Results 1 to 5 of 5

Thread: Idea: PIC and DDS for Fix Ch crystal replacement

  1. #1
    Administrator N8YX's Avatar
    Join Date
    Feb 2007
    Location
    Akron, OH
    Posts
    24,890

    Idea: PIC and DDS for Fix Ch crystal replacement

    Anyone who's owned or operated an early generation Kenwood or Yaesu hybrid is undoubtedly familiar with the provision for operating the rigs on a fixed frequency, via a crystal which is fabricated to a specified value then inserted into a socket within the radio. The crystal (or crystals) are then selected by means of a front panel switch.

    Sounds easy and cheap enough, right? 'Twas back in the day, when we had a variety of custom crystal manufacturers from which to choose. Nowadays, we have precisely one - Quartslab. At $20/rock, filling up a bank of four in your Kenwood might be acceptable

    820-fixed.jpg

    but loading up all 11 channels in an FT-301 costs as much as a used example of the radio itself!

    301-fixed.jpg

    What to do?

    I gave this a little thought over the past week or so. The use of a DDS as a replacement for a 5.0-5.5MHz analog VFO is getting to be fairly common practice, so why not extend that concept and use one to generate the same frequency ranges for those crystal oscillator circuits?

    One could use a PIC to scan the crystal-select lines. Given the devices only have a few inputs, a 16-4 encoder can be employed for the Yaesu setup. A set of data words (dependent on the DDS) is programmed into the PIC. Pseudocode is along the lines of: While the Select circuit is NOT in VFO mode, scan the Crystal Selection lines and see which position is selected. Then, send the appropriate string to the DDS. While that particular Select line is enabled and the current working frequency is the same, do nothing. If it changes, send the new data to the DDS.

    Upon selecting VFO again, an initialization sequence is sent to the DDS so it'll go into dormant mode and not generate unwanted output.

    There is a bunch of information online about getting a PIC to send serial data.

    Anyone else think this is a neat concept?
    "Everyone wants to be an AM Gangsta until it's time to start doing AM Gangsta shit."

  2. #2
    "Island Bartender" KG4CGC's Avatar
    Join Date
    Mar 2007
    Location
    EM84ru, Easley SC
    Posts
    46,711
    It is a neat concept. You are well advanced in the hobby. Have you considered publishing a practical DIY book?
    RIP Albi
    When do you tell a woman you're a ham?
    Does YOUR avatar represent a time in your life?


  3. #3
    La Rata Del Desierto K7SGJ's Avatar
    Join Date
    Feb 2010
    Location
    The Desert
    Posts
    16,627
    Quote Originally Posted by KG4CGC View Post
    It is a neat concept. You are well advanced in the hobby. Have you considered publishing a practical DIY book?
    Rumor has it that he just ordered a DIY book on how to do a DIY book.
    Last edited by K7SGJ; 06-28-2017 at 08:53 AM.
    Anger is one letter short of danger

    RIP ALBI-W3MIV RIP RUSS-W5RB RIP BOB-VK3ZL





  4. #4
    Volcano Tamer
    Join Date
    Oct 2009
    Location
    Buffalo, NY
    Posts
    22,555
    Cheaper than a decoder, use the PIC's analog input line, and a resistor ladder. Absent an analog input, you can use a matrix input network (Just cleverly arranged wires).
    Big Giant Meteor 2020 - We need to make Earth Great Again

    http://www.coreyreichle.com

  5. #5
    Administrator N8YX's Avatar
    Join Date
    Feb 2007
    Location
    Akron, OH
    Posts
    24,890
    Quote Originally Posted by KC2UGV View Post
    Cheaper than a decoder, use the PIC's analog input line, and a resistor ladder. Absent an analog input, you can use a matrix input network (Just cleverly arranged wires).
    That's another interesting thought. What is the resolution of the average PIC's analog input -250mV, 500mV, ? I have +5, +9 and +12v to work with in most rigs of that era.
    "Everyone wants to be an AM Gangsta until it's time to start doing AM Gangsta shit."

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •