US 4642639

Summary — US Patent 4,642,639

Pat. No.: US 4,642,639 (US4642639A) — "Multichannel DME ranging system"
Application: US 06/537,879, filed September 30, 1983
Issued: February 10, 1987
Inventor: David A. Nelson (Cedar Rapids, IA)
Original assignee: Rockwell International Corporation (El Segundo, CA); assignment recorded November 28, 1983
Current assignee of record (per Google Patents listing): Boeing North American Inc.
Legal status: Expired – Lifetime; anticipated expiration February 10, 2004. No reissue, reexamination, or litigation activity for this number appeared in my searches.

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Abstract (as published)

A multichannel DME ranging circuit capable of simultaneous multi-station operation. A microprocessor controls associated peripherals and the DME receiver/transmitter to multiplex frequency data input from up to three DME ground stations. Data from each station generates timing and interface signals controlling the DME receiver/transmitter and video processing circuitry. The video processor in turn supplies signals letting the ranging circuit independently determine range, velocity, time-to-station, and station identity for each of the up to three channels. Each channel operates independently to decode its own ground station identity, and identity information can be obtained and monitored for each channel essentially simultaneously because of the fast cyclical time-multiplexed operation relative to the slower identity coding scheme used in existing DME.

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Plain-language overview of the claims

According to the claim text as published (Justia listing), the patent has seven claims, with claim 1 as the sole independent claim:

• Claim 1 (independent): Apparatus that identifies at least three DME ground stations "substantially simultaneously" and decodes range from each in a "rapid cyclical sequence." Two elements: (a) a detector that picks up first, second, and third pulsed signals from the stations in sequence/cyclically, where those signals carry (i) station-specific coded identification having a long timing characteristic and (ii) distance information having a substantially shorter timing characteristic; and (b) a controller coupled to that detector that cycles it at approximately an order of magnitude faster than the identification timing characteristic, while keeping each cycle long enough to get at least one valid distance reading (on the order of the short timing characteristic) from each station each cycle.

• Claims 2–7 (dependent on claim 1): Each adds a specific implementation detail —

  • 2: the detector includes a programmable variable-frequency receiver.
  • 3: the controller includes a programmable stabilized master oscillator (SMO).
  • 4: the controller provides individual automatic gain control for each station.
  • 5: the controller samples, stores, and later asserts a signal-presence indication for each station, one after another.
  • 6: decoder means for the station identifying information, operating substantially simultaneously and in coordinated fashion, independently for each station.
  • 7: calculator means for the distance information, in a coordinated periodic manner, independently for each station.

In plain terms: the core inventive concept claimed is a time-multiplexing rate relationship — switching one DME through three mutually independent channels fast enough that the (slow) Morse-code station identity signals can be tracked on all three stations at once, while still capturing each station's (fast) range replies at least once per cycle.

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Context worth noting from the specification

• The patent contrasts itself with U.S. Pat. No. RE 30,069 (Wayne Miller, Aug. 7, 1979), which time-multiplexes a DME between only two channels and, per the patent, does not provide independent velocity and identity information for both stations.
• It cites a commonly-owned sibling application "DME Morse Code Identity Decoder," Ser. No. 537,880, filed the same day. My searches returned a document at US 4,651,158 whose specification text closely mirrors this patent's description, which is consistent with that sibling application — but I flag this as an inference from search results, not something I can confirm authoritatively from the patent text alone.
• Key implementation details: 84 Hz frequency alternation yielding 28 Hz sampling per channel; ~4 ms SMO slew delay; ~6 ms listen window; a 16-bit 6 MHz range counter; a Type II digital servo loop with four selectable time constants (5–45 s); four per-channel operating modes (no squitter, search, pretrack, track); identity detection by testing reply intervals against 740/1480 µs (1/1350 Hz and 2/1350 Hz).
• The specification states the method supports at least three stations with two valid range decodes within 100 ms and range coverage to at least 300 nautical miles.
• Claims list prior art including RE 30,069 (Miller), US 3,801,979 and US 3,821,523 (Chisholm), US 3,975,731 (Latham et al.), and US 4,032,756.

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Uncertainty / caveats

1. CAFC 2026 dockets: I ran targeted searches for this specific number in appellate/litigation contexts and found no CAFC 2026 docket entries for US 4,642,639. That is a negative search result, not proof of absence — I do not have a live, authoritative CAFC docket feed for this case and cannot certify that no 2026 appeal exists.
2. Claim set completeness: The claim text cited above comes from a Justia reproduction; the full patent text as fetched did not include the claims section, so if additional claims exist beyond published claims 1–7 I would be unaware of them. Claim 1 appears to be the only independent claim.
3. Assignee: Google Patents lists the current assignee as "Boeing North American Inc" with an explicit disclaimer that the listing may be inaccurate; the original assignee of record is Rockwell International Corporation. I did not independently verify the chain of title.
4. I found no evidence of any reissue, reexamination, or litigation involving this patent number.

I'll research litigation involving US patent 4642639. Let me run several targeted searches.

Initial results don't show relevant litigation. Let me search more targeted sources.

Litigation Search Results: US Patent No. 4,642,639

Conclusion: No litigation involving U.S. Patent No. 4,642,639 was found.

Searches performed

I ran web searches targeting (a) the patent number itself in both forms ("4642639" and "4,642,639"), (b) the patent number combined with litigation/ infringement terms, (c) the patent number with "Unified Patents," and (d) the patent title ("Multichannel DME ranging system") with court-case terms. I was not able to query the Unified Patents litigation portal, PACER, or the CAFC docket directly in this session; results reflect open‑web searching only.

What the searches returned

Every hit was a false positive — none involved the '639 patent:

No district-court complaint, ITC § 337 investigation, PTAB/IPR, or CAFC appeal naming US 4,642,639 surfaced.

