Don Jackson, W5QN

Every technical community eventually divides into two camps: those who repeat what has always been said about the equipment, and those who put the equipment on the bench, instrument it properly, and find out what is actually true. The Collins world has never lacked for reverence. What it needed — and what it got, beginning in the late 2000s — was a retired professional receiver designer willing to treat the S‑Line not as a relic to be worshipped but as a system to be characterised, measured, modelled in SPICE, and, where the data justified it, improved. That engineer is Don Jackson, W5QN, of Garland, Texas.

Don came to Collins collecting late, by his own account, and that turned out to be the community’s great fortune. He arrived without folklore and without sentiment about “the way it’s always been done” — but with more than four decades of professional HF and microwave receiver design experience behind him. What followed was one of the most substantial bodies of analytical writing ever produced about the Collins amateur line: multi-part treatments of AGC theory, S-meter stability, receiver dynamic range, amplifier instability, and power supply behaviour, published quarter after quarter in The Signal and archived in the CCA’s technical library, where they remain required reading today.

From an Allied Kit to a Career in Receivers

The arc is a classic one for his generation. First licensed in 1960 while in high school, Don started ham life the way thousands of Novices of the era did: with an Allied R-100 kit receiver and a Heathkit DX-40 on the transmit side. The kit-building teenager became a University of Florida engineering student, graduating with his BSEE in 1966, and then a professional at Texas Instruments — the beginning of a career of more than forty years spent designing HF and microwave receivers.

Think about what that means for the Collins hobby. The S‑Line receivers Don would later analyse were designed in the late 1950s by professional receiver engineers working with the best tools of their day. When Don retired and turned his attention to a 75S-3B on his own bench, the equipment was, for perhaps the first time, being examined by someone whose entire working life had been spent solving exactly the class of problems its original designers faced — noise figure, gain distribution, intermodulation, AGC loop dynamics — but with fifty additional years of measurement technique, simulation tools, and accumulated RF systems knowledge. It was less a hobbyist inspecting an antique than one generation of receiver designers auditing another. The S‑Line, to its enduring credit, largely passed the audit.

The Technical Conscience of The Signal

Don’s association with The Signal, the official magazine of the Collins Collectors Association, began as a contributor and grew into something closer to an institution. His early pieces — a thorough analysis of the 516F-2 power supply resonant choke, followed in the first quarter of 2009 by his study of S-meter stability in the 75S-3 and 75S-3B — established the pattern immediately: pick one circuit the community thought it understood, instrument it, and report what the numbers actually said. By 2014 he was sharing the editorial desk with then-editor Bill Carns, N7OTQ, and when Scott Kerr, KE1RR, later assembled his editorial team, Don Jackson held the Technical Editor chair alongside Historical Editor Jim Stitzinger, WA3CEX, and Layout Editor Josephine Toynette.

The Technical Editor role in a publication like The Signal is mostly invisible when done well. Every author’s schematic gets checked, every claimed measurement gets a second look, every proposed modification gets weighed against the unwritten first law of the Collins community: do not degrade the radio. Successive CCA presidents have publicly credited the Kerr–Jackson–Toynette team with making the magazine something members drop everything to read cover to cover. That reputation was earned one carefully-reviewed article at a time.

The AGC Papers

If one body of work defines W5QN’s contribution, it is the multi-part series on automatic gain control that ran in The Signal across 2011 and 2012. Nothing like it had appeared in the Collins literature — or, frankly, in most of the amateur literature — before. Part by part, Don built up the complete picture: the static behaviour of the AGC loop, the dynamic analysis of attack and decay, the trade-offs between loop stability and response speed, the mode-dependent choice of decay constants, and finally the practical operating conclusions that let an ordinary owner set up a fifty-year-old receiver intelligently.

Along the way he demolished and rebuilt the community’s understanding of the S-meter. His measurements showed that the AGC attenuation characteristic in a healthy 75S-3B is impressively linear — roughly 11.5 dB per volt, holding within about ±5% across the useful range — but that the clever bridge circuit converting AGC voltage into meter current is where the linearity goes to die, with the real value of an “S-unit” wandering significantly around its nominal 4 dB average across the meter’s swing. He characterised the grid-current drift mechanisms in V2, V6 and V7 that make the meter wander, verified the behaviour in SPICE simulation, and gave owners concrete procedures for taming it. The 2009 S-meter stability article and the AGC series together turned the most-watched instrument on the S‑Line front panel from a mystery into an understood, correctable system.

Dynamic Range, Service Bulletin 2, and Twenty Free Decibels

In the first quarter of 2016, Don published what may be the single most practically valuable receiver article in the modern CCA archive: an analysis of third-order dynamic range (DR3) in the S‑Line receivers and the effect of Collins’ own Service Bulletins 1 and 2. His careful walkthrough of what DR3 actually measures — the ability to hear a weak signal in the presence of strong out-of-band signals — was itself a service to a community raised on vaguer figures of merit. But the headline result was the payoff: implementing SB2, a modification Collins themselves issued for the 75S-3B/C but which applies across the S‑Line receiver family, typically buys around 20 dB of third-order dynamic range improvement. In one documented case he installed SB2 in the editor’s own 75S-3 and lifted its measured DR3 from 59 dB to 79 dB — transforming a 1950s design into a receiver that holds its own on today’s crowded bands, using nothing but the manufacturer’s own engineering and a few small capacitors.

