Woud a disguised Cobweb work the same?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by G1YBB, Sep 8, 2015.

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  1. G1YBB

    G1YBB XML Subscriber QRZ Page

    Actually, I had planned to drive out from Vegas one evening for a sunset at Valley Of Fire but we never bothered.
    And although we went to Monumenet Valley, as close as the pay booth to enter, the remnants of Norbert caught up with us there and it was thundering and lightning and HAMMERING down with rain, flash flooding the park so we never went in.
    We plan to try again in 2016!
    Route milage was 4000+ miles. Trip was 3 weeks, though we had 2 nights each in SFO and LA, and four nights in Vegas, so essentially 4000+ miles in 2 weeks :)
    LOVED every minute of it (I did all the driving)

    Ham rock is just a rock LOL. Balanced rock is more interesting.
     
  2. WA4SIX

    WA4SIX Ham Member QRZ Page

    Darn, I have friends that departed from Arches this morning. I will see if they got a pic of it.

    Ed
     
    G1YBB likes this.
  3. G1YBB

    G1YBB XML Subscriber QRZ Page

    @G3TXQ raising this one again Steve as making some progress now I have a couple of specific questions if that is OK.

    I'm following your design here, and was wondering if you would know if the wire you used was likely to be 16/0.2mm or 24/0.2mm (as two of the common sizes) as I have just measured some and get sizes of 0.9/1.7 and 1.1/2.0 for the conductor/insulation diameters respectively.
    I'm leaning towards the 24/0.2 as it's slightly larger (better bandwidth?) but of course at home it is a reel of 16/0.2 I have...

    For the balun, is the 510mm for the RG316 lengths for the length of complete undisturbed braid?
    I am assuming RD316 is fine, as the difference is the extra braid layer?

    Finally, the junction box 'bus bars', are they critical in length/width/type at all?
    I've seen some that are pretty industrial looking and some more compact like on yours.
     
  4. G1YBB

    G1YBB XML Subscriber QRZ Page

    Also, is this true about the cobweb?

     
  5. G3TXQ

    G3TXQ Ham Member QRZ Page

    I believe it was the smaller size. But any difference in tuning will be swamped by other environmental factors, and you certainly wouldn't notice any difference in SWR bandwidth.

    Yes, the double-braid variety is fine. The 510mm is not critical - it was just to give folk some sort of indication of how much they would need; if in doubt cut it slightly longer. The important thing is that all 4 lengths should be the same - within say 5mm.

    They are not critical - any differences will simply result in slightly different wire lengths when tuned.

    Whoever said that will be taken out and shot, come the revolution :)

    Steve G3TXQ
     
  6. G1YBB

    G1YBB XML Subscriber QRZ Page

    Thanks Steve.
    So as usual, higher is better?
     
  7. G3TXQ

    G3TXQ Ham Member QRZ Page

    Yes - it follows the same rules as other horizontal antennas. Take a look at performance vs height in this chart:

    [​IMG]

    You can interpret the vertical axis as "comparative dB"; so, for example, lifting the antenna from 20ft to 50ft would give you an improvement of around 6dB on a long-haul 20m path. Does that sound like 20ft is ideal ? :rolleyes:

    Steve G3TXQ
     
  8. G1YBB

    G1YBB XML Subscriber QRZ Page

    Thanks for the graph. I have always been a believer in bigger is better. :)
    So wanted to check.
     
  9. G1YBB

    G1YBB XML Subscriber QRZ Page

    @G3TXQ I have it all modelled up now to prove (to myself) it will all work mechanically.
    I've used your wire lengths as the start point, and kept the ends all 6 inches apart to start. (I'll actually start with longer wire of course but hopefully after trimming will be near that)
    Took some fiddling around in the 3D world ( a lot to be said for your 2D design in that respect! :) ) but I have all wires within 0.05 of an inch of suggested sizes, so my arm placements should work allowing for trimming the arms.
    I used the 17m wire as the 'straight line' reference point, which I notice in some threads (and some google images) you said often works out to be the way it lies.
    Everything in 3D model is taken from actual life measurements except for the hub, which will be 3D printed.

    I may well add some guys on a higher point on the pole if needed but not sure I will.

     
  10. G3TXQ

    G3TXQ Ham Member QRZ Page

    Good stuff - now you just need to add the washing to the model!

    Steve G3TXQ
     

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