Adding cursor to analog oscilloscope

[Bero]

Hello
I’ve saw on youtube this video, showing possibility
to add cursors or markers to old analog oscilloscope.
Of course, someone will tell that if you need something sophisticated,
buy a better scope, or advanced sweep generator.
However, like many of vintage radio collectors,
always considered costs for something used just for a hobby.
This man show how to use some of rarely used oscilloscope functions, at a rear of oscilloscope.
He used A-gate of the oscilloscope output,
which is on position 1 at the start of sweep cycle,
and position 0 at the end of the sweep cycle.
Transition caused pulse, which he used to delay through 555 IC-s,
and fed back narrow pulse to Z-axis of the scope.
This result will illuminated little dot on the screen,
the dot is movable between that time reference.
He said it is possible to calibrate pot used for moving illuminated dot,
and this can be a precise frequency position on the trace.
My question is, is possible something like that, referenced to the marker frequency?
I mean, if you don’t have sophisticated sweeper,
only with center marker (10,7) and analog scope to saw the trace,
it would be a great help to have side markers of 100 or 150 kHz.
But how to get pulse and time reference around center marker?
Is it something like that impossible, too complicated or is it ease, as it seems on this video?
This is a link to video:
#41: Use Oscilloscope Z-axis input to create "marker" on waveform - YouTube

Regards

[Diabolical Artificer]

I have an analogue scope with "markers" but to be honest they are hard to see and useless in my case, fairplay to you for having a go though.

Andy.

[kellys_eye]

Relatively simple if you ask me.

It's only a matter of timing and you can (could) break the horizontal axis down to whatever interval you wanted and count the 'steps' between any two.

If you use a double beam scope you could put the timing marks on the second channel and use a monostable to create a very narrow pulse that went to the extremes of whatever Y-axis setting you used to get a line rather than a pip.

All you need is access to the trigger signal (or you'd have to use the external trigger input for both the measured and the cursor signals). Doing it 'automatically' for each range adds difficulty so a 'basic' unit would have its own timebase setting that you'd have to match to the scopes.

[Bero]

Thanks for the answers.
The oscilloscope has two beams,
but in this setting the second input is already used
because it is necessary to use the x-y mode to display the IF curve.
As far as I saw in the video, he used an A-gate from an oscilloscope,
to get a reference time from the pulse generated
when the x-axis state changes.
Even if I don't think about the cursor, what I'm interested in
is how to use the Z-input of the oscilloscope to show the marker on the display?
Obviously then one needs to take the marker signal from the sweeper,
and make a circuit that produces a pulse exactly at the marker location,
and then impute it into the z-axis, to get different display illumination.

[Diabolical Artificer]

Would this be with a readout of frequency on the CRT or on a separate display?

Andy.

[kellys_eye]

Using the Z-axis is a case of applying a pulse to the Z-input that is delayed from the timebase trigger point by a variable amount. With a known scale length you can easily calibrate the delay to correspond to a time/frequency interval. If you went digital you could create a pulse stream of (say) 100 cycles (with appropriate counter) to correspond to a full width scan and have an accurate representation of exactly where the 'pip' was produced.

Since all the Z-axis input is doing is modulating the brightness of the scan you'll never get more than the 'pip' you originally described unless you used a discriminator to convert the Z-pulse into a +/- (very) narrow pulse and added it to the y-axis signal where it will display as a full 'bar'.

[Bero]

Originally Posted by Diabolical Artificer

Would this be with a readout of frequency on the CRT or on a separate display?

Andy.

The display on the screen would be like this.
Green is what I have now, my sweeper only has a central marker,
blue dots are what we are talking about here.
Of course, they are only placed in blue for display,
if this works they should be the same color as the trace, only bright dots on the curve.

[kellys_eye]

If the x-axis represents an arbitrary 1mS/cm then create a delayed pulse that starts at the first pip and is set to be as wide as where the second pip was meant to be situated. Use both a rising and falling edge detector to convert the pulse edges to sharp (narrow) pulses that feed to the Z-axis.

By varying the pulse delay (start) and the pulse width (representing the bandwidth you want) you will have two 'variable' markers.

As already mentioned, by converting the rising/falling edges of the pulse into voltage levels that suited the Y-axis, using a very narrow pulse) you could 'mix' this with the Y-axis signal and have defined vertical lines as markers rather than just pips.

The above description is analogue-based but could equally be achieved using an Arduino (or similar) counting a suitable clock stream and using an LCD readout for the marker positions and displayed in the units you require.

[kellys_eye]

Although I no longer have one, a typical lab pulse generator will be able to deliver the signals needed as they commonly have a sync input, delayed pulse and variable signal level controls (width etc).

[Bero]

It’s hard to find any meaningful text about it on the internet.
Here is the only schematic I have been able to find on this topic.
@kellys_eye, can you give an opinion about it.
It looks pretty simple, only two 7400s were used.
It seems to me that I could use the marker part.
I don’t think I need a VCO either, because I already use a sweeper
whose x-axis is connected to the x-axis of the oscilloscope.
Sweeper also has its own attenuator.
Do you think I could get a side marker display with this?