A question of Disrete spurious measurement
Several days ago, I measured the Discrete spurious of a TETRA handset at 813.525MHz, and I got the 2nd and 3rd harmonics, which are about -20dBm. I used MS8608A spectrum analyser, which has 40dBm maxim input power. The handset's output power is only 30dBm. So I directly connected the handset to the analyser with 1MHz RBW and 3MHz VBW.
But my colleague said the harmonics are caused by analyser because when using a attenuator of 30dBm, he couldn't see the harmonics. He said the analyser was overdrived when I connected the handset to the spetrum directly and brought the harmonics.
I don't know what he means, and he didn't explain. Before I measured GSM handsets using notch filters, but now I don't have notch filter for TETRA handsets. I don't know why I need an attenuator.
Can any kind tell me whether I'm wrong or my colleague is wrong and why?
Hello foxgan !
What you'll need to do, in order to verify you measuring the handest harmonics instead of the spectrum is to change the Attenuation of the spectrum manually in the following manner:
1. Locate on the screen the two tone test that you are incjecting to the DUT with another two signals, which are the 3rd order harmonics signals (f1-2f2 and 2f2-f1).
2. Put a marker on one of the 3rd order harmonic.
3. Lower the attenuator (manualy) by one step and notice if there's a change in the value of the signal you put the marker on:
a. If the value changed (it will be increased) than you probably seeing the
spectrum harmonics and you need to increase the Attenuation of the spectrum. Then continue from the begining until its not change.
b. If the value didn't change, its mean you reading the DUT harmonics accurately.
Good Luck,
Itzik !
Yeah, that is the way to check it!
I would also check to see if the spectrum analyzer is still alive after putting 1 watt unattenuated into it!