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Tuning 102" Whip?

Discussion in 'CB Antennas' started by buickid, Jun 3, 2013.

  1. W5LZ

    W5LZ Crotchety Old Bastard

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    I think there's a confusion in terminology. Very simply, you can use an impedance matching device to 'move' an antenna to a frequency it isn't resonant on but make it 'workable' or 'acceptable' to a transmitter. Since the thing is non-resonant it won't be as 'good' on that new frequency as it could be, but it'll work.
    Changing an antenna's resonant frequency means adjusting it's reactance to zero. That isn't done by that impedance matching device. Those are two completely different things or 'qualities'. Adding inductance or capacitance in the right amounts is being done in both instances, but for different purposes. They both may use the same components, but they are not doing the same thing.
    The biggy is that input impedance has nothing to do with resonance and resonance has nothing to do with input impedance.
    - 'Doc


     
    2 people like this.

  2. hookedon6

    hookedon6 W9WDX Amateur Radio Club Member

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    obtaining the "best match" at the radio and operating at the antennas resonant freq are often not the same.

    get the antenna resonant at the freq you want to operate on first,......

    if you want to, you can then make adjustments at the radio end (or use a tuner) to make the radio "happy".

    my antennas are almost always resonant at (or near) my operating freq. the "swr" the meter "sees" at the radio end will vary as the freq is changed.
     
  3. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    CP, you have me at a disadvantage, being as you’re an RF Engineer.

    Right off you hit me with facts, and I’m not sure what facts you’re referring to. I wasn't sure if the test results I suggested to #6, a hypothetical idea testing the theory with a load that showed a significant amount of reactance, would indicate what I thought it might.

    I have tested the ½ wave theory for a perfect matched at both ends of a tuned feed line using a dummy load, and I found very similar results to what I think the theory tells us.

    However, I have not tested a load in a similar type test with any significant mismatch. Frankly, I could not be sure which frequency to cut the tuned line at in that case. At least I wasn’t sure.

    I could cut the ½ wave length for the frequency where I was intending to tune my new antenna…knowing to start with that the match was likely not even close to my frequency of choice, and the match was not good either.

    Or, I could've use the tuned line length for the resonant frequency for the mismatch I would see at the feed point...whatever it was. Under those circumstances, I wasn't even sure I could tell accurately what the resonace was on a mismatched load.

    I knew for sure if I had a perfect match I should see a good match…the numbers should be very close to perfect, but I wasn’t sure what the mismatched setup was going to indicate. If this was your question, then this is why I hesitated on agreeing completly.

    I agree that frequency and velocity factor is what determines an electrically tuned ½ wave line length, but I still have this feeling that the magnitude of the load presented at the feed points also plays a part in our determining what the frequency is. As note above, IMO it is not a simple task to figure accurately what resonance is with a poorly matched load.

    I also said in my earlier post that I could be wrong, but IMO the load has something to do with the how the ½ wave line theory works from the feed point end back toward the source. If I'm wrong in this then my idea here is also wrong.

    You're right, this idea can get complicated, at least to talk about. However, it was not my intention to throw facts out the window as you suggest. It would just be an opinion that happened to be wrong. I want to talk about the idea of this theory here, not what I personally think about you.

    This idea, for me, is at least complicated to discuss. You talk about facts, but again you don’t tell us what facts you are referring to, and as a result I’m not sure I fully understand the point you’re making in some of this.

    No, I was not trying to describe a perfect matching feed point. I also said that a perfect match might be hard to come by. I used the word “perfect” here as a distinction, one that opposed the idea of a mismatch.

    I certainly don’t have any experience working the type of equipment you tell us about, but your words and experience seems to make my point…that about all we might expect with a match is to get really close like you claimed. What you describe is certainly is close enough for me.

    Did you use a tuned ½ wave or multiple length feed line so you could see the true match at the transmitter similar to what we are talking about here?
     
