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How the early radars could know the angle of a basic radar rotating antenna?
How the direction of the time base on radar screen is synchronized with the direction of the radar rotating antenna?

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  • \$\begingroup\$ Welcome to Electrical Engineering SE! Seeing that you have a particular amount of rep shows that you've been a user on StackExchange for a while so I'm assuming that you know about reading the rules here just like any other StackExchange. Check out our help center. With that being said, please do not expect us to do your homework. Asking these types of questions are considered vague because you're not asking a definitive question. Consider narrowing your question down to one idea and put in some effort on your side so that we can help you. \$\endgroup\$
    – user103380
    Commented Sep 28, 2018 at 18:47
  • \$\begingroup\$ Conventional solutions applicable to 80 yrs ago would be to use the rotor voltage commutation enabled once per revolution in a time window to get the phase voltage of the rotor with some gear ratio and an index switch and some flywheel for stability. THat's my guess. The same is done in all disk drives except using a Hall index sensor mark and for CRT's use H sync for blanking from flyback per raster sweep. \$\endgroup\$
    – D.A.S.
    Commented Sep 28, 2018 at 19:06
  • \$\begingroup\$ @KingDuken this is not a homework, i have already searched for the answer and found that selsyn is used for that purpose,but did not remember how it works \$\endgroup\$
    – AAEM
    Commented Sep 29, 2018 at 20:59

1 Answer 1

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Early radar sets used a pair Selsyn motors to transfer the rotary motion of the antenna platform to a sine-cosine potentiometer.

The terminals of the potentiometer were driven with complementary copies of the sawtooth waveform generated by the radar timebase, and the taps of the potentiometer fed the horizontal and vertical deflection amplifiers of the display tube, creating a radial scan at the correct angle that's synchronized to the receiver output.

Note that this system even allows the operator to interrupt the normal periodic scan in order to sweep the radar beam across a specific target. The display remains synchronized to the antenna at all times. Note also that "pan & zoom" of the display is possible by varying the gain and DC offsets of the deflection amplifiers.

Modern digital systems simply use a shaft encoder on the antenna.

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  • \$\begingroup\$ DO you know this for a fact is is this just a your guess since it was used by US in 1900. I don't think the Hungarians use that when they designed for the Germans in 1939. Citation, please. Latest Radar by Lockheed Martin uses a revolving electrified rail with magneto gears and a rotating dual radius rotor on an angle pivoting around \$\endgroup\$
    – D.A.S.
    Commented Sep 28, 2018 at 19:45
  • \$\begingroup\$ @TonyEErocketscientist. Custom shaft encoders can be as accurate as 16 bits or more, far beyond the price range of Ebay. With Klystron tubes the echo-delay is very precise. \$\endgroup\$
    – user105652
    Commented Sep 28, 2018 at 20:14
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    \$\begingroup\$ I helped design and debug CRNL/ Ontario Hydro's CANSCAN robotic scanners for maintenance of Pickering reactors, I could measure within 100pm real/reactive impedance on dual Eddy current probes in a SCADA Robotic custom system, I built, with 0.1mm resolution but reduced to 0.2mm to collect over 100km of secondary heat exchanger tubing in '77 in multiple reactor buildings with everything over 1 coax. Robotics, voice TV data and commands \$\endgroup\$
    – D.A.S.
    Commented Sep 28, 2018 at 20:29
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    \$\begingroup\$ It could detect molecular steel tube crystal flaw well before a leak occurred if managed properly that changed probe impedance in ppm. We used a 1mm calibration thru hole for full scale 0deg and and change in wall thickness of 50% as 90 deg and use the Sin/Cos Pot with servo to rotate the XY screen and null impedance to like a radar dot in the centre. Then linear 12 bit ADC gave me over 60dB down res so the angular resolution was in theory infinite limited only by servo noise, which was unmeasureable for theta impedance angle error. \$\endgroup\$
    – D.A.S.
    Commented Sep 28, 2018 at 20:47
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    \$\begingroup\$ THe "super-heated "heavy water" was normally at 10k Atmospheres for heat exchanger ( big boiler tubes ) using lake water as steam to exchange heat used run MW turbines. So annual inspection is always done as routine is a big job everywhere and makes Candu reactors much safer. \$\endgroup\$
    – D.A.S.
    Commented Sep 28, 2018 at 20:51

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