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| Joined: | Jun 8th, 2008 |
| Location: | Maine USA |
| Posts: | 74 |
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First...the 37.5 mhz is an arbitrary rf or radio freq probly readily available at the time; probly AM - the end of the main hf band is 30mhz (am, sideband, etc)...FM starts around 100mhz (megahertz).
The ir freqs for selective (diodes...) used together - the small differences are the (maybe) spiricom tone pitch frequencies, each a little bit wider in freq for ex 850-852-855-859 for a diff in 2, 3, 4 nm however finding ir (diodes) to match these freqs are imossible (I am missing something)...the main freqs are then filtered out leaving the remaining (spiricom) tone freqs with whatever noise at those rf levels (IR) may have been added...
The tones are then summed (?) as in the spiricom device...proportions used.
I didnt read into the details that much...the 37.5 mhz and IR 'tones' comprise the spiricom at those freqs instead of say 1500khz and audio tones direct as in the original spiricom.
I am amazed they tried IR devices in those days.
My only thinking is to use filters to provide the tone(s); generated freqs at that level have to be very stable.
Interesting.
MrZeta