Receiver noise floor [HF]
Groups.io の Elecraft のところで面白い質問が出ていたので、メモとして残しておきます。
次の Extra Class の Question Pool からの問題に対して、簡単な説明を求めていました。
E4C05 (B)
What does a receiver noise floor of -174 dBm represent?
A. The receiver noise is 6 dB above the theoretical minimum
B. The theoretical noise in a 1 Hz bandwidth at the input of a perfect receiver at room temperature
C. The noise figure of a 1 Hz bandwidth receiver
D. The receiver noise is 3 dB above theoretical minimum
E4C06 (D)
How much does increasing a receiver’s bandwidth from 50 Hz to 1,000 Hz increase the receiver’s noise floor?
A. 3 dB
B. 5 dB
C. 10 dB
D. 13 dB
これに対するコメントが
E4C05 (B)
What does a receiver noise floor of -174 dBm represent?
B. The theoretical noise in a 1 Hz bandwidth at the input of a perfect receiver at room temperature
The answer is B. Any resistor or conductor at room temperature generates thermal noise of -174 dBm per Hz of bandwidth, independent of the resistance value. This is called Johnson or Nyquist noise:
Johnson–Nyquist noise
E4C06 (D)
How much does increasing a receiver’s bandwidth from 50 Hz to 1,000 Hz increase the receiver’s noise floor?
D. 13 dB
The answer is D. 13 dB
Noise power is directly proportional to bandwidth. So the noise increases by 10 times the log (base 10) of the bandwidth ratio:
10 * log (1000/50) = 10 * log (20) = 13 dB
これに対して、" room temperature " って何という質問が続き、次のコメントが付いていました。
In the world of measurement standards there are two common standard laboratory air temperatures used.
For mechanical engineering and physical measurements the standard room temperature is 20.0 °C.
For electrical measurements the room temperature is 23.0 °C.
These are given in various ISO and legal metrology standards as well as ASTM standards etc.
For amateur radio testing if either 20 or 23 °C can't be maintained during the test the ambient at the start and end of the test should be reported.
勉強になりました。
次の Extra Class の Question Pool からの問題に対して、簡単な説明を求めていました。
E4C05 (B)
What does a receiver noise floor of -174 dBm represent?
A. The receiver noise is 6 dB above the theoretical minimum
B. The theoretical noise in a 1 Hz bandwidth at the input of a perfect receiver at room temperature
C. The noise figure of a 1 Hz bandwidth receiver
D. The receiver noise is 3 dB above theoretical minimum
E4C06 (D)
How much does increasing a receiver’s bandwidth from 50 Hz to 1,000 Hz increase the receiver’s noise floor?
A. 3 dB
B. 5 dB
C. 10 dB
D. 13 dB
これに対するコメントが
E4C05 (B)
What does a receiver noise floor of -174 dBm represent?
B. The theoretical noise in a 1 Hz bandwidth at the input of a perfect receiver at room temperature
The answer is B. Any resistor or conductor at room temperature generates thermal noise of -174 dBm per Hz of bandwidth, independent of the resistance value. This is called Johnson or Nyquist noise:
Johnson–Nyquist noise
E4C06 (D)
How much does increasing a receiver’s bandwidth from 50 Hz to 1,000 Hz increase the receiver’s noise floor?
D. 13 dB
The answer is D. 13 dB
Noise power is directly proportional to bandwidth. So the noise increases by 10 times the log (base 10) of the bandwidth ratio:
10 * log (1000/50) = 10 * log (20) = 13 dB
これに対して、" room temperature " って何という質問が続き、次のコメントが付いていました。
In the world of measurement standards there are two common standard laboratory air temperatures used.
For mechanical engineering and physical measurements the standard room temperature is 20.0 °C.
For electrical measurements the room temperature is 23.0 °C.
These are given in various ISO and legal metrology standards as well as ASTM standards etc.
For amateur radio testing if either 20 or 23 °C can't be maintained during the test the ambient at the start and end of the test should be reported.
勉強になりました。
コメント 0