A prescaler is an electronic counting circuit used to reduce a high frequency electrical signal to a lower frequency by integer division. The prescaler takes the basic timer clock frequency and divides it by some value before feeding it to the timer, according to how the prescaler register(s) are configured.

Mnemonic: think of -divisions- on a -scale-.

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From Wikipedia:

A prescaler is an electronic counting circuit used to reduce a high frequency electrical signal to a lower frequency by integer division.

Amps are used to boost signal strength, or to better receive a weak signal, not to change frequency. A flip-flop devides a frequency by 2.

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Just think - if it counts decades a decade is ten years or in this case just the number ten. So, for every decade it pulses once.

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The flip-flops are connected as a binary counter, with the first one providing the 50 kHz marker and the second one the 25 kHz marker.

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A standard quartz crystal oscillator is usually of the AT cut type, which has a frequency deviation on the order of several parts per million over a commercial or industrial temperature range. This stability is unsuitable for many demanding applications where maximum deviations of hundreds of parts per billion are required over a large temperature range, or low drift vs. time is required (aging effect). The most basic is a temperature-compensated crystal oscillator, which as the name implies attempts to pull the crystal into tight tolerance by measuring a nearby temperature sensor. The second type mentioned is a rubidium reference, which is a type of atomic reference with good long-term stability characteristics derived from a rubidium-based physics package. Third, a GPS signal reference is one that can be used to create a GPS-disciplined oscillator, which is a type of oscillator that is kept synchronized by using signals derived from atomic references on GPS satellites, with corrections that are traceable to NIST. The result is an oscillator with zero effective long-term drift and good local stability provided by a high-quality ovenized oscillator.

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Hint: the Purpose is to Provide and the Marker Calibrates

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The accuracy of a frequency counter is strongly dependent on the stability of its timebase. Highly accurate circuits are used to generate this for instrumentation purposes, usually using a quartz crystal oscillator within a sealed temperature-controlled chamber known as a crystal oven or OCXO (oven controlled crystal oscillator). For higher accuracy measurements, an external frequency reference tied to a very high stability oscillator such as a GPS disciplined rubidium oscillator may be used. Where the frequency does not need to be known to such a high degree of accuracy, simpler oscillators can be used.

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A frequency counter will tell the measured frequency of a device by reading the pulses using a counter.

For example, the counter could count a number of pulses in 1 second, display it on the screen, then count again over and over.

The answer is "counting the number if input pulses occurring within a specific period of time" because that is the basic operation of a frequency counter, and none of the other answers have to do with frequency counter operation.

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If you have an oscilloscope and can view one or more "cycles" of the oscillator, then you can determine, with reasonable accuracy, the frequency of the oscillator. It works like this:

Let's say that we can view one cycle of the waveform and it is a "sine" wave (typically what we see when dealing with radio frequencies). The beginning of the sine wave is at the left edge of the o'scope display (which has 10 major divisions with each major division being further divided into 5 smaller divisions) and completes one full "cycle" at the end of the 2nd major division. We should then see 5 full cycles on the full display of the o'scope. WE are ONLY interested in ONE cycle, the FIRST ONE!

Now, we need to look at the buttons and knobs of the o'scope to determine what "range" is selected for the "timebase" of the "sweep" of the oscilloscope. The displayed beam (bright line traced across the scale of the o'scope) completes a full sweep of the display in 10 timebase increments. Each major division of the o'scope display grid is ONE timebase increment.

The knobs and controls indicate that we are on the 0.1 uS (0.1 microsecond) timebase scale. This means that it takes 0.1 uS for the sweep to pass through ONE major division of the oscilloscope display grid.

WE determined that our oscillator displays ONE full cycle in TWO major divisions of the oscilloscope display grid which means that the PERIOD (inverse of FREQUENCY) is 0.2 uS for one cycle of our oscillator.

Now comes the FUN part! Mathematics. The universal language. Frequency and period are just two different perspectives of the same thing. Frequency is "cycles per second" and period is "seconds per cycle". Each is the inverse of the other. So, to determine the "frequency" of our oscillator, we divide 1 by 0.0000002 seconds (0.2 uS). That is, frequency (F) = 1/0.0000002 seconds with equates to a frequency of 5,000,000 cycles per second or 5 Megahertz. Thus, we have determined frequency with the alternative to a frequency counter, the oscilloscope!

Try this with a calculator both directions and see for yourself. I hope this helped and good luck with your continued efforts to obtain your Amateur Radio Operators License.

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