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Thread: Comet CHA-250Bx Antenna Interesting Approach to Improve Its Use

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  1. Lightbulb Comet CHA-250Bx Antenna Interesting Approach to Improve Its Use

    I fully understand the " vertical antenna haters' " opinions about this particular antenna. So, I decided to try a more positive approach to helping those that have purchased one of these antennas with the "hope" of having great success. In my research I discovered that one could attach an amplifier to boost the signal, but here's the catch: the maximum power that the antenna can handle is 250W SSB and 100W FM on 10M and 6M. Any amplifier UNDER that limit is OK.

    That being the case, most amplifiers push a greater limit then what can be handled by this particular antenna. Some transceivers now come with an adjustable wattage output, my TS-440SAT can be adjusted down to about 20W output. I "disengaged" the "antenna tuner" on the TS-440SAT. Turned the "CAR" knob to the left and reduced the output to 20W. Connected an "811" (amplifier) to the back, then connected an "antenna tuner", and then connected the antenna cable to the "tuner".
    With everything up and running I was able to push about 220W through the antenna. Made an improved difference!

    Since you have already spent your hard earned money on one of these antennas; make it work better. Home Owner Associations and Deed Restrictions are not always fully understood by some of our fellow Hams. The "compliance person" will squint to find a flaw. Work with what you've got.

    73's
    Last edited by W5DUH; 03-21-2012 at 06:58 PM.

  2. #2

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    Just adding a current balun and set of radials under it will improve it more than doubling power.
    What if soy milk is just regular milk introducing itself in Spanish?

  3. #3

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    The Comet CHA-250BX is a kind of wideband terminated antenna. The radiation efficiency on 7 MHz and below I estimate to be 1%.

    The best improvement to be had is to throw it away and replace it with anything, even a Hamstick.

    100 watts to the Comet is like 5 watts to a Hustler 5BTV.

  4. Thumbs up Thanks for your input.

    Thanks for your input.

  5. #5
    Join Date
    Feb 2004
    Location
    Bakersfield, CA
    Posts
    4,738

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    Improving the CHA-250X by runinnig more power to it just doesn't sound like the answer. As everybody else has said put more radiails down there more the merrier. They do not have to be in a spot where another radial already is. Heard of some folks that used loads of metal. Mostly aluinum and had a killer vertical. He also had one heck a mess. If it wasn't due to the fact that you are doing experiments with it that I for one will not tell you to sell it. But, if after trying everything you can and the antenna refuses to show improvement in it's present state then. Tear apart the antenna. Salvage what you can and make a better antenna. Therer are some antenna that are worth saving and tears have been shed over they. Thankfully the Comet CHA-250Bx isn't one of them. You can count this as a valuable learning experience and the oppoturnity to produce a fine antenna with the scrapes you will have. Or you can sell it to another newbie. I'm thinking there must be some of us that would buy that antenna and use it as internded.
    73
    Gary

  6. #6
    Join Date
    May 2002
    Location
    Venus, Texas
    Posts
    216

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    Say what you want ... I am VERY HAPPY with mine... I regularly make contacts over 2200 miles with 100w on 12m, 15m and 20m ... I do not have ANY RADIALS ... it is 40' in the air at the top of the antenna and attached to a 10ft 1 1/2" EMT attached to a 4x4 12ft in the air from my porch. At the base of the EMT it connects to a 10ga solid copper wire to the ground where it is attached to a 4 ft solid copper ground rod buried flush to the earth. I use 50 ft of RG8 with it. I can operate all bands 80m through 6m with less than 1.3 to 1 SWR and with a tuner I can operate on 160m as well. This is the BEST all around antenna. If a storm is coming I can take it down in less than 5 minutes since it only weighs in at 6-8 pounds ... then lay it horizontal on the ground until the storm passes .. of course I cover the matching coil with a plastic bag to keep out the water then put it up again when the storm passes!

    It is often quieter than my 20m Roof Dipole noise wise ... If I can hear the station which now that I have an FT-950 I can hear MUCH better than the previous kenwood I had on the same antenna ... I can work the station. Just last week I forgot I had my power turned down to 10 Watts to test swr after a passed storm and still made contacts into Alabama from Texas with 5-9 report .. once I turned up the power to 100W I was 5-9 +20db .... I have worked over 3200 miles into costa rica with 5-9 reports ... HF is great especially with the FT-950 and this antenna ... it is a true joy ...

    I am sorry others have such biased opinions on this antenna .. but it works great for me ...

    KD5SPX.

  7. #7
    Join Date
    Feb 2007
    Location
    Full Time RV'er, Anywhere U.S.A.
    Posts
    41

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    I also have the Comet 250Bx which I purchased used off the I/net. It is mounted on the rear of my motor home on the roof ladder about 12' off the ground. I use mine grounded to the MH chassis frame and have a small radial system on the MH roof. I removed the lossy mounting transformer and now feed it via a Icom AH-4 tuner with my IC-7000. My motivation was to have a easily raised, light weight, simple, vertical antenna. I made a swing up mount out of PVC water pipe which works great for raising the antenna for operation. Laid down on the roof, the 23' antenna travels well. The on-air results have been very rewarding considering what it is.
    Member of OFWA, APCO, ARRL, and Escapees.
    FCC Commercial GROL holder

  8. #8

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    With virtually any antenna and 100W it's pretty easy to "work everything I can hear."

    The issue is you have no idea what you're not hearing.

    Any antenna is better than no antenna, but having been spoiled by beams and towers and such over the past 45 years I know for sure what I'm "not hearing" when I use an antenna like that. Still, any port in a storm.
    What if soy milk is just regular milk introducing itself in Spanish?

  9. #9
    Join Date
    Feb 2004
    Location
    Bakersfield, CA
    Posts
    4,738

    Default

    Just a reminder that the propagation plays a very important role in the success of an antenna at certain times. Having reliable and repeatable results requires more than just good propagation. When the bands are good I can work the world with a screwdriver antenna and sometimes a wet string. That doesn't make it the best antenna in the world. It's when condition are marginal that tests the capabilities of an antenna system. To get your signal out there may require the use of different antennas at different times. As for the joy you expressed on your antenna, have you setup any other antenna and compared them? Just relying on a single reference is a faulty method. String something else up and compare that with what you now have. Then you can say what you want with greater authority.
    Just look at the antenna reviews and you will find numerous reviews that tell you their antenna is the best in the world. Maybe, maybe not.
    73
    Gary

  10. #10
    Join Date
    May 2002
    Location
    Venus, Texas
    Posts
    216

    Default

    Your right there. It wasn't until I got rid of that ken wood ts480 and got the ft950 that I realized what I wasn't hearing!!

    Kd5spx

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