Direct-Conversion Receiver

 
 

To get myself back on the air, I decided to start with a homebrew receiver. This project took about 15 months, beginning October, 2005. It covers the HF bands and is based on two important building blocks, the KK7B R2Pro direct-conversion receiver and the AA0ZZ IQPro DDS (direct digital synthesis) VFO. These basic designs I modified and then added features to suit my needs.


Here are the basic modules. Follow the links at right to see what’s inside.

  1. RF low-noise amplifier (LNA) and bandpass filters

  2. IQPro DDS VFO

  3. R2Pro downconverter

  4. Audio signal processing


    RECEIVER PAGES




Front End


Downconverter


IQPro DDS VFO


Audio Processing


S Meter and Other Ideas





    PERFORMANCE




Bands: 80 thru 10 meters


Modes: Image Reject or Binaural


Audio bandwidths: 2 kHz or 500 Hz (image reject); 4 kHz binaural


Noise Figure: 19.4 dB


Input IP3: +21.5 dBm


MDS: -128 dBn





 

I Always Wanted to Build A Receiver

Fabrication Techniques

The case is made of 1/2-inch birch plywood. The plywood is covered with 1/16-inch veneer cut on my bandsaw from a plank of peruvian pine, a fairly rare wood. I lined the inside of the cabinet with 3-mil copper foil, glued in place with spray adhesive. The rear panel is aluminum.


Except for the IQPro kit, all the circuits are built on pre-etched circuit prototyping board material. My favorite pattern has a ground plane and a 1/10-inch grid of plated-thru holes to individual pads (Twin Industries 8100-410, from Digikey). This gives me the advantage of having all that ground plane area and something with a nice grid into which all the parts are soldered. It’s great for small/quick prototypes, but also makes a robust finished product for the hobbyist.


Front_End.html

Next

The main modules are fabricated from brass sheet, mostly 50 mil thick. I have a machine shop, so I can mill parts to any size with accuracy. Note that there are no fasteners on the front panel. That’s because I machined numerous threaded brass standoffs which are soldered to the back of each panel. All the enclosures are soldered. I use an oxy-acetylene torch for most of the soldering because it heats a localized area quickly, thus avoiding a complete “meltdown” of the entire project!