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Ron Hatch: Compass Points

hatch-filter.jpgThe "Hatch Filter" Equations

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Engineering Specialties
System engineering and algorithm development with significant software work and limited hardware.

His Compass Points

  • “It is the glory of God to conceal a matter; to search out a matter is the glory of kings.” - Proverbs 25:2
  • Nancy, my wife of 47 years, our 13 children (ages 19 to 46), and eight grandchildren

His Namesake Equation
The “Hatch Filter” is used to smooth the code measurements so that code multipath noise is reduced. The equation can be written in a number of forms—this is one of the simpler, two-step forms. (See Example 1.)

This first step smoothes (or averages) the difference between the code and the carrier phase measurements.

Where: The subscript i refers to the current time epoch and the subscript i-1 refers to the prior epoch of time.
τ is the filter time constant and controls the level of smoothing. If τ is replaced by the value of “i” so that it changes each iteration, the filter becomes an averaging filter.

D is the smoothed code measurement.
Ρ is the unsmoothed measurement.
L is the carrier phase measurement after scaling by the wavelength.

The final step in obtaining the smoothed code measurement is simply to add the smoothed offset D to the carrier phase measurement L (see Example 2).

Where: Pi is the smoothed code measurement.

Engineering Mentors
John Walton, Tom Stansell, and Jim Litton, the three managers I worked for most of my career.

GNSS Event that Most Signifies That GNSS had “Arrived”
The United States turning off “Selective Availability” on GPS.

Influences of Engineering on His Daily Non-work Life
Studying and writing about alternatives to Einstein’s theories of special and general relativity in light of discoveries related to GNSS.

Popular Notion About GNSS That Most Annoys
That it proves Einstein’s special relativity.

Favorite Non-GNSS Activities
Reading good books (The Kite Runner is a recent favorite), watching games that have been TIVOed (Angels baseball and UCLA basketball), and attending church with Nancy and with our youngest daughter, when she makes it home from college for the weekend.

The Next Big Thing
When a significant number of satellites are transmitting on three frequencies, I believe that it will become possible to have a “Global RTK” system that does not need closely spaced base stations.

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