User:JA.Davidson
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An 1891 photograph of Cliff Palace, the largest cliff dwelling—a structure built within caves and under outcroppings in cliffs—in North America, located in what is now Mesa Verde National Park, Colorado, USA. There are about 150 rooms in the 288 ft (88 m) long structure, although only 25 to 30 of those were used as living space by Ancient Pueblo Peoples. it is estimated that the population of Cliff Palace was roughly 100–150 people. Photo credit: Gustaf Nordenskiöld |
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You may contact me using my talk page -- JA.Davidson (talk)
[edit] Coherers
After reading Thunderstruck I've gotten curious about 1900's radio technology in general, and the coherer in particular. 1) Did you build that coherer? 2) What does a coherer do in the year 2007? Doesn't it stay permanently stuck together because of the ubiquity of radio transmissions? Do ordinary broadcast-band and TV transmissions make a coherer cohere? Or were the early spark-gap transmitters actually producing more powerful signals than modern transmitters?
Do you know anything about the statement in the article that "The coherer saw commercial use again in the mid-1900 in a few primitive radio-controlled toys that used spark-gap transmitter controllers?" What kinds of toys? Why didn't the transmitters create enough interference to cause legal and regulatory problems for the toy manufacturer? Dpbsmith (talk) 17:27, 19 January 2007 (UTC)
- 1. Not that one, but I have built others.
- 2. Today it is a simple toy for technical people to play with.
- 3. It will continue to cohere if you put enough signal on it. It is not very sensitive though. It depends on the tuning and antenna. A Model T Ford spark coil at 100 yards will provide energy density needed to be selective over other signals provided you choose a reasonably quiet spot in the spectrum and tune.
- Early spark transmitters were transmitted many KW where todays transmitters can greatly exceed that. Appropriate selectivity can be done as a matter of antenna, proximity and tuning.
- There was a remote controlled robot from the 40s that had a spark coil in a hand held battery powered controller. It reportedly worked for several yards. I have seen pictures of it years ago. I think it was made in Japan and I expect they would have problems with todays FCC Part 15.
- John 01:24, 30 January 2007 (UTC)
