Hello group,
I posted a screen capture of an image showing a basic Amplitude Shift Key modulation:
The image shows the a diagram and equation. The equation is ASK(t) = s(t)*sin(2*pi*f*t). I assume s(t) is the baseband signal and sin(2*pi*f*t) is the carrier frequency.
In the image, is it possible for s(t) to have a higher frequency as sin(2*pi*f*t)? Please explain.
Thanks!
Try drawing such a case. How would a receiver interpret the resulting signal?
OK I'm probabbly being an idiot here... But is that picture right? You don't want the carrier to go to zero amplitude do you? Isn't this like AM radio?
George H.
-- Yeah.
Thanks John, That makes sense... sorta. Not the most 'robust' way to send data. Lose of the carrier means a zero... or that you've just lost the carrier.
George H.
'xactly. But a very _easy_ way to send data -- just turn the transmitter on and off.
-- www.wescottdesign.com
I think I'd call that on-off keying. For amplitude-shift keying, I'd expect one or more intermediate levels, not just off and on. Perhaps full amplitude and 50% (or a couple more intermediate levels to encode multiple bits in each interval.)
-- Peter Bennett, VE7CEI peterbb4 (at) interchange.ubc.ca GPS and NMEA info: http://vancouver-webpages.com/peter Vancouver Power Squadron: http://vancouver.powersquadron.ca
-- Agreed, but, taken to the lowest level of ASK, zero carrier and some level of carrier defines the difference between mark and space.
The loss would be a constant power drain on the battery of say, a wireless mouse or keyboard.
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Do you mean when it's working correctly, or most of the time?
-- www.wescottdesign.com
WWVB gets one baud.
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-- Yeah, but its not ASK in the sense that one level defines a 1 and another defines a 0, it's more like PWM with a carrier floor and the length of time the transmitter stays at the low floor level before it gets keyed on to full power out determines whether the bit sent is a 1 or a zero. http://tf.nist.gov/stations/wwvbtimecode.htm http://en.wikipedia.org/wiki/WWVB#Modulation_Format Pretty damn clever, in my book... JF
Especially when you consider when they first used it. A 10 dB carrier reduction to modulate the carrier in the early days of electronics, and was used to control clocks all over the country. A lot of metrology labs used a Fluke VLF receiver & WWVB for their frequency standard, until GPS based systems replaced it. I still have my Fluke receiver, but I will need to build a new PLL 10 MHz standard.
BTW, I found my homebrew copper 60 KHz loop for WWVB yesterday. I finally feel well enough to start cleaning out the small shop building, so I can get back to the bench. :) It is only 18 * 28 feet, but it suffered the least hurricane damage a few years ago. I tossed out a truckload of damaged cardboard boxes and very rusty hardware. I have a fairly clear shot towards WWVB from here, unlike the last place I lived.
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