차동증폭 전압이득

Using a differential op-amp, you automatically get a 6 db gain.  If the system impedance is 50 ohms, and the detector output is 200 ohm, and there is no resistor between the detector and the op-amp, and the op-amp has 8200 ohms in the feedback, then the gain is: 8200/200 = 41x.  The differential gain gives another 2x on top of this, giving a total of 81x, which is 38 db of gain. I have been thinking about writing an article in QST about DC receivers using the NC2030 as an example.  Some of the NC2030 ideas can also be applied to a superhet, and I have been thinking about doing a design around that as well. - Dan, N7VE   차동증폭의 경우.. 자동적으로 게인이 더블된다는 답변입니다.   8200/400=20 , 20*2=40 , 20log40=32db QRP2001에 내용이 틀린 걸까요?? ______________________________________________________________________________________ Re: Hello Dan. Thanks for kindly answering my interests. Someone said to me that Differential OP-amp give another advantages than Instruments . That is, noise cancellation funtion. He said Differ op-amp works as the passive receiver when used in balanced input construction. Even if Instrument op-amp construction has high CMRR and input impedance. Too much high impedance input give a affect to yield the Poor noise response in TR amp. and also said that It has limitations to getting the ultra low noise using OP-amp circuit. Probably He may be right... I became known for inserting 100 ohm resistor between Detector and OP-amp is trad-offs and isolation from your NC2030 manual.. I have confused concepts between Voltage gain and Power gain as Hans summers said. I understood what he said. and some my lacks of knowledge. It takes much time for getting Voltage Gain calculations in first pre OP-amp. (system resistor +input resistor=200 ohm+ 200 ohm) so, 20log (8200/400)= 26 db , not 32 db ..in QRP2001 circuit. Your RF Design articles give me the answer to this calculation. and NC2030 manual plus SDR1000 part1,4. Are you planning to write the article about Tayloe mixer to QEX magazine in the future? Thanks a lot Dan. 73 HL2DUS Park.