Comet CX-333 Comments

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K6XRA, May 26, 2019.

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  1. K6XRA

    K6XRA Ham Member QRZ Page

    I put up my Comet CX-333 Triband Antenna (2m, 1.25m,70cm) about 2 weeks ago.

    Its base is about 17' above the ground (tip at around 27'). I ran about 28' of LMR-400 Ultraflex from the radio to the surge protector just outside the house and then another 37' of regular stiff LMR-400 to the antenna (total of 65ft of LMR-400).

    The antenna seems to work quite nicely on all three bands.

    I checked the SWR in the middle of each band and I got: 2m = 1.6, 1.25m = 1.4, 70cm = 2.0

    As a new ham, I was interested in understanding this more, and so a friend came over with their RigExpert antenna analyzer.

    The reality is the the SWR curve is significant over the entire bands:
    For 2m, the curve ranges from roughly 2.0 to 1.1 with the low around 147Mhz
    one.jpg

    For 1.25m, the curve ranges from about roughly 1.7 to 1.2 with the low at about 224.5Mhz
    two.jpg

    For 70cm, the curve has a series of 5 or more peaks and valleys (it is a relatively wide band), ranging from roughly 2.5 to 1.1, with the low at about 433MHz.
    three.jpg

    Obviously, the cable run, surge protector, quality of the connectors and other factors make a difference. But for me, a new ham, understanding how the SWR actually varies significantly across the band was interesting.

    We also ran a TDR test, and that is also interesting as you can see a tiny bump where the surge protector is in the middle of the line.
    four.jpg

    As it is, I like the antenna!
     
  2. K6XRA

    K6XRA Ham Member QRZ Page

    Picture of the installed antenna!
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    W1TRY likes this.
  3. K6BRN

    K6BRN XML Subscriber QRZ Page

    I've used a CX-333 in Manhattan Beach, CA for more than 20 years. They're pretty popular around here as we have a high density of repeaters for 2M, 1.25M and 70 cm.

    The original antenna was pulled down about 5 years ago when I was refreshing the antenna stack due to corrosion damage to the A3S Yagi, mounted below it. The X-333 still worked fine, but everything was corrosion-welded together, despite liberal use of Penetrox when I first put it together. So I put up a new one. Still works great. Max power used is about 80W FM.

    Helped a friend put his up a year later. We're both "Happy Campers".

    We don't get any snow and very few windstorms here, so can't comment on how robust it is in bad weather.

    Have fun with the new antenna!

    Brian - K6BRN
     
    K6XRA likes this.
  4. K6XRA

    K6XRA Ham Member QRZ Page

    Nice day so I took a bunch of photos of the CX-333 and the pitched / sloped roof mount Easy-UP EZ SV-3.
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    Attached Files:

  5. VE7BPB

    VE7BPB Ham Member QRZ Page

    Did you check the swr for each band directly at the end of the coax or did you put a triplexer on and measure the swr at the various outputs?

    You may find a difference.

    Regards, Roy
     
  6. K6XRA

    K6XRA Ham Member QRZ Page

    This was directly at the radio end of the coax. (My triband radio has only one connector, no external triplexer.)
     
  7. VE7BPB

    VE7BPB Ham Member QRZ Page

    A friend of mine recently put up the same antenna and had the same results when he measured the swr. I suggested he measure through his triplexer and suddenly swr was fine across all bands. Remember, the UHF and VHF bands are harmonically related, so until you separate the signals with the filters in the triplexer (external or internal) the bands will interact with each other.

    regards, Roy
     
  8. K6XRA

    K6XRA Ham Member QRZ Page

    Interesting!
     

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