[time-nuts] Old Crystal.

[Dan Kemppainen]

Hi All,

Just to be clear, I am not the person who made the crystals glow blue. I 
just noticed some pictures of that happening on the auction site:

https://www.ebay.com/itm/8x-Quartz-Resonator-1000-kHz-Crystal-oscillator-gold-Sonoluminescence-effect-NOS/113862454353

https://www.ebay.com/itm/1x-Quartz-Resonator-1000-kHz-Crystal-oscillator-gold-Sonoluminescence-effect/113874435589

I certainly will not abuse these crystals this way!



As for measurements, I'm trying to take some measurements with the 
equipment on hand. Currently, that is an Agilent 33220A signal 
generator, and TDS3000B oscilloscope + Active FET Probe.

Years ago I put together a little Excel Macro program that sweeps the 
signal generator through a range of frequencies, and measures the 
voltage and phase of the signals on the oscilloscope. Basically, the 
sampled signals are run through a sine fit routine, which gives very 
good estimation of sine amplitude and phase shift (With frequency being 
set by the signal generator).

Using this setup, the first try involved making a voltage divider with a 
fixed resistor and the crystal. The signal generator was used to drive 
signal into the resistor, through the crystal to ground. A standard 10x 
probe monitored the signal generator voltage, and the FET probe in 
series with a 1K resistor (for more isolation) was used to monitor the 
crystal voltage. (The probes were compared before the test, and channel 
skew adjusted to zero).

Basically, this is a voltage divider made with a resistor and a crystal. 
 From this, a frequency response curve was generated. See attached image.
The -3dB and +/-45 deg phase shift points match well. They are also 
quite close to the Fs frequency (999,999.800 Hz). Those -3dB points come 
out to be 999,990.640 Hz and 999,990.910Hz.

However, I'm a bit concerned that the Q calculated with these numbers is 
a bit higher than expected based on what I've read. Running the test 
with a smaller series resistor (100 Ohm) results in a lower Q (As would 
be expected as the 'load' on the crystal is higher), although even these 
numbers are quite high.

In order to try to measure Rs, the voltages of the divider were measured 
at Fs, and RS was calculated accordingly (Easy calculation, as phase 
shift = 0 deg). This was repeated with several series resistor values 
(10, 100, and 1000 Ohm). These tests resulted in Rs = between 4 to 7 
ohms (depending on the series resistor).

My concern is, are there any potential pitfalls in this measurement 
setup? Is there something that will give more accurate results, given 
the equipment on hand? Certainly the Q value seems unreasonably high, 
and Rs seems quite low. However, these are large low frequency 
resonators (being 25mm in dia.).


Thanks,
Dan


On 3/6/2021 12:00 PM, time-nuts-request at lists.febo.com wrote:
> Message: 4
> Date: Fri, 5 Mar 2021 16:03:51 -0600
> From: Dana Whitlow<k8yumdoober at gmail.com>
> To: Discussion of precise time and frequency measurement
> 	<time-nuts at lists.febo.com>
> Subject: Re: [time-nuts] Old Crystal.
> Message-ID:
> 	<CADHrwpcb3_9xeeCHg3r30DS7oGq-CKsXYjW4XM=q=DT0Gv5OXA at mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
> 
> Blue LEDs under Nixie tubes might have a deeper purpose than appearance-
> they can also
> help the Nixie tubes get started upon turn-on (especially if they're
> getting old).  I once stayed
> in a hotel room whose light switches had neon indicators to help one find
> them in the dark,
> and the one near the entrance door was getting awfully marginal.  I
> happened to have a blue
> LED penlight with me, and I found that shining that on the switch face made
> a radical
> improvement in making the neon indicator keep going, even at a range of >
> 20 feet.  And
> this flashlight was no powerhouse either- it was a single LED with no
> auxiliary focussing
> optics.
> 
> Dana
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