Tunnel Diode Transmitter

 "Synchrony"

Schematic here

It's now clear to me why nearly all of the 1960's tunnel diode novelty transmitters were designed for phone rather than CW. Trying to keep a tunnel diode oscillator frequency-locked to a quartz crystal - while drawing staccato power from it - is akin to balancing a pea on your knife while jumping on a pogo stick! The problem is associated with the nature of non-linear oscillators in general. That is, the bias required for a reasonable output power in a keyed oscillator is higher than the bias needed for reliable frequency-locking to a quartz crystal; the circuit exhibits hysteresis. 

My solution to this problem is to employ a two-stage transmitter. The crystal-controlled exciter oscillates continuously under a light load. A small sample of the exciter energy is required to reliably synchronize the keyed, higher-power, heavily-loaded, LC oscillator to the exciter operating frequency. This circuit resembles a classic, master-oscillator-power-amplifier (or MOPA) transmitter; however, it's more accurately described as a master-oscillator, synchronized power oscillator circuit. I've named this two-stage design, "Synchrony."

 AA1MY has kindly made several recordings of my signal available here

Contact log from my QTH in Roxbury, Vermont 

Date      Station      QTH             My RST      Miles/Watt  Comments 

1/10/08  AA1MY  Bethel, ME          539             471k     Sked

1/11/08  AA1MY  Bethel, ME          539             471k     Contact "on and off" for 45 minute duration

1/14/08  AA1MY  Bethel, ME          539             471k     Same as above; 2 hour duration

1/15/08  AA1MY  Bethel, ME          439             471k     QSO marking the 50th anniversary of Leo Esaki's 1958 paper

1/16/08  AA1MY  Bethel, ME          549             471k     Best QSB peak yet

1/17/08  AA1MY  Bethel, ME          329             500k     New two-stage transmitter: "Synchrony"

1/20/08  AA1MY  Bethel, ME          349             500k   

1/21/08  AA1MY  Bethel, ME          549             471k 

1/24/08  AA1MY  Bethel, ME          229             833k     100miles/120uW

2/05/08  AA1MY  Bethel, ME          229             833k     All tunnel diode station used at AA1TJ

2/07/08  AA1MY  Bethel, ME          229            1052k    95uW; Surpassed the million mile per watt mark
 

Confirmed Beacon Reception Reports

1/28/08  AA1MY  Bethel, ME           329             833k    "Grail" 

1/28/08  N1RX    Newport, NH         429             475k    "Grail"

2/07/08  AA1MY  Bethel, ME           229           1052k    "Orion"  95uW

2/09/08  KM1Z    Burlington, VT                        308k    "Orion"

2/09/08  AA1MY  Bethel, ME           339             833k    "Amore"

3/08/08  AA1MY  Bethel, ME           249           2381k    "Esaki"   42uW

Seab, AA1MY, has repeatedly amazed me with his ability to pull my weak signal out of the noise. He uses an IC706-IIG and a homebrew tuner. Ladder-line drives a center fed, 176 foot inverted-vee antenna with the center located at a height of 50 feet. Here's a photo taken of Seab during one of our QSOs. 

Finally, here's the page that fired my enthusiasm for tunnel diode transmitters when I was fourteen years old. It's taken from The Transistor Radio Handbook, 1st Ed., 1963, by D. Stoner, W6TNS, and L. Earnshaw, ZL1AAX