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Tuning 102" Whip?

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

  1. The DB

    The DB Sr. Member

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    Buickid, I am curious, what research did you do to verify that?


    The DB


     

  2. Marconi

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

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    Buickid, some months ago you seem to have given up on your install of a Vector 4000 too.

    I told you back then the Vector will work Ok when close to the Earth, but I did not mean that in your particular situation close to your neighbor was a good idea. I also suggested that IMO no matter what you did using chokes or devices on your end of the issue was likely to help...since I think your problem had to do with direct radiation from your antenna being low, and RF from the antenna itself was getting into your neighbor's stuff. I don't think this was due to CM currents...even though a Vector can easily manifest such currents.

    I would love to see you have some good luck with some antenna you have installed, but I'm not sure I can help without a little more info.

    Are you up to doing a little experimenting with your 102" whip which is much more simple than working with your Vector?

    I think once successful using a good match...it might help improve your confidence and maybe your understanding using your 259b. These devices are far more useful than a simple SWR meter and when used with that mode alone...the results can still be misleading.

    You don't have to go very high with this idea so it should be convenient to work with, but don't look for it to solve your TVI problem with your neighbor.

    If you could beg, borrow, or steal a simple mobile mirror L bracket, and could get some common wire at least 8'-9' long for 4 radials, and a little rope, you could experiment using your analyzer on a good match. I think such a setup should show you a nice match with the radials slanted down at or below 45* degrees as support guy lines for the radiator. All you have to do is connect the wires securely to the L bracket, and attach the other ends to the ropes, and secured them to the ground. This is not exactly safe for children or pets, but maybe it will give you something to work with that works as you might expect.

    If you are successful, I think you will see your analyzer showing you the desired matching results for R, X, SWR, and Z you should expect, and then you can better learn more about the analyzer use and bandwidth curve.

    There is no way a radiator that is a 102" SS whip with a ground plane is going to show you resonance or a truly good match that is resistive at or near 31 mkz. What you see can only happen if you are abusing what your 259b can do, or you are just finding a low SWR somewhere well away from resonance due to simple feed line transformation...and you don't understand such results.

    You may not understand this now, but SWR results are not linear like your SWR bandwidth curve might show across a rather narrow range. As you get farther away from resonance, the SWR will likely produce a more sinuous type curve, varying up and then down, and this may be why you think you saw resonance way up near 31 mhz.

    Maybe I've already said this here in a previous post, but it is worth saying again in light of your reported results...which you cannot explain, and does not make any sense if you think about it. If you're already using more than a 6" extension in radiator length added to your 102" whip, and you're still near 30 mhz, how long do you think you'll have to go to get down to 27.205 mhz.

    I could be all wrong, but I don't think so.
     
  3. Lil'Yeshua

    Lil'Yeshua .......

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    Don't you use 108" radials pointed down at a 45 or more angle and a 102" vertical? I studied a little in this type setup. I'm running a 102"w/ 6" spring for a base with no radials and the tower/coax is the other half and a MFJ-971 to tune it. It's good for local out to 20 miles at least.
    P.S. the base of the 102" is at the top tv antenna boom to mast attachment point so the tv antennas may affect it somewhat
     
    #33 Lil'Yeshua, Jun 7, 2013
    Last edited: Jun 7, 2013
  4. buickid

    buickid Active Member

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    Don't recall what sites I read, but upon further research, it would appear that impedance matching your antenna is the key. All of the locals here tell me my feedline is far too short and that I'm going to burn my box. I don't believe I need a certain length of feedline, but they swear by it, and by golly... they get out.

    The hams using antennas on multiple bands are using tuners, which I (maybe falsely) understand to be impedance matching devices. I think what I need to build is a impedance matching circuit of sorts.

    I appreciate your help, with the Vector and this antenna. Unfortunately such radials would not work in the case of my Vector, as it is mounted near the property line, about 2 feet from a dividing wall, and 3 feet on the other end from a patio/deck, so 8-9ft radials would be rather difficult to attach. As I understand it, the antenna is simply too close, really not much I can do about that at the current time, so be it. Later I might throw up a dipole on the side of the house in the middle of the lot, at least a little further from the neighbors on both sides. I'm almost tempted to just buy a box stock radio and let er rip with the Vector. Let the neighbor deal with his poorly shielded electronics.

    As far as my mobile, I'm willing to experiment, at least I don't have to climb a tree to get to my gamma match. I'll run a few more tests with my buddy's MFJ and note the results paying attention to X and ohms, but with just the spring and antenna, X was still lowest far above 27MHz. I understand what you're saying about SWR acting in a sinusoidal manner, but does resonance act the same way? What steps do you suggest I take to try and correct this situation? I don't know how much longer I'll have to make it to get it resonant at 27.205, so thats what I was going to experiment with next, but I'll hold off pending further advice. Once I can get it resonant, I think the key is impedance matching the antenna, but I'm not entirely sure how to about doing that. K0BG gives a good primer, but doesn't go in depth. I'm still not entirely sure why I'm needing to extend the antenna SO much to get it resonant down to 27MHz. Thanks again for your help!
     
