Cheap HF; Now with CW!

Discussion in 'Survival Communications' started by WastedDaze, May 15, 2017.

  1. WastedDaze

    WastedDaze Monkey+

    The saga of the cheap HF rig continues...

    In the manual for the SEA222 they have the schematic for the CW option board. It consists of a keyed transistor switch that pulls the PTT line low. Also a keyed 1khz oscillator used to modulate the mic input and an audio amp connected to the speaker for sidetone.

    I built it on copper clad circuit board material using "Manhattan" style construction. That's little pieces (islands) of clad circuit board glued to a larger piece. The islands allow you to solder components while the larger piece is the ground plane. Simple and effective.

    Had to sub a few parts like the audio amp that is obsolete so used an LM386N. Q2 is replaced by a generic 2N3904 NPN transistor. Used an IRF510 instead of the MPF910. Wired and tested on the bench then installed in radio. All parts I have on hand, didn't have to buy anything.
    Set levels. Transmitted into dummy load while I had my rice box HF radio connected to another dummy load and listening on 7.100 MHz. Sounds pretty good. Set modulation for 75 watts out. Now we have a multi-mode cheap HF radio that will do AM, USB & CW from 1.7 MHz to 24 MHz. 50 watts AM carrier, 150 watts peak SSB and 75 watts CW. I even installed a little 40mm fan on the back to keep the finals cool.

    All this for less than $100.

    Here's the schematic
    The board installed and wired

    The radio on the bench ready to first CW QSO. The toggle switch turns the power off to the CW board.

    With all the work I've done on this one thing I haven't tested is receiver sensitivity... seems very good but would like to see what it will do on the IFR service monitor.
    Last edited: May 16, 2017
    stg58, Bandit99, Tully Mars and 3 others like this.
  2. DKR

    DKR Raconteur of the first stripe

    But that is MCw and not 'true' CW.
  3. BTPost

    BTPost Stumpy Old Fart Snow Monkey Moderator

    Good job...
    sec_monkey likes this.
  4. WastedDaze

    WastedDaze Monkey+

    I thought the same thing. When I looked in to it I came to a different conclusion. When a SSB signal is modulated by a pure tone it produces a pure RF carrier. The key just turns it on and off, hence CW.

    Now true Modulated CW is when you superimpose a tone on a RF carrier such as AM or FM signal. Like low frequency NDBs.
    Last edited: May 16, 2017
    stg58 likes this.
  5. WastedDaze

    WastedDaze Monkey+

    Thanks Bruce! That means a lot coming from an 'ol radio mechanic like yourself.
    sec_monkey likes this.
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