80m Receiver ROX-80

Compact 80m Direct Conversion ARDF receiver

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This design was inspired by the innovative SM5CJW receiver.
The form factor is much smaller and lighter than other designs. The ergonomics are very good, and the receiver is easy to operate using a single hand, so it is an ideal receiver suitable for a beginner or orienteer.

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After building and experimenting with the SM5CJW design , a modified version incorporating personal preferences  has inevitably evolved.
Here are the key differences.

  • Front-end cascode amplifier with gain control (from a design by WB6BYU).
  • VXO using a Ceramic resonator.
  • Conventional ferrite rod winding and sense antenna.

The receiver form factor and audio amplifier is the same as in the SM5CJW design.
My original build used a VFO and had unacceptable drift .
I was advised by SM5CJW that very few smd chip inductors are, in fact, suitable for a VFO.  I had no great stock of inductor chips which I could compare for stability testing, so I started looking at the use of a ceramic resonator in a VXO circuit, as an alternative.  The final design gives a repeatable VXO range of at least 60kHz covering 3.52Mhz to 3.58Mhz.
This frequency range is fine for UK event usage, but it must be noted that it may not be  suitable for  international  events, particularly foxOring and sprint, where a  band spread of 3.51 to 3.6Mhz may be used.
The big advantage of the VXO is rock-solid stability with a low sensitivity tuning rate, making it ideal for beginners (and me!).

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click on the schematic to view a full pdf version

As this receiver uses the same front end as the  Dale Hunt, WB6BYU receiver you could use his loop antenna design instead of a ferrite rod. click here for details.

Documents available, updated 2-Nov-2014

 

 

 

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