Portsdown Noise Meter - Revision history

G8GKQ at 19:01, 27 April 2024

2024-04-27T19:01:58Z

G8GKQ at 16:20, 6 October 2023

2023-10-06T16:20:27Z

G8GKQ: /* Differential Noise Measurement */

2023-09-08T18:41:51Z

Differential Noise Measurement

G8GKQ: /* Carrier Level Measurement */

2023-09-08T18:41:19Z

Carrier Level Measurement

G8GKQ: /* Differential Noise Measurement */

2023-09-08T18:40:50Z

Differential Noise Measurement

G8GKQ: /* Absolute Noise Measurement */

2023-04-22T19:50:56Z

Absolute Noise Measurement

G8GKQ at 19:49, 22 April 2023

2023-04-22T19:49:48Z

G8GKQ: /* Carrier Level Measurement */

2023-04-22T19:48:56Z

Carrier Level Measurement

G8GKQ: /* Differential Noise Measurement */

2023-04-22T19:39:44Z

Differential Noise Measurement

G8GKQ: /* Absolute Noise Measurement */

2023-04-22T19:31:44Z

Absolute Noise Measurement

@@ Line 1: / Line 1: @@
-The Portsdown Noise Level Meter uses a LimeSDR to measure and indicate noise or carrier power levels.  It has 4 modes:
+The Portsdown Noise Level Meter uses a LimeSDR or a Pluto SDR to measure and indicate noise or carrier power levels.  It has 4 modes:
 * Absolute Noise Measurement
@@ Line 8: / Line 8: @@
 Absolute noise measurement is used to measure Sun or Moon noise.  The system can be "zeroed" against cold sky, and then the meter will indicate the increase in noise averaged over a wide bandwidth.  Differential noise measurement can be used to measure the strength of DATV transmissions or possibly to optimise aerial/receiver matching.  The noise power in a reference (quiet) frequency range is measured and compared with the noise power in a frequency range that contains a DATV signal.  The Carrier Level measurement can compares the peak level of a carrier within a defined frequency range with the average noise level in a quiet frequency range otr just measure the absolute level of the carrier.
-The Noise Level Meter is selected from Menu 2, Test Equipment.  Web view (but not web control) is implemented for the Noise Level Meter.
+The Noise Level Meter is selected from Menu 2, Test Equipment.  Web view and web control is implemented for the Noise Level Meter.
 [[File:Noise_Meter.png|400px]]
@@ Line 14: / Line 14: @@
 ===Absolute Noise Measurement===
-On starting the meter, select the frequency and bandwidth required.  Connect the receiver or preamp to the input of the LimeSDR and, on the setup menu, adjust the Lime Gain so that the noise level is around -60 dB.  Noise background noise levels below this are outside the linear range of measurement.  Press the "Establish Baseline" button and the meter should read near zero.  Any increases in noise from the baseline level will then register on the meter.  The spectrum plot allows interfering signals that may upset the reading to be seen.  The "DC spike" in the centre of the spectrum is rejected from the calculations.
+On starting the meter, select the frequency and bandwidth required.  Connect the receiver or preamp to the input of the SDR and, on the setup menu, adjust the Gain so that the noise level is around -60 dB (Lime) or 50 db (Pluto).  Background noise levels below this are outside the linear range of measurement.  Press the "Establish Baseline" button and the meter should read near zero.  Any increases in noise from the baseline level will then register on the meter.  The spectrum plot allows interfering signals that may upset the reading to be seen.  The "DC spike" in the centre of the spectrum is rejected from the calculations.
 The meter scale can be changed through 6 ranges by touching the right and left sides of the meter face.  The ranges are

@@ Line 1: / Line 1: @@
-The Portsdown Noise Level Meter uses a LimeSDR to measure and indicate noise or carrier power levels.  It has 3 modes:
+The Portsdown Noise Level Meter uses a LimeSDR to measure and indicate noise or carrier power levels.  It has 4 modes:
 * Absolute Noise Measurement
 * Differential Noise Measurement
-* Carrier Level Measurement
+* Carrier Level Measurement with reference to noise
-Absolute noise measurement is used to measure Sun or Moon noise.  The system can be "zeroed" against cold sky, and then the meter will indicate the increase in noise averaged over a wide bandwidth.  Differential noise measurement can be used to measure the strength of DATV transmissions or possibly to optimise aerial/receiver matching.  The noise power in a reference (quiet) frequency range is measured and compared with the noise power in a frequency range that contains a DATV signal.  The Carrier Level measurement compares the peak level of a carrier within a defined frequency range with the average noise level in a quiet frequency range.
+Absolute noise measurement is used to measure Sun or Moon noise.  The system can be "zeroed" against cold sky, and then the meter will indicate the increase in noise averaged over a wide bandwidth.  Differential noise measurement can be used to measure the strength of DATV transmissions or possibly to optimise aerial/receiver matching.  The noise power in a reference (quiet) frequency range is measured and compared with the noise power in a frequency range that contains a DATV signal.  The Carrier Level measurement can compares the peak level of a carrier within a defined frequency range with the average noise level in a quiet frequency range otr just measure the absolute level of the carrier.
 The Noise Level Meter is selected from Menu 2, Test Equipment.  Web view (but not web control) is implemented for the Noise Level Meter.
@@ Line 34: / Line 35: @@
 The frequency ranges are indicated by the shaded areas and can be adjusted from the Config Menu.  The adjustment figures are percentages of the span width.
-===Carrier Level Measurement===
+===Carrier Level Measurement with reference to Noise===
-Carrier level mode is selected from the Mode Menu.  Again, the average level of noise in one frequency range is used as the reference.  However, the peak level of the strongest signal in the second frequency range is used for comparison.
+Carrier/Noise level mode is selected from the Mode Menu.  Again, the average level of noise in one frequency range is used as the reference.  However, the peak level of the strongest signal in the second frequency range is used for comparison.  With no carrier, it is comparing peak noise with average noise, so the reading will be about 2.5 dB.
 [[File:carrier_mode.png|400px]]
@@ Line 42: / Line 43: @@
 The position of the peak is indicated by a green line.  The time smoothing is automatically increased in this mode to obtain a stable reading suitable for use in the optimisation of systems.
-A "Flat Top" windowing function is used to measure the peak amplitude, which provides an almost constant reading across 2 fft "bins".  While this is good for stability, there is a 4 dB reduction in apparent sensitivity compared to the Hanning windowing function used in the absolute and differential modes.
+===Absolute Carrier Level Measurement===

