New answers tagged amplifier
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You would need the following:
Antenna - an inverted 'L' antenna using insulated wire strung between supports about 30' apart and 30' high.
Earth - an underground metallic water pipe would make a good earth connection.
Tuner - a parallel-tuned circuit (a coil with a variable capacitor across it) tuneable across the medium wave broadcast band.
Detector - a ...
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You may find the SA612 chip more readily available than SA602. I believe the SA602 is an identical chip with slightly tighter specs than SA612. SA612 is pin-compatible replacement.
As for the LM387 (IC2) low-noise preamp - you might substitute a two-transistor amplifier instead, shown below. It will give better low-noise performance, with similar gain (...
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https://www.futurlec.com/Linear/LM387Npr.shtml
This site claims to sell them. I do not know anything about the company, just the first source that came up.
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To answer the last part of the question, the detector for an AM receiver is basically a rectifier, which rectifies the RF and the signal that it was modulated with.
Once the RF has been rectified, it has superimposed on it the original signal that the carrier was modulated with. This is then usually put through a low-pass filter to turn the "rectified RF ...
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The way I understand it, the tuner is an LC circuit forming a parallel tank that is designed to give maximum impedance at the desired frequency. This mean at that frequency, more current will flow through the detector and headphones than through the tank. At other frequencies, the tank circuit presents a low impedance and those signals are sent to ground ...
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The tuner is whatever allows the frequency to be selected. Tuners usually involve some kind of resonant circuit.
For a very basic AM receiver like you describe, the tuner is probably nothing more than an LC circuit, with one or both of the inductor or capacitor being variable.
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If the frequency counter is measuring -5.3 dBm, then before 20 dB of attenuation the power was 20 dB more than that, so 14.7 dBm.
"dBm" means decibels relative to 1 milliwatt. 14.7 decibels can be converted to a ratio like so:
$$ 10^{14.7/10} = 29.5 $$
So 14.7 dBm is 29.5 milliwatts.
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