2007 One Active Device Contest
Macrohenry's Radio

Right click on pictures to view full size pictures

Baseboard is 18" x 12"Antenna tuner left, radio tuner right

Transistor and diode mounted in IC socketDrive pulleys and cable


     Antenna is 60 foot vertical with base 20 feet above ground level.  See below for details.

     Antenna coil is contrawound 660/46 Litz on 4.5" dia styrene form.  Tank coil is on 6" ferrite rod.

     Instead of 8 ohm speaker, I'm using 32 ohm HiFi headphones, adjusting taps on a 70v line transformer.  Regeneration/selectivity is controlled by positioning hand wound RF transformer relative to 6" ferrite core tank coil.

     RF transformer is made of 1/4" x 1" cutoff section of old transistor radio ferrite core.  Primary is 40 turns 36 ga enameled magnet wire; secondary is 150 turns of the same wire.

     Reflex ckt is Robert Bazian's design with minor modifications.  Bazian may not necessarily have intended this design for DX or selectivity; he optimized it for loud local reception. Although his latest design controls regeneration so no heterodynes are heard, I find that increasing regeneration and using heterodynes is more effective for DX work.

     I have a loud station 11 miles from my house on 590.  Without traps, I'm able to tune distant stations at 580. This WAV file demonstrates selectivity.  It was recorded  in front of an 8 ohm speaker driven by this radio.  This WAV demonstrates sensitivity; WWL is 460 miles away, coming through loud and clear.

Antenna and Ground

     This tall vertical antenna has no capacity hat because it has so much capacitance without it. I built Ben Tongue's antenna-ground capacitance bridge and thusly learned that this antenna has a ton of capacitance (forgot how much and lost my notes on that). I use an inverted Tuggle tuner on the input. That is, a second varicap goes between the antenna and the antenna tuner varicap, rather than from the antenna tuner varicap to ground (see schematic above.). For tuning simplicity throughout the contest the first varicap was at a fixed setting of 60 pf.

     The antenna is a 20 foot Wonderpole Crappie pole on top of five telescoping sections of electrically bonded galvanized electrical conduit from Home Depot.  If I had to do it over, I'd use different piping because this conduit will rust. The five telescoping sections sit on a rooftop base 22 feet above ground level. Adjusting for the loss of length by telescoping, it tops out at about 80 feet. The highest 20 feet is a loose 16 ga magnet wire tied to the top of the carbon fiber fish pole.  The large conduit diameter accounts for some of the capacitance.

     The ground system consists of four 8' long copper pipes driven 6' into the ground at least 8' apart. I try to keep the four pipes wet. They are soldered to thick bare copper grounding wire from Home Depot, which also is laid in the grass so that it follows two sections of back yard fence for about 75 feet. The additional wire is terminated on a pipe driven a few feet into the ground, so that it serves as a better ground conductor as well as a counterpoise.

     Even with all this, my soil is so poor that my antenna-ground resistance seems to hover between 50 ohms and 100 ohms. According to Ben Tongue, I could get 3dB more signal for every halving of that resistance.

     Because I've done all I know to do to cut the ground resistance, I decided to see what a high antenna would do. It works pretty well.