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Entry  Thu Mar 3 18:32:33 2011, Larisa Thorne, Update, Electronics, Harmonic distortion calculations for RF distribution box RFdistribboxcalcs.pdf
    Reply  Fri Mar 4 09:47:46 2011, Suresh, Update, Electronics, Harmonic distortion calculations for RF distribution box 
Message ID: 4374     Entry time: Thu Mar 3 18:32:33 2011     Reply to this: 4377
Author: Larisa Thorne 
Type: Update 
Category: Electronics 
Subject: Harmonic distortion calculations for RF distribution box 

Finished calculations for harmonic distortion at each of the 10 outputs of the RF distribution box. The diagram can be found on Suresh's post  http://nodus.ligo.caltech.edu:8080/40m/4342


THD calculation consisted of gather data on the dBm at harmonics of the fundamental frequency. These dBm values were converted into units of power and plugged into the appropriate THD equation pulled from Wikipedia: 
\mbox{THD} = \frac{P_2 + P_3 + P_4 + \cdots + P_\infty}{P_1} = \frac{\displaystyle\sum_{n=2}^\infty P_n}{P_1}

On the table, the number 1-6 correspond to the harmonic number of the input frequency used. For example, the first five PD's listed used an 11MHz source, while the second set of five PD's listed used a 55MHz source. Values listed under certain harmonics are dBm measurements at the corresponding frequency. The P-subscript values are essentially the dBm measurements converted to units of power (Watts) for ease of calculation in the equation above. THD is then calculated using these power units; I have converted the ratios to percentages.


It should be noted that as with all THD calculations, the more data points collected, the more precise the THD % will be.

By the way, the outputs on the physical RF distribution box for REFL165 and AS165 are actually labeled as REFL166 and AS166. 

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