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Ham Radio - A 6 meter cage dipole using window line.

Discussion in 'Amateur Radio News' started by KB7TBT, Mar 23, 2021.

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  1. KA2RRK

    KA2RRK Platinum Subscriber Platinum Subscriber QRZ Page

    Taking your previous Google ( I spell it -Grrrrooogle) I found out that none other than the folks in Hollywood invented this concept for a Hero...

    giphy(2).gif

    RRK
     
    N7LOH and AK5B like this.
  2. KM1H

    KM1H Ham Member QRZ Page

    The boarding ladder was invented hundreds of years earlier. No fun learning how in choppy waters the first time aboard ship or a chopper.
     
    AK5B likes this.
  3. KE8QEP

    KE8QEP XML Subscriber QRZ Page

    He had two pairs (4 conductors). Does a cage dipole need more than 4 conductors to be considered a cage? I'm asking the question honestly. Does his dipole have complications that other cage dipoles also have?
     
  4. W1LWT

    W1LWT Ham Member QRZ Page

    so much drama on a nice idea and concept....great idea to experiment with....Drama isnt needed It wil chase young new HAMs away.....let talk about the concept to work from...
     
    N4GST and AJ6KZ like this.
  5. N2EY

    N2EY Premium Subscriber QRZ Page

    No.

    The honest answer is no. Four wires can be a "cage dipole". Heck, three wires can be a "cage dipole". But see below.

    The main issue is that there's a considerable amount of added mechanical complexity to get a wider SWR bandwidth which won't be used because, by his own admission, practically all his operation is confined to the lowest 500 kHz or so of the band.

    IOW, why all the complexity just to get a lower SWR on frequencies he doesn't use?

    Almost as important is the fact that his design is more mechanically complicated than a simple dipole made of tubing or pipe.

    That said, what's good about the video is that it clearly demonstrates how increasing the effective diameter of dipole elements increases the SWR bandwidth.

    All a "cage" does is give the effect of elements of large diameter with less material. On 6 meters one could just use 1/2 inch or 3/4 inch tubing for elements to get the same effect, but at lower frequencies doing so becomes impractical very quickly.

    The 80/75 dipole at W1AW is a cage about 3 feet across that gives low SWR across the entire band. It is based on a design by WA4DRU in QST for December, 1980 ("Broad Band 80 Meter Antenna"). This is the article linked to be @KA0HCP.

    The antenna described by WA4DRU is a four-wire cage 3 feet in diameter, 124 feet long, with an average height above ground of about 60 feet. The calculated SWR is just above 2 to 1 at the band edges; the measured SWR is considerably lower (1.6 to 1 at 3500 kHz, less than 1.4 to 1 at 4000 kHz, 1 to 1 for about the middle 100 kHz of the band.

    The article includes the relevant formulas for things like the effective diameter of multiwire cages, and how the increase in diameter affects the overall length compared to resonant frequency (the thicker the effective diameter, the shorter the dipole needs to be to resonate at a given frequency.

    One interesting factor given in the article is that the number of wires in the cage affects the effective diameter of the resulting conductor.

    The article gives the following results for N wires arranged in a circle of diameter D.

    With 3 wires, the effective diameter is 0.4214 times D
    With 4 wires, the effective diameter is 0.5903 times D
    With 5 wires, the effective diameter is 0.7563 times D
    With 6 wires, the effective diameter is 0.9200 times D

    As can be seen, there's little reason to go beyond 6 wires. Two spreaders spaced 90 degrees works for 4 wires, and three spreaders spaced 60 degrees works for 6 wires.

    The Big Problem is the increased weight - four wires plus the spreaders every so many feet. At both W1AW and WA4DRU, the antenna is supported at the center as well as at the ends.

    ----

    There's another solution that is seen less often - the "fan" or "biconical" dipole.

    Back about 25 years or so, a Field Day group I was involved with wanted a dipole that would cover 80/75 meters with low SWR. The solution I devised was a "fan" or "biconical" dipole, which looked like this from above:

    ><

    Just four wires, a hefty center insulator, and two wooden spreaders at the ends. All four wires were the same length (60 feet as I recall), and the end spreaders were about 8 feet long. The resulting antenna covered the whole band with less than 2:1 SWR. Much simpler than a cage, but it took a bit of experimenting to get the design right.

    (Do not confuse this kind of "fan dipole" with the same term applied to a multiband dipole that uses wires of different lengths for each band).

    Cage antennas aren't new; they were in use in the 1920s and earlier. What has increased interest in them in recent decades is that modern radios and amplifiers (particularly solid state) want low-SWR loads, and many operators don't want to have to deal with a Transmatch (aka "tuner"), particularly for high power. On the 60 through 10 meter HF bands a single-wire have-wave dipole usually gives acceptable results because the bands are narrow as a percentage of center frequency, but 80/75 and 160 are a different case. (Divide the width of each band by the center frequency and you'll see the problem.)

