HF to LF Converter

Posted on Feb 5, 2014

Any mode (e. g. CW, AM, SSB, FSK) which is initiated in the HF transmitter or transceiver can be regenerated at LF (100 to 200 kHz) using this simple converter. The output at LF can be used to drive an LF Power Amplifier. The February, 2000 issue of Amateur Radio (ref. 1) contained an article I had submitted on an LF transmitter. The transmitter wa

HF to LF Converter
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s designed for CW operation but the power amplifier was operated in a linear mode and it was only a matter of replacing the VFO with some form of AM or sideband generator with an LF output to operate on speech. The article was followed up with a further article (Amateur Radio September 2000, ref 2) on a Single Sideband Generator using the phasing technique. The design aimed at making a stand-alone unit because of the possibility of using the unit at a site away from the amateur station. However it was pointed out that a simpler arrangement might be achieved at the amateur station site by heterodyning down from the HF output of the local HF transceiver. This third article describes a circuit designed to do that conversion and provide sufficient LF output level to drive the original power amplifier. The circuit diagram of the converter is shown in figure 1. The conversion takes place in V1 (type NE602). The V1 circuit is almost identical to that used in my Active Loop Converter (Amateur Radio July, 2000 - ref 3) except that the input and output frequencies are reversed. I used the same 4 MHz xtal as in the receive converter as I had another one spare. Most HF amateur transceivers tune up to 4 MHz on the 3. 5 MHz band so that it is simply a matter of setting the transceiver frequency to 4 MHz minus the LF transmission frequency. (4 MHz plus LF transmission frequency could also be used if the transceiver is tuneable above the 4...

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