Patent and ownership context (from the authoritative patent record)

• Patent: US 4,642,639 A, "Multichannel DME ranging system"
• Inventor: David A. Nelson
• Original assignee: Rockwell International Corp. (assigned Nov. 28, 1983)
• Current/last assignee of record: Boeing North American Inc.
• Filing / priority date: Sept. 30, 1983; Issued: Feb. 10, 1987
• Legal status: Expired – Lifetime (anticipated expiration Feb. 10, 2004)
• Related application cited on its face: Ser. No. 537,880, "DME Morse Code Identity Decoder," filed the same day (Sept. 30, 1983)

Why no litigation is plausible

The patent's 20‑year term and its 2004 expiration mean any infringement action would have had to be filed by roughly early 2004 at the latest (subject to the six‑year § 286 damages look‑back). A 1987 avionics/DME patent assigned to Rockwell and later Boeing was never a likely candidate for the post‑2010 patent‑assertion campaigns that populate most litigation databases, and the patent record shows no reissue, reexamination, or assignment to a non‑practicing entity.

Caveats

• I could not confirm negative results against Unified Patents' litigation caselist, PACER, or the CAFC docket directly; my finding is based on open‑web search only. A definitive negative would require a keyword query of those specific databases.
• The related '639‑family patent from Ser. No. 537,880 (DME Morse Code Identity Decoder) could be litigated under its own number; I did not search for that separately.

Bottom line: Based on the sources available, there is no known litigation involving US 4,642,639. I cannot state this with absolute certainty for pre‑digital-era cases that may exist only in paper dockets, so a direct PACER/Docket Navigator or Westlaw KeyCite search on "4,642,639" would be the proper confirmation step if a privileged opinion is required.

I'll verify the structured data against live sources before drawing conclusions.

Let me run a few more targeted checks to make sure I'm not missing anything indexed under a different naming convention.

PTAB / AIA Trial Analysis — US 4,642,639

Patent: US 4,642,639 — "Multichannel DME ranging system"
Inventor: David A. Nelson · Original assignee: Rockwell International Corp. (current listed: Boeing North American Inc.)
Filed: 1983-09-30 · Granted: 1987-02-10 · Expired: 2004-02-10 (17-year term, pre-URAA)
Claims: 1 (independent) and 2–7 (dependent)
Source of record: patents.google.com/patent/US4642639/en

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Proceedings overview

Total AIA trial proceedings on file: 0. Breakdown: 0 active, 0 claims invalidated, 0 claims sustained, 0 settled, 0 institution denials — the USPTO Open Data Portal returns no IPR, PGR, or CBM proceeding naming US 4,642,639, and my independent searches surfaced no unindexed petition either. The defensive posture this gives a defendant is therefore not "the patent has been hardened by surviving IPRs" — it is the much stronger one: the patent expired on 2004-02-10, so an IPR was never economically rational, and no PTAB challenge exists to analyze. Any demand letter citing this patent today is asserting an expired patent whose damages window closed roughly two decades ago. The absence of PTAB activity is a rational non-event, not a signal of patent strength or weakness.

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Proceedings

None on file

No AIA trial proceeding has ever been instituted against US 4,642,639. Because the proceeding list is empty, every per-proceeding field in the requested template (petition grounds, institution decision, FWD, panel, settlement, appeal) is inapplicable. I am explicitly not filling those fields rather than speculating.

Two structural reasons this is expected, stated for the record:

1. Statutory ineligibility of two of the three AIA vehicles. CBM review was limited to patents claiming a "financial product or service" — a secondary-radar/DME navigation patent does not qualify. PGR reaches only patents with an effective filing date on or after 2013-03-16; this patent's effective filing date is 1983-09-30. Only IPR (35 U.S.C. § 311) was ever theoretically available.
2. No live infringement exposure. The patent expired 2004-02-10. Post-expiration activity cannot infringe, and 35 U.S.C. § 286 caps recovery at six years before the complaint — so unless a suit was filed by roughly 2010, there is nothing left to litigate. No rational petitioner spends IPR fees to invalidate a patent with no recoverable damages.

False-positive warning on the identifiers (important). Web searches for "639 patent" against PTAB materials return a large volume of hits that are different patents, and none of them is this one. These include, among others:

• IPR2020-00272, a denial where the Board refused institution for failure to identify corresponding structure for means-plus-function terms under 37 C.F.R. § 42.104(b)(3) — that proceeding is captioned to US 8,023,639 B2, not 4,642,639 (Banner & Witcoff copy of the decision).
• IPR2014-00887 (Gelead v. Teva), concerning US 5,977,089; the "639 patent" discussed there is an Emory racemic β-FTC patent (docketalarm exhibit).
• An IPR (petition nos. 1475835 / 1557132 in PTACTS) concerning a spot-welding cap magazine '639 patent, and another concerning US 6,935,548.
• Judge panels, institution dates, and claim outcomes from any of the above must not be attributed to US 4,642,639.

What is on the public record for this patent (useful context, but not PTAB activity):

• It is still cited as prior art by later applicants — e.g., Chinese patent CN108512587B, a DME ground-station coverage-verification system, lists "US 4642639 A, 1987.02.10" as a cited reference in its search report. Technical relevance persists; litigation relevance does not.
• It is discussed in avionics circles as the architecture behind the Collins DME-42 (early 1980s): "time-multiplexing of up to three DME interrogations and signal processing on a single RF transceiver" (euroga.org forum thread). Product documentation, not a proceeding.
• The patent's own "Cross-Reference" section points to a commonly-owned sibling application, "DME Morse Code Identity Decoder," Ser. No. 537,880, filed the same day. That is a different, separately-prosecuted application and forms no part of this patent's PTAB history.

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Strategic summary

Claim status of 4,642,639. Claims 1–7 all stand untested, unadjudicated, and un-cancelled — but that is a statement about PTAB history only. Claim 1 (independent) recites an apparatus for "identifying at least three distance-measuring equipment ground stations substantially simultaneously" with a cyclical operating frequency "approximately an order of magnitude faster than" the stations' identity timing characteristic; claims 2–7 add a programmable variable-frequency receiver, a programmable stabilized master oscillator, per-station AGC, signal-presence sampling, and independent identity decoding/distance calculation. None of these claims has been cancelled, narrowed by certificate, or construed by the PTAB or the Federal Circuit. The only binding constraint on the claims is not a validity ruling at all — it is the 2004-02-10 expiration date, which is dispositive and far more useful to a defendant than any IPR outcome.

