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Simulation Fun: Rotary 5-Band Antennas - Let's Compare Them

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by SP3L, Jan 25, 2016.

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  1. N4XYZ

    N4XYZ Ham Member QRZ Page

    Hi, I have a CL-33WARC and my SWR is much like the model indicates. It is up 31 ft but it is close to my house so as it swings over the house I don't know how that affects performance. I have not learned to use the modeling SW yet but have been thinking of adding 12/17 reflector to add a bit of gain on those bands. I thought that it would have to go next to the director so 12/17 would be reversed. I would love to hear what you model says for a 12/17 reflector.
    Thanks for all the work and education
    73, Dave N4XYZ
     
  2. SP3L

    SP3L Ham Member QRZ Page

    Cat’s Whiskers and Cat’s Whiskers Beam

    Part 1

    As we need to wait for a while for Ben to report his CL-33-M WARC improvements, I take the liberty describing the antenna I have just started to built.

    I developed the antenna to fit my personal needs. If you have similar requirements, it may be interesting for you, too. My requirements were:

    1) the new antenna should give me a noticeable increase of gain in DX contacts (>3 dB) when compared to my present Cobweb antenna;

    2) it should be able to transmit at least 100 W continuously;

    3) it should be very light (<7 kg or ~15 lb.) to allow me to hoist it up on my push up mast; note that the lightest reliable rotator will add another 3.5 kg (~7 lb.) to the weight;

    4) assembled on the ground, it should not require any further tuning; once hoisted up, it should cover any amateur frequency from 14.000 through 29.000 MHz;

    5) it should be easy to mount the antenna on my push up mast; the mast, when lowered, is only 1.6 m high (5.25 ft.);

    6) to avoid touching a nearby tree, the antenna turn radius should be less than 4.5 m but 4 meters (~13 ft.) is very desirable.

    From the commercial antennas, probably only the light version of Hexbeam was close to meet all my requirements. However, it was about 10 kg and I was not sure about the requirement no. 4. Will it really not require any tuning after assembling on the ground? I was rather sceptical about that. I did not like the prospect of hoisting it up and drawing it down a number of times to cut wires. So, why not to design something new?

    My first step was to design a broadband driven element. The first option to consider was the Origami already described in this thread. Just to refresh your memory, this is how the Origami looked like:

    upload_2016-5-10_14-38-45.png

    However, its hub is 2 meters above the bottom wire what means that I would have to mount it on a not fully collapsed push up mast – at the height of approx.. 3.3 m (~11 ft.). Moreover, its turn radius seemed to be a bit too big.

    That’s why I modified the Origami in such a way to bring the hub closer to the bottom wire. And in this way, the Cat’s Whisker was born.

    upload_2016-5-10_14-40-15.png

    The Cat’s Whisker turn radius is smaller than the Origami but its height is a somewhat greater. The hub is now 0.5 m (~1.5 ft.) above the bottom wire what makes mounting the antenna on a mast more comfortable. Its structure is still based on 4 spreaders on which a rectangular wire frame is stretched (see the picture below).

    upload_2016-5-10_14-41-4.png

    The spreaders do not have to be non-conductive ones as in the Cubical Quad. You can even make them with aluminum tubes. Their lengths are approx.: 5.4 and 3.7 m (17.7 and 12.1 ft.). I estimate the antenna weight as 4…5 kg (8…10 lb.) if the spreaders are made of fiberglass poles.

    The performance of the Cat’s Whiskers is similar to the Origami.

    SWR is low and nicely flat in the 14-30 MHz range (balun 6:1 must be used).

    upload_2016-5-10_14-43-44.png

    If fed with 30 meters of RG-58 coax, the SWR at the transmission line end will be below 2:1 for any frequency in the whole range. More precisely less or equal to 1.85:1. Seems that even a transceiver without an ATU can run it.

