General > General Technical Chat
Frequency Divider for older Oscilloscopes??
<< < (9/13) > >>
tggzzz:
Here's a simple question that I have asked interviewees in a job interview...

"I want to observe a signal that is between 990MHz and 1000MHz. What is the minimum sampling frequency that I need to use?".

Those answering 2GS/s faced an uphill struggle.

(And I'm not surprised that the OP hasn't had the courtesy to respond)
tggzzz:

--- Quote from: bdunham7 on July 19, 2021, 03:54:59 am ---
--- Quote from: Jorge Ginsberg on July 19, 2021, 02:55:15 am ---
And any oscilloscope has a trigger circuit.  There is no difficulty in that.

No correlation with anything is necessary.
 
Put your ingenuity to work and see if you can figure out how to achieve all that in a simple way.


--- End quote ---

OK, I can see generally what is needed.
--- End quote ---

I have a 50 year old scope (battery powered, can be operated in driving rain and stored underwater :) ). It displays signals up to 4GHz with, IIRC, 37kS/s. It contains transistors, 741s and a few SSI logic gates (dual JK flip flops and nand gates), but no memory or anything like that. The full service manual contains schematics and circuit descriptions.

Watching the display twinkle is hypnotic, but I can't capture the effect in a video



Or see the attachment for another example circuit, from http://www.redrok.com/Circuits_1GHz-samplig-Oscilloscope-Front-End.pdf
Jorge Ginsberg:

--- Quote ---
OK, I can see generally what is needed.  Making a reliable trigger may not be an insurmountable challenge, but picosecond jitter.... I suppose it doesn't have to be that good to nominally work.
--- End quote ---

If you use semiconductors for UHF, if you use very stable voltages, and if you use constant temperatures, the jitter and drifts are so low that you hardly notice it.
Jorge Ginsberg:

--- Quote from: tggzzz on July 19, 2021, 08:02:15 am ---Here's a simple question that I have asked interviewees in a job interview...

"I want to observe a signal that is between 990MHz and 1000MHz. What is the minimum sampling frequency that I need to use?".

Those answering 2GS/s faced an uphill struggle.

(And I'm not surprised that the OP hasn't had the courtesy to respond)

--- End quote ---

Dear TGGZZZ... what kind of waves do you expect to find between 900 Mhz and 1000 Mhz? do you expect to find square waves? do you expect to find saw teeth?
When you work in the high UHF zone and enter the microwave zone, ALL waves are already sine waves.
An oscilloscope is useless at those frequencies.
At very high frequencies, a resistor can behave like a coil and a capacitor can behave like a delay line. Transistors already behave differently.  The "h" parameters are no longer used in the design, but the "s" parameters are used.
At very high frequencies all the electronics change.
Intel uses UHF and microwave engineers for the development of its chips.  Imagine a microprocessor running at 3.6 Ghz.....
A good technician or engineer in audio or industrial electronics becomes a perfect ignoramus when working above 1 Ghz.
It is true that to observe correctly a 100 Mhz square wave you would need a 1000 Mhz oscilloscope, otherwise the square wave would be very distorted in its rising and falling edges; but it is never necessary to "look" at 1000 Mhz waves. In the vast majority of cases it is enough to know if that wave exists and what is his amplitude. For example, people who buy the Tektronix MDO3000 oscilloscope, whose bandwidth is 1Ghz, do not do it to see 1 Ghz waves but to be able to see correctly the 100 Mhz waves, because when you look at a 1 Ghz wave, the only thing you see is a sinewave...
Those of us who work on UHF or microwave radio links only use spectrum analyzers.  By looking at the spectrum you know if you have just a sine wave or if you have a more complex wave.  In that frequency range it doesn't matter the shape of the waves, the only thing that matters is their harmonic content.
Jorge Ginsberg:
The good thing about all this talk is that it doesn't end in a production.
I say again what I said before: nowadays none of this is worth it. You can buy a good 100 Mhz oscilloscope for 400 dollars or even less.
The appeal of all this talk is that we exercise our minds and find out how this device can be created analog, cheap and simple.
Think of the human ingenuity displayed throughout history.
In 1879, Albert A. Michelson measured the speed of light.  At that time, laser beams did not exist. There were no atomic clocks.
Michelson measured the speed of light using only mirrors and a rotating disk. And he determined the speed of light with an error of only 200 miles/hour !! AWESOME ...
In 1653 the astronomer Christiaan Huygens determined the distance between the earth and the sun. What technology existed at that time to achieve such a feat?
And more than 2500 years ago, the Babylonians already knew that the Earth was round and even calculated its diameter.
And all this was achieved thanks to human ingenuity.

That is why I wanted to tell you here that more than 30 years ago I built a device that allowed me to see UHF signals on a modest oscilloscope with a bandwidth of only 10 MHz.  And I will give you hints about how I did it because the truly beautiful thing about electronics is the way it sharpens our ingenuity.

If GlennSprigg was expecting to receive a ready-made design and simply copy it... I'm sorry to disappoint him.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod