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I simulated a radio-receiver circuit, where I have actually build a part of the circuit which helps to amplify a AM carrier 550 kHz frequency of microvolts (antenna voltage) into several volts, however, I do not see any amplification on the output voltage as highlighted above. I am not sure what have I done wrong. I have attached my LTspice file at google drive here for edit and just click on download and if possible, edit and simulate it in LTspice to prove that there is amplification.

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  • \$\begingroup\$ You could draw the schematic a little bit more readable. Otherwise, you're lucky for the default Rser=1m for theinductor, otherwise you'd be getting voltage loop errors. Also, L1, C1 are absolutely useless here (they're in parallel with a voltage source, which has zero internal resistance). If you meant to simulate an antenna then a current source would have been better. \$\endgroup\$
    – a concerned citizen
    Commented Oct 7, 2022 at 18:46
  • \$\begingroup\$ youtu.be/CJi93dBBUJ0 Here's an AM radio I built on a breadboard. I believe this schematic has a number of issues. In the book I told you about, there's a very similar design (also based on the LM386) without those issues, plus you don't need a special germanium diode in the book design, but only a simple silicon one. You could choose a different book of course, but in general I'd recommend a book over internet schematics. \$\endgroup\$
    – ee_student
    Commented Oct 29, 2022 at 9:39

2 Answers 2

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You need a resistor from the output of D1 to ground for the demodulator to work.

A value of 10k or so is a reasonable starting point.

Th resistor is necessary or the node from the diode will just charge up to the max voltage of the RF then stay there. (It may even have difficulty simulating Spice often doesn't like nodes without a DC path to ground).

C2 is rather large to get a reasonable audio bandwidth - 1000pF would be better.

In your simulation you should couple the voltage generator B1 loosely to the inductor. That loose coupling could be a small capacitor, maybe 10pF.

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  • \$\begingroup\$ To better simulate the AA119, which is a germanium diode, one could put a resistance in parallel with it. Per the data sheet, somewhere around \$200\mathrm k \Omega\$ to \$1 \mathrm M \Omega\$ may be about right. Or use a Shottkey, or find a SPICE model of a germanium diode. \$\endgroup\$
    – TimWescott
    Commented Oct 7, 2022 at 23:26
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You can try this Google Drive link to AMDecoderEquationModulator.asc (contents copied below)
The mixer equation must be multiplied by 1000.
The diode should be a schottky type.
There should be a capacitor on the output to filter the high frequencies.

AMDecoderEquationModulator.asc

Version 4
SHEET 1 1348 680
WIRE 656 -288 480 -288
WIRE 480 -272 480 -288
WIRE 656 -240 656 -288
WIRE 480 -160 480 -192
WIRE 656 -128 656 -160
WIRE 656 -128 560 -128
WIRE 688 -128 656 -128
WIRE 784 -128 752 -128
WIRE 864 -128 784 -128
WIRE 560 -112 560 -128
WIRE 288 -96 240 -96
WIRE 240 -80 240 -96
WIRE 288 -64 288 -96
WIRE 656 -16 656 -128
WIRE 784 0 784 -128
WIRE 240 16 240 0
WIRE 864 16 864 -128
WIRE 240 32 240 16
WIRE 240 32 160 32
WIRE 256 32 240 32
WIRE 352 32 336 32
WIRE 432 32 416 32
WIRE 480 32 432 32
WIRE 560 32 560 -32
WIRE 560 32 544 32
WIRE 592 32 560 32
WIRE 160 96 160 32
WIRE 240 96 240 32
WIRE 432 96 432 32
WIRE 160 240 160 176
WIRE 240 240 240 160
WIRE 240 240 160 240
WIRE 432 240 432 160
WIRE 432 240 240 240
WIRE 656 240 656 80
WIRE 656 240 432 240
WIRE 784 240 784 80
WIRE 784 240 656 240
WIRE 864 240 864 80
WIRE 864 240 784 240
WIRE 656 272 656 240
FLAG 480 -160 0
FLAG 656 272 0
FLAG -48 48 0
FLAG -48 208 0
FLAG -48 -32 HI
FLAG -48 128 LO
FLAG 288 -64 0
FLAG 240 16 MIXED
SYMBOL ind 176 192 R180
WINDOW 0 36 80 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName L1
SYMATTR Value 200µ
SYMBOL cap 224 96 R0
WINDOW 0 40 22 Left 2
WINDOW 3 40 45 Left 2
SYMATTR InstName C1
SYMATTR Value 300p
SYMBOL schottky 352 48 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D1
SYMATTR Value 1N5817
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL cap 416 96 R0
WINDOW 0 42 31 Left 2
WINDOW 3 37 52 Left 2
SYMATTR InstName C2
SYMATTR Value 100n
SYMBOL npn 592 -16 R0
SYMATTR InstName Q1
SYMATTR Value 2N2222
SYMBOL voltage 480 -288 R0
WINDOW 0 37 53 Left 2
WINDOW 3 37 68 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 12
SYMBOL res 640 -256 R0
WINDOW 3 36 57 Left 2
SYMATTR InstName R2
SYMATTR Value 10k
SYMBOL cap 544 16 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C3
SYMATTR Value 220n
SYMBOL voltage -48 -48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value SINE(0 1.5m 550k)
SYMBOL voltage -48 112 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V4
SYMATTR Value SINE(0 1m 1.5k)
SYMBOL bv 240 16 R180
WINDOW 0 172 53 Left 2
WINDOW 3 35 34 Left 2
SYMATTR InstName B1
SYMATTR Value V=1000*V(HI)*V(LO)
SYMBOL res 544 -128 R0
WINDOW 0 41 57 Left 2
SYMATTR InstName R3
SYMATTR Value 470k
SYMBOL cap 752 -144 R90
WINDOW 0 38 53 VBottom 2
WINDOW 3 40 49 VTop 2
SYMATTR InstName C4
SYMATTR Value 220n
SYMBOL res 768 -16 R0
SYMATTR InstName R1
SYMATTR Value 47k
SYMBOL cap 848 16 R0
SYMATTR InstName C5
SYMATTR Value 6.8n
SYMBOL res 352 16 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 50
TEXT 40 296 Left 2 !.tran 0 6m 5m
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