Martin, I concur 100%. With our many years of experience in this area we continue to utilize BJT technology. In those electrically hostile environments, our testing has confirmed the vulnerability of devices like MMiCs, ICs (video amps have been used extensively) and even FETs. This is kind of a general statement, but specific to many of the popular designs. Qualities like dynamic range, intermod and noise are always of concern in the design and testing process. Specifically selected BJTs can be found that fit those criterion, even though, as stated, their obsolescence is always of concern. Interestingly, the noise factor isn't always such a villain as one might expect. In Rf work, It's always admirable to look for the "quietest"? device available, however if the noise generated by the device is not detectable by the system; ie; lower than the system's noise floor, then that is noteworthy. Ultimately, when the receiver is on the test bench and measured with, and without, the external amplifier (preamp, multicoupler, preselector, tuner, etc) and no noise factor increase is observed, it would seem fruitless. For many years (in the old days) we used the likes of 2N3904, 3906, 222, etc. Today there are better options, but it would seem that the semiconductor folks will quickly obsolete a device that is not a quantity seller. That's shame, but still a fact of life.
Bob, N1KPR
Engineering, where enigma meets paradox
On Saturday, March 18, 2023 at 06:05:06 AM EDT, Martin via groups.io <martin_ehrenfried@...> wrote:
On Sat, Mar 18, 2023 at 08:42 AM, Fred M wrote:
there ist no ultimate choice transistor
I would agree. However the problem we face, is that as wireless devices are increasingly moving up in frequency, and although excellent devices with high gain, low noise and unbelievable values of ft now exist, they are very fragile, and not at all suited to HF broadband amplifiers, as they will fail when exposed to the slightest whiff of ESD. This is why medium power BJT transistors are so popular for this application, but unfortunately with changes in communication trends they are no longer produced in the vast numbers that they once were, so our choices are very limited. Any of the devices in the top ten of Steve's list are likely to be suitable, but our final design choice is more likely to be defined by what we can get hold of rather that which is the absolute ultimate performer. Regards, Martin
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Bob, N1KPR