Posted on Nov 26, 2012 9014
Among the signals below 550 kHz are maritime mobile, distress, radio beacons, aircraft weather, European Longwave-AM broadcast, and point-to-point communications. The low-frequency converter converts the 10 to 500kHz LW range to a 1010 to 1550kHz MW range, by adding 1000kHz to all received signals. Radio calibration is unnecessary because signals are received at the AM-radio`s dial setting, plus 1 MHz; a 100-kHz signal is received at llOO kHz, a 335-kHz signal at 1335 kHz, etc. The low-frequency signals are fed to IC1, a doubly-balanced mixer.
Transistor Q2 and associated circuitry form a Hartley 1000-kHz local oscillator, which is coupled from Q2"s drain, through C8, to IC1 pin 8. Signals in the 10-550 kHz range are converted to 1010-1550 kHz. The mixer heterodynes the incoming low-frequency signal and local-oscillator signal. Transistor Q3 reduces IC1"s high-output impedance to about 100 !l to match most receiver inputs. Capacitor Cl5 couples the 1010-1550 kHz frequencies from Q3"s emitter to output jack ]3, while blocking any de bias. Inductor L6 couples tire de voltage that"s carried in the rf signal cable from the rcvr/dc adaptor. The de voltage and rf signals don"t interfere with one another; that saves running a separate power-supply wire, which simplifies installation at a remote location. Capacitors Cl4 and Cl3 provide de supply filtering. The kit is available from North Country Radio, P.O. Box 53, Wykagyl Station, NY 10804.