Height vs. monoband

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K5TBA, Nov 20, 2018.

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  1. K5TBA

    K5TBA XML Subscriber QRZ Page

    I'm curious what people would deem more important.

    I have 5 New Carolina Windom (NCW) monoband dipoles for 80-40-20-15-10m (incorporating vertical radiation for better take-off angle at shorter heights) on a single mast that work well. Due to the weight and bulkiness I can only handle them by myself up to a height of 25'. I don't want to spend the money on or deal with a tower but am contemplating a push-up pole. And I don't want to have to rely on another person helping me raise/lower the antenna when needed. So if I stick with my 1.25" steel mast, would you rather leave things the way they are or switch to a single multiband NCW antenna which I could manage up to 40'? I have an external tuner that can handle the multiband SWRs.
     
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    A word of caution. Putting an OCF antenna's feedline parallel to (and close to) a metal support is fraught with problems. Ask me How I know...
     
    NH7RO likes this.
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I'm not familiar with a 'New Carolina Windom Monoband' that sounds like an oxymoron as Carolina Windoms have historically been a variation on an OCFD and multiband by definition.

    So it sounds like it's some form of OCFD optimized for single band operation and including the voltage balun at the feed point and a current choke at the bottom of the vertical radiating section. If so, I can see how five of these would place a lot of strain on your mast.

    But in terms of your basic question, outside of some specific low frequency NVIS applications it's always best to get horizontally polarized antennas up as high as practical. If that requires fewer antennas or a lighter set of antennas I'd go with something like a balanced feed line fed Doublet (perhaps with a remote tuner at the base of the mast and coax back to the shack) or a set of parallel (aka fan) dipoles which should be lighter as it would only have a single 1:1 current choke balun at the feed point and not a pair (voltage balun and line choke) per antenna not to mention one coax feeder, not five. With a well designed set of parallel dipoles you should only need 4 pairs of radiating elements to cover the five bands you listed as the 40m elements should tune pretty well on 15 meters.
     
    Last edited: Nov 20, 2018
    NH7RO likes this.
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    The NCW is discussed here: http://www.hamuniverse.com/k4iwlnewwindom.html

    How did you put five of them on a single mast? Are they inverted vees aimed in different directions, or parallel, or what?

    How do you keep the vertical radiator portion away from the supporting mast?
     
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  5. K5TBA

    K5TBA XML Subscriber QRZ Page

    What I have is hybrid NCW's, they're center-fed instead of off center-fed which works better for monoband. The NCW aspect is the RG-58 vertical radiating coax. The top portion of mast that all the vertically radiating coax is attached to is a 20' fiberglass crappie pole so no metal. The five individual coax feeds go into a remote switch at the bottom of the fiberglass pole. There's a 1' length of coax between the switch box and a 1:1 current balun. LMR400 feeds the rest of the way from the radio. If you look up my QRZ page, there's a picture of it all.
     
  6. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Hmmmmm, if the antenna is well balanced which you'd expect with a center fed there isn't likely to be a whole lot of common mode on that unchoked vertical 'radiating coax'. Sure even dipoles with well measured and equal elements can have some imbalance and common mode, hence the common recommendation for a 1:1 current balun at the feed point. But unless the installation forces an awful lot of current imbalance I'd be surprised if there was enough common mode RF current to substantially improve the pattern when the antenna was hung low. IOW, the vast majority of the RF current will flow in the horizontal elements in a center fed antenna. It would be interesting to measure how much RF common mode is actually on that vertical section of coax with the antenna in its installed position.

    I'd scrap all but one center insulator and reuse the wire elements in the form of a fan dipole and choke it with a 1:1 current choke at the feed point. It's a tried and true approach, will eliminate the need for the remote antenna switch and should reduce weight on your mast allowing you to raise it up higher.
     
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  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    ^I agree.

    Going to center fed rather than OCF pretty much invalidates any advantage of the vertical coax intentional radiator, since common mode should be very small.
     
  8. NH7RO

    NH7RO Ham Member QRZ Page

    ^^Me three.
     
  9. KP4SX

    KP4SX XML Subscriber QRZ Page

    Ditto.
     
    WA8FOZ likes this.
  10. K5TBA

    K5TBA XML Subscriber QRZ Page

    Thanks for the replies and analysis. Over the past 3 years I've gone from a 40m NCW OCF to a fan dipole and then the separate monoband antennas. The fan was frustrating because 10m would never play nice with the other radiators (SWRs and broadbandedness was lost when it was combined with more than one other set of radiators) so I split it off and had to move it 4' down the mast before it quit reacting to the others. Once I split it off I thought why not split the others off in order to get them not to react to each other as much but still using a single feedline (similar to the way a hexbeam is set up) but the SWRs were a constant battle (tuning one antenna affected the others). At that time I didn't know about remote coax switches but figured there must be something out there that would allow me to have one coax to feed 5 antennas and once searching I found the Ameritron switches. That led to the current configuration and as I mentioned earlier it has worked very well (making contacts in Africa on 80m at only 25' high!). which also made me think that the vertical radiation must be working.

    If I removed the remote switch it would subtract about the same weight as a 10' section of steel mast and help alleviate some of the unwieldiness so that's something to think about but I don't want to go back to a fan dipole.

    This is just something I've been kicking around and what I may do is move my 40m G5RV to the opposite side of the yard from the array and make it an 80m NCW OCF at 40' to compare.

    Thanks again!
     

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