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23026RE: [regenrx] Re: OOPS!

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  • davidpnewkirk
    Mar 1 5:35 AM
      It seems to me that if "listen to really weak signals alongside really strong signals" performance is what you're after, you're in the wrong forum. And if you're continually reading back into the tube-based literature to get clues toward obtaining that performance, you're reading in the wrong region of the literature.

      Getting the basics of that sort of performance is so easy that few experimenters--especially those who love the romance of tubes and regeneration--don't want to hear of it.  And yet building a basic such receiver--one with strong-signal performance that outshines the strong-signal receiving performance of the best vacuum-tube gear ever described in the amateur literature-- is almost ridiculously easy. Here's what you do to get it:

      Obtain a good CW-width crystal (not mechanical) filter. (Mechanical filters you can afford won't have the shape factor of a crystal filter of similar cost.) International Radio ( http://www.inrad.net/home.php?xid=86728f6c05e16b8f51a08c2f086c9137 ) has a wide selection of filters at various bandwidths and operating frequencies.

      Build or buy a "Level 7" diode-ring mixer. (That's "Level 7" as in "requires a local-oscillator signal of 7 dBm [5 mW] in a 50-ohm load.")

      Build a frequency-appropriate local oscillator using a JFET Hartley amplified by Roy Lewallen's (W7EL's) long-established 2N3904-2N3904 buffer amplifier and connect its output to local-oscillator port of the diode ring.

      Assuming that your band of interest is 160, 80, or 40 meters, build a double-tuned-circuilt filter for that band and connect one end of it to your antenna system and the other end of it to the RF input of your diode double-balanced mixer.

      Build a wideband post-mixer amplifer based on a 2N5109, 2N3866, or two paralleled 2N3904s, connect it to the output of the diode mixer, and follow it with a 6-dB 50-ohm attenuator pad. (Two 2N3904s work fine.)

      Hook your crystal filter to the output of the attenuator pad, via whatever impedance matching/termination is appropriate.

      Build an NE602-based product detector (use its internal oscillator as a BFO) and audio stages as appropriate, and connect this to the output of your crystal filter, via impedance matching/termination as appropriate. Make sure you build in an AF GAIN control.

      Now you've built a receiver that--

      - Hears down the band noise at 160, 80, or 40 meters
      - Exhibits an intermodulation distortion dynamic range of 90 dB or better
      - Exhibits a blocking dynamic range of 100 dB or better
      - Exhibits excellent adjacent-channel selectivity
      - Lets you listen to weak signals quite close in frequency to very strong ones

      and you did it without any test equipment at all.

      Few hobbyists, even those who love to fiddle with receivers, will build such a receiver because rather than seeking to actually implement and use excellent basic receiver performance they are addicted to the romance of junk and perpetual circular discussions about same.

      For those interested in understanding and implementing excellent basic radio performance, the book to start with is Hayward, Campbell, and Larkin's _Experimental Methods in RF Design_ ( http://www.arrl.org/shop/Experimental-Methods-in-RF-Design/ ). There's no shortcut to excellent basic radio performance because no shortcuts to that performance are needed.

      Best regards,

      Dave
      amateur radio W9BRD







       
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