Hi For a modern build, the PZT3904’s and PZT2222’s are a pretty good way to go with this amp.
For normal distribution to instruments, there’s really no need to do anything this complex. Bob > On Nov 25, 2014, at 2:34 PM, Charles Steinmetz <csteinm...@yandex.com> wrote: > > A couple of people were asking about NIST isolation amplifiers recently. I'm > attaching circuit diagrams of the 5-10 MHz amp from 1997 and the 1-200 MHz > amp from 1990. I think Bruce has the papers linked at his ko4bb.com pages. > > I built some of the 5-10 MHz amps with minor variations and they work very > well (I used a separate capacitance multiplier for the base divider string, > and changed the first 4.3k resistor to 6.65k to achieve symmetrical clipping > and a small increase in headroom). I used 2N3904s for the two lower > transistors and a 2N2219A for the top transistor, which dissipates over 300mW. > > I tried some fancy transistors with very low base spreading resistance, which > reduced the noise -- but the increased junction capacitance made the AM to PM > conversion worse, so the overall residual PM was worse. On the other hand, > GHz transistors had higher noise due to lower gain. So the 3904/2219A > combination appears to be just about optimum. (Note that the 200 ohm > resistor at the input contributes about half of the circuit's noise, and you > can't use the Norton trick because it would ruin the isolation.) > > The transistor stack draws 32mA and the base divider stack draws ~1.5mA. The > amplifiers have an input impedance of 250 ohms, so paralleling the inputs of > 5 sections creates an overall 50 ohm input impedance. When a circuit has > reverse isolation of well over 150dB, as this one does, you need to pay very > careful attention to shielding. > > Best regards, > > Charles > > <NIST_200_iso.png><NIST_5_10_iso_amp.png>_______________________________________________ > 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. _______________________________________________ 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.
