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I am analyzing a signal jammer circuit for prototyping on LTSpice. The amplifier takes a square wave signal input from NE555 IC and is supposed to transmit it at ~2.4GHz using a tank circuit at collector. The whole circuit is powered by a 9V DC voltage. I'm using 2N2222 transistor for simulation to check the functionality, whereas I plan to use BFU690F RF transistor for the actual circuit.

Circuit Schematic

Input Signal

I'm stuck at calculating the amplifier voltage and power gains as I'm only familiar with calculations on collector resistors and not tank circuits. LTSpice shows the following frequency response, which is a flat line at -210dB for all frequencies whereas the amplifier seems to be amplifying.

Output At collector of Transistor

The frequency response at collector

Is it the case that 2N2222 is not working on LTSpice in this frequency range or is there a more serious design issue?

EDIT :

  1. Figure 2 is measured between C1 and Q1
  2. Figures 3,4 are measured between Q1 and C3
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  • \$\begingroup\$ Use node alias names not n00x because they are meaningless. \$\endgroup\$
    – Andy aka
    Commented Jun 6, 2023 at 10:41
  • \$\begingroup\$ @Andyaka Have included the details in edit. \$\endgroup\$
    – Shubham Agrawal
    Commented Jun 6, 2023 at 11:07
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    \$\begingroup\$ The simulation works good, the NE555 produces a signal of around 2 MHz, the small capacitor C6 (2 pF) is absurd, dominant is the chip pin capacitance. The switching edges produce some higher frequency ringing in the RF tank. I expect, a real world circuit would do nearly the same. \$\endgroup\$
    – Jens
    Commented Jun 6, 2023 at 18:54

2 Answers 2

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"Is it the case that 2N2222 is not working on LTSpice in this frequency range". I don't know. A 2222 won't work in real life at 2.4 GHz, so, to the extent that LTspice is managing to simulate reality, it shouldn't work in LTspice.

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I solved this by replacing the NE555 circuit with a square wave voltage source as AC analysis requires you to have one or more independent sources with "AC" flag enabled.

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  • \$\begingroup\$ LTspice should've thrown an error saying No AC stimulus found. Did that not happen for you? \$\endgroup\$
    – Ste Kulov
    Commented Jun 6, 2023 at 15:18

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