Dear all,
I have question about spectrum and results on the display, when measuring power signals (50 Hz).
I did measurements:
- in my office,
- outdoors near transmission lines,
- and today we tried to calibrate our NF-5035 unit in calibrating laboratory (they generated signals of 50 Hz with different amplitudes).
In all cases, Spectran shows spectrum which has two peaks:
one at 47 Hz, and second at 51 or 52 Hz.
Peak is almost never at 50 Hz.
Why is that?
Why two peaks? Why not one?
Why not 50 Hz?
Does it have something to do with Spectran Unit?
Any idea?
Find exaples attached.
For these examples, I used following settings:
center 50 Hz
span 30 Hz
RBW 3 Hz
VBV 3 Hz
SpTime 2000 ms
Atten is 0dB for weaker signal, and Auto for stronger signal
3D
First of all you are using a non allowed frequency range (see manual under DFT-Mode). Why dont you use the power hotkey (key 2) instead?
For a better resolution simply use a smaller RBW like 1Hz or use the NON-DFT mode (see manual).
Snip
First of all you are using a non allowed frequency range (see manual under DFT-Mode).
I am confused with this, please let me know WHAT I am doing wrong.
Manual, page 39:
DFT mode is automatically activated when the following settings are used:
a) an RBW of 0,3Hz, 1Hz or 3Hz (I used 3Hz)
AND
b) a SPAN smaller than 200Hz (I used span of 30Hz).
Page 34:
b) a SPAN smaller than 200Hz, but at least 10Hz is chosen (30Hz is ok)
c) only use SPANs which are multiples of 15 like 15Hz, 30Hz, 45Hz etc. (30Hz is ok)
d) always use SPAN which is smaller than the difference between 0Hz abd the chosen starting frequency "low" (SPAN of 30Hz is smaller than start freq. of 35Hz).
Plus, I used 2000ms sampletime to avoid UNCALL display.
First of all you are using a non allowed frequency range (see manual under DFT-Mode).
I am confused with this, please let me know WHAT I am doing wrong.
Manual, page 39:
DFT mode is automatically activated when the following settings are used:
a) an RBW of 0,3Hz, 1Hz or 3Hz (I used 3Hz)
AND
b) a SPAN smaller than 200Hz (I used span of 30Hz).Page 34:
b) a SPAN smaller than 200Hz, but at least 10Hz is chosen (30Hz is ok)
c) only use SPANs which are multiples of 15 like 15Hz, 30Hz, 45Hz etc. (30Hz is ok)
d) always use SPAN which is smaller than the difference between 0Hz abd the chosen starting frequency "low" (SPAN of 30Hz is smaller than start freq. of 35Hz).Plus, I used 2000ms sampletime to avoid UNCALL display.
You have to add the "multiple of 15Hz" at 0Hz start frequency e.g. 15Hz to 30Hz would be OK but NOT 17Hz to 32Hz etc.
In your case (50Hz center and 30Hz span) you use 35Hz to 65Hz which is not allowed. You would need to change it to 30Hz to 60Hz or 30Hz to 75Hz.
For perfect frequency readings in that frequency range use the short sampletime (default setting) or long sample time for perfect level measurement.
Also see viewtopic.php?f=31&t=1096
Snip