  4. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    My antennas tend to see the opposite matching condition. The resistive part of the match being best across a nice range of the bandwidth, and changing more slowly as I change frequency. The reactance is typically off a little more, and tends to change more rapidly as I change frequency.

    I can't tell if there is any difference in performance either way however.

    I may be wrong regarding what I see, but my main point about the stuff on the 1/2 wave line was more about what I see happen, in some cases, when I change line length.
     
  5. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    The facts I was referring too was about the 1/2 wave line repeating the true antenna impedance. To me, last night when I was awake for over 30 hours, it sounded like you were somewhat unsure about that.

     
  6. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    This is exactly as it should be. I can't see where hookedon6 has said anything differently. SWR will change with any change in impedance whether it is the resistive component that changes or the reactive component. Since the reactive component is truly dependent on frequency much moreso than the resistive component it is the part of impedance that will vary much more widely than the resistive component.
     
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  7. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    I think I'm just getn' too old and set in my ways.
     
  8. hookedon6

    hookedon6 W9WDX Amateur Radio Club Member

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    well, that is better than the alternative<More audio>
     
  9. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Alternative, what alternative? You don't have to be scared to say what you mean with me #6, "...I don't bite, I ain't got no teeth." :thumbdown:

    I could just shut up talking about my ideas. I think CP was suggesting that the other day when he posted that I was throwing known scientific facts out the window. I tried to tell him my part of the discussion was primarily about feed line length, and how it can effect the match at the feed point, and it was just my opinion, right or wrong. He told me he needed some rest.

    I think I have more to talk about, but I don't what to get into personal bickering with CK. I just have an idea that I want to discuss, again right or wrong. Maybe a discussion could help me understand better if we don't get to casting barbs, daggers, and other personal accusations. I also realize my idea here may not be popular, even while I think a lot of CBr's consider the idea of using a 1/2 wave line to tune their antenna...is the only way to go these days if they want to get their antenna matched very close to perfect.

    #6, I know you suggested using a 1/2 wave multiple as a working feed line, for the primary purpose of monitoring the matching condition at the feed point. This too is an issue considered as a viable use for a 1/2 wave or multiple by many CBr's as well.

    I don't agree necessarily, but that to is just my opinion.

    My opinion here is if you get your match close, also according to the theory, the results for the match you see at the transmitter end should also show about the same as the feed point end. Either way with a well matched feed point, you will see the match at both ends of your working feed line or the tuned 1/2 wave line showing about the same. Plus you don't have to deal with the problems associated with a 1/2 wave line, and common mode currents, like another theory suggest.

    I can't argue with the success other's might have when using any idea they come up with, but sometimes I try to talk about the idea. In my experience with a lot of those cases it quite often happens that I ask a question, and then all exchanging of ideas and information tends to just stop.

    If that is that what you guys prefer, then I can do that.

    CK also suggested I was being too precise by using the term "perfect" with my idea, just because I used the term "perfect" as a distinction in order to try and describe a good match...as opposed to a match that was not so good to start with. Here I am suggesting what might happen with a newly constructed antenna, with a matching device, and little construction details including tuning where the initial match is way off and a guy is using his idea for a tuned 1/2 wave line to help him tune.

    Below is a link from a previous discussion I tried to have on this subject with Booty Monster about tuning his homemade Vector. Here is the thread:

    http://www.worldwidedx.com/cb-antennas/147251-using-1-2-wave-electrical-line-tuning.html

    In this thread he provided the link below. I think this was his source as he understood the use of a 1/2 wave idea while tuning an antenna that showed an initial match that was way off. Reference the part captioned: "What Length?."

    Coax information

    #6 and CP, I've been looking for a good definition for the 1/2 wave idea, I'm curious if either of you agree this might be a reasonable definition for the 1/2 wave theory...that is good enough for understanding the basic idea so a typical CB guy might understand?

    I'm not trying to convince an RF engineer of what he should know here.

