WB4KDI Engineering Notebook

HELP! I Just Got a R-1000

Under Construction
The Kenwood R-1000 is a fine 1980s vintage communications receiver drawing on Kenwoods experience with similar circuit designs in the TS-120/TS-130/TS-430 Amateur transceivers. There are a few areas that need to be checked out before use, like the fuse wiring below. The main tuning is a little fast but should be OK for a general purpose receiver. Some improvements, though, are also needed: There is plenty of room to provide I and Q outputs as well as install an FM demodulator as future projects.
  1. Initial Checkout
    1. Check the fuse wiring.
      Many R-1000 were wired wrong. The AC fuse is in the neutral!
    2. Check power supply.
      • Check and replace C209, 4700 uf @ 25 Volts on the power supply board.
      • Check for cold solder joints on diodes, resistors, power transistors and regulator ICs.

    3. On the main RX board, check and replace C186 and C191, both 1000 uf @ 16 Volts.

  2. Mods
    1. Change attenuator steps from 20db to 10db. See SB-823.
    2. Improve MW and LW performance.
      • Remove MW/LW RF pad, R161, R163 and replace R162 with a jumper.
      • Remove MW/LW IF pad, Q8, R87, R88, R212, and C112.
      • Use attenuator as necessary to reduce front-end overload.
      • Change LW frequency roll off of input filter (how?).
        Parallel 4700 pf across C7 and across C8. Roll off now about 100kHz.

    3. Improve low frequency audio response.
      • Replace C183 with 100 uf @ 16 Volts.
      • Remove C158, Q47, R227, R228
      • Does changing C183 increase audio IMD?

    4. Add RF gain control and new AGC circuit.
      • Remove C138(?), C139, C140, R119, and R213.
      • Use design from TS-120S. Circuit provides smooth AGC, fast and slow settings.
      • Modify tone control to be RF gain control.
      • Parts -
        • Leave R226 and C217.
        • Change R117 to 2.2M ohms.
        • Add n-jfet (2n5457, etc.).
        • Add 68K, 100K ohm resistors.
        • Add 4.7K ohm from cold side of RF gain to ground.
        • Add 50K trim pot from hot side of RF gain to 9 Volt source.
      • Apply 9 Volts to top of 68K ohm resistor for slow AGC.
      • Rewire DIM push button to be AGC fast/slow selection.
      • With RF gain fully clockwise, adjust 50K trimpot to just before the point where the gain decreases.
      • Schematic

    5. Mode switch changes to allow for mode and bandwidth selections. (future)
      • New mode table:
        USB+AMN+AMW?? 12kHzSSB
        LSB+AMN+AMW?? 12kHzSSB
        LSB+USBLSB? CW FilterSSB
        LSB+USB+AMN?? 6kHzSSB
        LSB+USB+AMW?? 12kHzSSB
        LSB+USB+AMN+AMW?? 12kHzSSB
      • Items in RED, three or more buttons pressed, are probably not useable.
      • Items in YELLOW are to be designed. CW filter selection by pressing LSB+USB not easily done.

    6. Improve antenna switching/selection. (future)
    7. Improve receiver muting and grounding of antenna inputs when muted. (future)
    8. FM demod (future)
      • An FM demodulator designed around a TBA120U has been presented.
        Is all of that additional IF gain and limiting really necessary?
      • A simpler demodulator based around a PLL could be used instead.

    9. I and Q outputs for SDR experimentation. (future) Tayloe Detector?