absolute power in db

hi all,

I need help with the hp 4751a network analyser (which is outdated in agilent) . I want to measure the oscillator output power using this analyser. first , i measured a reference signal which is 200MHz 1Vp-p square wave. The impedances on both reference and the network analyser is 50Ohms.

There was no option for display in dBm in that analyser. It shows absolute power in dB. the value i get in spectrum is -43dB for this measurement.

Can anyone help me understand the value of this power? is it jus 10*log(V^2/50)? where V = .5? if i did that, I am getting -23dB.

When i measure without any source, the measurement is around -115dB.

please help me in understanding this.

thanks in advance

amar

It might measure in Watts..
So your oscillator has -13dBm..

It si not clear how you want to use a network analyzer to measure an oscillator. You should use a spectrum analyze, I think.
take a look at http://www.minicircuits.com/pages/pdfs/vco15-15.pdf
I hope it can help.
Mazz

I could not find anything on a 4751A network analyzer. Basically there are 2 types of network analyzers:

1) a scalar network analyzer that uses a diode detector to measure power magnitude. This type of analyzer CAN measure absolute power in dBm's, but you might have to calibrate it with a known power source at the same frequency.

2) a vector network analyzer. This type of analyzer can NOT measure absolute power, only relative power (as in the insertion loss of a two port component. It can measure the power coming out of the device under test, and compare it to the power coming into the device under test by making a ratio [10 dB pout/pin]).

So what type do you have?

The 4751a is an outdated network analyser. I have an ocr conversion of the manual.

The manual mentions it is a vector network analyser. But, in the manual it says that it measures the absolute power amplitude at the port.

In the options, I had set the source power to 0dBm but as per the manual it is power output at RF out port rather than the input port.

Added after 31 minutes:

i have attached the manual in this post. At page 125(6-6 in manual), it says it measures the absolute power at the input.

At page 130(6-11 in manual), it says that the dB scale is the absolute power in dB scale versus frequency.

Am i missing something and the values doesnt match for me. please help..