I was looking at building the preamp on this page using a gear-driven capacitor from a TS-130s VFO in the tank. My first thought was to model it in simsmith using a tank with a reasonable Q directly into the Jfet biased as shown in the schematic, but that doesn't seem to be working in simsmith (could be my error)...
So I decided to try something different in simsmith to achieve better power transfer, couple to 50Ω output (where the jfet would be) using a capacitor and got this
and then I got to thinking, the JFET can have any resistor value at the gate, so why not get rid of the coupling cap and got this
Truth is, I have no clue what I am doing. Is it better to stay with the original schematic, couple the tank to 50Ω using a capacitor and use a 50Ω preamp, or do the last one and put the required 1.84kΩ resistor at the gate? I always thought lower resistances had less noise voltage, so the 1MΩ gate bias resistors is throwing me off. What should I do?
Thanks!!
Edit: just to clarify, L is the antenna, I forgot to rename that. Pigtail is the inch of wire where the coax splits off and gets soldered to the coil, about 20nH per inch, TankBelowTap and TankAboveTap are representing the tank inductor with a tap point, TankCap and Variable are both the tank capacitor, my variable only goes from 10pF to 40pF and it needed more. C1 is the coupling cap I used to prevent the tank from being loaded down and OutputLead is the same as the pigtail, the trace or wire going to the jfet or output connector.
So I decided to try something different in simsmith to achieve better power transfer, couple to 50Ω output (where the jfet would be) using a capacitor and got this
and then I got to thinking, the JFET can have any resistor value at the gate, so why not get rid of the coupling cap and got this
Truth is, I have no clue what I am doing. Is it better to stay with the original schematic, couple the tank to 50Ω using a capacitor and use a 50Ω preamp, or do the last one and put the required 1.84kΩ resistor at the gate? I always thought lower resistances had less noise voltage, so the 1MΩ gate bias resistors is throwing me off. What should I do?
Thanks!!
Edit: just to clarify, L is the antenna, I forgot to rename that. Pigtail is the inch of wire where the coax splits off and gets soldered to the coil, about 20nH per inch, TankBelowTap and TankAboveTap are representing the tank inductor with a tap point, TankCap and Variable are both the tank capacitor, my variable only goes from 10pF to 40pF and it needed more. C1 is the coupling cap I used to prevent the tank from being loaded down and OutputLead is the same as the pigtail, the trace or wire going to the jfet or output connector.
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