# Sinusodial FM using AD9958 eval board software

Question asked by sums on Dec 15, 2015
Latest reply on Dec 17, 2015 by KennyG

Dear all,

I want to use the Eval-AD9958 (2 Channel 500MSPS DDS evaluation board) to generate two coherent signals:

1. A FM signal with carrier frequency fc=125MHz, modulation frequency fM=20MHz and a peak frequency deviation of about  Δf=10MHz (modulation index  η=0.5): y0(t)=sin(2πfct+ η*sin(2πfMt))
2. A reference signal y1(t)=sin(2πfMt)

I guess, this might be possible but just from looking at the eval board software I cannot be sure. This is why I'm asking here.

1. My first intuition for channel 0 was to calculate 16 frequencies within fc±Δf (125.0, 128.83, 132.07, 134.24, 135.0, 134.24, 132.07, 128.83, 125.0, 121.17, 117.93, 115.76, 115.0, 115.76, 117.93, 121.17) MHz... and enter those into the 16 "Frequency xx" fields inside the Eval software
2. Channel 1 ist basically a single tone signal at 20MHz.

But how can I define the rate (modulation frequency) at which the different frequencies are applied to the output of channel 0? Can I determine this rate / delta t / modulation frequency anywhere inside the software or do I need another external device? I appreciate your help :) sums