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You need to be more specific. What are you trying to amplify? How much gain and bandwidth do you need? What is your input signal level? What are your source and load impedances?Reitan said:I am having trouble determining how to bias an NPN small-signal transistor for different operating frequencies. I would prefer a common-base design for a 2N2222, with a mid-range around 3 MHz. Anybody out there have any idea how this works?[/b]
The circuit below should give you a place to start.Reitan said:I am trying to amplify shortwave signals between 2 and 4MHz. I would prefer to put the amplifier between the antenna and the tank. My antenna is a 6 foot dipole tv antenna, but I am familiar with winding transformers for impedance matching,so imput Z can be variable. The output will be attatched to a germanium diode detctor circuit at first, then later to a transistor detector set-up. Again, I can compensate for Z on the output. I would like the gain to be sufficient to drive the diode, but if I have to, I can forward bias the diode a bit to get it demodulating. I appreciate any help I can get with figuring this out.
What did you use for a detector, and how did you connect it? A schematic sure would help.Reitan said:I have a bunch of ferrite cores I've parted out from junk radios, but I'm not sure what the permeabilities are. Without a inductance meter, I'd pretty much be taking a stab in the dark as to how to wind them. I'm guessing most am ferrite bars are around 125 on the permeability scale,but you never can be sure. Also, every time I use a ferrite core, I get radio disney saturating my coil- it's the most god-awful station on earth.It bleeds through even when I decouple the antenna! Maybe a soup can would have less permeability,but just enough to help pull in the low SW stations. I suppose I could also try a tunable ferrite slug as well. Anyhow, I scrapped the "radio" this morning,except the tank(that took me abut 2 hours to make last night), and I rebuilt it with a better layout. Now there is no hum, but on a piezeoelecric earphone I can hear something,like intermittent crackles.I've built a couple AM regens, so I can tell there is a signal there, I'm just not getting it yet.I also only used 7 volts for the power supply, so before I make any changes I will try 12 volts and see what happens. I do have a question, though. Does anyone know what the output impedance of this circuit is? My earphone has a gazillion ohms of impedance,and I'll probably need to adjust my output. I know tht there is a WWV station on 2.5MHz, but not sure what else,but I aim to find out. I have a shortwave radio on my bench, but it's not the same as listening to your own,no matter how bad it might sound or how hard is is to tune.