There seems to be an incoherence between what I see with my oscilloscope, and what I see with my spectrum analyser.

I have a signal of about 1MHz (if I'm not wrong), 5mV, from an antenna, through RG174 coaxial. It is clearly seen in the following picture of my oscilloscope screen.

enter image description here

Then I connect the same cable to my spectrum analyser, and see nothing like this apparently (see next picture).

Is my spectrum analyser damaged, or am I missing some point ?

Additional information:

OSCILLOSCOPE: AC, 50 ohm, 1ns/div, 5mv/div

SPECTRUM: 50 ohm, start frequency 500kHZ, stop frequency 15MHz, ref level 1mV, attenuation 0db, 10 db/div, set in average mode for clarity, but the same problem subsist in non average mode.

enter image description here

  • 2
    \$\begingroup\$ 1ns/div, and a bit more then 1 division top to top on the waveform, isn't that nearly a GHz? \$\endgroup\$ Jan 2, 2019 at 12:06
  • \$\begingroup\$ @Unimportant is right, 1.2ns =~ 833Mhz \$\endgroup\$
    – Damien
    Jan 2, 2019 at 12:12
  • \$\begingroup\$ All of these types of questions should have the instrument's model numbers listed \$\endgroup\$
    – pipe
    Jan 2, 2019 at 13:17

1 Answer 1


Your oscilloscope shows an oscillation with a frequency in the \$\frac{1}{1\,\text{ns}}=1\,\text{GHz}\$ range. (So, yes, you're wrong, that's not a 1 MHz oscillation. I'm jealous of your oscilloscope, by the way.)

Your spectrum analyzer is set to cover 400 kHz to 15.14 MHz. You can't see a GHz oscillation in that range.

  • \$\begingroup\$ Oh I am stupid ! \$\endgroup\$
    – MikeTeX
    Jan 2, 2019 at 12:19
  • 2
    \$\begingroup\$ no, you're (probably) not, mistakes just happen! \$\endgroup\$ Jan 2, 2019 at 12:20

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