I am building a LW receiver/amplifier like this: https://sidstation.loudet.org/hw-en.xhtml
My Max 275 filter (https://www.maximintegrated.com/en/products/analog/analog-filters/MAX275.html ) will arrive (I hope) Monday. I have added some small capacitors (8.2 to 22 pF) across the TL082 op-amps I am using as low-pass filtering. With just three stages ( about 60 dB gain) I am picking up something strong around 100 kHz. My target (center) frequency for this project is 250 kHz. Attached is a really crude LT Spice schematic that shows a close approximation of what I built. Some of the resistor values were changed to accommodate what I had on hand. The capacitor values are what I used.
What could it be? Location = NE Ohio about 40 miles West of Cleveland. My first assumption is it is some sort of oscillation that I will need to deal with. But just in case someone knows of a LW beacon in the area, I thought I would ask.
John
Edit: In real life, the coupling capacitors are not shorted. I did that to see the effects on the simulation.
My Max 275 filter (https://www.maximintegrated.com/en/products/analog/analog-filters/MAX275.html ) will arrive (I hope) Monday. I have added some small capacitors (8.2 to 22 pF) across the TL082 op-amps I am using as low-pass filtering. With just three stages ( about 60 dB gain) I am picking up something strong around 100 kHz. My target (center) frequency for this project is 250 kHz. Attached is a really crude LT Spice schematic that shows a close approximation of what I built. Some of the resistor values were changed to accommodate what I had on hand. The capacitor values are what I used.
What could it be? Location = NE Ohio about 40 miles West of Cleveland. My first assumption is it is some sort of oscillation that I will need to deal with. But just in case someone knows of a LW beacon in the area, I thought I would ask.
John
Edit: In real life, the coupling capacitors are not shorted. I did that to see the effects on the simulation.
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