(a) Estoppel landscape: there is none. Section 315(e)(2) estoppel arises only from a petitioner's IPR that reaches a final written decision. With zero proceedings, no party is estopped from anything, and there is likewise no § 315(b) one-year-time-bar trap and no § 325(d) "same or substantially the same art" issue. Conversely, no prior art has been "cleared" by a PTAB win for the patent owner. Practically, this is a non-issue: a defendant facing this patent needs an expiration defense, not a prior-art defense.

(b) Pattern signals: unremarkable, because the case is over. No petitioner has filed even one IPR, let alone a serial campaign. The patent owner (Rockwell, now via Boeing North American) has never appealed anything to the Federal Circuit on this patent — and note that Rockwell's appellate activity in this era (e.g., the MOCVD cases, Rockwell v. United States, 147 F.3d 1367) concerns unrelated patents. No defensive aggregator (Unified Patents, RPX, AST, Open Invention Network) appears anywhere in the chain; the "Unified Patents portal" hits returned by search concern unrelated wireless-sensor publications, not this patent. A patent that expired before the AIA's IPR regime matured was never a candidate for crowd-sourced invalidation.

(c) The real defensive picture. The patent is expired, unasserted in any indexed PTAB or appellate record, and more than two decades past its enforceable life. The residual theoretical avenues — ex parte reexamination under 35 U.S.C. § 302 (no time bar, no estoppel, requestable anonymously) — are pointless here, since there is no live claim to invalidate and no damages to defeat.

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Recommended next steps

If you are a defendant receiving a demand letter citing US 4,642,639:

1. Lead with expiration, not validity. Cite the Google Patents record showing legal status "Expired – Lifetime," anticipated expiration 2004-02-10 (patents.google.com/patent/US4642639/en). Post-expiration acts cannot infringe; § 286's six-year lookback forecloses recovery for anything after roughly 2010 absent an already-filed complaint. This resolves the matter without touching prior art.
2. Ask for the lawsuit, not the claim chart. If the sender asserts this patent, request the civil action number and filing date. An expired patent asserted in a fresh complaint is a Rule 11 / § 285 exposure for the sender; the letter should be treated as a document to preserve rather than a claim to answer.
3. Do not commission an IPR. Filing an IPR against an expired patent buys a final written decision that cannot be deployed against any live claim, and § 315(e)(2) estoppel would attach to grounds you would rather keep in reserve. There is no pending statutory deadline forcing action — no institution decision date, no oral hearing, no one-year FWD clock is running, because there is no proceeding.
4. If you need a validity opinion for a contract or warranty representation, direct it to comparable live DME or secondary-radar patents in your portfolio or adversary's, not to this one.

Bottom line: the "no PTAB activity on file" result from the ODP is confirmed and correct, and for this patent it is the least important fact about it. The dispositive fact is a 2004-02-10 expiration date. There is no FWD to link, no Federal Circuit docket to check, and no claim-level disposition to report — state that plainly rather than manufacturing an analysis.

I'll research the assignment record for US 4642639 before building the analysis.

Let me dig into the specific assignment records and the sibling patent.

I found strong product-embodiment evidence. Now let me hunt for the actual recorded assignment data.

Ownership & Assignment Reconstruction — US 4,642,639

"Multichannel DME ranging system" · Appl. No. 06/537,879 · filed 1983-09-30 · issued 1987-02-10 · Appl. No. 06/537,879 · status Expired – Lifetime (anticipated expiration 2004-02-10)

Data-access caveat (read first). My tool access for the live USPTO Assignment Center (assignmentcenter.uspto.gov / assignment.uspto.gov) was exhausted before I could run the patent-number query, so I could not retrieve reel/frame numbers, correspondents, or execution dates directly. Everything below is grounded in the Google Patents record and the documents I could reach, and I have flagged each gap explicitly rather than filling it in. No reel/frame numbers are stated anywhere in this report because I did not verify any.

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Inventors

• The issued face of the patent and the sibling case both give Nelson's residence as Cedar Rapids, Iowa. A 1989 Rockwell sales-office listing confirms Cedar Rapids was the home of Rockwell's Collins avionics divisions (Collins General & Air Transport Aviation Division; Collins Government Avionics Division), so the "employer at filing" call is solid, not inferred from the assignee name alone.
• Unusual-pattern check — nothing flagged. This is a single-inventor case with a garden-variety employee assignment: application filed 1983-09-30, inventor-to-corporation assignment recorded 1983-11-28 — i.e. ~2 months after filing, which is the normal pre-issue employee-assignment cadence. There is no evidence of inventor departure, and a lone inventor cannot exhibit the "all inventors left within 12 months" fire-sale precursor pattern.
• Family context: Nelson is also the sole inventor on the commonly-owned sibling US 4,651,158, "DME Morse Code Identity Decoder," Ser. No. 537,880, filed the same day (1983-09-30) and issued 1987-03-17 — cited in the '639 specification under CROSS-REFERENCE. Both cases claim the same Rockwell DME-42 work.

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Original assignee

Rockwell International Corporation, El Segundo, California — named on the issued patent and the recorded assignee of the inventor's interest. (Note: Google Patents' auto-generated "Current Assignee" field additionally lists Boeing North American Inc; see the caveat below — that entity is not named on the patent and no assignment recording to it appears in the legal-events record.)

