Telegraphist's Equations

• http://www.amazon.com/gp/product/0521646456/
• at Google Book Search
  
• Page 82:
• As an historical example, we can analyze the first transatlantic telegraph cable, laid in 1865. The cable was 3,600 km long and weighed 5,000 tons. The insulator was a vegetable gum called gutta-percha . For this cable L = 460 nH/m, C = 75 pF/m, and R = 7 mQ/m. At a frequency of 2.4 kHz, wL = R, and so the high-resistance assumption is well satisfied for frequencies below 100 Hz. At 12 Hz, we can write a and v as
  
• a = v/wRC/2 = 4.4 x 10...
  
• v = ...
  
• The loss for the entire line is al = 140 dB and the delay is l/v = 210 ms. For comparison, at 3 Hz, the loss in dB and the delay change by a factor of 2, to 70 dB and 420 ms. Thus the 12-Hz component attenuates 70 dB more than the 3-Hz component. In addition, the 12-Hz component arrives 210 ms ahead of the 3-Hz component. In order to improve these characteristics, the signalling speed had to be drastically reduced, to about one word per minute, which was twenty times slower ...
  

Signal Noise Ratio

• http://www.librarything.com/card_card.php?book=325583
• http://www.amazon.com/gp/product/0521646456/
• Page 137:
  • "Right at 1,200 Hz, signal tones can be detected if they have sound pressure levels of 57 dB or larger. This is 3dB below the noise. This means that Morese Code can be received when the signal power is comparable to the noise power within the critical bandwidth. By contract, an AM or TV boadcaster aims at 50-dB signal-to-noise ratios over much larger bandwidths to provide a clear sound and picture. This means that the NorCal* 40A can communicate at distances of thousands of mile with a transmitter power of 2 W, whereas a broadcaster might use 50 kW for coverage in a single city."

t:	signal
t:	noise
t:	ratio
t:	radio
t:	electronics
Created:	20060502
t:	morse
t:	code
t:	power
t:	shannon

---

EditText | BrowseFacets | RecentChanges | FindPage