    Here is the question I have, if you will answer "yes" or "no" first, and then you can explain all you feel is necessary to explain, it might help me better understand the idea.

    Does the theory in the link above tells folks that a tuned 1/2 wave feed line cut to resonance at say 27.205 mhz will indicate the same results, at both ends of that tuned line, exactly as indicated at the feed point, even though there is a mismatched load showing resonance somewhere else, just as an example at 25.5 mhz, which could have shown a similar matching result to what Booty Monster found when he first tried to tune his new homemade Vector with his idea for a 1/2 wave tuned line?

    If you answer yes, then I will shut up and say my idea here is not right.
     
    #69 Marconi, Jun 13, 2013
    Last edited: Jun 13, 2013
  10. bob85

    bob85 Supporting Member

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    eddie the link does not describe a 1/2wave as i understand it from maxwell and friends, it describes it as many people think it works,

    the claim is that the 1/2wave shows the same input as at the antenna so you can measure swr as it is at the antenna with 1/2wave multiple lines,

    i don't agree with this, i like maxwells version ;)
     
  11. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Thanks bob85. If I read you right here, you're saying "No," to my question, so I don't have to shut up and I can still add words and thoughts to this subject. Thanks!

    I'm not sure if just using an SWR meter will provided enough detectable information to make such a claim, whatever claim Booty Monster might make about using a tuned 1/2 wave line to tune. Obviously a lot would depend on how bad a tune was presented. I'm not even sure anybody would know what the info shown on an SWR meter was indicating, much less which direction one has to go toward a good tune. BM and I talked about this in the thread as I recall, but I'm old and my ideas are out there sometimes, and so are my comments and ideas. They might be right, they might be wrong, I'm just fishing for a discussion that is informative and convincing, and that is hard to come by around here any more.

    I'm just trying to think about this use like a CB'r might when thinking about how he would use this idea that is always suggested in a "matter of fact manner."

    I don't have the Maxwell idea close at hand, but I've hesitated to use any reference, except maybe what others might provide. I was concerned that all the Captain had to do was to talk over my head and discredit my idea further without helping me understand. You know..........I've talked to you about such stuff before concerning the words we get from Cebik and W8JI, among others.

    If you have the link to Reflections II maybe you could post it.
     
  12. Staybolt

    Staybolt Well-Known Member

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    How y'all do to tune one of dem' thar' 102" wip antennies????
     
  13. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    You just put 3 or 4 x 102" radials at the bottom of the 102" radiator, and you're in like fin, no tuning guaranteed.
     
  14. bob85

    bob85 Supporting Member

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  15. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Well Eddie at first I thought I had you figured out and that you were just looking a little too hard at something. Then I thought that maybe I didn't quite have it figured out what you were trying to get across, note, not that I thought you were misunderstanding something but rather had problems expressing it. Now I don't know what to think. You obviously took what I said in the wrong context. I was not putting you down or anything other than suggesting that perhaps you were looking for the perfection that generally is impossible to obtain other than on paper.

    Now I see this. "I could just shut up talking about my ideas. I think CP was suggesting that the other day when he posted that I was throwing known scientific facts out the window. I tried to tell him my part of the discussion was primarily about feed line length, and how it can effect the match at the feed point, and it was just my opinion, right or wrong. He told me he needed some rest."


    NO Eddie I was NOT suggesting that you just shut up talking about your ideas. That is YOUR idea. You did seem to be simply rejecting facts and for some reason can't understand that the length of cable does not affect the match at the feedpoint. It does affect what the meter sees is the match when that meter is not located at the feedpoint.As for telling you I needed some rest before continuing the discussion well please excuse me. I have a job that involves working two 12 hr days followed by two 12 hr nights. I just came home from my last night shift as I told you. I had been up for something like 30+ hours with a 12 hr shift in the middle of that and had about 4-5 hrs sleep since the morning of the day before. Now that my head is indeed clear I can clearly see that it is both of our best interests if I do NOT continue any further with this.
     

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