How to measure signal level on an analogue spectrum analyzer?

[neazoi]

I have an old analogue spectrum analyzer, that does not have any markers to measure things on the screen.
How can I measure a signal level?

A way I have figured is this:

Input a second signal (apart from the first signal I want to measure) of known amplitude at the input of the SA. Then use the SA front end stepped attenuator to bring the level of the second signal to the same level on the screen, as that of the first signal (the one I want to measure). Then the level of the first signal in dBm will be: the level of the second signal before attenuation (in dBm) minus the amound of attenuation (dB) of the second signal after attenuation.

Is this method correct?

How else can it be done?

 

[chuckey]

Your method sounds OK. The HP SAs we used had a very accurate 100MHZ output. You looped that into the input instead of the signal, then adjusted the trim pot to sort out the last +- 1 dB. Then read the level from the screen which was tied into the RF attenuator.
Frank