Bruce Griffiths wrote: > Gerhard Hoffmann wrote: > >> Hi all, >> >> after reading "A low noise 100 MHz distribution amplifier for precision >> metrology" >> by M. Siccardi, S. Römisch, F. W. Walls, and A. De Marchi (NIST), >> I have implemented a homebrew version of their design. >> >> Circuits, simulation & measurement data are contained in: >> >> http://www.hoffmann-hochfrequenz.de/downloads/distri.zip >> >> >> Suggestions & ideas are welcome. 1:1 board layout of the next >> iteration will be available as .pdf or Gerber. >> >> >> >> >> regards, Gerhard, dk4xp >> >> >> Gerhard
Your layout could be a little cleaner. Use a 47 ohm resistor in series with each of the emitter of Q4 and use an 82 ohm resistor in series with each emitter connection of Q3. More space between Q2, Q3, Q4 would be conducive to higher reverse isolation. The bypass capacitor pads need to have lower inductance connections to the ground plane (several vias in parallel) and the base. A linear RF path would also be useful, the connection from Q2 emitter to Q3 emitter can be a 42 ohm section of microstrip and the connection from Q3 collector to Q4 emitter can be a section of 23 ohm microstrip. Instead of cramming 6 or 7 amplifiers onto a relatively small board, use a larger board and spread them out more leaving space for RF shielding to improve reverse isolation. For 5MHz and 10MHz the other NIST design has significantly higher reverse isolation which can be improved somewhat along with reduced distortion by using a 2 transistor input stage. No dc flows in the input and output transformers reducing distortion. It is also possible to design the output stage so that it wont saturate when driving a high impedance load with a + 13dBm input. 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.
