we all know that the goal of an oscilloscope is to take the signal on
your device and accurately represent it on the screen all of the scope advice
and how to input there is centered around this idea but what if you don't
actually care about getting an accurate representation what more can you do with
your scope hi i'm daniel bogdanoff and today we're gonna push the traditional
boundaries of an oscilloscope with what I like to call a spec hack it's not a
normal hack it's more of a creative way of pushing your gear beyond what it
could normally do throughout history we as humanity have pushed the limits of
our tools just because we can think about lawnmower racing or mountain
biking tools used for yard maintenance or transportation have been extra ly
modified into something that behaves in a whole new way so I got to thinking
what could you do with the scope if you didn't care about getting a great signal
reconstruction and this occurred to me if you don't care about a good
reconstruction you could exceed the bandwidth of your scope if you aren't
familiar with the ins and outs of bandwidth check out the video on that
topic there's a link in the description but here's the short version any
frequency components higher than your scopes bandwidth will be attenuated
they'll appear smaller but you'll still see a signal even though you can't see
the signal as it exists on the device you can still see it which means you can
do something with it or at least learn something from it one of the things we
can learn is the signals frequency granted the frequency components won't
look right on the screen but the actual toggling of the signal up and down will
give us frequency information all we need to measure that is a good trigger
and the frequency counter built into the scope you could also use the on-screen
frequency measurement but the frequency counter is actually a better fit here
because it uses the Scopes trigger circuitry and here's where it gets
really interesting the triggers circuitry and signal path is actually
separate from the acquisition path the trigger circuitry gets its own signal
conditioning and uses a couple comparators since we don't care about an
accurate reconstruction of our signal we don't need to use the signal going into
the ADC we can use the output from the comparators to measure the frequency
those trigger comparators are pretty convenient because that's exactly what
we need for our frequency counter it's called a frequency counter because that
literally counts it counts the number of edges
that sees in a specified amount of time called the gate time the frequency is
then the number of pulses divided by the gate time a basic frequency counter is
essentially just a comparator which identifies signal edges and a
microcontroller to count the output and display the results this is all already
in place with the trigger comparators in scope processor I also just happened to
have this signal generator which goes up to 44 gigahertz which for today will
probably be sufficient so the question becomes how high of a frequency can we
measure let's find out.
So now that these have automatically stacked themselves to
be convenient for our close-up camera we can plug in a frequency and see how high
of a frequency we can measure. Keep in mind that this is a 70 megahertz scope.
so I'm going to turn on my RF signal and I have a 25 dBm 1 megahertz signal going
in. 25 dBm is about eleven point two volts peak-to-peak so it's pretty big.
let's sweep up the frequency and see what happens - and I'm just gonna crank
this wheel in 1 megahertz increments. Let's go up to 70 and you can see we are spot on.
Let's also turn on our frequency counter
and we can see 70 megahertz no problem
let's go higher 200 megahertz and we are still going strong I'm gonna scale the
signal a little bit because the frequency counter also operates on the
Scopes time per division settings so let's go even higher
350 400 megahertz and we are still there I'm gonna zoom in I'm gonna start going
down to 1 megahertz increments and we'll also have to play with our trigger a
little bit just to make sure that we are still able to see this signal so with a
little finagling we were able to get four hundred and ten megahertz have
measured on the frequency counter that is almost six times the bandwidth of the
oscilloscope on another 100 megahertz oscilloscope I was able to get over 520
megahertz on a 100 megahertz oscilloscope so your mileage may vary
from scope to scope but there you have it it ain't pretty but it works quick
sidenote this is that same eleven point two volts signal going in and we are at
50 millivolts per division so about eleven point two volts signal has been
attenuated down to maybe a hundred and fifty millivolts I always love finding
little gems like this in my test gear have you found anything like this in
your gear let me know in the comments and if you want to learn more about
using oscilloscopes make sure to check out the e-book six essential tips for
getting the most out of your oscilloscope it's free there's a link
for that in the comments and the description and of course make sure to
like this video subscribe to the keysight labs youtube channel i'm daniel
bogdanoff and thanks for watching