@@ Line 32: / Line 32: @@
 [[File:differential.png|400px]]
-The frequency ranges are indicated by the shaded areas and can be adjusted from the Config Menu.  The adjustment fugures are percentages of the span width.
+The frequency ranges are indicated by the shaded areas and can be adjusted from the Config Menu.  The adjustment figures are percentages of the span width.
 ===Carrier Level Measurement===

@@ Line 40: / Line 40: @@
 [[File:carrier_mode.png|400px]]
-The position of the peak is indicated by a green line.  The smoothing is automatically increased in this mode to obtain a stable reading suitable for use in the optimisation of systems.
+The position of the peak is indicated by a green line.  The time smoothing is automatically increased in this mode to obtain a stable reading suitable for use in the optimisation of systems.
 A "Flat Top" windowing function is used to measure the peak amplitude, which provides an almost constant reading across 2 fft "bins".  While this is good for stability, there is a 4 dB reduction in apparent sensitivity compared to the Hanning windowing function used in the absolute and differential modes.

@@ Line 28: / Line 28: @@
 ===Differential Noise Measurement===
-The differntial noise measurement mode is selected from the Mode Menu and compares the noise level in 2 frequency ranges.
+The differential noise measurement mode is selected from the Mode Menu and compares the noise level in 2 frequency ranges.
 [[File:differential.png|400px]]

← Older revision		Revision as of 19:48, 22 April 2023
Line 35:		Line 35:

	===Carrier Level Measurement===		===Carrier Level Measurement===
		+
		+	Carrier level mode is selected from the Mode Menu. Again, the average level of noise in one frequency range is used as the reference. However, the peak level of the strongest signal in the second frequency range is used for comparison.
		+
		+	[[File:carrier_mode.png\|400px]]
		+
		+	The position of the peak is indicated by a green line. The smoothing is automatically increased in this mode to obtain a stable reading suitable for use in the optimisation of systems.
		+
		+	A "Flat Top" windowing function is used to measure the peak amplitude, which provides an almost constant reading across 2 fft "bins". While this is good for stability, there is a 4 dB reduction in apparent sensitivity compared to the Hanning windowing function used in the absolute and differential modes.

← Older revision		Revision as of 19:39, 22 April 2023
Line 28:		Line 28:
	===Differential Noise Measurement===		===Differential Noise Measurement===

		+	The differntial noise measurement mode is selected from the Mode Menu and compares the noise level in 2 frequency ranges.
		+
		+	[[File:differential.png\|400px]]
		+
		+	The frequency ranges are indicated by the shaded areas and can be adjusted from the Config Menu. The adjustment fugures are percentages of the span width.

	===Carrier Level Measurement===		===Carrier Level Measurement===

@@ Line 13: / Line 13: @@
 ===Absolute Noise Measurement===
-On starting the meter, select the frequency and bandwidth required.  Connect the receiver or preamp to the input of the LimeSDR and, on the setup menu, adjust the Lime Gain so that the noise level is around -60 dB.  Noise background noise levels below this are outside the linear range of measurement.  Press the "Establish Baseline" button and the meter should read near zero.  Any increases in noise from the baseline level will then register on the meter.
+On starting the meter, select the frequency and bandwidth required.  Connect the receiver or preamp to the input of the LimeSDR and, on the setup menu, adjust the Lime Gain so that the noise level is around -60 dB.  Noise background noise levels below this are outside the linear range of measurement.  Press the "Establish Baseline" button and the meter should read near zero.  Any increases in noise from the baseline level will then register on the meter.  The spectrum plot allows interfering signals that may upset the reading to be seen.
-The meter scale can be change through 6 ranges by touching the right and left sides of the meter face.  The ranges are
+The meter scale can be changed through 6 ranges by touching the right and left sides of the meter face.  The ranges are
 * 0 to 30 dB (default)
@@ Line 23: / Line 23: @@
 * 0 to 5 dB
 * -5 to +5 dB
 ===Differential Noise Measurement===