Comet 250B

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KX2U, Feb 28, 2021.

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  1. KX2U

    KX2U Ham Member QRZ Page

    I have read a number of threads on this antenna and I own one. It is about 38-40' in the air measured from the ground tot he bottom of the antenna. I have found 3 different guides on this antenna with different measurements but basically used the 4 inch and 8 inch rule on it. SWR are at 1.3:1 but I cannot seem to get any good reception or xmit. I was thinking about adding either a counterpoise or radials but wanted to hear if anyone has had luck with those ideas and if so what coax did you use and how did you install the counterpoise and or radials? I have some thoughts and will try when the weather gets better.
     
  2. KD8DEY

    KD8DEY Ham Member QRZ Page

    Had one before I lost everything when the XYL passed.
    Local 10m net could barely hear me....
     
    AK5B likes this.
  3. K6BRN

    K6BRN XML Subscriber QRZ Page

    Hi Ken:

    We may have talked about this already...

    The Comet CHA-250B is a compromise antenna that goes up easily but has mediocre performance - low TX efficiency, low power handling and picks up quite a bit of noise.

    It's basically a vertical random length antenna with a complex, multimode matching transformer at the base that dissipates a lot of the TX power as heat. The transformer can't handle more than about 75-100 watts of average power (varies with band) without overheating - driving it hard will damage or destroy it.

    Adding radials or counterpoise or trying to tune the CHA-250B antenna length is futile, in my experience. Getting it higher is the only step that really helps - and yours is already up pretty high.

    Oddly enough, this antenna is quite usable on the power-constrained, fairly low interference 60M band and can be used (lamely) on 160M at low TX power (25-35 watts).

    RX is not usually a problem, though it picks up a lot of man-made noise, as any vertical antenna is prone to do. So your RX experience is a little odd - the matching transformer may be damaged.

    When I received mine and put it up as a temporary antenna (when my MFJ A3S Yagi failed repeatedly), it had a few problems and I discovered the matching transformer was defective. I contacted Comet, they mailed me a new one, I put it in and all has been fine since. BUT, if the matching transformer has been overheated, the same problem could happen. If the damage is bad enough, it will affect RX as well as TX performance.

    Your best bet is to get a better antenna. The Comet H422 rotatable dipole works much better than the CHA-250B as does the MyAntennas EFHW-8010-2K wire antenna. And a great solution would be a multi-band Yagi and rotator.

    I still use my CHA-250B as a diversity RX antenna and for TX/RX on 60M (FT8) where it does OK.

    Best Regards,

    Brian - K6BRN
     
    AK5B and KG7QJB like this.
  4. KI8DJ

    KI8DJ Ham Member QRZ Page

    Antenna might not be as bad as you think. Propagation has been pretty poor lately.
     
  5. KG7QJB

    KG7QJB XML Subscriber QRZ Page

    I know people who have them , many actually call them dummy loads. I guess in the world of antennas they are all a compromise to some degree. I have had a Hustler 5BTV up for 5 years and would not take for it . I changed the top coil which now gives me a range of 60 kz on 80 meters without a tuner. I do not need a tuner on 10,15,20 or 40 across the band. I am a General. It is the berst investment I ever made in an antenna.
     
    AK5B likes this.
  6. AK5B

    AK5B Ham Member QRZ Page

    "Oh no, another CHA250B thread..."

    ---my first thought when I saw this.

    Very sorry for your [signal] loss.:(
     
    WG8Z and KD8DEY like this.
  7. W1VT

    W1VT Ham Member QRZ Page

    Have you tried CW or the digital mode FT8? These modes work a lot better than SSB or AM if you need to use a compromise antenna.
    I find CW better than FT8 for working DX. FT8 is so popular everyone calls new calls or DX stations, so it is hard to get through quickly. Too many callers and it isn't as fast as CW.
    A good CW Operator can quickly whittle down a CW pileup. These days you may not have to wait long to get your turn to work a DX station as everyone seems to be on FT8.

    Zak W1VT
     
  8. KH6AQ

    KH6AQ Ham Member QRZ Page

  9. G8FXC

    G8FXC XML Subscriber QRZ Page

    For those of us that have small gardens or restrictive covenants on our houses, the CHA250B may be the best that we can install. The thing which always puzzles me is when I read a post form someone who has a CHA250 or similar at the top of a 50 foot mast or tower with a significant ground plane and are complaining about its performance - if you can put one up high like that, then why on earth do you not have a 30 or 40 foot resonant vertical mounted at ground level instead???

    Martin (G8FXC)
     
    AK5B likes this.
  10. KG7QJB

    KG7QJB XML Subscriber QRZ Page

    Hustler 5 BTV is a small footprint when ground mounted and a much avenue for HF.
     

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