EEVblog #386 - Glass Delay Lines Part 2 - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: November 18, 2012, 11:47:18 am
content: Dave.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: November 18, 2012, 03:11:11 pm
content: You're triggering off channel 1 (the input from the waveform gen) throughout the video. I would have preferred a trigger level of maybe 100 or 200 mV which probably would have reduced the jitter and spurious triggers to almost nothing.

author: kg4arn
author_rank: Unknown
timestamp: November 18, 2012, 05:13:47 pm
content: Very interesting device.To get 64uS delay from RG58 coax requires 47,000 feet!Dave,Since you have the RIGOL Spectrum Analyzer and the DG4162, how about a 2 tone IMD test on this delay line?It would be interesting to see how much distortion is introduced by the RF --> ultrasonic --> RF conversion.

author: kxenos
author_rank: Frequent Contributor
timestamp: November 18, 2012, 07:56:09 pm
content: I wonder if it would be possible to make a 0 tempco, jitter-free clock source out of these things.It would be easy to make a clock by amplifying the output back to 5 volts and returning it to the input, but would it be any better than the already existing crystals?

author: SeanB
author_rank: Super Contributor
timestamp: November 18, 2012, 08:13:00 pm
content: Low Q and limited frequency range. They are great as a wideband delay, but the output signal is very low. Perfect for TV, where the noise on the colour signal would only present as slight colour shift, not as brightness variations.For an oscillator use a SAW filter, as they are optimised for frequency response, and have a very short delay and very poor response outside of the band they are designed for. In TV sets pre digital tuners you would have one with 2 outputs, centred on 39 MHz, with one being optimised to give the video signal to the demodulator without having the sound carriers present and the other output just passing the sound carriers without the video being present. This got rid of both sound on vision and video buzz at the same time, AFC being used to give the maximum signal out of the video side before the FM demodulator made the baseband video, and the sound was mixed down to a typically 4, 4.5, 5, 5.5, 6, 6.5 MHz ceramic filter ( system dependant) before it was demodulated into 1, 2 stereo or a NICAM audio signal. Started off as a big piece of printed board but ended up as a single chip that did it all except for NICAM, which was still a multi chip arrangement.

author: EEVblog
author_rank: Unknown
timestamp: November 18, 2012, 08:35:43 pm
content: Quote from: kxenos on November 18, 2012, 07:56:09 pmYou won't get jitter free, as you have to amplify the thing, adding all sorts of nasties.And you have the "seed" it with the initial signal at start-up as well, as in this configuration these are circular memories and initially contain nothing.Dave.

author: ftransform
author_rank: Frequent Contributor
timestamp: November 19, 2012, 07:08:25 am
content: as tensions between the uk and australia escalate......so mike, whats your next move. Thermal analysis of a delay line with your IR? Pumping 3 megawatts into a delay line and making it explode/melt (slow motion camera)?Team up with photonic induction? Link a bunch of delay lines?I think we need a high power signal in a delay line asap.

author: EEVblog
author_rank: Unknown
timestamp: November 19, 2012, 08:01:29 am
content: Quote from: ftransform on November 19, 2012, 07:08:25 amI tried the opposite, a piss-ant 1mW laser into it to see if it would bounce around, but no joy, no internal reflections at allMight work with some form of silver mirrored edge, but that's pretty lame.Dave.

author: ejeffrey
author_rank: Super Contributor
timestamp: November 19, 2012, 09:44:48 am
content: Quote from: EEVblog on November 19, 2012, 08:01:29 amThat should work fine, but you do have to launch it through the 45 degree face. It looked like most of that face is covered by the actuators.

author: EEVblog
author_rank: Unknown
timestamp: November 19, 2012, 11:39:44 am
content: Quote from: ejeffrey on November 19, 2012, 09:44:48 amIt is, but I scrapped some of one off. Still works though as seen in my latest video shot after I did that, but probably reduced amplitude?Dave.

author: apis
author_rank: Super Contributor
timestamp: July 13, 2014, 08:49:41 pm
content: I had never seen one of these before, thanks for showing them! I love this sort of devices with strange looking mm-scale patterns, they remind me a bit ofmicrostrip filters.Not sure if it was mentioned in the video but I would guess the reflection is from when the wave hit the output transducer edge, a part of the wave would be reflected back and travel backwards to the input, there some of it bounces back again and return to the output with a total of 3*64 us delay. If you look at the input signal (around 29.00 in the video) you can see the reflection returning to the input (yellow ch1) at about 2*64. That's my guess on what's going on at least.

author: Richard Head
author_rank: Frequent Contributor
timestamp: July 20, 2014, 03:33:44 pm
content: That was an interesting video clip. Thank you.It would have been interesting to see how much intermodulation distortion the device introduces. You would need two sig gens and a spectrum analyser.