Series-resonant 11 MHz in HC-49/U
The ECS-110-S-1X operates in series resonance with zero external load capacitors — the crystal is specified at its series-equivalent resonant frequency, which means the oscillator circuit drives it directly without the shunt capacitance a parallel-resonant part would require. The 30 Ω ESR is the impedance the oscillator sees at the drive point; lower ESR means the Pierce or Colpitts circuit can start and sustain oscillation with less power delivered into the crystal. 11 MHz in fundamental mode is squarely in the range where a standard MCU oscillator stage will start reliably at room temperature — the startup margin narrows at cold, but 30 Ω ESR is not a concern for most logic-level oscillator circuits at this frequency.
±80 ppm total frequency accuracy
Frequency tolerance is ±30 ppm at 25 °C and frequency stability is ±50 ppm across the operating temperature band — these stack, so a worst-case design budget is roughly ±80 ppm total from nominal. At 11 MHz, ±80 ppm represents a ±880 Hz frequency error at room temperature and over temperature: fine for a UART baud reference (a UART tolerates 1–2% without error), acceptable for timing a polled sensor loop, but tighter than a USB full-speed reference where the oscillator must stay within ±2000 ppm including the microcontroller's own trim accuracy. The buyer sourcing this for a USB application should verify the host controller's trim range covers the crystal's actual tolerance band, not just the datasheet nominal.
HC-49/U through-hole footprint and deployment
The HC-49/U package stands 13.46 mm seated height in a 0.447-inch-long, 0.183-inch-wide barrel — a through-hole part that survives wave soldering and is forgiving of board warpage in large panels. It is specified over -10°C to 70°C, which is a commercial temperature grade: adequate for indoor instrumentation, consumer equipment, and office-grade control boards, but not the industrial -40°C lower limit. The through-hole lead spacing and the package's mechanical robustness make it a reasonable choice for legacy boards still on the production line or for designs where SMT reflow is not available on the assembly floor.
Active production — ECS Inc. HC-49UX family
The HC-49UX family spans a wide frequency range in the standard HC-49/U outline, so single-source risk on this particular frequency is low within the same manufacturer series. No official L* successor is cited for this order code.