Tower rotator coax loop

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by VA2CST, Aug 22, 2019.

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  1. VA2CST

    VA2CST Ham Member QRZ Page

    Hello everyone,

    I was curious how do you guys install coaxial loop between the tower and rotating mast ?

    I will need 4 coax in the tower (1hf beam, 2 yagis v/u and 1 gp9). The coax I have is 9913 which is pretty rigid and I am having difficulties to make this work properly on top of all, my azimuth rotor is 450°.

    Any suggestions on how to build a proper coaxial loop for leaving loose between the tower and rotating mast ?

    Thanks !
     
  2. WA2CWA

    WA2CWA Ham Member QRZ Page

    When I first used 9913 for a number of feedlines up the tower, I terminated each of them below the rotator with a length of RG-213 (nice flexible cable) which then went to each beam antenna. Now providing coax slop around the rotor was no longer a problem.
     
  3. VA2CST

    VA2CST Ham Member QRZ Page

    so a couple questions, if you terminated the 9913 runs below the rotator, that means you did need female/female adaptor and then terminate again RG213 runs also. I suspect you were using these for HF purpose which I think is not critical but how about loss in all those connectors ? I was about to do something like you describe but how would it affect UHF antennas ?

    Also, do you think that joining different type of coax cable with different velocities can cause issues ? If you were doing that install procedure for HF antennas, have you ever thought of trying to find the resonance lenght of your coax cables ?

    And lastly, how did you arrange the loop of RG213 ? on top of the top plate and roll the coax cables around the mast ? When I did try this manually, the loop became too loose and got cought around the tower when I started to go back in the other direction...
     
  4. WA2CWA

    WA2CWA Ham Member QRZ Page

    I did this for a 5 element HF tri-bander, 6 meter beam, and 2 meter beam. I think I also did it for a 432 beam but it was only up for a few years. The rest of the arrangement was up for about 20 years. Never worried about any loss which in all probability was minimal.
    HF antenna cable had UHF connectors; VHF stuff had N connectors.

    I wasn't looking to turn this into a technical project. The goal was to get it around the rotor without stretching or breaking when the rotor was turning.
    The flexible coax came from each antenna and was bundled above the rotor on the vertical mast. The rotor and antennas were pointed North and roughly 3 or 4 feet of the flexible coax (all bundled with tape and ties) was hung loosely and then attached below the rotor (in my case to the tower (rotor was inside the tower)). The junction of the RG-213 and the 9913 was in this area.

    I have a bunch of tower pictures somewhere but not handy. If you Google "coax loop around the rotor", you'll see other examples of how it can be done.
     
  5. VA2CST

    VA2CST Ham Member QRZ Page

    Thanks for the suggestions and reply. Yes this is what I was trying to find on google picture but I did not find many things that looked nice... seeing a bunch of tiewraps crushing coax cables as they twist around the tower and mast wasn't what I was looking for...

    https://images.app.goo.gl/gdW2hCQV6gLuWzmt8

    https://images.app.goo.gl/4ojdmaGwS73dG13eA

    https://images.app.goo.gl/exE3toa7osePEi2DA

    But I think the best looking one I did find was on eham totally by hazard because I was reading about grounding tower...

    Check out that installation : https://www.eham.net/ehamforum/smf/index.php/topic,121912.msg1089182.html#msg1089182

    Really nice but when I did try it, having a 450° azimuth, it made a huge droopy loop and became really tight when it was turned the other way around... and it must have cost a fortune of hardware to make this work and seal everything !

    Anyway, thanks for all your suggestions and input. I guess I am looking into too much details with the coax resoance and so on...

    73 de Claude VA2CST
     
  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    All the coaxial cable runs on both my towers are Andrew Heliax. The Heliax is secured at the top of the tower and then RG-213/U goes from the female connector on the Heliax (using a barrel between 2-male connectors works fine as well) and is secured, to the mast, a few inches above the top of the tower.

    Rotate the antennas half way before securing the flexible coaxial cable to the mast. Leave at least enough flexible cable so that the antenna can rotate both directions. I, generally, leave a "bit" more even enough for the antennas to rotate at least a complete turn. We are talking about maybe no more than a couple feet of flexible cable between the secured points and then more up the mast to the antenna. Even on 432 MHz, the loss in the RG-213/U is not enough to worry about.

    Glen, K9STH
     
  7. VA2CST

    VA2CST Ham Member QRZ Page

    Hi Glen,

    yeah, I think I am going to go that route, I did not wanted to add connectors and barrels but I guess it wont have that much impact specially on HF and VHF.

    Out of curiosity, like I did ask to the previous poster, did you take into account the coax resonance and cut it to the right lenght or you did not take attention to that ?

    Thanks for the suggestions, I appreciate it.
     
  8. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    CST:

    Having the coax cable a "certain" length, except for very special use like when stacking antennas, is a CB "old wives tale". How long the cable, around the rotor and then up to the antenna, has to be is "just long enough" to do the job. Since the impedance of the main cable is the same as the short cable around the rotor, it is, basically, like the cable is continuous.

    Yes, with a time domain reflectometer, you can see a VERY slight "bump" where the connectors are located. However, as far as the performance of the cable is, you will not be able to tell that there are 2-different cables involved.

    Glen, K9STH
     
  9. K4ZA

    K4ZA Ham Member QRZ Page

    Am responding because, once again, there's a post which mentions "connector loss" or loss in coaxial cables
    at HF/VHF which is simply insignificant.

    The critical issue here is your rotator (likely Yaesu) proving 450-degrees of rotation. Whenever I encounter this, I find myself wondering why, et cetera. But I digress....ending the Heliax or 9913 in your case near the tower top is, of course, step one.
    Use wire ties or Kellem grips so it is absolutely secure. Install proper adapters to mate with RG-213. The 213 will run from each Yagi feedpoint, down the boom & then down the mast, to this point. I allow six feet for the rotation loop. I always
    try to use the lowest Yagi boom as the "departure point" for the bundle of 213 runs. This keeps it out, away from the tower (especially important if you have a flat top) & allows it to hang freely in space. Doing this "after the fact," as I think you want to do, will be very very hard, as those 213 runs need to be measured precisely, from feedpoint to the 9913 junction. They are simply taped together (Scotch 88) every six inches or so, & should provide years of trouble-free service. If the lower Yagi will not allow or provide a convenient place to attach the bundle, I often install a small aluminum angle "yardarm" to provide the attachment point.

    GL 73 Don K4ZA Tower Works Charlotte NC
     

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