Message	Date	From	Subject
120	2006-09-03 11:01:14	Stan	Universal QRP transmitter changes question
Ref: Solid State Design, QRP Classics, Universal QRP Transmitter MK II, Tuna Tin All of these designs have a common root. A major changes occurred in the MK II. The recent circuit changes (2006) were to the oscillator feed back caps and lst stage tuned circuit. Assumptions I have made: 1) I believe the basic oscillator circuit is a Colpitts 2) The capacitive feedback (Xc:Xcx) is 4:1 in the original designs (expected typical value) 3) The higher C in the osc tuned circuit on the original design results in a high Q circuit In the MK II the capacitive feedback seems to be reverse (Ref QST 2006) from what I expect to see in a Colpitts. (?) What am I missing here? In the MK II the tuned osc C was lower which would result in a lower Q circuit, broadband ? Was this really required? Would like to understand the designer's thinking and why the changes ? Thanks, Stan ak0b
338	2007-01-13 07:39:59	homsleyt	Re: Universal QRP transmitter changes question
Did you ever get an answer to the questi

Ref: Solid State Design, QRP Classics, Universal QRP Transmitter
MK II, Tuna Tin

All of these designs have a common root. A major changes occurred
in the MK II. The recent circuit changes (2006) were to the
oscillator feed back caps and lst stage tuned circuit.

Assumptions I have made:

1) I believe the basic oscillator circuit is a Colpitts
2) The capacitive feedback (Xc:Xcx) is 4:1 in the original designs
(expected typical value)
3) The higher C in the osc tuned circuit on the original design
results in a high Q circuit

In the MK II the capacitive feedback seems to be reverse (Ref QST
2006) from what I expect to see in a Colpitts. (?) What am I
missing here?

In the MK II the tuned osc C was lower which would result in a lower
Q circuit, broadband ? Was this really required?

Would like to understand the designer's thinking and why the
changes ?

Thanks, Stan ak0b