    Gain is greater than a half wave dipole (2.15 dBi) and increases with frequency:

    upload_2016-5-10_14-45-52.png

    And the combined gain of the antenna and transmission line compared to the other single element antennas looks like that:

    upload_2016-5-10_14-46-52.png

    To be quite sure that I can trust the results, I additionally simulated the Cat’s Whiskers in the MMANA-GAL program. The results were similar although the MMANA-GAL was more optimistic.

    upload_2016-5-10_14-47-41.png

    Every of the two models had to be slightly modified in order to overcome the NEC2/MININEC engines limitations. In the 4nec2 model, there are short transmission lines used near the feed point, while in the MMANA-GAL model, additional 5 cm (2”) long vertical wires are inserted between the bottom wire and the rest of the wire structure to avoid very acute angles. These modifications are so small that I do not expect them to noticeably impact the antenna characteristics.

    The Cat’s Whisker can be used as a standalone antenna if you are satisfied with the performance equal or only slightly better than a half wave dipole.

    To get more gain, you need to add some reflectors and directors. I will describe the Cat’s Whiskers Beam in the next post.

    Jacek, SP3L
     
  3. SP3L

    SP3L Ham Member QRZ Page

    Cat’s Whiskers and Cat’s Whiskers Beam

    Part 2

    To create the Cat's Whiskers Beam, I added a perpendicular boom and got a structure as shown below. The boom is shown in red ink.

    upload_2016-5-10_16-34-40.png

    Then, I connected several V-shaped directors and reflectors to the front and rear section of the boom. In this way, I created a hybrid solution: non-resonant broadband driven element and resonant reflectors and directors. The picture below shows all the wires needed to build the antenna. To avoid the problem with different band elements interaction, I used the same trick as Nick did in some of his designs: the antenna radiates backwards in the WARC bands.

    upload_2016-5-10_16-35-31.png

    In a real world implementation, the director and reflector wires must be extended with pieces of rope so that they can be attached to the ends of four spreaders used for the driven element. The antenna turn radius increased to 4 meters as I had to make the boom long enough for 20 m band. Such radius was still acceptable to me.

    The performance of the Cat’s Whiskers Beam.

    The SWR is no longer as flat as in the single element version.

    upload_2016-5-10_16-36-15.png

    The antenna gain (forward direction, transmission line not included).

    upload_2016-5-10_16-36-57.png

    The antenna gain (backward direction, transmission line not included).

    upload_2016-5-10_16-37-29.png

    The gain of the antenna and transmission line compared to the other antennas looks like that:

    upload_2016-5-10_16-37-54.png

    The Cat’s Whiskers Beam when simulated in the MMANA-GAL produced almost identical results.

    upload_2016-5-10_16-38-22.png

    The F/B ratio of the antenna is not very impressive but acceptable to me.

    upload_2016-5-10_16-39-15.png

    When “tuning” the Cat’s Whiskers Beam in the simulator, I was changing the length of the directors/reflectors in 5 cm (2”) steps. Actually, in the lower bands, it was even 10 cm increments. Thanks to the broadband driven element, the antenna SWR and gain were changing much more gently than in an antenna with a resonant driven element. That’s why I believe that when making this antenna with reasonable accuracy of, say, 1 inch you will not have to take it down to re-adjust elements length.

    I did not updated the table and model pack yet. I will do that tomorrow (I hope).

    Jacek, SP3L
     
    UA3TW likes this.
  4. AE7F

    AE7F Ham Member QRZ Page

    As discussed, I've been contemplating the addition of a 12/17m trapped director element about (61.9 inches in front of the WARC dipole driven element). I just added the WARC dipole components to the antenna and since 2 trap coils get replaced, I have 2 leftover. For about $13 dollars (plus about $30 for shipping/handling from DXE .... uggh ... need to look elsewhere), I can get enough 1 inch aluminum tubing to make a director element and it will fit perfectly with the leftover traps.

    But since I don't have the 12 inch trap tubes, that "capacitive" part of the trap (tube) is now missing. However, shouldn't there still be capacitance between the coil wire itself and the aluminum tubing element which passes through the coil form itself? In other words, the trap should still function as a parallel LC circuit but now the coil is on the outside of the element instead of inside the element (trap tube). If the modified configuration will still function as an LC trap, this may be a very worthwhile, inexpensive addition to make this antenna much more comparable to the other fine antennas posted by Jacek in this thread.

