No. 115. Plainfield, N. J., Oct. 24, '05.
Will you please tell me if granulated carbon could be used in the coherer (wireless) instead of nickel or other metal filings, thereby eliminating the decoherer? If not, why?
Is it very essential that the particles in the coherer be in a vacuum ? W. A. G.
Granulated carbon could be used in a Marconi type coherer in connection with a telephone receiver instead of the relay, but the results would not warrant its use except on a short distance experimental station.
The silver filings in a coherer measure an indefinite number of ohms until the wave crosses the filings chamber, when the resistance drops to a few hundred ohms.
This great variation admits of the use of a sensitive relay, and the supplementary sounder and Morse recorder, while in carbon-granules, as has been shown in the telephone transmitter button, there is a variation in the resistance, but not to a sufficient extent for wireless receiving purposes.