keep at it, even though many of the concepts are difficult for many to understand. This is engineering level stuff after all, even if it was written in such a way to try and make it easier to understand...


The DB
 
I wonder why it's called "antenna theory" . . . Everyone has a theory except the antenna. :)

About tuning with a matcher -

Below is a matching network I made yesterday to put on the bottom of an EFHWA. The truth is that when I put it on the antenna what will happen is if I've made it properly it will provide a match between the very high impedance of the antenna (2000 - 5000 Ohms) and the coax feed line (50 Ohms), or transform the impedance. What has not happened is that I change the impedance on the antenna side of the matching network. What has happened is that I have tuned my entire antenna system to provide a 50 Ohm match to my transceiver.
At this point it is a matter of perception as to whether my antenna system (everything from the back of the radio to the tip of my antenna, including but not limited to, the location, height above earth, materials used, coax, choke, antenna itself) is a 50 Ohm system, or if my antenna is a 50 Ohm antenna. The question one answers for himself is whether the matching network is part of the antenna, or antenna system, or not.
For me, the transmatch device (matching network, matcher, tuner, etc) is a part of my antenna system no matter where it is placed on the feed line (at the antenna or the radio end of the coax). Also, to me, once I mount the matcher onto my antenna physically, it is a part of my antenna. I now have a 50 Ohm antenna at the feed point side of the matching network, and a multi-k Ohms antenna above the the matching network.
Naturally, whatever kind of antenna I use each having different natural impedance to their designs determines the kind of transformation I will use to provide a 50 Ohm match to my radio.
That, my friends, is my theory. My antenna doesn't have one.

20151227_212123.jpg
 
  • Like
Reactions: Slowmover
That, my friends, is my theory. My antenna doesn't have one.

Very wise comment Homer BB. I am with you on that .
It makes a very effiecient system.
Tune for maximum smoke and match for best results and you will have an effiecient system.


Tony 73
 
  • Like
Reactions: HomerBB
The idea has been there from the 70"s when we had them "al-u-minium mirrors" I guy I worked with quit his job as a Teamster driver and opened up a radio shop, go figure,
His was called the Rooster Booster and it came in two flavors, one was one 5 foot francis with an insulator in the bracket facing up and one 5 foot francis facing down with out the insulator facing down to make it "cold". The other was a custom block with one up and two short legs pointing down at 45%. There were a couple of others made.

I still drive and slipseat daily with Volvos, Freightliners, and Macks ,glass trucks and experience all the problems.
While I can't quote theory, I do know what works in trucks. My vertical dipole you can hold out the window in your hand and still have a 1.5 swr so it works, however it doesn't out perform my Wilson 5000, with a short ground strap to the cab.
Here's one that I made:
verticle diople.jpg

Here's a link to an article that may help you.http://www.hamuniverse.com/cbstrongtie.html
 

dxChat
Help Users
  • No one is chatting at the moment.
  • @ AWP:
    Is it possible to be on a lake and have a homing directional beam being emitted from the shore so a person could navigate to that beam's source? For example at night to a jetty.
  • @ BJ radionut:
  • @ wavrider:
    sea que sea que,
    +1