Is anyone able to help with the following Spectrum Analyzer question please:
The RF Input connector of a Spectrum Analyzer states the following:
- RF Input 50ohms
- MAX +30dBm/50VDC
I take that to mean I can input a signal of up to +30dBmW (or 1W)and a dc signal of up to 50Vdc. But I am not sure that is
true for the dc voltage input spec. I would think the 50ohm termination has to be considered. So is it correct to say that I can only go to: P = V^2/R => V = sqrt(P*R) = sqrt(1*50) = 7Vdc and not 50Vdc?

 

- RF Input 50ohms

That is the impedance of the coax.

 

The 50 V value is for the blocking capacitor on the input - it has a Vmax of 50 V DC. The 30 dBm value is the maximum input power into a 50 Ω system.

Both values are absolute maximums and shouldn't even be approached. Considering the cost of a top-of-the-line spectrum analyzer, you should try to keep these values at half the maximums.

 

The 50 V value is for the blocking capacitor on the input - it has a Vmax of 50 V DC. The 30 dBm value is the maximum input power into a 50 Ω system.

Both values are absolute maximums and shouldn't even be approached. Considering the cost of a top-of-the-line spectrum analyzer, you should try to keep these values at half the maximums.

Thanks so much for the reply! Okay I believe I’m following. So I shouldn’t look at it as the dc input voltage and the Analyzer’s 50 ohm input load exceeding the power rating through ohm’s law. This because the Analyzer’s built-in 50Vmax cap is going to block the dc.

 

To put it another way, the input is AC coupled, and the internal 50 ohm resistive load does not see the DC input.

 

To put it another way, the input is AC coupled, and the internal 50 ohm resistive load does not see the DC input.

Ok, got it. Thanks for your help!