Hartley Oscillator amplitude problem

[TMTYB]

I have used LT spice IV (https://www.linear.com/designtools/software/ltspice.jsp)
to simulate the attached circuit, and it works perfectly.



But when I build the circuit on a bread board, Everything works okay, except that the amplitude is allot smaller than expected (on simulation 10V p-p.. Built circuit 180mV p-p).

I have checked the built circuit for errors such as wrong pins in wrong places. ect. but havent found any fault there.

I need a 4Vp-p signal output.

Help would be appreciated.
Tnx.

 

[martine1212]

Did you checked you bias current level??

Second, from your schematic I just see ideal component in the LC tank and everwhere (except the transistor).
So the Q of your tank is basically infinite (zero loss), if you include the losses you will see a much smaller amplitude.

 

[keith1200rs]

I am not sure of the reason for your problem, but a few comments:

1. I think the Hartley has a tapped inductor, nut I am not sure. You have drawn it as two separate inductors. I cannot see any mutual coupling.

2. the inductors are very small and the capacitors very large for the frequency you are trying to achieve. Ideally you want to use NPO/COG capacitors in an oscillator or filter. I am guessing your capacitors will be something like X7R.

3. the inductors will have parasitic resistance which you have not taken into account in your simulation. The non-ideal characteristics of the capacitors have also been ignored.

My suggestion would be to first reduce your resonant capacitor and increase the inductors and use COG for the resonant capacitor. The coupling capacitors do not matter - just the resonant one (C1).

Keith.

 

[TMTYB]

Thank you all for the input, will try the info you gave me.