Thread: how is multi-tone internally generated in E4438C?


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hudla

Posts: 26
Registered: 09/07/07
how is multi-tone internally generated in E4438C?
Posted: Oct 25, 2011 4:34 AM
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Dear all,

I have a problem to generate user-defined multi-tones using E4438C generator. The generator only allows 64 tones and I would like to generate more (I know, Signal Studio for Multitone Distortion exists, yet I want to do it by myself). Which multi-tone definition is used in E4438C?

I tried to generate a 64-tone signal using E4438C (from the front panel) and then to capture the I, Q components of the signal using E4440A spectrum analyzer, B7J Basic option. At the same time I generated an "ideal" multi-tone signal in Matlab (the same sampling frequency, the same number of samples as captured by E4440A):

m(t) = SUM (exp(j*phi)*exp(j*k*2*pi*df*Ts)), where k = 1, ..., Number_Of_Tones (equal tone amplitudes, all phases = 0), df = tone spacing, phi = tone phase, Ts = sampling period

The baseband I and Q components (ideal and captured by E4440A) do not have the same shape nor spectrum (I also tried several other multi-tone definitions), so apparently some other definition must be used. Or is the multi-tone internally created in the frequency domain and then converted back to the time-domain using IFFT?

Thank you,
Martin
tabbott


Posts: 1,427
Registered: 07/24/09
Re: how is multi-tone internally generated in E4438C?
Posted: Oct 26, 2011 9:53 AM   in response to: hudla in response to: hudla
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Hi Martin -

For the E4438C, without the Signal Studio option N7612A/B it can only generate up to 64tones.

There are other setting such as the amplitude level and the phase which you need to take into consideration. Here’s a guide on Multitone Generation, which is on the E8247C but it can be used with this model as well. http://cp.literature.agilent.com/litweb ... 7689EN.pdf

Regards -

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