Atlas 120A

Discussion in 'Mobile Radio Systems' started by WB4FCU, Oct 10, 2021.

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  1. WB4FCU

    WB4FCU Ham Member QRZ Page

    Has anyone had problems with antenna extending, but not retracting. I have two and both do the same. Trying to determine if problem is with antenna circuit board, or maybe a radio problem?
    Larry - WB4FCU
     
  2. N1IPU

    N1IPU Ham Member QRZ Page

     
    WB4FCU likes this.
  3. WB4FCU

    WB4FCU Ham Member QRZ Page

    Thanks for your input! I have reset radio on both antennas but with same results. Still trying to determine if problem is with radio or antennas. A new circuit board is over $100. If I was sure it’s the culprit, I would order.

    Larry WB4FCU
     
  4. KK9W

    KK9W Ham Member QRZ Page

    I don't have the link but there is a guy who repairs the ATAS antennas and on his page he has a troubleshooting guide which tells you what voltage extends and retracts the antenna. If you can make it work properly with a variable power supply and leads you may want to try a different piece of coax because if the loss is enough to drop the required voltage it will not retract.

    Also, I performed the cleaning steps outlined here and my tuning issues were solved.
    http://kb5wia.blogspot.com/2009/12/atas-120a-disassembly.html
     
    N2PQW likes this.
  5. N7WR

    N7WR Premium Subscriber QRZ Page

    This is but one reason those antennas are poorly rated. Check your antenna ground. Inadequate grounding seems to cause a lot of the ATAS antenna problems
     
    K0UO and AK5B like this.
  6. N2PQW

    N2PQW Ham Member QRZ Page

    Larry,
    The first things I would check would be the coax connections, and look for breaks in the coax itself. The radio sends a DC voltage, from about 8v or less (for retract) and 10v or more (for extend), and approx. 9v for 'at rest'. This is, however, at fairly low current, so the coax has to be in good shape.

    I purchased my ATAS-120A about 13 years ago, 3rd-hand, from a friend who is now an SK, so I can't say what was done before I got it. I can say that it had appeared to have been completely disassembled (including the sealed base!) and rebuilt, but was not working when I purchased it.

    Here's the only trouble I could find:

    At the base of the circuit board is a blocking capacitor, and the solder connection to the board had failed. I cleaned off the old solder, applied new, and it had worked perfectly for many years.

    At some point, 1067 tree limbs and approx 50,000 road miles later, the antenna failed to tune. I separated the base from the main tube, and found the solder connection had opened up again. 10 min later, it was back on the truck, good for many more miles / years / tree strikes.

    I believe that the base of the circuit board must actually be taking some of the mechanical stress of the impacts and wind loading, and this flexing injures the capacitor's connection.

    For what it's worth, the replacement part for the cap is under $3US including the mounting bracket it's bonded to, if you decide it needs to be replaced. I recall that the board ("Remote Unit") is much more than that, perhaps over $100, so I'm ok with the cap being a sacrificial part.

    upload_2021-10-16_12-2-23.png
    I feel badly for all those haven't had success with this great antenna. I've met many other hams that have installed them properly, and we love them.

    Let us know if you find the trouble.

    Cheers,
    David / N2PQW
     
    Last edited: Oct 16, 2021
  7. N2PQW

    N2PQW Ham Member QRZ Page

    My only concern with KB5WIA's tutorial is where he describes removing the nylon washers at the base of the main tube, and taking measures to ground it to the base.

    In my opinion, the main tube is DESIGNED to be isolated from the base, not bonded to it. There is a gap between them created by the o-ring on the base assembly, and the nylon washers provide insulation, and to a certain extent, prevent over-tightening of the screws that would collapse the tube against the base.

    If you take time to understand the signal path in the clever design of this antenna, it makes perfect sense.

    Cheers,
    David / N2PQW
     
  8. KK9W

    KK9W Ham Member QRZ Page

    I did as he stated and my issues with intermittent tuning and crazy SWR were solved. The O-ring is merely a seal and doesn't prevent metal to metal contact, nylon washers or not. Where I once couldn't use the antenna and wanted to throw it away it now produces acceptable results.
     
    Last edited: Oct 17, 2021
  9. K0UO

    K0UO Platinum Subscriber Platinum Subscriber QRZ Page

    Overall that's a poor excuse for a mobile antenna. And it's not a cheap antenna on top of that.

    "In fact, the Yaesu ATAS antenna is the least efficient, remotely controllable, HF mobile antenna, money can buy! The list price is over $460,"
    http://k0bg.com/antennas.html
     

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