On 26-Aug-16 5:06 PM, Phil Allison wrote:
, Phil Allison wrote:
most of you know former regular on this NG, David L Jones, who
reinvented himself as a video star with his EEVblog site. I
stumbled on one of his many hundreds of blogs recently - please
take a look.
The blog attempts to explode a "myth" about analogue and digital
scopes in relation to display noise - particularly that DSOs are
inherently noisier. While I am not sure just what Dave is trying to
prove, some of his
assertions are very dubious. The facts are that an analogue scope
normally has a sharp trace
revealing a great more detail of waveform being viewed. This is
also a direct result of having: 1. Constant bandwidth ( 20,50,100MHz )
plus the same rise time at
all sweep speeds. 2. Continuous vertical screen resolution of around 1
part in a
thousand. 3. Absence of any artefacts due to sampling or quantising.
All this results in an accurate display of any continuous signal,
including random noise. The clean trace shown on an analogue scope
with no input is because there is no noise to be seen. FYI: This might
seem at odds with an input impedance of 1Mohm and
bandwidth of 50MHz which has a calculated thermal noise of almost
1mV rms - with regular peaks over 4mV. The simple answer is that
1Mohm is in parallel with 20pF, so the impedance falls steadily
from 8kHz onwards down to 160 ohms at 50MHz. Thermal noise is
reduced by this to about 15uV rms. The random noise spiking seen in
the traces of the DSOs in the
blog is mainly due to quantising errors plus the discontinuous,
vertical screen resolution of only 200 pixels in case of two of
them. When the sampled value falls between pixels, random toggling
occurs. Lastly, when Dave turns up the brightness on his Tek 2225,
the trace thicken ( due to mutual repulsion between electrons in
the beam ) and also some background pattern appears. The background
pattern is in the CRT's anti glare screen, which
lights up when you do that revealing any imperfections in the
plastic. He should have detached it. Also when he uses the digital
camera, the image becomes over
exposed which again results in trace thickening. The story about
"revealing missing noise" is a furphy. BTW:
In the first few second of this blog on the Tek 2225, Dave seems
to contradict himself. https://www.youtube.com/watch?v=8GR_6QH3uZk
At the end of the day he may make some mistakes (who doesn't) but to
give him credit he's build a large following and has probably
contributed quite a bit to folk learning more and doing more around
electronics. His forum is very active, aus.electronics is dead. :(
** AFAIK, EEVblog Forum posters are predominately Yanks and it's
moderated by Dave himself as the "administrator".
I haven't done a head count but the mix seems pretty even, plenty of
At the moment, I have no great wish to join up and suspect I might
even be barred anyhow. OTOH, David L. Jones can appear here any time
he cares to.
Bah! Just create a nym.
It seems odd that one would find fault and start a post on Usenet
** Not odd at all, the topic itself is very interesting - Analogue
V. Digital scope performance is red hot, debatable stuff these days.
I still keep my old Philips analog CRO around, it's good for some
Do I detect a hint of " I *heart* Dave " going on ??
Not really he's entertaining and seems motivated by the right things.
My voice is like his, hence me not doing videos....
Heh! A wise man.