Timothy Normand Miller wrote:
On 3/4/07, Dieter <[EMAIL PROTECTED]> wrote:
Will OGC be able to output arbitrary waveforms, or only video? If
OGC can generate sine waves, square waves, triangle, etc. it would
be very useful as a piece of test equipment. It could be a
tracking generator for the spectrum analyzer?
I thought it would be interesting to generate RF signals entirely in
the digital domain and use a video DAC to turn it into analog. For
instance, you can have a sine-wave generator, that's completely
digital, and it has parameters that you can use to adjust the
frequency, within a band. BOOM. You have an FM transmitter. Attach
an amplifier, and you can send audio to a nearby radio.
You can purchase such devices as lab equipment -- Arbitrary Wave
Generator -- but they were rather expensive, but it is possible that the
price of the needed technology going down has changed that.
Say we could do this where we mix a complete TV signal, on channel
3/4, video with color subcarrier, and the audio channel. Voila. No
more need for a TV chip, and we can get both s-video and encoded.
If the granularity of our control of the signal is 330Mhz, can we
encode all of the information in the TV signal?
The color signal is very messy even with SD-NTSC. You are going to need
a DSP to compute it in real time.
Would the steps between digital levels (1024 of them) be too noisy?
Could we fix that with a low-pass filter?
I don't know how much of an effect quantization noise would have on
color TV. The output LP filter will not eliminate quantization noise,
it only removes the unwanted higher frequencies generated by using the
digital output.
I do know, for instance, that IP-over-power-line decoders do
everything in the digital domain.
Most current modems are digital as well.
If you were to transmit the signal on a single band, the amplitude
would interfere with electronic devices, so they use multiple
low-power channels instead. The decoder doesn't use caps and
inductors to decode each channel, however. They use a band-pass
filter that gets all of the channels at once. Then they digitize it
and use a taylor series approximation of a FFT to split out the
channels entirely in the digital domain. We would be doing this in
reverse, which is even easier.
Actually, I think that a digital demodulator is easier (then a
modulator) for complex signals. For example, with SD-NTSC color TV, you
have two color signals which are used as x & y to vector modulate
(amplitude and phase) the color subcarrier which is then added to the AM
luminance signal. Except for the quadrature, this is simpler in analog.
--
JRT
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