• Did they ship a product embodying the claims? — Yes, and the evidence is unusually direct. The cross-referenced sibling patent US 4,651,158 contains Appendix A, captioned "DME-42 SERIAL DATA FORMATS," describing the Collins Pro Line II data bus, the ARINC 568 six-wire output, the three-channel source identifiers (DME 1 / DME 2 / DME 3), the search/pretrack/track status bits, the Morse-identifier ASCII output block, and the self-test that plays identifier "AOK." That appendix is the software spec for the Rockwell Collins DME-42, a 3-channel DME — i.e. a commercial product shipping the very architecture claimed in '639 claim 1 ("at least three distance-measuring equipment ground stations substantially simultaneously") and claims 2–7 (programmable variable-frequency receiver, programmable SMO, per-station AGC, signal-presence sampling, simultaneous identity decode, independent per-station range calculation).
• Rockwell Collins' own production discontinuance bulletins confirm the product: the DME-42/442 are "3-channel (max) unit[s]" that compute slant range, closure rate and time-to-station and "provide a decoded station identifier"; the successor DME-4000 is described as "tracking three DME stations at once" with "the Collins exclusive echo monitor circuit" — the echo-monitor function being exactly the logic at FIG. 8a, blocks 830–866 of '639.
• Primary line of business: aerospace/defense, avionics, automotive and industrial automation. Rockwell's 1989 revenue was ~$12.5B, with avionics reported at ~40% share of its addressed market.
• Current status: Rockwell International no longer exists under that name. Its aerospace and defense businesses were sold to Boeing in 1996 and consolidated as Boeing North American, Inc. (defense/aerospace lines: Autonetics, Rocketdyne, North American Aircraft, Space Systems). Its avionics/Collins business was spun off as Rockwell Collins, Inc. in 2001 (later United Technologies, then Collins Aerospace / RTX), with the residue renamed Rockwell Automation, Inc. No bankruptcy. The DME-42/442 product line was serviced and ultimately discontinued by Rockwell Collins in 2019 — which is evidence the product line traveled with the avionics spinoff, not with the 1996 Boeing defense sale, and casts doubt on the "Boeing North American" current-assignee field.

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Assignment timeline

The record I could reach contains exactly one recorded assignment. I could not reach the Assignment Center to confirm whether additional records exist.

• executed date not exposed / recorded 1983-11-28 — Reel not exposed in the sources reached
  • Conveyance: Assignment of assignors' interest (per Google Patents legal events: "ASSIGNED TO ROCKWELL INTERNATIONAL CORPORATION — ASSIGNMENT OF ASSIGNORS INTEREST")
  • Assignor: NELSON, DAVID A. (sole inventor)
  • Assignee: Rockwell International Corporation
  • Correspondent: not exposed in any source I could reach. Consequence: signal #3 (repeat correspondent) cannot be tested at all, because only one link exists and its correspondent field is unretrieved.
  • Context: Ordinary employee/inventor-to-corporate-employer assignment accompanying filing — not an acquisition, fire-sale, securitization or transfer-to-asserter.

No post-issuance assignment appears anywhere in the record I could reach. The Google Patents legal-events list for US 4,642,639 runs: 1983-09-30 filed by Rockwell · 1983-09-30 priority to 06/537,879 · 1983-11-28 assigned to Rockwell · 1987-02-10 granted · 1987-02-10 published · 2004-02-10 anticipated expiration · Expired – Lifetime. The "Boeing North American Inc" entry in the Info panel is a separate auto-generated field that Google itself annotates: "The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed." It is not supported by any assignment event in the legal-events table, so I decline to treat it as a recorded link. Treat the post-1983 chain as unverified rather than as empty.

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Timeline diagram

timeline
    title Ownership of US 4642639
    1983 : Filed 30 Sep by David A Nelson
         : Inventor assignment recorded to Rockwell
    1987 : Patent issued 10 Feb
    1996 : Rockwell defense units sold to Boeing
    2001 : Rockwell Collins avionics spun off
    2004 : Patent term expired 10 Feb

(1996 and 2001 are corporate-history context lines with no corresponding recorded assignment; 2004 is the de jure end of the patent right.)

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NPE / troll-pattern signals

1. Shell-entity transfer — not present. No assignment to any "IP / Holdings / Licensing / Ventures" entity appears in the record. The only recorded transferee is an operating aerospace manufacturer.
2. Known asserter in the chain — not present. The only assignee of record is Rockwell International Corporation. The auto-generated "Boeing North American Inc" field is a defense prime contractor, not any entity on the Acacia / Marathon / IV / Wi-LAN / Conversant / Vringo / Pendrell / Round Rock / Innovatio / MPHJ / Lumen View / Spangenberg lists. No Ryan, no "reel 012345/0001"-style Marathon link exists here.
3. Repeat correspondent across the chain — unclear / untestable. With one assignment in the chain and the correspondent field unretrieved, recurrence cannot be assessed. This is a data gap, not a negative finding.
4. Cascading transfers — not present. One link over a 43-year life. No chained LLCs, no sub-24-month relay.
5. Pre-litigation transfer — not present. I found no infringement litigation naming US 4,642,639 in any source reached, and the assignment predates issuance by 3+ years. The patent expired 2004-02-10, so no suit can now be filed on it.
6. Bankruptcy fire-sale — not present. Rockwell's end came via planned sales and tax-free spinoffs (1996 Boeing sale; 2001 Rockwell Collins spinoff; remainder → Rockwell Automation), not a Chapter 7/11 estate sale. There is no Kodak/Nortel/Polaroid-style auction in this chain.
7. Privateering — not present. No operating-company-to-NPE transfer and no NPE assertion campaign on Rockwell's behalf was surfaced.
8. Defensive aggregator — not present. The chain does not terminate at RPX, AST, LOT Network, Unified Patents or OIN. (The patent is nonetheless de facto neutralized by expiry, which is a different thing.)

Signals found: 0. One signal is genuinely untestable (#3) because of the Assignment Center access limitation.

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Verdict

Insufficient data — only the original assignment is of record.

Justification: The only recorded conveyance I could reach is the 1983-11-28 inventor-to-Rockwell International Corporation assignment (Google Patents legal events, US 4,642,639), executed two months after the 1983-09-30 filing; there is no post-issuance assignment, no NPE assignee, no litigation, and no correspondent data, which leaves the mandated shell/repeat-correspondent tests unevaluable. Substantively there is zero NPE evidence — the patent was worked into a shipping product (Rockwell Collins DME-42, per Appendix A of US 4,651,158 and Rockwell Collins' own discontinuance bulletins) and expired for term on 2004-02-10, so it is not assertable today; but because the post-1983 ownership chain (Rockwell → Rockwell Collins vs. Boeing North American) is unverified, "insufficient data" is the only verdict the record honestly supports rather than a clean operating-company call.

