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+======  Atomic counter  ======
+Atomic counter is a frequency counter designed for an accurate frequency measurements. It has a PPS output from GPS used as a frequency normal ((GPS satellites have several atomic clocks onboard, hence the name ‘atomic’ counter)). Its construction is now implemented in two variants:
+  * ACOUNTER01A -  Produced using [[en:s3an|FPGA board]]
+  * ACOUNTER02A - Produced using microcontroller [[en:pic16f87xtq44|PIC16F887]] and several other modules.
+Accuracy of both variants is determined by a used GPS and a quality of incoming signal. However, generally, each measurement needs to be averaged over a longer time period, because the time stamps only have a short-term accuracy in order of tenths of ns. Individual measurements can therefore have a relatively wide Gaussian scattering, which has to be eliminated by averaging.
+===== ACOUNTER01A =====
+{{ :cs:designs:tools:atomiccounter_big.jpg?direct&300 |}}
+This version work up to approximately 600 MHz.
+==== Construction ====
+Atomic counter contains following modules:
+  * [[en:s3an|S3AN01A]]
+  * [[en:gps|GPS01A]]
+===== ACOUNTER02A =====
+{{ :cs:designs:tools:acounter02a.jpg?direct&300 |}}
+Using [[en:clkgen]] module, a functionality up to at least 850 MHz has been verified. However, as the divider's input [[en:clkdiv]] works up to 3 GHz, we expect the counter to be operational up to this frequency.
+===== Related articles =====
+  * [[en:gpsdo]]