A relay good idea

Discussion in 'Radio Circuits, Repair & Performance' started by KL7AJ, Jan 7, 2020.

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  1. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Well, I was rummaging through my countless parts bins and found a whole pile of miniature DIP single pole double throw relays, with convenient 5 volt coils. I was wondering to myself,"Self, what should I do with all these relays?" And Self answered back, "You should build a precision ladder attenuator or two or three for your direct conversion receivers." So I agreed with Self, and I will start on this project. The only question is how do I want to encode these relays...Or should I configure them to simply switch in attenuation in 3dB steps across the entire range. Decisions, decisions.

    Stay tuned.
     
  2. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Ahh...after perusing Ye Olde Handebooke, I decided to lift the 71 dB attenuation scheme described....6x10dB sections, 1x1, 1x2, 1x3, and 1x5. A fairly simple TTL driver/encoder will allow this to sweep the 71 dB in 1 dB increments.

    (How come it's old guys like me who always build this kind of stuff. Where are the yuteful lads n lassies?)
     
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Well if you can live with a bit less total attenuation you could build a binary sequenced attenuator to get 0 to 63 dB of attenuation in 1 dB steps which only requires 6 relays and 6 corresponding binary sequenced attenuation stages.

    IOW stages with:

    1 dB
    2 dB
    4 dB
    8 dB
    16 dB
    32 dB

    Will give you 0 to 63 dB with only 6 stages to switch. Add one more 10dB stage and you get 0 to 73 dB of attenuation in 7 stages instead of the 10 stages it takes with the design you referenced but the control coding takes a bit more thought.
     
    AI3V likes this.
  4. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Ahh...very good...I shall consider that. I can use a seven segment decoder to simplify things a bit
     
  5. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Hey! I just realized something. I wouldn't even need to do any BCD decoding: I could just wire the relays up as a "thermomometer" A/D. The reason is, if I incorporate this in a feedback look (Audio derived control voltage), I WANT a logarithmic function.....it will have almost the ideal built-in compression algorithm.
    Stay tuned!
     
    K7TRF likes this.
  6. WN6U

    WN6U Subscriber QRZ Page

    Micro-controller? Wifi enabled?
     
    AI3V likes this.
  7. WB8NQW

    WB8NQW Ham Member QRZ Page

    I have a commercial attenuator with 3 - 20db switches 1 - 10db switch and 1- 5db switch. Allows 5db steps up to 75db. If necessary you could add a 3db and a 1db step.
     
  8. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    It will be incorporated in an AGC loop.
     
  9. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Or, you could use a digital attenuator chip for a few bucks.
     
  10. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    But then
    But then I'd still have all these leftover relays. :)
     
    K8AI and AI3V like this.

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