Verify at: https://assignmentcenter.uspto.gov/ (or https://assignment.uspto.gov/patent/index.html) — query 4642639 as the patent number, then capture reel/frame, correspondent, and execution date for every hit. Patent record: https://patents.google.com/patent/US4642639/en · Sibling patent with the DME-42 appendix: https://patentimages.storage.googleapis.com/40/df/56/e447215277182f/US4651158.pdf

Open items I could not close: (a) reel/frame for the 1983-11-28 assignment; (b) identity and firm of the recording correspondent; (c) whether any Rockwell→Boeing North American or Rockwell→Rockwell Collins assignment covers this patent; (d) any litigation docket (I searched general web sources only, not PACER/Docket Navigator).

I'll research the prior art cited on the face of US 4,642,639. Let me run several targeted searches.

I have the "Referenced Cited" list. Let me research each reference in detail.

Scope and method note (read first)

I ran open‑web searches this session. Two calls returned usable data before I hit the tool step limit, so I could not independently verify every bibliographic field of every cited reference. Specifically:

• The list of references cited on the face of US 4,642,639 was obtained from the Justia reproduction of the patent (https://patents.justia.com/patent/4642639, "Referenced Cited" block), and cross‑checked against the Google Patents record (https://patents.google.com/patent/US4642639/en). I did not get a direct read of the USPTO PatentCenter "References Cited" field for this number.
• I verified the title and subject matter of US 3,801,979 (Chisholm) directly from Google Patents.
• I could not verify the titles of US 3,821,523, US 3,975,731, and US 4,032,756, and could not retrieve any content for FR 2,538,560. Where I lack a verified title, I say so rather than guess. This is a real gap, not a formatting choice.

Per the operating rules I have not auto‑corrected any number or date. All identifiers below are reproduced literally as found.

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1. References cited on the face of US 4,642,639

Note the prosecution also cross‑references the inventor's own concurrently‑filed application, Ser. No. 537,880, "DME Morse Code Identity Decoder," filed Sept. 30, 1983 (the '639 spec's CROSS‑REFERENCE paragraph). That is a related application, not a cited prior‑art reference.

Prior‑art date framework. US 4,642,639 has a filing/priority date of Sept. 30, 1983. Under pre‑AIA § 102:

• Items 1–5 all published more than one year before Sept. 30, 1983, so each is § 102(b) prior art if it discloses the claimed subject matter. Their own publication dates are self‑authenticating.
• Item 6 (FR 2,538,560, June 1984) postdates the Sept. 30, 1983 filing date by roughly nine months. ⚠️ Flagged contradiction: on its face this document cannot be § 102(a), (b), or (e) prior art against this patent. It may be a mis‑transcribed date in the secondary source, or the reference may have been cited for a non‑§102 purpose. I could not resolve this and I am not asserting a title or content for it. Treat the entry as unresolved rather than as prior art.

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2. Reference‑by‑reference analysis

Reference 1 — RE 30,069 (Miller), Aug. 7, 1979 — the primary reference

• Full citation: U.S. Reissue Patent RE 30,069, inventor Wayne Miller, issued Aug. 7, 1979. (A reissue takes the filing/priority date of the original patent; I did not verify the original patent number in this session and will not assert one.)
• Description (as characterized in the '639 specification, which is my source here): a multiranging DME system that time‑multiplexes a single DME between two channels, accepting multiple frequency inputs from two separate ground stations. Per the '639 patent, its operation is asymmetric — "the known technique primarily uses one channel to obtain distance and velocity information and the other channel to obtain distance information," so "the operation of the channels is not independent and is incapable of providing velocity and identity information for each of the selected ground stations."
• Claims potentially affected: Claim 1 is the only claim at risk, and it is not anticipated. Claim 1 requires identification of "at least three" DME ground stations plus a specific rate relationship (cycling ≈ an order of magnitude faster than the identification timing characteristic, with each cycle long enough for a valid range reading). RE 30,069 discloses two channels, and per the '639 record does not provide per‑channel identity or velocity. Because claims 2–7 all depend from claim 1 and incorporate its limitations, Miller likewise cannot anticipate any dependent claim standing alone.
• Correct role: the closest prior art and the principal § 103 reference. The '639 patent is, in substance, a rebuttal to Miller — it adds the third channel and the independent per‑channel identity/velocity processing. Expect any validity attack to start from Miller plus a secondary reference supplying independent‑channel and identity‑decoding teachings.

Reference 2 — US 3,801,979 (Chisholm), April 1974 — the most technically relevant secondary reference (verified)

• Full citation: U.S. Pat. No. 3,801,979, inventor Chisholm, issued April 1974. Verified title: "Integrated collision avoidance, DME, telemetry, and synchronization system."
• Description (verified from the Google Patents text): a "time‑sharing cyclic time slot system in which DME range measuring functions, collision avoidance functions, clock synchronization functions and/or data telemetry functions are all combined into an integrated repeating time sharing cycle in a non‑interfering manner… by the orderly exchange of pulse signals between participating ground stations and/or aircraft." Cost is minimized "by using already existing ground and/or airborne VORTAC/TACAN/VOR/DME equipment and tuning the airborne transmitters and receivers in an agile manner to the various frequencies assigned for the performance of the above functions." It expressly contemplates a TACAN/VORTAC transmitter and receiver that "can now tune in about 1 millisecond… or in about 20 microseconds," and notes typical units perform "about 10 DME measurements per second."
• Claims potentially affected: Claim 1 is arguably not anticipated — Chisholm's resource sharing is organized around the CAS time‑slot epoch, not around a cycle rate that is "approximately an order of magnitude faster than the identification timing characteristic," and the reference is directed to collision avoidance/telemetry sharing rather than decoding of per‑station Morse identification (the element that defines claims 1 and 6). The reference is, however, directly relevant to dependent claims 2, 3 and 5:
  • Claim 2 (detecting means includes a programmable variable‑frequency receiver) — closely tracked by Chisholm's agile‑tuned airborne receiver.
  • Claim 3 (control means includes a programmable stabilized master oscillator) — closely tracked by Chisholm's agile‑tuned transmitter/receiver frequency selection.
  • Claim 5 (sampling/storing/later asserting a signal‑presence indication sequentially per station) — Chisholm's monitoring of time slots and determination of vacancy/occupancy is analogous.
  • Because claims 2, 3 and 5 depend from claim 1, no single‑reference § 102 rejection of those claims is sustainable on Chisholm alone; the realistic posture is Chisholm as the secondary reference in a § 103 combination with Miller.

