Radio Frequency (RF) & Wireless Design

Years ago (back in the 90's) i performed research to determine the 'most common' crystal frequency and my results turned up that the 16 MHz crystal was the most common crystal frequency, thus it is also the most common oscillator frequency.

Now bear in mind that i am talking about a fundamental crystal frequency here, not a overtone or harmonic filtered frequency, which is typical for frequencies over 100 MHz.

So in doing this research, here's what i found as data based upon searching for whole number crystal frequencies above 1 MHz , regardless of case size, stability, tolerance, . . . etc

From the data below, you can see that crystals in the mid to upper 20's such as 25 MHz as well as neighboring 24, 27, 26, 32, 30 are the most common crystal frequencies today.

This is important whether you are choosing a PLL frequency synthesizer, or for a simple Micro-Controller (MCU).

So if you are wondering which crystal frequency to choose (especially with supply chains these days), consider finding a fundamental crystal frequency that will allow you the flexibility for packages, availability, cost, and many other options. [Note : whole number crystal frequencies not listed are going to be less than 1 available ]

The pattern i noticed here is that starting from 52 MHz and moving downward in 4 MHz octaves, the pattern becomes something like this :

52, 48, 44, 40, 36, 32, 28, 24, 20, 16, 12, 8 MHz

Those not covered in the 4 MHz octave pattern are these crystal frequencies (above 1K quantities) :

50, 30, 27, 26, 25, 13, 10 MHz

But notice that 25, 26, 27 MHz (25 MHz +/- 1 MHz) are some of the most popular crystals, even though they are not in the 4 MHz octave range. (I am not sure why it this point, other than they may be prime frequencies or possibly frequency dividers for 25 MHz are 1, 5, 25, and 2.5, 0.25 = 1/4) - - - maybe because of the popularity of Citizens Band (CB) radio, when plug-in crystals were all the fad (https://en.wikipedia.org/wiki/Citizens_band_radio).

But more likely as an base frequency input for 100 Mbps Ethernet that can be synthesized from a Phase Lock Loop (PLL) that might also have been used in FDDI, Token Ring, or ARCNet (https://en.wikipedia.org/wiki/Ethernet).

Also for the follow up i will investigate the most common PCB case size, but my suspicion is that it will be these PCB crystal cases :

• Thru-Hole (TH) metal can = HC-49U
• Surface Mount Technology (SMT) metal can = HC-49SM
• SMT ceramic case = 7050 (7mm x 5mm)
• 
  

I will check next weekend and see ! - - - What's your guess ?