More Amp ideas
I have been working on the calculations for the tank. I calculated my Tune capacitance range - roughly 10-500pf for 1.8-54mHz. I used an equation I found on AG6K's website (part 5 of "Amplifiers").
After looking at the Handbook for additional information regarding tank circuit calculations I see the equation I used is the same. However, there are two different systems for calculating the rest of the values - those with respect to a Pi network and a Pi-L network.
I want a Pi-L on the output for better harmonics/IMD supression, so thats what I am going to work on here.
The Handbook gives two different schematics for a Pi-L. One has a Pi circuit going to Rm (Image Impedance) followed by an L. The other one is your standard Pi-L - a Pi followed by an L, where your R2 is the output (50 ohms). This is getting kind of confusing because the calculations are all based off the first one with respect to Rm = 300ohms. They say that the L in the first example transforms Rm to R2. Thats a lot of number twisting!
I guess where I am hung up now is why in the world they would plug in 300ohms for Rm when the output impedance needs to be ~50ohms to match to the coax? I suppose if you were loading 300ohm ladder line that would be one situation where 300ohms would be needed.
Another note is all exact values in this are THEORETICAL. Once I get the circuit together things are bound to be different - stray capacitance with component locations, extra resistance in the inductors, etc. With so many unknowns I will surely be doing some tweaking on this once it is together.
Anyway, more number crunching to come.
If you have or know where I can get a couple decent vacuum variables - 5-500pf or 10-500pf @5-10kv, and another up to 1000-1200pf @5-10kv let me know!
I also thought about doing a 5-250 on the input with a 250 doorknob in series for the low bands.
After looking at the Handbook for additional information regarding tank circuit calculations I see the equation I used is the same. However, there are two different systems for calculating the rest of the values - those with respect to a Pi network and a Pi-L network.
I want a Pi-L on the output for better harmonics/IMD supression, so thats what I am going to work on here.
The Handbook gives two different schematics for a Pi-L. One has a Pi circuit going to Rm (Image Impedance) followed by an L. The other one is your standard Pi-L - a Pi followed by an L, where your R2 is the output (50 ohms). This is getting kind of confusing because the calculations are all based off the first one with respect to Rm = 300ohms. They say that the L in the first example transforms Rm to R2. Thats a lot of number twisting!
I guess where I am hung up now is why in the world they would plug in 300ohms for Rm when the output impedance needs to be ~50ohms to match to the coax? I suppose if you were loading 300ohm ladder line that would be one situation where 300ohms would be needed.
Another note is all exact values in this are THEORETICAL. Once I get the circuit together things are bound to be different - stray capacitance with component locations, extra resistance in the inductors, etc. With so many unknowns I will surely be doing some tweaking on this once it is together.
Anyway, more number crunching to come.
If you have or know where I can get a couple decent vacuum variables - 5-500pf or 10-500pf @5-10kv, and another up to 1000-1200pf @5-10kv let me know!
I also thought about doing a 5-250 on the input with a 250 doorknob in series for the low bands.
posted by Steve at
6:10 PM
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