Reference 3 — US 3,821,523 (Chisholm et al.), June 1974 — title not verified

• Full citation: U.S. Pat. No. 3,821,523, inventors Chisholm et al., issued June 1974.
• Description: Not verified in this session. Given the common inventor name, issue date three months after US 3,801,979, and the same assignee line of avionics work, this is most plausibly a companion disclosure in the same integrated time‑shared DME/collision‑avoidance family. I am flagging this as an inference, not a finding.
• Claims potentially affected: On the same reasoning as Reference 2, likely relevant to claims 2 and 3 (agile/programmable tuning), and possibly claim 5. Not a plausible standalone § 102 reference against claim 1.

Reference 4 — US 3,975,731 (Latham et al.), Aug. 17, 1976 — title not verified

• Full citation: U.S. Pat. No. 3,975,731, inventors Latham et al., issued Aug. 17, 1976.
• Description: Not verified in this session. Cited on the face of a DME multichannel patent and dated in the mid‑1970s DME development window; I will not characterize its disclosure.
• Claims potentially affected: Cannot be assessed without the reference text. Given its position in the list (between two Chisholm references and the Jezo reference) it was most likely cited as general DME arts background rather than as the primary anticipatory reference. This is an inference only.

Reference 5 — US 4,032,756 (Jezo), June 28, 1977 — title not verified

• Full citation: U.S. Pat. No. 4,032,756, inventor Jezo, issued June 28, 1977.
• Description: Not verified in this session.
• Claims potentially affected: Cannot be assessed without the reference text. The "Jezo" surname with a 1977 DME‑era issue date suggests DME ranging/signal‑processing art, but I have no basis to map it to a specific claim. I decline to speculate.

Reference 6 — FR 2,538,560, June 1984 — date anomaly / not § 102 art

• Full citation: French patent document FR 2,538,560, dated June 1984.
• Description: Not verified. No content retrieved.
• Claims potentially affected: None, on the face of the record. A June 1984 publication date is after the Sept. 30, 1983 U.S. filing date and therefore cannot be prior art against US 4,642,639 under § 102(a), (b), or (e). Either the date as listed is wrong, or this document was cited for some non‑prior‑art reason. This is the single most important data‑integrity flag in this analysis, and I recommend a direct PatentCenter/Global Dossier lookup of FR 2,538,560 before relying on it.

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3. Bottom line on anticipation (§ 102)

No reference cited on the face of US 4,642,639 appears to anticipate any of claims 1–7 under 35 U.S.C. § 102 as a standalone reference.

The reason is structural, not a matter of degree: claim 1 is the only independent claim (claims 2–7 depend from it), and claim 1 requires the concurrence of:

1. reception of pulsed signals from at least three DME ground stations in a rapid cyclical sequence;
2. those signals carrying both station‑identifying code with a first (longer) timing characteristic and distance information with a second, substantially shorter timing characteristic; and
3. a controller cycling the receiver at approximately an order of magnitude faster than the first timing characteristic, with each cycle long enough to obtain at least one valid distance reading per station.

No single cited reference shows all three. RE 30,069 (Miller) supplies the single‑DME time‑multiplexing concept but only for two channels and, per the '639 record, without independent per‑channel velocity and identity processing. US 3,801,979 (Chisholm) supplies agile, programmable multi‑frequency tuning and time‑shared DME operation, but organizes that sharing around a collision‑avoidance time‑slot epoch and does not show per‑station Morse identification decoding at the claimed rate relationship. Since each dependent claim incorporates claim 1, nothing in the cited set anticipates claims 2–7 either.

Practical posture: the cited set is a § 103 obviousness set, not a § 102 set — the expected combination being Miller (RE 30,069) as primary with Chisholm (US 3,801,979 and/or US 3,821,523) as secondary for the agile/programmable tuning and signal‑presence limitations of claims 2, 3 and 5. The novelty that carried the patent is the third independent channel plus per‑channel identity decoding, i.e., the rate relationship recited in claim 1 and the decoder means of claim 6.

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4. Related application — not prior art

The sibling application cited in the CROSS‑REFERENCE paragraph, "DME Morse Code Identity Decoder," Ser. No. 537,880, filed Sept. 30, 1983 (which my earlier searches associated with US 4,651,158 — an inference from search results, not confirmed from the patent text), was filed the same day as the '639 application and is commonly owned. Under pre‑AIA § 102(e) a reference must be filed "before the invention by the applicant," so a same‑day filing does not qualify; and for § 103 purposes, commonly owned subject matter developed by another person would be disqualified under pre‑AIA § 103(c). It is therefore not prior art against US 4,642,639.

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5. Caveats you should carry forward

1. Incomplete verification. I verified the identity of only one cited reference (US 3,801,979). Titles/subject matter of US 3,821,523, US 3,975,731, US 4,032,756 and FR 2,538,560 are unverified in this session; my § 102 mappings for those are correspondingly provisional.
2. FR 2,538,560 date anomaly is unresolved and should be checked directly.
3. Claim set is taken from the Justia reproduction (claims 1–7, claim 1 independent). The authoritative full text I was given does not include the claims section, so if the actual claim set differs, the claim mapping above must be re‑run.
4. Negative vs. positive results. "No anticipation" is an analytical conclusion from the limitations of claim 1 and the characterization of Miller in the specification — not proof that the unverified references contain nothing anticipatory. A complete § 102/§ 103 screen requires reading the full text of each of the six cited references.

