Frequency counter pre-amp

Thread Starter

upand_at_them

Joined May 15, 2010
905
I'm trying to simulate a frequency counter pre-amp, taken from "Arduino Projects for Amateur Radio". I don't understand why the conditioned signal is AM modulated. I verified the circuit is the same as the book.

5-26-2022 3-28-22 PM.png
5-26-2022 3-27-51 PM.png
 

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ronsimpson

Joined Oct 7, 2019
2,161
I added this command. .ic V(N002)=5 V(N003)=5
Power up time =0nS. Power must charge up C2,4 and this causes L1,2 to have very high current at startup.
I set the two nodes (N002, N003) to 5V at start up. This keeps the power up power supply surge from "ringing" the LCs.
 

Thread Starter

upand_at_them

Joined May 15, 2010
905
So this is more of a simulation issue that a design issue? I assumed the inductors are there to prevent the input signal from getting on the power rail.
 

Bordodynov

Joined May 20, 2015
2,995
No, it is not necessary, but it is necessary to consider the parasitic parameters of the choke. In particular, the series resistance of the inductance. I took the choke designed for the smallest current in the LTspice program base. In this case this is a plus. The probability of parasitic oscillation is lower.
 
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