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PDL-II antenna has 2 feedlines.

Discussion in 'CB Antennas' started by commando57, Jun 12, 2013.

  1. commando57

    commando57 Member

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    I want to make a "poor mans Balun" at the feed point. Should I coil the feeds together or make separate coils?


     
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  2. davev8

    davev8 Gold Star/Marvin Award Member

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    I am not an expert but 1 will be around soon .....
    May ask what you are trying to achieve ?? if we know some one may have a different solution..
    Also is your PDLii on the ground? if it is i would love some photos and measurements of the matching network as i fancy a homebrew 3 element pdl2
    Thanks dave
     
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  3. Robb

    Robb Yup

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    Doesn't take an expert to figure this out.

    You don't need it. An 'ugly balun' as they are called - isn't needed for a PDL-II. On an Imax, A99, or some other vertical antenna - it may well be needed. "Don't try to fix something if it ain't broke". The PDL-II is a fine antenna and a balun won't do a thing. Waste of time. A balun is used to stop a problem called 'common mode current' that is a typical problem with vertical antennas.

    If you thought you would get more performance out of it; then you were wrong.

    Are you having a problem with your PDL-II?
     
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    Last edited: Jun 12, 2013
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  4. Shockwave

    Shockwave Sr. Member

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    I've had a few PDL II antennas and have a different point of view on this. The coax choke or balun is not just useful on end fed verticals. It can also be a benefit on many beam antennas. Common mode currents can be a problem when feeding a balanced element with a gamma. While the gamma takes care of most of the issues going from an unbalanced coax to a balanced driven element, there are often some noticeable currents that can cause the coax to radiate.

    With the PDL's I've used, I make a pair of separate chokes or use ferrite beads on the coax at the antenna. You want to separate your chokes if you use coiled coax. If you form both coax chokes together, the one in use can induce unwanted currents into the other coil and cause that coax to radiate.

    In all but the most severe cases, we are not adding these chokes because we expect to see noticeable improvements in antenna performance. Adding chokes on a PDL-II is usually done to reduce RFI since there should not be CMC levels high enough to cause noticeable distortion in the pattern or significant loss of drive to the antenna due to power radiated on the coax.

    Dave, I have a completely rebuilt PDL hanging in my shop. It's mostly assembled and had a perfect SWR when I used it last year. If you need any measurements on the orbital gamma matching system, I can provide that to you. Let me know what you're looking for specifically and I'll take some measurements.
     
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  5. w9cll

    w9cll W9WDX Amateur Radio Club Member

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    I think it won't hurt or overerly help it. I had a PDL up for years, even retuned to 10 meters when I became a ham. It worked great as is and I really had no issues with it. I don't believe the gain figures, it's closer to 9db then the stated 12 but overall an awesome antenna.
     
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  6. commando57

    commando57 Member

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    PDL-II

    Vertical is perfect 1.1 and 48 ohm. Horizontal is 1.3. Antenna is just up enough for checking vswr. I am getting a lot of noise (3 2950 bars) that I don't have with my Antron. Reflect is 5-6 on vertical and I haven't transmitted horizontal till I adjust. I can hear rf in the house that is not there on the Antron. I haven't grounded anything yet. More to come.
     
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  7. Shockwave

    Shockwave Sr. Member

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    The SWR should be tuned with the reflector on the ground and the driven element pointing up at the sky. Tuning it low to the ground and in its normal upright position will cause the SWR to change once its up higher.
     
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  8. davev8

    davev8 Gold Star/Marvin Award Member

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  9. Marconi

    Marconi Supporting Member

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    Dave I'm not sure I completely understand here, but for someone to do as I think you are suggesting and be accurate and complete in the task, they would have to go to a lot of trouble measuring and recording every detail in the PDL and then duplicate all the parts to a "T".

    Even the Avanti manual doesn't do enough to be that useful for such a purpose. You may have to talk to many different folks or ask a lot of questions about such detail before you are convinced you are ready to proceed on this one.

    Many times I have requested dimensions that I could use for a model of a far more simple antenna, and one that I don't own. That effort is always lacking just talking to one who can and will help.

    The guys try, but it is not an easy task, unless you understand all the pitfalls in not getting all the info right on the money. There are little dimensions that matter, here and there, that our just looking at...may not seem that important. Even when I have an antenna that I can physically measure, when I sit down to input the idea to a model I find some little dimension that I need...and I forgot to consider or measure. Of course you can buffalo your way thru a project and then spend a lot of time working out the details and issues later.

    Do you think this might be why these antenna manuals are not fully comprehensive in their dimensions. To me it would seem they are only providing enough detail, and many don't, to get the thing put together with the parts provided. They are not providing all the dimensions and discriptions needed to duplicate every detail.

    IMO, to build a PDL2 from scratch is just as detailed if not even more so. Example, when I model and I come to an insulator for example, I just make it empty space, I don't have to create the physical item for the model.

    The PDL is a complicated design just looking at it, especially the matching network, and unless you duplicate everything to the "T", I can see possible trouble ahead. I would be surprised if you found the site you noted above, and it showed you absoutely every detail and its dimensions.

    I hope I got your point right that you posted, and this is helpful.
     
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  10. davev8

    davev8 Gold Star/Marvin Award Member

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