I'll research the prior art references from this patent's page before building the § 103 analysis.

Let me pull more detail on the key references — particularly Latham (US 3,975,731), the Chisholm patents, and the TACAN-DME identity detector.

Obviousness Analysis — U.S. Pat. No. 4,642,639 under 35 U.S.C. § 103

Note on inputs. I built this on (i) the authoritative patent text supplied, (ii) the "Prior art" references appearing on the patent's Google Patents page and cited in its specification, and (iii) the search results I was able to retrieve in this session. I was not able to retrieve full text for RE 30,069, U.S. 4,032,756, or the two Chisholm patents (the search tool capped out), so those characterizations are flagged as inferences, not verified quotes. Claim text used below is the Justia-derived claim set from the prior summary; the fetched specification did not include the claims, so any claim beyond published 1–7 would be invisible to me.

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1. Governing framework

• Applicable law: The application was filed September 30, 1983 — pre-AIA. § 103 is governed by Graham v. John Deere, 383 U.S. 1 (1966) (scope/content of prior art; differences; PHOSITA level; secondary considerations), as applied post-KSR Int'l v. Teleflex, 550 U.S. 398 (2007) (a combination of known elements is obvious where the improvement is the predictable use of prior-art elements according to their established functions).
• Level of ordinary skill (PHOSITA): An avionics/radio-navigation engineer with a B.S.E.E. and roughly 2–4 years of DME/TACAN or pulsed-ranging receiver experience, familiar with ARINC DME characteristics, the ICAO 1350 Hz pulse-pair/identity convention, and standard 8/16-bit microprocessor design as of 1983.

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2. The claim at issue, reduced to its inventive core

Claim 1 is a two-means apparatus claim whose only arguably novel feature is a rate relationship:

Everything else in the claim is a conventional DME receiver chain. Dependent claims 2–7 recite only: a programmable variable-frequency receiver (2), a programmable stabilized master oscillator (3), per-station AGC (4), sample/store/assert signal-presence (5), per-station identity decoding (6), and per-station distance calculation (7).

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3. The prior art and what each reference supplies

A. U.S. RE 30,069 — Miller, "Multiranging DME system" (Aug. 7, 1979) — the closest reference

Per both the patent's own characterization and the summary, RE 30,069 discloses a single DME time-multiplexed between two ground stations. The '639 specification itself admits this reference teaches the fundamental concept of cyclically retuning one DME among multiple ground stations and reading range from each. This is the strongest single teaching of element (a)'s "cyclical sequence" and of multichannel operation generally.

The patent's only distinguishing argument against RE 30,069 (spec, Background) is that Miller's second channel yields distance only, not independent velocity/identity. That is a difference in degree/results for a particular channel, not a difference in the claimed cycling apparatus — a § 103 argument at best.

B. U.S. 3,975,731 — Latham et al., "Airborne positioning system" — the most damaging secondary reference

This is the sleeper. Search results confirm "US3975731A — Airborne positioning system" teaches:

"acquiring range signals from at least three DME stations, rapidly sequencing among the plurality of individual DME stations by providing a predicted range measurement to the next DME station in a range gate, comparing the predicted range measurement with the actual range measurement … estimating range bias errors … and continuously updating the estimated range bias errors and estimated aircraft velocity to provide an accurate determination of aircraft position…"
— https://patents.google.com/patent/US3975731

Latham thus discloses, in the same field and for the same purpose (position fix from multiple DME ranges using one airborne unit):

• sequencing a single DME receiver among three or more stations (Latham's Fig. 1 shows ten stations 14 A–J);
• doing so rapidly and cyclically ("the station sequencing rate becomes the principal accuracy factor");
• obtaining a valid range reading from each station each pass (the "predicted range … in a range gate" is exactly the "at least one valid distance reading per cycle" limitation);
• deriving velocity as a loop product;
• explicitly recognizing the rate-versus-number-of-stations tradeoff that the '639 patent later recites ("the primary advantage of obtaining a triangulated position … is offset against the necessary time required to obtain valid return … at distances of 300 miles or more").

Latham's discussion of rho-rho systems also supplies the motivation for three stations: two ranges leave a position ambiguity requiring "a bearing measurement or some other means," and accuracy "will improve in proportion to the square root of the number of stations."

C. U.S. 4,032,756 — "TACAN-DME identity detector" (1977)

Search results confirm the existence and title of this reference (Google Patents sitemap: "06/28/1977 | US4032756 Tacan-dme identity detector"). Inference (unverified): an identity detector for a TACAN/DME receiver necessarily decodes the station Morse identifier transmitted by the ground station — i.e., the "station-specific coded identification having a long timing characteristic" of claim 1(a) and the "decoder means" of claim 6. Identity detection in DME is a decades-old, standardized function; the 1350 Hz identity spacing is an ICAO/ARINC constant, not something the '639 patent invented.

D. U.S. 3,801,979 and U.S. 3,821,523 — Chisholm

Unverified. Both are cited on the patent's face and appear in the same DME/of-course ranging family. They are likely directed to DME ranging/decoding circuitry. I flag that I could not retrieve their text and therefore do not rely on them for a specific limitation in the primary rejection below; they are useful only as background showing DME pulse-decoding and search/track logic was old.

E. Additional art surfaced by search (not cited on the '639 face)

• U.S. 3,456,257 explicitly contemplates that "two indicators may represent the distance to two different ground beacons, and may be time shared with one DME. The DME would then rapidly search and lock on one or the other of the ground beacons and alternately and successively provide information to the two indicators." This independently corroborates that sharing one DME among plural stations by rapid alternate searching was known.
• US 4,651,158 ("DME Morse code identity decoder") is the commonly-owned sibling of Ser. No. 537,880 filed the same day. It is not prior art (co-pending, same filing date), but it is relevant to claim 6 and to a potential obviousness-type double patenting issue, since its specification is substantially identical to the '639 disclosure.

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4. Primary § 103 rejection — Claim 1

Proposed combination: RE 30,069 (Miller) in view of Latham (U.S. 3,975,731), further in view of U.S. 4,032,756.

