EEVblog #381 – How Do Ultrasonic Delay Lines Work?Posted on November 9th, 2012 3 comments
How do glass ultrasonic acoustic delay lines work? The kind used in PAL video recorders.
This is Part 3 of the Sony CCD Video 8 Camcorder Teardown.
PART 1 HERE
PART 2 HERE
Service Manual is HERE
Forum Topic HERE
I would like to see that wire-wound delay line unwound. I might be using an Ayrton-Perry Bifilar Winding technique to reduce or control inductance. See here:
The Ayerton-Perry bifilar winding technique is often optimal when an axial-leaded bifilar wound device is desired. Otherwise for a radial device a standard bifilar winding may yield lower parasitics:
If done right, bifilar wound devices will have very little parasitic inductance. The bifilar winding is often used for low-reactive high power resistors and broadband delay lines. In the case of the delay line shown in the video however, perhaps they wanted to filter as well, and a lumped element LC delay line was a better choice. Even-so, I would not be surprised to still see an Ayerton-Perry wind to reduce or control inductance.
A video explanation of bifilar and trifilar would devices would be nice someday. The windings are sometimes difficult to visualize on paper, so a video would enrich the experience.
1. You should really look at old Grundig Video 2000 manuals. They not only had everything you’ve mentioned, but also detailed texts on the operation of the format.
2. Beware, this might blow your mind: What does it take to transcode between a 60Hz NTSC signal and a 50 Hz PAL signal? Well the BBC did it by switching lots of lots of delay lines. So they apply an increasingly high amount of delay to the signal so change the standard. I think I actually have some video actually comming out of that device. I can get that to you if you want. It produced some noticable artefacts, though it did look considerably better than 1990s CNN International.
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