A Superhet/Direct Conversion AM receiver for 181.818 kHz
by Dick Cappel
A simple portable receiver with the antenna being the only LC circuit.
Downloads
Overview
This is a description of an experimental AM receiver for VLF. It is crystal controlled to receive 181.818 kHz (more or less) and operates as either a single conversion superhetrodyne or a direct conversion receiver. The bandwidths are expected to be 15 Hz to 3.5 kHz in superhet mode and 15 Hz to 10 kHz in the direct conversion mode. Operation is from a single +5 volt regulator and it can be powered from a 9 volt radio battery or other source of +8V or higher. The reason I built this was to verify some of my assumptions about these components would work together, having had numerous discussions of the SA-612/MK-484 and SA-612 direct conversion receiver concepts over the last year or so with my friend Jeff, besides that, I want to have a direct conversion receiver on hand for some planned experiments.
So, why 181.818 kHz? Its near the middle of a band of frequencies in which some countries, including the United States, allows unlicensed operation. For the U.S., see Code of Federal Regulations, Title 47, Volume 1, Section 15.217 Operation in the band 160 - 190 kHz. U.S. Government Printing Office, or look for it on the web. This particular frequency is easily derived from some common microcontroller crystal crystals, in this case a 6 Mhz crystal. Of course with the current generation of on-chip clocks, starting with the ATtiny series, crystals aren't really necessary for some applications. Other projects using this particular frequency are in the works.
Link to Site: http://cappels.org/dproj/dmrcvr/DualModeReceiver.html
by Dick Cappel
A simple portable receiver with the antenna being the only LC circuit.
Downloads
Overview
This is a description of an experimental AM receiver for VLF. It is crystal controlled to receive 181.818 kHz (more or less) and operates as either a single conversion superhetrodyne or a direct conversion receiver. The bandwidths are expected to be 15 Hz to 3.5 kHz in superhet mode and 15 Hz to 10 kHz in the direct conversion mode. Operation is from a single +5 volt regulator and it can be powered from a 9 volt radio battery or other source of +8V or higher. The reason I built this was to verify some of my assumptions about these components would work together, having had numerous discussions of the SA-612/MK-484 and SA-612 direct conversion receiver concepts over the last year or so with my friend Jeff, besides that, I want to have a direct conversion receiver on hand for some planned experiments.
So, why 181.818 kHz? Its near the middle of a band of frequencies in which some countries, including the United States, allows unlicensed operation. For the U.S., see Code of Federal Regulations, Title 47, Volume 1, Section 15.217 Operation in the band 160 - 190 kHz. U.S. Government Printing Office, or look for it on the web. This particular frequency is easily derived from some common microcontroller crystal crystals, in this case a 6 Mhz crystal. Of course with the current generation of on-chip clocks, starting with the ATtiny series, crystals aren't really necessary for some applications. Other projects using this particular frequency are in the works.
Link to Site: http://cappels.org/dproj/dmrcvr/DualModeReceiver.html