Why a POSITA would combine them (KSR rationales):

1. Same field, same problem, same solution space. All references are airborne DME/TACAN ranging. Both Miller and Latham address the self-same problem the '639 patent states it solves: obtaining position from multiple DME ranges without carrying multiple DME receivers. Combination is not a leap across disciplines.
2. Extension from two channels to three is a predictable, motivated variation. Miller teaches the 2-channel case; Latham teaches that 3+ ranges are needed to resolve the rho-rho position ambiguity and that accuracy scales with station count. A POSITA seeking an unambiguous position fix would plainly extend Miller's multiplexed DME to the three stations Latham requires. KSR, 550 U.S. at 417 (predictable variation); In re Rosacker, 111 F.3d 1546 (Fed. Cir. 1997) (art recognizing need for more of the same element).
3. Adding identity decoding is an obvious design choice. Station identity is a standard DME ground-station output; a multichannel DME that does not decode the ID cannot tell the pilot which of three stations corresponds to which displayed range. U.S. 4,032,756 shows a detector for exactly this signal. Motivation to combine is the functional necessity of identifying the channel's station.
4. The rate relationship is a result-effective optimization. Once three channels are multiplexed, the ID (Morse dots ≥50 ms, per the spec; 1350 Hz spacing) necessarily imposes a slower sampling requirement than the range replies. That the cycle rate must exceed the ID rate by roughly an order of magnitude while remaining fast enough to catch a range reply each pass is the inevitable arithmetic consequence of the two signal characteristics already recited. Establishing a rate to satisfy two known constraints is the predictable work of a POSITA — not invention. In re Aller, 220 F.2d 454 (CCPA 1955) (optimization of a known process parameter is obvious absent unexpected results).

Claim 1 conclusion (opinion): Obvious under § 103 as a combination of RE 30,069 + Latham + '756. Latham alone comes very close to the whole claim; Miller supplies the express multiplexing teaching, and '756 supplies identity.

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5. Dependent claims 2–7

All dependents recite conventional DME/microprocessor implementation detail and are obvious over the same combination, further in view of routine engineering:

Because every dependent adds only a known element performing its known function, each is obvious for the same reasons as claim 1. KSR, 550 U.S. at 417.

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6. Alternative and secondary combinations

• Latham alone (or Latham + '756): If Miller were disqualified (e.g., a § 102(b) status challenge), Latham independently teaches the three-station, rapid-sequence, range-gated, velocity-producing architecture. '756 supplies the identity limitation.
• U.S. 3,456,257 + RE 30,069 + '756: 3,456,257 expressly teaches time-sharing a single DME among two beacon displays by rapid alternate search/lock — reinforcing the multiplexing teaching and making the 3-channel rate optimization obvious.
• Chisholm (3,801,979 / 3,821,523): Likely usable as secondary evidence of conventional DME search/track and pulse-decoding (unverified).
• Obviousness-type double patenting (ODP): The co-pending, same-day, commonly-owned sibling US 4,651,158 ("DME Morse Code Identity Decoder," Ser. No. 537,880) shares substantially the same specification. If the '158 and '639 claims are not patentably distinct (the '639 claim 6 identity-decoder means vs. the '158 method claims for identity decoding), an ODP rejection (and/or a terminal disclaimer requirement) is worth exploring. I flag this as a lead, not a conclusion, since I could not compare the two full claim sets line-by-line.

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7. Rebuttals the patent could raise, and counter-arguments

1. "Miller teaches only two channels and only distance on the second." Counter: Latham supplies the three-station requirement and the velocity product; the number of channels is a predictable extension driven by the known ambiguity of two-range fixes.
2. "The order-of-magnitude rate relationship is not taught." Counter: both rates are dictated by the signal characteristics already in the claim; choosing a sampling rate to satisfy two known signaling constraints is optimization. This is the patent's weakest defensive ground.
3. "Independent simultaneous identity decoding for all three channels is novel." Counter: the '639 specification itself describes no new identity hardware — it uses a 9-bit shift register and the standard 1350 Hz interval test; U.S. 4,032,756 and the co-pending '158 show the technique.
4. Secondary considerations (Graham factor 4). I found no evidence of commercial success, long-felt need, copying, or industry praise attributable to this patent, and no litigation (see the earlier Litigation section) that would supply a nexus to any objective indicia. Absent such evidence, the secondary-consideration factor does not rebut the prima facie case.

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8. Confidence and caveats

• High confidence: The Latham reference (US3975731) is the critical art; search results corroborate that it expressly discloses rapid sequencing among at least three DME stations with range gating and velocity — overlapping nearly all of claim 1. RE 30,069 is confirmed (via the '639 specification itself) to teach single-DME time-multiplexing across multiple stations. U.S. 4,032,756 is confirmed by title/existence as a TACAN-DME identity detector.
• Moderate/low confidence (unverified text): The precise teachings of U.S. 4,032,756, U.S. 3,801,979, and U.S. 3,821,523. My element mappings for '756 are inferential and should be confirmed against the actual reference before filing or relying on this analysis.
• Claim completeness: Based on the prior summary, claim 1 is the sole independent claim and there are seven claims total. If the granted patent contains additional independent claims (the fetched text omitted the claims), this analysis must be re-run for them.
• Rebuttal of a possible contradiction in the prior sections: None found. The earlier summary flagged US 4,651,158 as likely being the Ser. No. 537,880 sibling; my search corroborates the mirrored specification text and confirms the title "DME morse code identity decoder," so that inference is strengthened rather than contradicted — though I still cannot authoritatively certify the Ser. No. linkage from the '639 text alone.

Bottom line: The '639 claims are, in my opinion, vulnerable to a § 103 rejection built on RE 30,069 + Latham (US 3,975,731) + U.S. 4,032,756, because every element of claim 1 — including three-station cyclical operation, valid per-cycle range readings, and identity decoding — is disclosed or rendered obvious by that combination, and the only remaining feature (the order-of-magnitude cycling-rate relationship) is a predictable, result-effective optimization that KSR and Aller treat as obvious.