Characteristically, the article did not stop at the recipe. He worked through the second-order consequences — the increased second-mixer plate impedance, the interaction between SB1 and SB2, the S-meter recalibration implications, even which capacitor values the 1975 manual specified versus the bulletin — so that an owner would understand not just what to do but what they were doing to the radio.

Taming the 30L-1

Owners of the Collins 30L-1 amplifier had muttered for decades about instability on 15 and 10 metres at certain combinations of tune and load capacitor settings. In the fourth-quarter 2013 Signal, Don did what nobody had quite done: he characterised the instability properly and published the fix. The analysis traced the misbehaviour to the amplifier’s parasitic-critical input circuitry, and the remedy he documented — replacing the 39 µH choke L3 with a 72 µH part of adequate current rating, bypassed with a 3.3k resistor — has since become standard practice, repeated in restoration write-ups across the community, usually with the phrase “as documented by Don Jackson, W5QN” attached. In the CCA’s own technical index the piece is catalogued simply as “30L-1 Instability — A Don Jackson Analysis.” When your surname becomes part of the article title, the community is telling you something.

The Sampler That Went Around the World

Not everything W5QN published required a Collins nameplate to be useful. His construction article Build a Quality RF Power Sampler, hosted on the CCA site, describes a simple, properly-engineered directional sampler — a toroid, a length of coax, two resistors — that lets any operator safely connect a transmitter or amplifier output to a spectrum analyser or modern instrument like a TinySA. It has become one of the most widely replicated pieces in the CCA’s public library, built by hams from Texas to Bangladesh who may never own a piece of Collins gear but who found, via a search engine, exactly the well-documented design they needed. Alongside it sit his Spectrum Analysis — A Primer, his survey of general-coverage receiver development and characteristics, his 516F-2 resonant choke analysis, and his treatments of the 32S-3 ALC zero-adjust instability and the 75S-x gain reduction problem in transceive mode — a shelf of references that quietly raises the measurement literacy of everyone who reads them.

Why He Belongs in This Series

The Boatanchor Legends series exists to document the people whose contribution reaches beyond their own shack. Don Jackson qualifies several times over. As an author, he produced the deepest analytical literature the Collins amateur line has received since the original factory engineering notes. As Technical Editor of The Signal, he has served as quality control for an entire community’s published knowledge. And as a working example, he demonstrated the mindset this hobby most needs to preserve: that a sixty-year-old receiver deserves the same rigour as a new design, that folklore should be tested rather than repeated, and that the highest form of respect for classic engineering is to measure it carefully enough to understand why it works.

His own station says the rest. Ask the man who has characterised the S‑Line more thoroughly than anyone alive what he actually operates, and the answer is a 75S-3B, a 32S-3, a 30L-1 and a 312B-4 — the very equipment he writes about, in daily service, performing to numbers he has personally verified. And ask him his favourite piece of Collins gear, and the receiver designer’s answer is telling: the 75A-4. Some judgements do not require a spectrum analyser.

Published Works — The W5QN Catalogue

Links to issues of The Signal point to complete-magazine PDFs hosted by the Collins Collectors Association; the later files are large scans and may download slowly. All items below are indexed on the CCA’s public “RX For Your Collins” technical library at collinsradio.org/rx/.

Sources & Further Reading

• The Signal, Official Magazine of the Collins Collectors Association — Issue 53 (Q1 2009), 75S-3/3B S-Meter Stability Improvements and Observations, by Don Jackson, W5QN, with contributor biography. collinsradio.org
• The Signal — Issues 64–65 (Q4 2011 / Q1 2012), AGC Theory series Parts 2–4, by Don Jackson, W5QN, with contributor biography. collinsradio.org
• The Signal — Q1 2016, editorial introduction by Scott Kerr, KE1RR, naming the editorial team and summarising the S-Line dynamic range / Service Bulletin 2 findings. collinsradio.org
• The Signal — Q2 2014, co-edited desk column by Bill Carns, N7OTQ, and Don Jackson, W5QN. collinsradio.org
• CCA “RX For Your Collins” technical index — listings including 30L-1 Instability — A Don Jackson Analysis, Build a Quality RF Power Sampler, Spectrum Analysis — A Primer, Understanding your 516F-2 Resonant Choke, S-Line AGC Theory/Stability & Improvements, and related Jackson articles. collinsradio.org/rx/
• eHam.net, “Rebuilding the Collins 30L-1” — community application of the W5QN Q4 2013 instability analysis and L3 modification.
• S21RC.net, “RF Sampler” — an international build of the W5QN RF power sampler design.