T
Tim Williams
- Jan 1, 1970
- 0
Schematic:
http://webpages.charter.net/dawill/Images/20MHz_Amp.gif
Pictures:
http://webpages.charter.net/dawill/Images/20MHz_Amp1.jpg
http://webpages.charter.net/dawill/Images/20MHz_Amp2.jpg
With the 100 + 10pF on the +in transistor and 10pF on the tail, I've
eliminated the UHF/microwave oscillation as best I can tell. It no longer
changes gain or bias when I wave my hand around and touch parts. My
laptop's wifi probably stays connected, too (I didn't have it with me when
I did this).
Now I can concentrate on the characteristics. The squarewave response is
good, but it has a strong bounce on it. In fact, hooking it to an RF
generator (Eico 322, not much output into 50 ohms, but frequency appears to
be accurate) I see a substantial rise of perhaps 20dB at 26MHz! It is of
equal and opposite amplitude on both outputs (viewing with 10x probes, one
with somewhat more capacitance), so I suspect it comes from the LTP.
Feeling around the circuit produces no change (aside from loading down the
2N5179 collectors, which predictably reduces HF gain overall, not
specifically the 26MHz peak), implying it might be an LC sort of thing.
Ideas?
Tim
http://webpages.charter.net/dawill/Images/20MHz_Amp.gif
Pictures:
http://webpages.charter.net/dawill/Images/20MHz_Amp1.jpg
http://webpages.charter.net/dawill/Images/20MHz_Amp2.jpg
With the 100 + 10pF on the +in transistor and 10pF on the tail, I've
eliminated the UHF/microwave oscillation as best I can tell. It no longer
changes gain or bias when I wave my hand around and touch parts. My
laptop's wifi probably stays connected, too (I didn't have it with me when
I did this).
Now I can concentrate on the characteristics. The squarewave response is
good, but it has a strong bounce on it. In fact, hooking it to an RF
generator (Eico 322, not much output into 50 ohms, but frequency appears to
be accurate) I see a substantial rise of perhaps 20dB at 26MHz! It is of
equal and opposite amplitude on both outputs (viewing with 10x probes, one
with somewhat more capacitance), so I suspect it comes from the LTP.
Feeling around the circuit produces no change (aside from loading down the
2N5179 collectors, which predictably reduces HF gain overall, not
specifically the 26MHz peak), implying it might be an LC sort of thing.
Ideas?
Tim