Controlling Freeks

Discussion in 'Technical' started by KA4KOE, May 15, 2015.

  1. KA4KOE

    KA4KOE Guest

    For those that use broadcast transmitters, what type of freek control do you use?

    1. Crystals?
    2. DDS VFO?
    3. Analog VFO; eg. Johnson 122 or equal?

    I'm undecided at the moment. I figure I would need

    1885 KC
    3873 KC
    3880 KC
    3885 KC.

    The Gates accomodates two crystals. Of course, without major rework, 40m is a no-go on the mostly stock Gates 1T.

    I'm a long way from throwing the PLATE CONTACTOR switch (in deference to the manual, I AM living right and I do feel lucky).
     
  2. W5HRO

    W5HRO Administrator

    Analog tube VFO's are ok as long as you get in there and use solid state 6.0V DC regulators on the filaments. That's always a must do to eliminate drift due to your line voltage moving around. You can just use a separate DC supply or a voltage doubler circuit to step up any existing 6.3V that's available. There's also those X-Lock boards that can be installed if you want to take it a step further. Jim, JKO could give you the details on that.

    Another option is something with a Collins PTO. My transmitter is using the exciter from a T-368 which has the PTO, but I'm also regulating the filaments on a few of the tubes as well. Still a must do regardless.

    Remote digital VFO's (DDS) are ok too and I often recommend them. Something well buffered with a large LED display always looks nice.

    I think the last thing you would want to do is use xtals. A VFO is the only real way to go with maybe the xtals installed as a backup.
     
  3. KA4KOE

    KA4KOE Guest

    For a remote digital vfo, does anybody's OTS product come to mind?
     
  4. W5HRO

    W5HRO Administrator

    A lot of that requires home-brewing or at least partial home-brewing after getting the kits, but there are a few sites around like the one below.

    Standalone_Front.gif W9BHI.gif
     
  5. W5HRO

    W5HRO Administrator

    P.S. One thing to mention is to use those DDS VFO's remotely often requires a separate buffer/driver amp installed inside of the VFO or in-line after it. They generally won't output enough all by themselves to drive the input of your transmitter through a long run of cable so a buffer/driver amp is usually needed. I think one or two of those DDS websites sell a driver or a driver kit as well. It would probably be best to find a kit for both then build it inside of the same box, but it also may require another board installed at the transmitter itself to drive the high Z grid. Basically the DDS to a buffer/amp then through the run of coax to a low Z to high Z driver installed at the transmitter.

    Attached below is a CQ article about it and the guy also sells them on his website I think.
     

    Attached Files:

  6. WD5JKO

    WD5JKO Member

    All good stuff!

    Phillip, any chance you have Retro75 XCVR kicking around with the built in VFO? Those put out about 2 watts carrier, and the VFO, although analog, is quite stable since it runs all the time. It is converted to 75 meters in a mixer stage. Two watts is 10V rms, or 14v peak into 50 ohms..

    Jim
    Wd5JKO
     
  7. KA4KOE

    KA4KOE Guest

    Dunno. I'm leaning towards using a Johnson 122....but that's a way off. Gotta get the bottom chassis done first.