W8KHK Adds First-Hand Context to W2DU’s Laboratory History
W8KHK Adds First-Hand Context to W2DU’s Laboratory History
Rick Maxwell describes how his father Walt Maxwell, W2DU, developed a progressively more capable RF laboratory while investigating reflections and conjugate matching.
Richard A. “Rick” Maxwell, W8KHK, is the second son of M. Walter Maxwell, W2DU. His account supplies family and laboratory detail that is difficult to recover from published technical papers alone.
Rick explained that W8KHK had been his father’s original callsign in 1933, when Walt was 14. He later adopted that callsign himself. His recollection follows Walt’s laboratory from relatively simple bridges and couplers to instruments capable of measuring both magnitude and phase.
Historical-evidence boundary: this page presents Rick Maxwell’s attributed first-hand account. Instrument identities, dates and family details remain recollections unless an independent citation is linked. The measurement discussion below explains what the named instruments can establish under controlled calibration conditions.
Rick Maxwell’s Account
Hello Joeri,
I am his second son, Richard A. Maxwell, now W8KHK—which was Dad’s original callsign in 1933, when he was 14 years old.
His laboratory resources were upgraded over the long period that followed the start of this work in the mid-1960s.
Early on, he used rudimentary directional couplers and bridges. For better accuracy, he soon used the General Radio 1604 bridge; HP 606, 608 and 612 generators; a slotted line; the PRD 219; and an HP 415 meter.
When they became more affordable, during retirement soon after 1980, he acquired an HP 8640A generator, an HP 8405A vector voltmeter and its associated directional couplers, along with an HP 4815A vector impedance meter. He also acquired a Tektronix spectrum analyser with a tracking generator.
Although HP vector network analysers were in use at the RCA Astro Electronics Division, he had no access to those resources after retirement. The many sequential measurements made with the vector voltmeter and vector impedance meter took considerably more time and effort.
Many calculations assume lossless networks. These are theoretical and do not exist in practice. The intended guidance to amateurs, concerning practical coupling and matching techniques for this class of communications, retains lasting value for most readers.
Warm regards,
Rick Maxwell, W8KHK
ex-WB4GNR, WB2HKX, AFC2HKX
Editorial note: Rick Maxwell gave explicit permission to publish his message and to remove repetition and make minor editorial corrections. The selected passages above retain his technical meaning while focusing this page on the laboratory history.
What the Named Instruments Could Measure
An HP 8405A vector voltmeter with suitable directional couplers can compare RF voltage magnitude and phase. An HP 4815A vector impedance meter can measure complex impedance. Sequential readings from instruments of this kind can be used to reconstruct impedance and reflection relationships when calibration, loading and reference planes are controlled.
That does not make every sequence automatically equivalent to a calibrated vector-network-analyser result. Directivity, source match, tracking, connector repeatability, fixture behaviour and error correction determine the uncertainty. A similar Smith-chart trace can be assembled from sequential data, but equivalence belongs to a declared measurement method and uncertainty budget—not to the instrument names alone.
Agreement between calculation and observation supports a model for the tested linear source, network and load. It does not by itself establish the same behaviour for every transmitter topology, source impedance or nonlinear operating state.
Linear Matching and Later Transmitter Topologies
W2DU’s practical matching work developed in an era dominated by vacuum-tube finals with tuned output networks, followed by increasingly common solid-state finals with broadband networks. Switching-amplifier theory was already developing during that period: Nathan and Alan Sokal published their Class-E paper in 1975. Amateur adoption of Class-D, Class-E and software-defined transmitter architectures became more visible later.
The source model still matters. Conjugate-match and available-power relationships are precise for the stated linear network assumptions. A practical transmitter may include protection, output filtering, control loops, compression or switching behaviour that changes the relationship between terminal impedance and delivered RF power.
Why First-Hand Laboratory History Matters
Published diagrams and articles rarely capture every instrument, fixture and working habit used over decades. Rick’s account adds the sequence: early bridges and generators, later vector instruments, and the continuing role of careful sequential measurement after Walt’s retirement.
It also preserves an important engineering distinction. Better equipment can narrow uncertainty and expose more detail, but a measurement remains meaningful only when its reference plane, calibration, loading and assumptions are stated. That principle connects W2DU’s laboratory practice to modern RF work.
Mini-FAQ
- Who is W8KHK? Richard A. “Rick” Maxwell is the second son of M. Walter Maxwell, W2DU, and now holds his father’s original callsign.
- Is this an independent inventory of W2DU’s laboratory? No. It is an attributed first-hand family account, with independent sources linked where available.
- Can a vector voltmeter replace a VNA? Sequential magnitude-and-phase measurements can reconstruct comparable quantities, but equivalence requires controlled calibration, reference planes and an uncertainty budget.
- Do measurements prove the conjugate-match theorem universally? Measurements can support predictions for the tested source, network and load. They do not prove every transmitter and load condition.
- Why mention Class-E history? It separates the publication of switching-amplifier theory from its later widespread adoption in amateur equipment.