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.
 
 
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!