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Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
I assume it's a very precise thing, so a simple RC or logic delay wouldn't be good enough
Fairly precise, but the main thing is that it has to store a signal for a time much greater than 1/bandwidth, it is storing a whole video line, rather than just delaying a single edge a little, as an RC could do. It would be quite possible to use a coil of coaxial cable 64uS long to do the same job (I suspect the first prototypes did), but that would be big, expensive and lossy.
if you open up a quartz ossilator you ind something simmiler
if you open up a quartz oscillator, you will find something different. You will find a resonator. The only similarity is that it's made of quartz. On that basis, all things made of silicon are similar to each other (may I have an Althlon 3000 please? will this similar HC4046 do sir?). Incidentally, a cable equivalent of a quartz resonator is a short length of cable. This equivalent is good enough to explain the prescence of both fundamental and harmonic oscillation frequencies.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
I've hacked a quartz module before now to generate strange frequencies (they use an internal divide-by-n chip)
Here's a thought, if you drill a really small hole in the can of a crystal or oscillator module, and install a blue LED will the radiation from the LED cause the properties of the crystal to change enough to affect the frequency?
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
well, this is horribly off topic, by I would say that sure it will change the frequency. A decent blue led is about 30mw, so just from heating the quartz you should see a measurable difference (although it might take one of the uber expensive meters that read to .001hz out of a 100mhz.
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
Quartz is transparent to blue light. The light would just go through the crystal. Do you have any sugestions for why this would affect the frequency. Granted that the heat from the led would make a small difference. Leds are rather expensive heaters. On the plus side, it is very easy to measure tiny changes in frequency. You mix the output with a second oscilator output and listen to the difference tone. With a couple of 10MHz crystals you could easily spot a change of a couple of parts per million.
Registered Member #311
Joined: Sun Mar 12 2006, 08:28PM
Location:
Posts: 253
Older TVs also typically also had a transmission-line type delay line to delay the luminance signal to match the processing delay through the chroma path. The type pictured used a carefully chosen path that bounced around the crystal a number of times to keep the size small. I remember seeing one many years ago which was from before they figured out how to do this & used a single bounce from end to end, and it was huge - about 4 inches long.
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unusual component