    I assembled the WARC dipole addition and have tested it with the analyzer but I am not yet ready to post the data until I am sure the beam is behaving like it should. Presently, 12m and 15m are dipping higher than expected and I ran out of time last night before I could investigate further. Since the 12m and 15m driven elements are driven together, I expect that a slight change in length of one element may also affect the other. I may be able to figure it out and post results later.

    Hopefully it will prove to be not such a bad antenna. Measurements to follow later...
     
  5. AE7F

    AE7F Ham Member QRZ Page

    Jacek, what an interesting antenna you are building! So this beam will be constructed of wire and string?

    It actually looks like it would perform very well. I am very impressed and look forward to looking at your model in 4nec2...
     
  6. SP3L

    SP3L Ham Member QRZ Page

    Ben,
    here they are: the new models added to the pack and the comparison table updated.

    And some extra information below.
    Dimensions.
    upload_2016-5-11_15-47-59.png
    upload_2016-5-11_15-58-31.png

    I estimate that the Cat's Whiskers Beam will weight about 8 kg. I am afraid 7 kg is not feasible.
    And finally, a few radiation paterns.

    upload_2016-5-11_16-5-59.png

    upload_2016-5-11_16-6-15.png

    upload_2016-5-11_16-6-33.png

    upload_2016-5-11_16-6-51.png

    upload_2016-5-11_16-7-5.png

    And now back to the "drawing board". The central support for the spreaders is still to be designed.

    Jacek, SP3L.
     

    Attached Files:

  7. AE7F

    AE7F Ham Member QRZ Page

    SP3L likes this.
  8. AE7F

    AE7F Ham Member QRZ Page

    Since 12m and 15m were dipping too high, I suspect the 12m inner joints and the connections between the inner elements and 15m trap tubes were poor. I actually cleaned the trap tube screws, trap tubing, and joints (removed Penatrox) and now the SWR curves are dipping very close to what is expected. I think high resistance or no continuity between circuit segments was the issue.

    Now I am going to have to go through each joint and connection on the DIR and REF elements as well. If those elements are not working properly, the beam will show good SWR but will behave like a dipole and not a Yagi...

    After everything is cleaned up and ready to go, I will post the SWR curves and we will compare with the model. I also plan to test the traps for L/C in addition to using a grid dipper on them as well....
     
  9. UA3TW

    UA3TW Ham Member QRZ Page

    This pentabander model is rendered from it's MMANA prototype. It is rather raw for 4nec2. The dimensions exactly the same as in MMANA, apart from the driven elements assembly. The driven elements assembly in MMANA has 47pF capacitor in parallel to the source. Since I do not know how to make that in 4nec2, I slightly trimmed the driven elements assembly for better SWR, to move it lower than 2 in the middles of the bands at least. (In MMANA SWR is much better everywhere). The radiation patterns do not differ from MMANA ones.
    The idea of this antenna is such.
    Take a good 20-15-10m interlaced tribander. (I have taken 3-4-6 RA3XAR good design).
    Add some 12m and 17m driven elements. Here they are wire ones.
    Enlarge 15m directors and reflector so, as to tune the antenna for 17m band. They do not change their boom position.
    Enlarge 10m directors so, as to tune the antenna for 12m band. They do not change their boom position.
    Envelope 17m directors with 15m wire (sheath) directors.
    Envelope 12m directors with 10m wire (sheath) directors. (I put "sheath" in brakets since it is of my own coin and i am not sure the term will live and such element will live)
    Tune the antenna hard until proper parameters are reached.
     

    Attached Files:

    Last edited: May 27, 2016
  10. SP3L

    SP3L Ham Member QRZ Page

    Thanks Nick for yet another contribution. If I only find some time next week, I will process your model. I am busy with the Cat's Whiskers now.


    My neighbours say they are impressed but they probably think I am crazy.

    Jacek, SP3L
     
    W7CJD likes this.

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