Atlas 210x with carrier oscillator way off frequency...

Discussion in 'Radio Circuits, Repair & Performance' started by KB0MM, Oct 25, 2015.

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  1. KB0MM

    KB0MM Ham Member QRZ Page

    Hello fellow amateurs,

    Having put in some hours diagnosing my Atlas 210x, I found the carrier oscillators for lower and upper sideband
    are high in frequency by over 100 kilocycles! The normal frequency for lower sideband is 5520 KC and for upper
    sideband supposed to be 5523.3 KC. The oscillator board doesn't look like it has been removed and modified.
    What could cause crystals to move up in frequency that much? It will have to sit on the shelf until I figure
    out this conundrum. In the meantime, I need a pair of the above mentioned crystals or possibly an Atlas
    parts radio. I would love to hear if there are any parts of this nature in someone's junk box. It's a nice
    old radio so would like to revive it if possible. Maybe there are some other brands of radios that use a
    5520 KC intermediate frequency but I am not aware of any myself. Any ideas or comments regarding
    this would be welcome.


    best 73 de KB0MM Burt
     
  2. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Just to clarify, when the 210X is connected to an antenna, there is absolutely no reception.
    Is this correct?
    If you have reception, then either the 8 pole crystal filter is also at the 100KHz higher level or your method of measuring the oscillators has a problem.
    If you consider the possibility the crystals drifted that far away then you'd also have to consider the crystals inside the 8 pole filter have also drifted. In that case you'd need both, new oscillator crystals and a crystal filter.
    I hope this is not the case.
    Just Googled the crystal filter and Sherwood Engineering has them for $55.00. Not a bad price.
    The frequency is, however, at 5645KHz. This appears to have been a factory change in the IF frequency and that might account for your deviation. Here's the filter information;http://www.sherweng.com/filters.htm#atlas

    Hope this helps
    73
    Gary
     
    Last edited: Oct 26, 2015
  3. KB0MM

    KB0MM Ham Member QRZ Page


    The manual says the IF frequency is 5520KHZ. I'm using my Kenwood TS-440 to listen for the carrier oscillator. It receives to a fashion with
    the antenna connected but sideband signals sound like the BFO is turned off. I also have a functioning Atlas 210X and I can easily hear the carrier oscillator
    by listening to 5520KHZ on the Kenwood. Crystals just don't move 100KC in my book so am completely baffled by this condition. I have had radio crystals
    in my junk box that are over 50 years old and none of them have ever moved any measurable amount. The only thing I can think of is that someone before
    me must have replaced the crystals.....but why?

    Thanks, Gary for your response. Maybe the best thing for this radio would be to use it for spare parts.

    Burt
     
  4. KO6WB

    KO6WB Premium Subscriber QRZ Page

    You did catch the part where the factory moved the IF on some of their units up 120KHz from what the manual states.
    There was apparently some reason for that switch and it's not unusual for the factory to make such changes and not tell anybody.

    Hope this helps
    73
    Gary
     
  5. N7EKU

    N7EKU Ham Member QRZ Page

    Hi Burt,

    I have a 210X also with the CIO way way off. I checked it and basically, the crystals just didn't age well. This can be due to sealing problems, internal mounting issues, or some kind of internal contamination. I still need to order mine, but here's the info I received on replacements:

    $23.25 each 3 weeks ARO

    Thanks
    Lisa Falconer
    800-725-1426x243
    International Crystal MFG
    10 N Lee Ave
    Oklahoma City, OK 73102

    73,


    Mark.

    P.S. Unfortunately this could also mean that the crystals in the filter may also be suspect so checking the filter on a VNA or something before you invest too much $ is probably a good idea.
     
  6. KB0MM

    KB0MM Ham Member QRZ Page

    Gary,

    That would explain it then as my crystals oscillate 120 kilocycles higher than the book values. That puts a whole new light to the subject. Thanks!
    Yes, that helps a lot!

    Burt
     
  7. KB0MM

    KB0MM Ham Member QRZ Page

    Mark,

    Thanks for the information. If I end up needing crystals, I will know where to order them.

    Much appreciated,

    73,

    Burt KB0MM
     
  8. N7EKU

    N7EKU Ham Member QRZ Page

    Sure Burt,

    Since Atlas did end up changing freqencies, I think they usually print the IF frequency on a sticker on the back of the rig. At least mine had one on it.

    73,


    Mark.
     
  9. G3YRO

    G3YRO Ham Member QRZ Page

    If I remember rightly, aren't these Atlas rigs single conversion on 80 and 20m, with a VFO around 9 MHz mixing with a 5 MHz IF? And then pre-mixing the VFO for the other bands?

    If that's the case, the shift of the chosen IF frequency on later rigs might be to get round bad mixer products - it's particularly hard to make a rig using these frequencies work on 160m. (That's why you can't modify an FT200 to cover 160m without getting in-band spurious products)

    Regarding your problem - if you can't adjust your crystals to be on the edge of the filter passband, why don't you put a little tuned circuit in there instead of the carrier crystals (temporarily), and adjust it to see where they actually need to be for the right response?
     
    Last edited: Oct 26, 2015
  10. KB0MM

    KB0MM Ham Member QRZ Page

    Just an update for now: Having come to the realization that the carrier frequency is 5645, I have since returned the oscillator board back to the original circuit
    and after disassembling and cleaning the crystal, the oscillators work fine and the radio seems to receive quite nicely. A big thanks to all who have posted
    and helped me along. My next phase in this project is to find out why it does not transmit. I'm getting a little signal at the the beginning of the main RF board so
    next I will have to work my way through and find the problem. I have an Ailtech service monitor so will use the scope in that to help determine what has failed.
    I know the driver transistor is bad because it failed the conduction test with an ohm meter. I'm presently waiting for parts.
     
    K5UOS likes this.

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