Software-controlled VFO for TS-820

Discussion in 'Homebrew and Kit Projects' started by W0KEH, Nov 24, 2020.

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  1. W0KEH

    W0KEH XML Subscriber QRZ Page

    I recently purchased a used Kenwood TS-820. It's great for voice (haven't tried CW) but I'd like to experiment with digital modes. Ideally what I'd like is to be able to adjust the frequency (within a given band - I know that I need to re-tune the rig for different bands) using my computer, so I can automatically scan up and down the entire band for digital signals.

    The TS-820 has a connection for an external VFO. If I were to attach a VFO that output the same IF as the Kenwood external VFO using that connector, that would do it, right?

    I can find the pinout for the VFO plug, but I don't know the IF or the output levels the rig is expecting. I also don't know how to build an external VFO, but hopefully I can figure that out. :D
     
  2. KM3F

    KM3F Ham Member QRZ Page

    VFO Frequency is 5.0 to 5.5 mhz.
    If your not experienced in building circuits, stability is a major requirement.]
    These radios had external VFO offered as an option.
    I would take some time looking for a unit for sale and dispense with trying to build one unless you bent on trying it.
    Same VFO option is used for the 520 and 820.
    Good luck.
     
  3. W7UUU

    W7UUU Principal Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Why not just start with putting it on the air "as-is" and worry about building a scanning system later? You know - sort of "get your feet wet and see how things work" at first and once you're comfortable that the stability is there and you have a good "baseline" with lots of contacts in your log, and then start studying up on how to build a "scanning VFO" system. There's likely a LOT more to that than you're considering..... you'll have to build a scanning system that's capable of IDENTIFYING the digital mode it might encounter. There are over 100 digital modes. And these days, 99% of the activity is on FT8 - you don't need a scanner for that mode.

    Just a suggestion

    Dave
    W7UUU
     
  4. N8YX

    N8YX Ham Member QRZ Page

    Furthering this comment:

    Get acquainted with the rig on the air. If you still want to run it on FT8, see the control labeled "Fix CH"? The '820 has an internal provision for 4 crystals. The formula for determining their frequency for a given spot in the band is listed in the owner's manual. Figure out which frequencies you need for the 80/40/20/15M FT8 channels then contact Quartslab (UK) and give them the details. In a couple of weeks you'll have your rocks. Maybe get them for 160 and 10 as well but you'll have to swap the crystals around if running all 6 bands the '820 covers.

    Caveats...I ran a TS-820S/R-820 combo on RTTY for a number of years; always at reduced power. Even still, constant-carrier modes love to eat up driver tubes. Make sure you have a supply of 12BY7A available. What I would advise here is to get a solid-state rig whose PA is spec'd for high duty cycle carrier modes and use that instead.
     
  5. AF5XF

    AF5XF Ham Member QRZ Page

    per the service manual for the vfo-520 output level is 1v +/- 3Db into 470 ohms.


    I built a VFO based on NT7S's DDS using the si5351.
    its just a single frequency vfo, no split or RIT options.
    it has a start frequency set in software whenever you power in on/off
     

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