Thanks, Bruce, for the circuit. I don't recognize the transformer numbers in your schematic. Can you tell us more about the nature of the transformers you have specified? Bruce Griffiths wrote: > George > > The circuit schematic for a BJT version of the JFET frequency is attached. > The biasing is a little more complex as it is necessary set each > frequency doubler BJT collector current at about 1mA or so to maximise > conversion gain. > The input impedance is also around 50 ohms. > Have also minimised the number of different component values used. > Other transistors may be substituted but some care is required as the > reverse voltage across the base emitter junction is about 2V for a > +13dBm input. > Some filtering of the output waveform is required. > The intended output load is 50 ohms. > > The 200 ohm emitter series resistors together with the transformed > source impedance ensure that there is sufficient degeneration to keep > the phase noise low. > > Obtaining suitable transistors for this circuit should be much easier > than obtaining suitable JFETS for the JFET doubler. > > Whilst a diode doubler (at higher frequencies this may be the only > sensible option) could be used it would need both an input amplifier and > an output amplifier. > > Bruce > > ------------------------------------------------------------------------ > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

Rex wrote: > Thanks, Bruce, for the circuit. I don't recognize the transformer > numbers in your schematic. Can you tell us more about the nature of the > transformers you have specified? > > > Rex These are standard Minicircuits through hole mount RF transformers that have (with an appropriate termination) low VSWR for frequencies around 5-10MHz or so. They also make surface mount equivalents. They have impedance ratios of 16:1 (4:1 turns ratio centre tapped on the high impedance side). Although a centre tapped transformer isnt needed for the output I elected to use the same part to keep the number of different parts down especially when they appear very similar. Bruce

Thanks. Great! Commonly available part.. I agree one part for both is good. Bruce Griffiths wrote: > Rex wrote: > >> Thanks, Bruce, for the circuit. I don't recognize the transformer >> numbers in your schematic. Can you tell us more about the nature of the >> transformers you have specified? >> >> >> >> > Rex > > These are standard Minicircuits through hole mount RF transformers that > have (with an appropriate termination) low VSWR for frequencies around > 5-10MHz or so. > They also make surface mount equivalents. > They have impedance ratios of 16:1 (4:1 turns ratio centre tapped on the > high impedance side). Although a centre tapped transformer isnt needed > for the output I elected to use the same part to keep the number of > different parts down especially when they appear very similar. > > Bruce > >

Rex wrote: > Thanks. Great! Commonly available part.. I agree one part for both is good. > > > Rex One caveat is the dc current flowing in the output transformer may cause too much distortion (actual specification on the data sheet is somewhat unclear/ambiguous), in which case capacitively coupling the output transformer and using an inductive shunt feed arrangement will cure this problem. Of course the ideal location for series tuned shunt traps (tuned to fundamental and say 4th harmonic) is from the output collectors to ground. These short unwanted harmonic currents to ground allowing a relatively simple low pass filter to be used to cleanup the output without contributing significant phase shift and associated tempco to the desired second harmonic output. The net dc current flowing in the input transformer secondary will be very small. Bruce