Does anyone have a schematic for a Daiwa CN-101L

Discussion in 'Ham Radio Discussions' started by AC0FP, May 6, 2012.

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  1. AC0FP

    AC0FP Ham Member QRZ Page

    I just bought a (used) Daiwa CN-101L Watt/SWR meter, no condolences please, does anyone have a schematic for this meter?


  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I don't, and Daiwa's pretty famous for not providing schematics.

    I did download the 3-page "manual," and found the note about the warranty being valid only in Japan.:p
  3. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    Someone slap me if I ever buy one of those.
  4. K8ERV

    K8ERV Ham Member QRZ Page

    I bot one, works well.

    $5 at a yard sale.

    TOM K8ERV Montrose Colo
  5. KD8DEY

    KD8DEY Subscriber QRZ Page

    I got a workman....
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I got two of them! They cut the grass, clean the yard, take care of the pool...:eek:
  7. W3WN

    W3WN Ham Member QRZ Page

    I picked up one of those a few months back, brand new from a dealer. Thought I was getting a nice bargain on a dual meter bridge. Hah!

    Frequency range is ~26 - 30 MHz, and they ain't kidding. The meters won't read SWR too well below about 15 MHz, and it was totally useless on it's intended band (dedicated 160 station).

    At least I moved it at the next hamfest for what I paid for it.
  8. AC0FP

    AC0FP Ham Member QRZ Page

    The meter I bought works just fine but the peak reading scale is a joke. From reading on the web this is a common problem, probably a design problem. I figured with the schematic I should be able to modify the circuit in short order to get a reasonable working PEP reading circuit. I guess I may have to open it up and see what they have done!


  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I don't have that particular meter, but I do have a different Daiwa "AVG/PEP" meter which also does not use any active circuitry and it's way off. Actually, it would be almost dead on if the signal envelope was a pure and consistent sine wave. It's far off for any other kind of envelope. If you open it up (I did, lots of times) I think you'll find the "PEP" function is nothing more than a capacitor that charges up with the applied signal from the detector, prolonging the meter decay time.

    That's not "PEP" at all. It just makes the meter slower.

    A real PEP meter has substantial active circuitry and requires DC power from a power source like a battery or power supply.

    Here's a reasonable writeup on this, with schematic and board layout for someone who wishes to "roll their own" PEP adapter for an average reading wattmeter like the Daiwas: Topics/PRWM.html


  10. AC0FP

    AC0FP Ham Member QRZ Page

    Thanks for the circuit help, however, the circuit is just a redundant peak detector. D2 is a diode positive peak detector followed by an Op-Amp positive peak detector. The next Op-Amp is a AC to DC peak detector/filter. The third Op-Amp is a DC voltage follower.

    I was hoping to build a PEP (peak to peak) detector. A good accurate one would use Op-Amp's but in a different arrangement. I think I can build a passive one (no power supply) but diode drops would cause the circuit to read a little low. Of course that could be corrected with a single Op-Amp buffer amplifier, the meter does have a 13.8V input for a lamp.


    Last edited: May 8, 2012
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