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 40m Log Not logged in Message ID: 10070     Entry time: Thu Jun 19 12:10:18 2014
 Author: Akhil Type: Update Category: Electronics Subject: Gain plots to Characterize UFC-6000 RF Frequency Counter

The goal is to characterize the Mini-Circuits RF FC (Model UFC-6000)  by plotting Gain Plots.

Work Done:

The sampling rate of the UFC-6000 RF FC is 1s (should look into making the sampling time smaller). So to satisfy Nyquist criterion, the maximum modulation frequency is 0.5 Hz beyond which  aliasing effects are seen.

The measurements taken (mentioned in my previous elog) are used to plot Gain vs Modulation frequency for carrier frequencies of  5 MHz and 25 MHz.

Calculations:

A modulated signal can be represented as X(t)= A*sin (Fc*t+D*sin(Fm*t+phase1))  where Fc and Fm are carrier and modulation frequencies respectively and D is the modulation depth.

This signal Y(t) is input to the FC and the output frequencies of the FC are recorded.

Let the output of the FC is Y(t)= A'*sin(Fc*t+D'*sin(Fm'*t+phase2));

Gain = D'/D;

phase = phase2 - phase1;

D' is calculated by subtracting the carrier frequency from the output frequency and calculating the amplitude of the resulting fitted sine wave.

The phase can be calculated if the phase of the input is known(which will be done next).

Plotting the Bode plots would give response of the FC to modulation.

The plots generated  will be used to estimate:

1) Transfer Function of FC to be known to build an FOL-PID loop.

2) Quantization noise from Power Spectral Density(PSD) vs Hz.

To Do Next:

1)Calculate the phase difference  to complete the Bode plot. This would require interfacing of the ADC on raspberry pi.

2)Estimate the quantization noise from the digital output.

 Attachment 1: GainVsFreq.png  17 kB
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