In the boat anchor radio community there is a particular kind of legend — not the collector who amasses the most gear, nor the restorer who achieves the finest cosmetic finish, but the thinker who studies a classic receiver at the circuit level and then quietly publishes a modification so elegant and so effective that it becomes the standard by which all subsequent work is measured. Dr. Dallas S. Lankford IV was exactly that kind of legend.

Over a career spanning roughly four decades, Lankford produced a staggering body of technical writing covering receiver modifications for Collins, Hammarlund, Racal, JRC (Japan Radio Company), Icom, Telefunken, and Watkins-Johnson equipment, as well as an entire parallel library of innovative receiving antenna designs, preamplifier circuits, antenna phaser networks, and audio processing techniques. His articles were published in the Hollow State Newsletter (HSN), shared across the R-390 mailing list at QTH.net, and eventually archived by his friend and fellow DXer Bjarne Mjelde of Kongsfjord, Norway — ensuring that this body of work survived his passing in 2020.

The Mathematician at the Workbench

Dallas Lankford was, by professional training, a mathematician. His academic publications include research on decision algorithms for finitely presented Abelian groups — work squarely in the domain of abstract algebra and computational mathematics. He held a doctorate and was frequently addressed as “Dr. Lankford” in the amateur radio press. But it was at the workbench, not the blackboard, where Lankford made his most lasting impact.

Based in Ruston, Louisiana, Lankford was an avid medium-wave (MW) and shortwave DXer who demanded the absolute best performance from every receiver that passed through his hands. When a receiver fell short of what its design should have allowed, Lankford did not simply accept the limitation — he analyzed the circuit, identified the deficiency, and designed a modification to correct it. He then documented the modification in exacting detail, complete with component values, voltage readings, and before-and-after performance measurements, and published the results for the benefit of the community.

This combination of academic rigor and hands-on practical skill is what set Lankford apart. His writing style was technical and demanding — readers needed to bring their schematics and their thinking caps — but those who followed his instructions were consistently rewarded with genuine, measurable improvements in receiver performance.

The Collins R-390A: Lankford’s Masterwork

If one receiver defined Lankford’s legacy, it was the Collins R-390A/URR — the legendary 26-tube military HF receiver that is arguably the finest tube-era communications receiver ever built. Lankford regarded the R-390A as a remarkable engineering achievement, but he also recognized that the receiver was designed in the early 1950s primarily for AM and CW reception. As the amateur and military world transitioned to single-sideband (SSB) operation, the R-390A’s AGC system proved poorly suited to the task. Lankford set out to fix that.

The 2-Diode SSB AGC Modification

Lankford’s most famous contribution is the 2-diode SSB AGC modification, first published in Hollow State Newsletter issue #1 and refined through HSN issues #10, #23, #27, and #36. The modification adds two small-signal diodes (originally 1N270 germanium, later 1N4148 or 1N914 silicon) in parallel with resistors in the AGC circuit of the IF deck. No parts are removed, no holes are drilled, and the modification is completely reversible.

The effect is transformative. With the Lankford AGC mod installed, the R-390A’s automatic gain control actually functions properly on SSB signals. Operators can listen to SSB nets at full RF gain without riding the gain control — something that was essentially impossible with the stock AGC design. Lankford also recommended increasing BFO injection by paralleling a 47 pF capacitor across the existing 12 pF C535 injection capacitor, which prevents audio distortion in the detector during SSB reception.

The modification became so widely adopted that references to “the Lankford mod” on the R-390 mailing list require no further explanation. The R-390A FAQ at r-390a.net documents it extensively, and the 21st Century R-390A/URR Reference (Y2K-R3 manual) cites Lankford’s work in its discussion of AGC behavior and IF deck modifications.

Beyond AGC: A Complete R-390A Technical Program

The AGC mod was only the beginning. Lankford’s published R-390A work, archived at kongsfjord.no, encompasses an extraordinary range of topics. He developed a full-wave bridge AM detector inspired by the Telefunken E 1501’s envelope detector design, which improved AM audio quality to near-synchronous-detector levels without requiring complex external hardware. He published detailed alignment procedures rewritten from his own bench experience (HSN #29), analyzed Cosmos PTO linearization techniques, documented carrier meter modifications and worn gain control replacements, investigated 3TF7 ballast tube substitutes, and explored BFO fine tuning methods.

