Hi Grant, Grant Hodgson wrote: > The Janus board in the HPSDR project uses LT1128s, which are > single-eneded low noise op-amps. > [...] > or the even lower noise LT1115s
Both LT1128 and LT1115 are excellent op-amps. Maybe even the best available! I am using them both as low noise preamplifiers with loop antennas for reception of "natural" ELF/VLF signals. So far I cannot tell the difference between LT1028 and LT1115, they are both *very* quiet compared to common op-amps like TL071 etc. However, beeing bipolar chips, with unusually high bias current in the input differential stages, LT1028/LT1115 generate a considerable amount of noise current that flows OUT from the INPUT pins, about 1pA/sqrt(Hz) according to the data sheet. This noise current creates a corresponding noise voltage across the internal impedance of the source and there is a "break-even" around 1kOhm source resistance where En equals In - the noise generated by the op-amp across the source impedance equals the "internal" op-amp "voltage noise". With s high impedance signal source, the LT1028 is *extremely* noisy!! 72 Johan SM6LKM
