Spectrum Analyzers.

[lord loh.]

I have never used a spectrum analyzer before. Now I have got a spectrum analyzer in our college that has no user manual.

It's model is HM 5006 from Hameg. The control on the spectrum analyzer states MHz/div... When I feed signals from the function generator, I see many spikes when I feed in square and sawtooth waves... However, I see no peak corresponding to the fundamental frequency...

I am trying to feed in a few Khz signal...

There is always a peak at the left end of teh spectrum even when there is no input signal or when I short the two terminals of the input.

I am not able to figure how to us the instrument....

Thank you

 

[Papabravo]

If you think about it for a minute all of your observations are consistent with the respective input situations.

With no input or the terminals shorted any energy at all will be at DC or very low frequency. Non linear waveforms are rich in harmonic content. A Fourier Analysis of square and triangle waves will demonstrate this observation. Finally a sine wave will produce a strong peak at the fundamental frequency and depending on the amount of distortion peaks of lower amplitudes at the harmonics.

Lastly you might have the instrument because it is compromised or broken and nobody else wants it. You might try to contack the original manufacturer.

 

[lord loh.]

Irrespective of the imput signal, I see the peak at the same position.... there was a slight change in the peak height at 1.3Mhz that the maximum my function generator could supply...

 

[RadioRon]

You can download the manual for free in either English, German or Spanish at this site:

http://www.hameg.com/68.0.html

 

[RadioRon]

The first thing to note is that this model is only rated to go down as low as 500 Khz with rated accuracy. This means that it is quite posssible that if you put a signal in that is too low in frequency then it will be attenuated too much and not be visible. So, if you try to put in a 5 KHz signal, you may not see the fundamental because it is attenuated too much.

If you are seeing a lot of lines at higher frequencies, you are seeing the natural harmonics of a rectangular wave. However, if you are putting in too much voltage, then you are probably also seeing the effects of distortion of the signal that is occurring inside the spectrum analyzer. We call this situation "over driving" the front end of the spectrum analyzer. You will be overdriving the analyzer with signals stronger than roughly -10 dBm, which translates to about 70 mV of signal. So, it would be wise to turn down the level of the function generator below this voltage and see if things simplify on the spectrum analyzer display.

Another thing to realize is that the frequency calibration of this spectrum analyzer is not terribly precise. So, you can't trust the display to show exactly a certain frequency, only about +/- 100 KHz unless you take additional steps. One useful thing is to recognize that the line that exists when there is no input is exactly DC and so you can use this to calibrate the x position of the trace on your display.

 

[RadioRon]

here is a couple of tutorial links:


https://www.radio-electronics.com/info/t_and_m/spectrum_analyser/spectrum_analyzer.php

https://www.tutorialsweb.com/rf-measurements/spectrum-analyzer.htm

 

[RadioRon]

It is unfortunately all too common that spectrum analyzers get damaged when someone puts too much power into the input. Many types, like HP models for example, will burn out if you put more than 1 Watt into them. I note that the Hameg 5006 has a max rating of only 10 dBm or 20 dBm at higher input attenuator settings. Someone may have put more than this into the instrument and burned it out. I hope not.

 

[JimB]

There is always a peak at the left end of teh spectrum even when there is no input signal or when I short the two terminals of the input.

This is quite normal for most spectrum analysers.
The effect is due to the local oscillator which converts the signal to be measured to the SA intermediate frequency.
As you try to measure a very low frequency, the LO frequency approaches the IF frequency and feeds through the IF amplifier and is displayed on the screen.

JimB

 

[lord loh.]

Thanks for the manual download link....Somehow I could not find it on Hameg site....

I used all sort of voltage levels and also considered distortion. There are 4 -10dB attenuators on the front panel and I used all combinations of them.

There is also a display on which changes as one rotates the center frequency knob. However, there is no units mentioned for the digits that appear on the display. It varies from 000 to 999. When I take the left most peak to the center of the screen, it reads zero.

 

[Julkar Nain]

hej, Is there anyone who can answer this question.I am confuesd about my problem.

*** In the Spectrum analyzer it sometimes is impossible to set the input attenuation to lower values (e.g it is not possible to set the attenuator to 0,10,20 dB but higher values are possible) why does this phenomenon occur????

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