Need help with designing a bottom fed rotatable delta loop for 20 meters.

Discussion in 'Homebrew and Kit Projects' started by KB0VFT, Jan 26, 2019.

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  1. KB0VFT

    KB0VFT XML Subscriber QRZ Page

    I have been considering constructing a bottom fed vertical rotatable delta loop using 2 telescopic fishing poles. If my calculations are correct each side would have to be around 23.5 foot long and would be bottom fed with a balun.
    I am having trouble finding suitable telescopic fishing poles in a suitable length. I suppose I would need a pair of 25 foot long poles to be long enough, or better yet a 7 meter set of poles. Some that seem to be the strongest I have seen were made from carbon fiber, others fiberglass. I am also not sure if the carbon ones would affect performance. EA Antenna sells one at DXEngineering that is made from aluminum tubing, but I am trying to reduce my cost by constructing it myself. Any ideas out there for me? I also know a 2:1 balun would be needed at the feed point.
    Terry KB0VFT Shivering in Minnesota with a 37 below zero wind chill.
  2. AA7EJ

    AA7EJ Ham Member QRZ Page

    Terry, I was going to suggest bamboo, but it may be tough to get in Minnesota HI HI .
    It is getting scarce in TX too.
    From my experience with delta on 20 - it does not do well with "flimsy" support.
    Fishing poles of most material will dance around.
    I had best luck with plastic cammo poles , however they are NOT UV friendly!
    Do not use bare hands when working with them after few years of Sun exposure.
    Take a closer look at delta radiating pattern, it may not be that advantageous to make it rotable.
    Perhaps two of them 90 degrees apart will do.
    Or you can go wild and feed it on side and switch the feed points as needed.
    But feeding on side gets to be mechanical challenge - see the "dancing" remark.
    As far as balun goes - if the purpose is to convert impedance - simple 1/4 wavelength matching stub works wonder.
    I used cheap 75 Ohms coax of odd multiples of 1/4 wavelength with success.
    Go to run,,,,honeydo...
    73 Shirley
  3. AA5CT

    AA5CT Ham Member QRZ Page

    I made a BIG roughly 16' x 16' vert rotatable loop a few years back using a lash-up of a couple 4 ft mil tent poles for the center support and one long cane/bamboo pole stuck in that, and then a series of two long cane/bamboo poles either side of that to hold the wire out.

    All those poles were tie-wrapped to gusset plate which was a shelf from a plastic shelving unit.

    With the five poles it kinda looked like the five-sided Chrysler/MOPAR star emblem.

    It worked well, while the bamboo held up ... it was a bear to take off one support and move it to another, but it was fun to do different experiments with, to null the ground wave during the day and watch the signal come up when sky wave picked up. Did these tests with KD6RF east of me on 80 meters using WSPR.

    When the loop was directly in-line to his station we would have a "circuit', rotating the loop and the circuit went away until the sky wave picked up!

    Overall wire length was 64 ft, or a QW on 80 meters, 1/8 WL on 160 meters.

    I used the feed network that Ben Edginton G0CWT describes on his webpages.

    I would still like to build another one using maybe telescoping fiberglass poles and masts like Max-Gain systems sells.

    Added: On 20 m a 4:1 balun should be all that is needed for a matching network for a 64 ft circumference loop. Delta or otherwise, +- windage.

    Last edited: Jan 26, 2019
  4. WA7ARK

    WA7ARK Ham Member QRZ Page

    @KB0VFT ,

    Since you are talking about two poles, I assume that you are asking about a loop in the shape of an inverted isosceles triangle with the apex at the bottom?

    If so, how high agl will you put the apex?

    How high agl the top wire?

    btw-per the ZED's posting requirements, this should be move to the Antenna forum.
  5. SM0GLD

    SM0GLD Ham Member QRZ Page

    I have a rotatable 20m deltaloop on my car using 10m long telescopic fishing poles.
    Using an LDG_Z11pro to do the tuning.
    The one with biggest mobile antenna wins:D
  6. KB0VFT

    KB0VFT XML Subscriber QRZ Page

    Your photo looks exactly like what I would like to do. I just have been having trouble finding a set of poles long enough to work. I plan on installing it with a light rotator on my 5th wheel camper that is stationary. I have a telescopic guyed mast. I have a MFJ 939 tuner to use with my IC-7100. Where did you find the fishing poles? And thanks for the reply and photo!
  7. SM0GLD

    SM0GLD Ham Member QRZ Page

    Here in Sweden, far from you I am sorry.
    DX-Wire have fiberglass poles
    And Spiderbeam
    I am sure fiberglass fishing poles are available in US as well.
    I am using about 7.5 meters of the 10m. The top sections are to flimsy to be useful.
    My rotator is built like an office chair with wheels and can be rotated by hand.

    Last edited: Jan 29, 2019
  8. KB0VFT

    KB0VFT XML Subscriber QRZ Page

    Thank you for your reply and photos! I will be thinking hard about this project until spring. I'm sure it's cold there as well. It was -30 degrees F here last weekend. I will keep looking for suitable poles here in Minnesota.
  9. VK3YE

    VK3YE Ham Member QRZ Page

    deleted - wrong thread

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