Heathkit® HeathFreq

Heathkit® HeathFreq (TM) helps you understand, choose, and design with crystals, and work with frequency data.

Crystal harmonic or overtone information is computed. Special features help users of piezoelectric crystals for electronics design and radio operating. This helps you find uses for your crystal collection effectively, and identify interesting frequencies. Also provides easy access to a large library of radio-frequency usage data.

QUICK START

Touch the data entry field and enter a frequency in kiloHertz (no punctuation needed).
Then touch either "Calculate crystal overtones" to calculate the first 25 harmonics;
or touch "Calculate reverse overtones" to calculate 25 subharmonics of the entered frequency.
Results are annotated with "interesting" frequencies, including amateur radio and shortwave bands and band plans.


BACKGROUND ABOUT CRYSTALS

Crystals are used for a wide variety of purposes--setting watch frequencies, alternative health therapies, setting the clock rate of microprocessor-based circuits, making electronics or radio-electronics circuits highly stable, and reliably setting the frequency of an amateur radio transmitter or shortwave receiver.

When electricity is applied to a crystal, it vibrates at a single very specific frequency--its "fundamental" frequency--which depends on how the crystal was cut. This well-known physical phenomenon is called the Piezoelectric Effect. In addition, a vibrating crystal generates weaker energy at integer multiples of the fundamental frequency.

Thus although the crystal may be cut to a thickness that makes it resonate (oscillate) at a fundamental frequency in one band, it also may be usable in other higher-frequency bands that are multiples (harmonics) of its fundamental frequency.

A crystal is physically complex, and its true overtone vibration frequencies may not precisely equal its mathematical harmonic multiples. But the overtones usually are quite close--usually within ~1 kHz depending on temperature of the crystal, the design of supporting electronic circuitry, and other factors.

The chart of harmonics computed for you by this app provides a very close and useful approximation to the actual physical and electronic overtone vibration frequency of any crystal.

It can estimate crystal overtone frequencies for your amateur radio transmitter, or find the crystal in your collection that puts you on or close to a desired frequency using a harmonic. This is helpful for operators of vintage radio equipment that use crystals to set frequency (e.g., the Heathkit® DX-60B transmitter).

It also is helpful in the design of electronics, e.g. frequency multipliers, superheterodyne designs, or similar circuits where at least one oscillator frequency is set by the fundamental or overtone frequency of a piezoelectric crystal.

HOW TO USE THIS APP

HeathFreq computes either the harmonics or subharmonics of a frequency you enter. The amateur radio or short-wave band, if any, of each harmonic is identified. It also tells you if any harmonic is close to an "interesting" radio frequency.

HeathFreq has 3 modes of operation:
1. Enter a crystal fundamental frequency and select "Calculate crystal overtones". HeathFreq reports its first 25 harmonics, approximating its predicted overtone frequencies, and flags "interesting" frequencies.
Example: If you enter 7113 kHz and choose "Calculate crystal overtones", its third harmonic of 21340 kHz is identified as an interesting frequency, specifically the Slow-Scan Television (SSTV) calling frequency.
2. Enter a frequency and choose "Calculate reverse overtones". HeathFreq reports the first 25 subharmonics.
Example: To operate a transmitter on 144.6 MHz, enter 144600 kHz into the frequency field and choose "Calculate reverse overtones" to identify crystals that have 144.6 MHz as an overtone (such as 6025 kHz, its 24th subharmonic).
3. Enter a frequency and press either button to see what "interesting" activity occurs nearby.