Game for the antique test equipment folks? - Page 1
Forum section: electronics / general

author: paulca
author_rank: Super Contributor
timestamp: November 28, 2019, 07:15:17 pm
content: Seen this thought of you, kinda thing...Some of this era of surface to air missiles literally have oscilloscopes to target them.

author: edy
author_rank: Super Contributor
timestamp: December 01, 2019, 08:18:04 pm
content: I don't know but I believe a lot of vector graphics games would suit oscilloscopes just fine. They do not rely on drawing via a video memory and scan line raster-based graphics. Instead there are drawing routines that modify X-Y voltages to an oscilloscope (or a CRT display directly to deflection plates) and draw each element that way. A routine is made to draw lines... arrays of lines are drawn to form a sprite and then multiple sprites make up the game. A classical example is Astreroids:You can program this on a device like a Raspberry Pi or Arduino as long as you can output variable (analog) voltages or you make a DAC using a resistor ladder. Some use audio output from a sound card to create the analog X-Y output to feed into the oscilloscope. Here is a nice write up with examples:https://www.nycresistor.com/2012/09/03/vector-display/

author: paulca
author_rank: Super Contributor
timestamp: December 02, 2019, 04:27:31 pm
content: What I meant was that the original real world SAMs use different types of oscilloscopes to find targets, track and fire on them. The game linked just simulates that, but it's all 1960/1970s (usually soviet era) surface to air missile tech.The search radar is just an oscilloscope turned around into a circle. The ranging thing is just a standard amplitude over time triggered on the outbound pulse. Some even just use a am-meter gauge.It's the missile tracking and locking scopes that appear to show raw feedback wave forms for the missile seeker head that I found interesting.No "computer" systems in sight, just humming, high power analogue electronics.

author: edy
author_rank: Super Contributor
timestamp: December 02, 2019, 06:24:04 pm
content: What looks so much like an oscilloscope is that they use one of those tiny round CRT's. The analog circuitry and functions that make it work like a radar and tracking are sure going to be much more sophisticated and different than your bench-top oscilloscope. However, I can see how you could build a "RADAR" using an oscilloscope set in X-Y mode. And as an extension to that, a SAM. The oscilloscope would be the display end of a much more complex system.You would do a circular "sweep" which is simply just 2 sine waves offset by 90-degrees fed into the X and Y channel (or sin X, cos Y). The magnitude of this signal is modulated by the distance to which you receive an echo. Meaning, a saw-tooth rise function would also be used that sweeps up linearly then back to zero. When a pulse is sent out, the saw function is at 0. As the signal pulse travels out... the saw function rises linearly. When the pulse bounces off a target and is detected back by the radar station, the height of that saw-tooth function at that moment would be used to set the magnitude of the beam for that specific sin X, cos Y. Which means that your oscilloscope will draw a dot on your screen somewhere along that line turned by whatever degrees, which will be at a distance from the origin based on how long it took for an echo.It is not much different than feeding your oscilloscope a Lissajous pattern... but the most simple one is a circle formed by feeding a SIN and COS function into X and Y which are exactly the same frequency/amplitude (or 2 SIN which are exactly 90-degrees apart):Then you use this saw function to modulate the amplitude of the X/Y signal... that will essentially make the Lissajous "circle" larger and smaller. Or another way, it will put the beam at different distance from the origin as a function of the saw-tooth which will be correponding to the echo-delay time for a pulse to bounce back.Finally, the actual signal being detected will be used to modulate the INTENSITY of the beam. So theoretically you won't see anything on your oscilloscope until you get an echo, and the signal you get back should be drawn on your screen corresponding to the angle that your radar antenna is at and at a distance from the origin corresponding to the echo-time delay (which gives would result in a higher amplitude of sawtooth at that moment, hence drawing the dot further out from the origin since your Lissajous circle would be larger). Hopefully that makes sense?The sin X, cos Y would be corresponding to the direction of the antenna sending out pulses. One full revolution of your antenna would be a complete 360-degree sweep through your sin X, cos Y function. To set the "distance range" you are trying to map, you would alter the sweep frequency of your saw-tooth function. The longer the spacing, the more time you are waiting for a signal bounce to be detected. The faster your saw-tooth function, the shorter distance you expect. This has to be calibrated though also with your antenna sweep as far-away objects take longer time to bounce, which by then your antenna has already turned a few degrees and no longer able to hear the echo. Otherwise artifacts start showing up.As far as the oscilloscope part, it acts as a nice vector-type display but you still need the electronics to feed into it the signals, and you need functions to control the beam, whether you want it to have a circular sweep function, or draw vectors like a "laser show" type of device (where pure vector signals are used to deflect mirrors with magnets offset by 90-degrees). The oscilloscope is just the final display head of a complex system, but it is versatile and fun to use. Hence why there are so many people having fun with vector art on them.Very cool indeed.

author: paulca
author_rank: Super Contributor
timestamp: December 03, 2019, 08:33:49 am
content: The thing is that most military radars (not all) do not respond to "echos" alone. Everything echos radar, air returns radar, ground clutter returns radar, clouds return some radar. Sure a plane will return more than a cloud, but it create a mess of clutter which is filtered out complete on most systems.What they look for is not a return, but a return with a Doppler shifted frequency. Higher frequency it's coming towards you a lower frequency it's going away. Same frequency it's filtered out. This removes almost all cluter and why real radar displays are not covered in fuzz and clutter.An interesting extension. To evade a radar or radar guided missile a technique commonly used is "notching" where you rapidly turn to place the radar directly abeam your plane, flying as close to perpendicular to the beam as possible. This reduces your relative speed (to the radar) close to zero.The amazing thing in terms of electronics is the reason it's called "notching", is that you are putting your plane into an orientation that the radar's Doppler "notch filter" will remove your return.If you have every wondered how air to ground attack radars work and how they can see a tank driving down an avenue of trees or through tall grass... it's because it's moving relative to the surroundings and the notch filter removes the surroundings.Some radars do have "pulse" mode, some only do "pulse", however due to it's limitations, most only do "pulse Doppler".But, in response to your elaboration of making a circular radar display, not all the displays are the traditional circular sweeping display, that's just the search radar. The tracking and targeting radars are more linear , X, Y, displays. That and the simulated control of powering up and managing all this high power valve driven analogue tech, I thought it would be of interest to some here to have a play with the game. I might not have picked the best video to show this, a lot of them are not in English and some are poorly narrated or not narrated at all.