  5. Marconi

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

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    I never suggested above that you should add radials to your Vector. At the point I stopped talking about your Vector I highlighted in bold print, from here on I would be talking about you 102" whip.

    I can't help any more regarding your Vector, you'll just have to work that out. I don't advise not considering your neighbors however. I should not have even mentioned the Vector, but I was reminded when I read your old post trying to remember where we hooked up before.

    You are totally lost if you think you have to tune your 102" whip or add any length. Literally 1000's of 27 mhz 1/4 wave whip installs have been used over the years and the only thing different between you and them is your installation.

    You will hear all kinds of well meaning BS on your 2 way radio, and for sure on the Internet as well, but don't be discouraged.

    Somebody has already posted to you that your problem had nothing to do with your 1/4 wave whip unless it is broken, and that too is more or less what I'm saying as well. Your problem is your ground plane, either the lack of or the excess of, or that puck you have installed.

    I think if you would take my advise and simply experiment a little with the whip like I describe above, I think you will see the difference. I'm 75 years old, and if I had a mind to, I could go out and in less that 30 minutes install my Marconi x antenna, as noted in the image you see next to my handle above. Then you could see that your ideas about a 102" whip with a suitable ground plane are all wrong. You don't have to take my word for it, you can prove it to yourself.

    I tried.
     
  6. The DB

    The DB Sr. Member

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    Impedance matching your antenna is key, if it isn't close to begin with as it is. A 1/4 wavelength vertical should need no impedance matching, and at resonance, give you a very reasonable SWR (but not a perfect SWR unless you are using angled radials).

    For a single antenna the only reason a half wavelength multiple of feedline would be of benefit is when you have an analyzer that is more capable than an SWR meter hooked up. When your radio is plugged in it cares about exactly one thing, and that is the SWR it sees is below its threshold (typically 2:1 or less). You could use that length for other things, like general operation, it definitely won't hurt anything, but it won't help either. Next time you see them try asking them why the length they want is so important, see if they have anything more than the "it will blow your radio" bs. I would like to know what they say.

    Tuners are one way of tuning antennas to multiple frequencies, and yes they do impedance matching. Some people think tuners merely hide the high SWR of an antenna from the radio, but there is more to it than that. Also, not all multiband antennas need tuners to have multiple resonant points with accompanying (or nearby at least) low impedance points. A fan dipole comes to mind, along with a trapped dipole.


    The DB
     
  7. buickid

    buickid Active Member

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    Sorry, I misunderstood your post. I've recently had little time during the day to get on WWDX, and after work, and other stuff is said and done, its late, and my brain isn't functioning so well :( When you said "but don't look for it to solve your TVI problem with your neighbor." I assumed you meant the radial experiment had to do with the Vector. As far as I know, the mobile doesn't bleed the neighbors.

    I am willing to do the radial experiment, and I believe you that it would work, but I can't drive around with the radials attached... :( I understand something must be wrong with either my coax, the puck, ground plane, or antenna, but I'm baffled as to what could be wrong. The coax is brand new, and connected securely, the puck is very well grounded to bare metal. Is it possible the shape of the puck is throwing things that far out of whack? It seems unlikely, but I could be very wrong. The antenna... well its a piece of metal, dunno what could possibly be wrong with it. I have to order a backing plate, the roof flexes a bit too much. When that comes in, I'll drop the headliner again and mess around with the puck and coax.

    Actually, I'm going to try bonding the vehicle and see if that helps the ground plane aspect of the installation. I've noticed there is a ton of structural glue at the seams of the car, not as many welds as one would imagine, perhaps bonding will make a difference. You are right, it seems unlikely that the antenna needs such extension to work properly, there is something else amiss here.

    Thanks again for your continued assistance Marconi, don't give up on me yet :D

    Alright, I understand. You made it pretty easy to understand there. You said that a half wavelength feedline would be of benefit with an antenna analyzer attached, is that to say that the MFJ would work better with such a feedline, as opposed to my random length that I have now?
     
  8. W5LZ

    W5LZ Crotchety Old Bastard

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    That electrical 1/2 wave length feed line has the characteristic of having the same impedance on the radio end as is at the other end. That means it's a way of having the analyzer (or transmitter) at the antenna feed point. The reactance in the feed line will affect what any meter will see, so that electrical 1/2 wave thingy is a nice thing to have.
    - 'Doc
     
  9. Lil'Yeshua

    Lil'Yeshua .......

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    Less head scratching too! (y)
     
  10. AudioShockwav

    AudioShockwav Extraterrestrial Admin
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    This is my own opinion and I may get heat for it, but 2:1 is fine, I have worked my radios and my DX500V into 2:1 swr for hours before at Approx 350 watts output.
    The time it becomes a problem is if you have a high dollar radio with high VSWR protection built in, or you have the thing running at redline.
    A lot of CB radios will work into a 2:1 swr almost infinitely at the rated output of the radio, it is when the radios are "peaked and tweaked" or amps are run at the edge of their ratings that it becomes a concern.
    Example is X-Force, they say that your SWR must be under 1:3 to 1, this is because they often rate the amp at the extreme edge of output, with voltage in excess of 13.8 volts.
    Ever notice that some SWR meters show a red line at 3:1 ?
    Or that experienced operators say that the guy on the other end will never know the difference between 1:3 and 1:8 ?


    73
    Jeff
     
  11. Marconi

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

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    To the buickid, no I wasn't thinking about your Vector again. I was just stating that if you experiment with the 1/4 wave whip close to the ground, like I described, you might still interfere with your neighbor. I use too many words already in my post, do I have to explain every previous work in order to get my points across? I fuss at guys for just looking at pictures sometimes and ignoring the text. Do you fit that category?

    Not the best setup maybe, but considering the whip could produce and almost perfect match, there is no question it will work, and I'm not sure you can tell the difference just using your radio.

    I don't know how bad you need the tuner in this case, or if you use the tuner just to see a very low SWR, but if you check it...that might tell you something about how bad the setup could be without the tuner.

    It could even be bad enough to see a performance difference if the install was done correctly. With such a setup, and not really knowing how this irregular ground plane is really effecting things, it might not be much better than a mobile install that is not producing a good match using a 102" whip or longer...like is also currently being discussed here in one of these threads.

    Right now I tend to get you and buickid mixed up. You both seem determined to make what might be considered by some as bazaar ideas work, and then when they produce issues, you look for the reasons. Nothing wrong with that as long as you're not looking for the best solution maybe.

    IMO, your last comment above is likely right on the money too, but I ask...is it any wonder, and is it important to know the answer.

    LY, are you fimilar with the story of Rube Goldberg and what he did in life? Check this out: Rube Goldberg - Wikipedia, the free encyclopedia
     
    #41 Marconi, Jun 8, 2013
    Last edited: Jun 8, 2013
  12. Lil'Yeshua

    Lil'Yeshua .......

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    I'm not familiar with Rube. My 1/4 wave 102" SS whip I use is temporary and the tuner is to fix any mismatches and to get the radio's output at the right power level. Plus,it's something I threw up just to get on the air. I have a new Vector 4000 still in the box but I won't deploy it until after I get settled after moving to the mountains. The CP Antenna I'm building soon is for right now something to occupy my time with.
     
  13. Marconi

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

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    I remember now somebody saying that a move was holding up their install of their Vector. Like I said earlier, I get you and buickid mixed up, so ya'll forgive me if I fuss at you for something that the other one said.

    I also understand temporary installs and convenience. Not that I'm always right, but my efforts would be to suggest pitfalls in approach if presented, and the ideas that come to my mind in the process of conversation.

    I have no fears however, that a 102" - 108" SS whip can and will work just like I've suggested for CB...providing a suitable ground plane is provided. And when I hear guys complain that this antenna does not work well, I know better. The problem is very often the ground plane, that the antenna sees well or not so well, and that is particularly true with mobiles.

    I have a mobile Eznec modeling presentation mostly ready, but it is complicated, big, and I don't think I can explain well enough for most to even come close to understanding what I'm trying to show so I probably won't post the idea.

    The gist of the idea is: due to the irregular shape and dimensions of various mobiles, the lack of good symmetry, and the fact it is impossible to really predict with much precision how the radiator responds to the ground plane...the performance suffers...even if the setup is working as good as we can possible make it. I compare this deficiency with a 1/4 wave antenna like the Starduster for convince. With the SD'r setup we can at least see the ground plane and change it for testing and comparisons.

    There are contesters that use certain well known vehicles with chareristic body shapes that claim helps them excel in performance. I guess that is the point I would make...whether such guys are right, wrong, or just guessing I figure some make their point clear by winning.

    Good luck,
     
  14. Marconi

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

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    'Doc, considering this 1/2 wave line idea does what you indicate, what happens to the values of R, X, and Z as seen at the transmitter end...if the load at the feed point is not perfect, the match is resonant somewhere else, and is not even close by say 20 ohms or more of reactance, which might be typical for an out of tune antenna?

    So, will the jumper you originally cut for your frequency of choice still show us pretty much the same load at both ends of this line that we would see if we had our analyzer directly connected at the feed point, instead of using the 1/2 wave tuned jumper?

    Whenever I use a tuned 1/2 line on a mismatched feed point, I still don't see the same values for R, X, and Z that I would see without the jumper connected and the analyzer directly at the feed point. I see feed line transformation values on the meter and they vary wildly.
     
    #44 Marconi, Jun 8, 2013
    Last edited: Jun 8, 2013
  15. W5LZ

    W5LZ Crotchety Old Bastard

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    All that I can say is that the impedance at one end of that electrical 1/2 wave is the same as the impedance at the other end. As for the specific values of 'R' and 'X', they may change slightly, but not much at all -IF- that section of feed line is really an electrical 1/2 wave length long. The times I've used such a thingy I found the correct length by using an antenna analyzer to determine that 1/2 wave length, not just calculating it and using a yard stick. The exact length of that electrical 1/2 wave length can change depending on the cable you are using. Not just from different brands/styles/sizes of coax, but between sections off of the same roll of cable. That's the only way I know to get it 'right'. I can't say why you are seeing different results.
    - 'Doc
     
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