    73 de Jim, N2EY
     
    AK5B, K2XT and KE8QEP like this.
  6. N2EY

    N2EY Premium Subscriber QRZ Page

    A bit of follow-up:

    I'm not sure of the exact dimensions of the window-line used, but let's be optimistic and assume the spacing is 1 inch. With four wires arrayed as shown in the video, the spacing between diagonally-opposed wires is about 1.414 inch. Multiply by 0.5903 (four wire cage) and we get an effective diameter of 0.834 inch.

    If the spacing of the window line is 3/4 inch, applying the same math yields an effective diameter of 0.626 inch.

    ----

    A bit of opinion:

    YouTube videos are great IF they are well done, and the video that started this thread is pretty good. In particular a good video can show things in detail and let you hear the results too.

    OTOH, videos aren't "random access" the way text material is - you can't scan through it looking for a particular part the way you can with a book or a posting, and the rate of information transfer is whatever the video maker decided - you can't really speed-read a video.

    That said, I applaud the ham who made the video, because he's at least trying to show what can be done with available materials. He's showing us what he's doing now, today - and what he says is technically correct even if it's not exactly the way you or I would do it.

    Heck, if I ever decide to get on 6 meters using a dipole antenna, I know how I'd make it - because of this video.
     
    AJ6KZ, AG5DB, AK5B and 1 other person like this.
  7. KM1H

    KM1H Ham Member QRZ Page


    Youre correct, sorry about that but my other statements still remain as do those from others that arent fans of this antenna.

    Altho in fairness since you havent written a biography on QRZ.com which may be new to you, or otherwise stated your qualifications ,what I said stands on its own merits.
    I also suggest no reply as I consider this subject CLOSED an continuation will be viewed as harassment.


    A question for others: How much loss is there in that antenna including the cage material AND PVC pipe it is attached to? Any loss automatically increases the bandwidth.

    Carl
     
    AK5B likes this.
  8. KM1H

    KM1H Ham Member QRZ Page

    You "devised" ? Id call it copied as that method has been around a lot longer. I had them for 80/75/low 160/high 160 all on one feedline in 1990 and copied it from an article that I dont remember where now. It was also picked up by YCCC members shortly after, of which I was one.
     
  9. K2XT

    K2XT Premium Subscriber QRZ Page

    One thing to keep in mind is in a fan dipole where the wires are for different bands there is minimal interaction and you end up with a low swr on each band.
    I'm going to have to model these configurations (KM1H and N2EY) and see if there is a difference because of the reduced coupling between segments., presumably, in the N2EY model because of the angle between the segments.
    So, Jim, your elements were equal length, and Carl, yours were not, is that right?
     
  10. W7ASA

    W7ASA Ham Member QRZ Page

    The author is on-the-road and thus constantly setting-up in new locations. Because this cage antennas SWR curve is flatter, the changing antenna environment from one location to the next: (height, foliage , ground moisture etc.) are far less impactful. Beside which, it's a good demonstration of how broader elements effect an antenna.
     
    AJ6KZ and N2EY like this.
  11. N2EY

    N2EY Premium Subscriber QRZ Page

    Yes. Perhaps the best description is "bow tie".

    I made no claim of originality. I got the idea from an early 1950s QST article. Its main attraction was mechanical simplicity.

    You might want to try modeling it as I drew it previously, and again with the far ends of the elements tied together so it looks like two isosceles triangles pointing at each other.

    73 de Jim, N2EY
     
    WS4JM likes this.
  12. KA2RRK

    KA2RRK Platinum Subscriber Platinum Subscriber QRZ Page

    Didn't Faraday prove that a cage was good for something already?

    RRK
     
    N2EY likes this.
  13. N8OX

    N8OX Premium Subscriber QRZ Page

    Personally, I didn't think your response was 'snotty.' Can't say the same for the other two by KM1H. If you don't like repetitive YT videos, why watch them? And if you can't provide something constructive, why comment at all? Build on what was there... improve it, not tear it down.
     
    AJ6KZ, N2EY, AG5DB and 1 other person like this.
  14. KM1H

    KM1H Ham Member QRZ Page

    Each inverted V was cut to low and high end minimum VSWR with a resultant Figure W display. Spacing was at or close to right angles for each band since I had sufficient room. Height was 160' with ropes ~ 30' high at tie down and end insulators "way up there". Trimming was a PITA since each end had to be lowered, trimmed and raised; each end was constructed with a pigtail so trimming did not require any extra work. The actual feedline end was brought outside and a MFJ 259B used. The tower end of the coax was well decoupled by large 43 mix toroids as I had years of common mode/signal leakage experience working on the CIA/DoD Tempest program for Sanders Associates, a major defense contractor, (now BAE) and then Wang Labs. I was fully aware of the shortcomings of this method but there werent many instrument choices back then. The barefoot rigs and amps were happy which was all I really cared about at such low frequencies.
     
  15. KM1H

    KM1H Ham Member QRZ Page

    Since KE8QEP and I settled it peacefully why did you see fit to Troll into the discussion and try to deliberately cause trouble.....which you didnt anyway as I saw you for what you were and hope others have also.

    Id thank you not to bother me again.

    Carl
     

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