How to do to have a signal of -30dbm SOLVED

[GGMM]

Hello,

Beginner’s question
I need to test a spectrum analyzer I built
I must inject a -30dbm signal but never exceed 0dbm otherwise the input chip will burn.
I have a FY6900 generator, I would like to start from a 1V (or other if it's need)  signal, otherwise the one is in the noise if too low.
My research gives me that a -30dbm signal corespond at a signal of 0.02vpp or 0.0070711 vrms
see here: https://coretechgroup.com/dbm-calculator/
I only have a telonic 0-80db variable attenuator but 75 ohm.
It can be used and what value to put to have about -30dbm?
You tell me you plug in the generator on one side and watch the box with an oscilloscope before plugging in?
In short, your best solution
cdt

[GGMM]

the project is here
http://www.carnut.info/tinySA/tinySA.html

 I drew inspiration from this site to build it
it's a simpleSA
cdt

[coromonadalix]

for this case  if you have friends or peoples who have professionals generators .... electronic shop ??

[BillyO]

Speaking of sine waves...

-30dBm is 7.07 mV into 50 ohms.

If you cannot manage 7.07mV you could try 224mV through a 30dB attenuator into 50 ohms.


Here's a good resource for such things: https://www.ahsystems.com/EMC-formulas-equations/dBm_Volts_Watts_Conversion.php

[radiolistener]

-30 dBm = 0.02 Vpp

But note that FY6900 shows amplitude for unloaded output and has 50 Ω output.

So, if you connect it to 50 Ω input device, you're needs to setup twice higher amplitude on FY6900, for -30 dBm you're needs to setup 0.02*2=0.04 Vpp. In such way you will get 0.02 Vpp on the output of FY6900 connected to your device input.

But note this is right if your device input has 50 Ω impedance, for other impedance you're needs to recalculate amplitude.

[radiolistener]

-30dBm is 7.07 mV into 50 ohms.

note that 7.07 mV is RMS voltage. But topic starter needs peak-to-peak voltage, because FY6900 doesn't support setup RMS voltage.

In short:

-30 dBm = 0.007071 Vrms = 0.01 Vpk = 0.02 Vpp


So, just setup 0.04 Vpp on FY6900 in order to get 0.02 Vpp on the loaded output and it will be -30 dBm.

PS: and don't forgot to setup sine waveform.

[GGMM]

Thank's for your answer.

I understood well how to do , you can lock my subject
thank you

cdt