I've been working a few days on this and have still come up with nothing. I am trying to make an AM radio using a silicon diode, but all of my attempts have failed. I believe my latest attempt most likely came closest, but it did not work. Does anyone have any plans for making a radio using a silicon diode I can look at? All of the plans I have seen have all used germanium or some other low voltage drop diode. The plans I've come up with have not worked.
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2\$\begingroup\$ If the input stage with the diode would be sensitive enough for the antenna signal, you are almost shorting it to ground through the 100 ohm resistor at the right of the diode. \$\endgroup\$– jippieFeb 17, 2014 at 6:17
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1\$\begingroup\$ What are your op-amp supplies connected to and what op-amp are you using? \$\endgroup\$– Andy akaFeb 17, 2014 at 8:43
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\$\begingroup\$ Opamp needs dual supplies above and below ground to work as shown. If "100" = 100 Ohms it is MUCH too low in both places it is used. \$\endgroup\$– Russell McMahon ♦Feb 17, 2014 at 14:36
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\$\begingroup\$ Crystal set society \$\endgroup\$– Russell McMahon ♦Feb 17, 2014 at 14:38
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\$\begingroup\$ The "latest attempt" is missing, which kind of invalidates the question. \$\endgroup\$– gbarryNov 16, 2014 at 3:51
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2 Answers
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There are many plans on the XTAL SET SOCIETY and Ben Tounge's websites, including both biasing of diodes for optimised detection and modeling of crystal radio circuits in SPICE.
Consider also using a Schottky diode (some of the HP types are fantastic for this and 'foxhole' razor blade diodes are essentially the same!) and zero-Vgs MOSFETs as reported about in Bob Cutler's 'High Sensitivity Crystal Radio Set' which is available online at the ARRL.
Of course, if you can get your Q high and tuning not so touchy and your local clear-channel is good enough, maybe that silicon diode is OK.
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Crystal Radio net have a basic circuit that includes a 1.5V battery. The idea of the battery is to put a DC bias on the detector diode, until it is almost conducting. This helps detect very weak signals.
In your case, you are using a silicon diode, instead of a germanium. Germaniums typically need 0.2V to turn on, your silicon probably needs about 0.6V to do the same.
Correcting for that DC bias should help a lot.