Each of these publications followed the same disciplined approach: a clear statement of the problem, a circuit-level analysis of the cause, a practical modification with specific component values, and measured results demonstrating the improvement. This was engineering in the truest sense, applied to receivers that their original manufacturers had long since abandoned.

Receivers Modified by Lankford

Beyond the R-390A, Lankford brought the same analytical depth to every receiver that crossed his bench, approaching each with a combination of engineering rigor, historical curiosity, and candid opinion that defined his writing style.

Antenna Innovation: Low-Noise Receiving Arrays

Alongside his receiver modification work, Lankford made equally significant contributions to receiving antenna design. His research focused on a central problem that plagues every serious DXer: how to maximize signal-to-man-made-noise ratio in environments where powerline noise, switching power supplies, plasma televisions, and other modern interference sources make weak-signal reception increasingly difficult.

Lankford’s antenna designs — including the Low Noise Vertical (LNV), phased flag arrays, phased delta flag arrays, MiniFlag and MiniLoop antennas, capacitor-terminated loop arrays, and dual staggered offset Beverage arrays — demonstrated that compact, carefully designed receiving arrays could match or exceed the performance of traditional long Beverage antennas while occupying a fraction of the space. His phaser designs allowed operators to steer deep nulls onto interference sources while preserving signals from desired directions.

His amplifier designs were equally important. Lankford developed Norton-type transformer feedback preamplifiers and push-pull line (PPL) amplifiers specifically optimized for use with his antenna arrays. These circuits achieved the high intercept points and low noise figures necessary to exploit the full potential of the antenna systems. Jack Smith later produced commercial kit versions of Lankford’s Norton amplifier and PPL “supercharger” designs, making them accessible to a wider audience.

The Hollow State Newsletter Connection

Much of Lankford’s early and most influential work was published in the Hollow State Newsletter (HSN), a small-circulation paper newsletter edited and published by Ralph Sanserino that served the boatanchor community for approximately 50 issues. As Perry (KM6FQV) noted on the R-390 mailing list, the HSN contains “a wealth of information by Dallas Lankford (SK) that goes far in depth about good mods.”

Lankford’s HSN contributions span an impressive range of issue numbers. The following table summarizes his known appearances, though additional contributions likely exist across the full run of the newsletter.

The full run of HSN issues is archived at vk6ada.com.au/hollow-state-newsletter, ensuring that Lankford’s foundational articles remain accessible to new generations of R-390A enthusiasts.

Audio Processing & the DXer’s Toolkit

Lankford’s technical interests extended well beyond receiver hardware and antennas. He published significant work on AM synchronous detector implementation and experience, developed elliptic low-pass audio filter designs optimized for communications audio, and produced a detailed analysis of the causes and cures of audio distortion in received AM signals due to fading — a phenomenon that affects every AM listener but which few had analyzed with Lankford’s level of rigor.

He also documented his experiences with early software-defined receivers (SDRs), providing the same objective, measurement-based analysis that characterized all his work. And his DX-pedition reports demonstrated that he was not merely a bench engineer but an active, accomplished DXer who put his own designs to the ultimate test: hearing signals that others could not.

Legacy & Preservation

Dallas Lankford died of natural causes on June 29, 2020, at his home in Ruston, Louisiana. He was 78 years old. The boat anchor and DX communities lost not only a prolific technical contributor but a generous correspondent who was known for exchanging detailed, handwritten letters with fellow experimenters — a style of technical communication that belongs to an earlier and perhaps more thoughtful era.

His work survives through several important archives. Bjarne Mjelde’s kongsfjord.no archive preserves the largest organized collection of Lankford’s articles, sorted by category: antennas and preamplifiers, antenna phasers, audio processing, and receiver-specific modifications for Collins, Hammarlund, Icom, JRC, Racal, Telefunken, and Watkins-Johnson equipment. The R-390A FAQ at r-390a.net preserves his R-390A contributions within the context of the broader R-390 knowledge base. The Hollow State Newsletter Archive at VK6ADA ensures that his foundational HSN articles remain available. And DXer.ca has captured additional collections of his files for the MW DX community.