ICOM AT-180 Shutting Off

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N3TIP, Nov 17, 2020.

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  1. N3TIP

    N3TIP XML Subscriber QRZ Page

    Hello, I’m using an ICOM AT-180 tuner with my ICOM-718. Recently, while transmitting CW, the tuner will shut off by itself and the SWR will spike. I’ve tried setting the Auto Tune Mode to ON from the default mode of OFF but it doesn’t seem to make a difference. I have not changed the AT-180’s internal switches so they are set to default at “NORMAL CONDITIONS.” I’ve never experienced this problem before. Has anyone else? Any suggestions for a fix? Thanks!

    Peter
    N3TIP
     
  2. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Does the problem occur at QRP power levels?
     
  3. N3TIP

    N3TIP XML Subscriber QRZ Page

    Thanks for the reply. No, this does not happen at QRP levels. It usually occurs between 85 and 100 watts. Does this mean it’s beyond the tuner’s capabilities using my particular antenna, which is a direct feed random wire? Thanks.
     
  4. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Well, it's much more likely that you have common mode current coming in on the outside of the coax shield that is disrupting the operation of the microprocessors in the tuner. This is especially true if you are not using a counterpoise of some kind, or an inadequate counterpoise.

    However, you are correct in inferring that the Icom AT 180 is not really designed to work with this kind of antenna. It has an approximately 3:1 SWR tuning range, and the SWRs provided by an random length end fed wire are often (usually?) outside of this range. The AT 180 is really intended to extend the bandwidth of antennas that present an impedance much closer to 50 ohm unbalanced, not to match antenna systems that have inherent feedpoint values far from 50 ohms.

    Although you may have had some success with this system in the past, it is probably because of unknown factors that are no longer present (such as soil conductivity that varies by season).

    To sum up, you cans spend some time finding the exact problem and fixing it, or you can invest the same time in building a better antenna system. I think perhaps you have reached the limitations of the system you have, and the time has come to consider more orthodox antennas.
     
  5. KI8DJ

    KI8DJ Ham Member QRZ Page

    Feed that random wire with a 9 to 1 unun. The tuner won't have to match extreme impedences. An icom ah 4 is more suited to that type of antenna.
     
  6. N3TIP

    N3TIP XML Subscriber QRZ Page

    Thank you both for your reply. there's a log to consider here!
    73s
     

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