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Crystal-stabilizing a Regenerative Receiver

Discussion in 'Homebrew and Kit Projects' started by W0RIO, Dec 11, 2017.

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  1. W0RIO

    W0RIO Ham Member QRZ Page

    I had an interesting idea about using a crystal to stabilize a regenerative receiver.
    I spent a few hours modifying my Piglet regenerative receiver and managed to get some
    big improvements compared to using the normal LC resonator circuit.

    A standard ham FT-243 crystal was inserted into the regenerative feedback loop,
    the receiver tunes from the crystal frequency to about 25Khz down from the marked frequency.
    You can really hear the circuit "pop-in" when the tuned circuit is resonated with the crystal and
    CW signals get much louder and less "drifty". CW stations from around the country
    could be copied relatively easily in the narrow frequency range.

    After I got the circuit running, I did a Google search
    on crystal regenerative receivers and discovered that this has been tried by others (no surprise).
    I added some links to similar experiments at the bottom of my article.

    Here's the modified schematic:

    PigletRcvrV2.png
    More details on the project can be found here:
    http://www.solorb.com/elect/hamcirc/pigletregen/index.html

    The original Piglet receiver worked very well for listening to WWV and short wave broadcast stations,
    the crystal-stabilized version could probably be used for real ham QSOs, although it would be a
    challenge since regens are touchy and sensitive to overloading from nearby signals.
     
    VK3YE likes this.
  2. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Hmm.

    Adding a crystal is sorta like putting handcuffs on as a bandaid for other problems. It seems like the wrong approach to solving the stability issues. I think attention would be better directed at things like voltage stability, thermal stability, component size and spacing, wire routing and shielding.
     
  3. VK3YE

    VK3YE Ham Member QRZ Page

  4. W0RIO

    W0RIO Ham Member QRZ Page

    No doubt adding the crystal is like putting a "wart on the side of a kludge" to quote Tracy Kidder, but
    note that the original receiver was already fairly stable and well shielded and the regen control
    (screen voltage) was already regulated.

    Going from a wideband 5-10 Mhz coverage receiver to a 40M CW receiver did require improving the mechanical
    stability of the tuning system. I plan on adding an additional diagonal bracket to reduce movement between the front panel
    tuning cap and the chassis.

    However, the crystal greatly improves the resonant circuit's Q compared to the original LC tuning circuit.
    With no crystal, weak signals were nearly impossible to copy, with the crystal in the circuit, they are now
    easily copied. It's still a tweaky regen receiver, but now it's much better at picking out narrow CW signals.
     
    KA0HCP likes this.
  5. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Great. I"m wondering if increasing the feedback would improve the sensitivity.

    Thanks for the point to this project. I've saved it for a rainy day. Cheers! b.
     
  6. K8ERV

    K8ERV Ham Member QRZ Page

    What are those circles with dashed lines in them?

    TOM K8ERV Montrose Colo
     
  7. W0RIO

    W0RIO Ham Member QRZ Page

    GlassFETs.
     
    KA0HCP likes this.
  8. W0RIO

    W0RIO Ham Member QRZ Page

    The receivers in your videos are quite impressive for regenerators, especially the large frequency span you get from pulling the
    ceramic resonators. Where did you purchase your resonators? I tried eBay and AF4K with no results, digi-key.com
    does have a 7.16 Mhz resonator.
     
  9. VK3YE

    VK3YE Ham Member QRZ Page

    http://www.minikits.com.au/components/passive/frequency-control/ceramic-resonators has a good range for 80 & 40m
     
  10. N2UHC

    N2UHC Ham Member QRZ Page

    Funny looking transistors.
     

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