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External input power

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  • john07242000
    Okay...I ve reviewed the posts but was wondering will the DX-440 work okay using an external 12 vdc? According to the user manual...there are 3 ways to power
    Message 1 of 2 , Oct 3, 2012
      Okay...I've reviewed the posts but was wondering will the DX-440 work okay using an external 12 vdc? According to the user manual...there are 3 ways to power the radio... one is using the 12 volts from a cigarette lighter jack in a vehicle. The guide does not mention knocking it down to 9 volts. The repair manual mentions in the power supply testing section, to connect 12 vdc - refer to page 13.

      Seems the radio can handle external 12 vdc and rgulate it to 9-10 vdc. I'm planning to make a harness with an external tip negitive and connecting it directly to a 12 vdc car battery. Or I can make a voltage divider.

      Comments please
      John
    • cybercat@cyberus.ca
      Go with the NINE volts! I bought my DX440 when I worked in the RS service centre years ago. Saw more than a few that did not survive higher input voltage well.
      Message 2 of 2 , Oct 4, 2012
        Go with the NINE volts!

        I bought my DX440 when I worked in the RS service centre years ago. Saw more than a few that did not survive higher input voltage well. You see - the unloaded voltage on 12vdc supplies is either not regulated or poorly regulated. It can approach 18 to 20 vdc in some cases. Think of the surge at turn on. Even automobile electrical systems are 13 to 14 vdc in reality. Mobile radios are usually designed for 13.8 vdc even though 12 vdc is stated. Many state an operating voltage range.

        You can take your 12 vdc (or higher) supply and run it through a "three terminal regulator" IC designed to give 9 vdc output. For optimal results, a few other components are needed and possibly some heat sinking but that will get you started. Typical chip would be a 7809 (for "+" regulation). I used to find these chips in discarded VCR's.

        As the input voltage to the radio gets higher you aproach (and sometimes exceed) the working voltage rating of a few of the electrolytic capacitors.

        - Bill H. / va3hwa

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