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Help with TR-7

Discussion in 'Homebrew and Kit Projects' started by N2LWD, Nov 10, 2008.

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  1. N2LWD

    N2LWD Ham Member QRZ Page

    This is not easy to explain. Here is what i have. The power output of the transceiver cannot be controlled. The power amp works fine when I test it on the bench and drive it with a signal from a signal generator. The output is clean on all bands when observed on a spectrum analyzer. The signal from the transceiver exciter is clean and can be controlled (reduced) with the drive control. When I connect the power amp to the exciter I get full power output with spurs across the entire HF spectrum and cannot reduce the output power. The power supply shuts down due to excessive current.
    Has anyone run into this problem and what did u do to fix it. i am posting this for the person that is working on my TR-7. any help would be greatly appreciated.
     
    Last edited: Nov 10, 2008
  2. SM0AOM

    SM0AOM Ham Member QRZ Page

    This very much looks like a ground loop induced self-oscillation.

    Check that all mounting hardware and ground connections are tight, and also check carefully that the shield of the coax feeding RF to the PA is securely connected at both ends.

    Another thing to verify is that the leads carrying 13.8V DC to both the exciter and PA are free of RF. If the self-oscillation changes in any manner if the leads are grasped by hand, there is RF floating around. If so, check all RF bypasses on both the exciter and PA modules.

    Hope this helps.

    73/

    Karl-Arne
    SM0AOM
     
  3. N2LWD

    N2LWD Ham Member QRZ Page

    Tnx Karl,
    I passed ur information on to the ham working on the TR-7. if it turns out that it is the problem i will let u know.
     
  4. N8YX

    N8YX Ham Member QRZ Page

  5. N2LWD

    N2LWD Ham Member QRZ Page

    Thank you everyone for the input. still not able to get the damn thing working. may be time to turn it into a for parts radio.
     
  6. N2LWD

    N2LWD Ham Member QRZ Page

    Update

    Got a call from the ham working on the TR-7. turns out the problem was in a couple of "pin diodes". The shorted diodes were allowing the RFoutput to bleed into the input causing the runaway problem. All is stable now.
    Thanks for the help.
    73
     
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