Mark sent me this
interesting article with his QSL card, and I was so impressed I asked if I could
reprint it! It was first published in NCJ (The National Contest Journal,
published by the ARRL) for July/August 1998, pp 12-13 - Ed
Mark, K5AM in his homebrew shack.
project was not all planned out from the beginning! In 1948, as a typical
high-school freshman in Wisconsin with a new ham license, I was trying to set up
as W9ECV with a 25-cent weekly allowance. Snow-shovelling jobs helped out
in winter, and lawn mowing in summer. Even so, there was no hope of buying
a factory rig. Thus my first one-tube transmitter and regenerative
receiver were homebrew, built using salvaged parts from large 1930s-style AM
broadcast receivers. A few years later, I began to use the military
surplus gear, which was such a bargain at that time. Converting this gear
to ham use provided a good deal of technical experience, mostly of the
trial-and-error variety. But 10 metres was in excellent condition, and the
inexpensive war surplus receivers did not tune that high. Necessity
dictated the need for building a receiving converter. That's when the
homebrew bug first bit me for good.
The result 50
years later is a totally homebrew contest station. At some point necessity
ceased to be the driving force, but homebrewing continued because it was so much
fun! Transverters, amplifiers and numerous gadgets followed for decades.
By 1990 practically everything in the shack was homebrew, and I suddenly
realized that only the transceiver stood in the way of a 100% homebrew station.
That's when a homebrew transceiver was planned.
took three years to design and build. It has dual VFOs, dual-receive,
digital read-out, IF shift, RIT, RF speech clipping and filtering,
panel-adjustable CW offset, a 200 Hz CW filter, a super- sensitive integrating
squelch for SSB and CW (mainly for six metre DX), a high-performance, no-pop,
no-click AGC circuit, a non-crunching noise blanker, and full CW break-in (QSK)
with no dit shortening, no lag, and 50 wpm break-in ability. I wanted
optimum performance, no matter how long it took to build. It needed only
142 transistors, 189 integrated circuits, 236 diodes and one 200-watt tube.
But no microprocessor, no synthesizer, and no phase-lock loops. No phase
noise, no spurs, and no birdies!
contest station operates at 1500 watts on everything from 160 metre DX to two-metre
moonbounce; a block diagram of the station is shown in Figure 1. The
oldest piece of gear in daily use was built while I was still in high school in
1951: a small six metre amp, now used as a driver. My first three years of
clumsy bread boarding are sadly lost and not available for on-the-air use.
This loss no doubt benefits nearby TV watchers.
It is typical
for old-timers that old homebrew gear was not saved. This reflects the
fact that the gear was usually built simply to get on the air; homebrewing was
done mainly out of necessity because the coveted factory equipment was often not
affordable. That old 1951 amp was given away in 1962 when it was replaced
by a larger amp. Only 25 years later, when the homebrew and boatanchor
nostalgia set in, was it relocated thanks to the kind efforts of several
friends. It had changed hands five times, and was found in a garage under
heaps of junk. Now the gear in constant use at K5AM spans almost the full
50-year homebrewing effort.
All the gear
was newly designed and built from scratch. But I was not about to reinvent
the superheterodyne. Each project begins with a thorough study of the
handbooks and relevant magazine articles. I glean ideas from all previous
builders, to whom many thanks are due. Design means selecting and choosing
the best ideas which will help produce the intended results. Individual
circuits are described in the handbooks; the real design work is to combine them
into a complete functioning unit. Getting a whole station built in a
finite interval of time meant using mostly tried-and-true methods, and setting
to work without trying to invent a new circuit for each stage. Only a few
circuits are truly new: a self-adjusting, splatter-stopping ALC circuit for
tetrodes, an integrating squelch, a non-crunching noise blanker, and a
high-performance AGC system. I've written up these new circuits for the
ham magazines, along with a few of the other designs. References are
listed at the end of the article.
This station is
used in the most demanding situations: from 160 metre DX with weak signals and
high noise levels, to Sweepstakes on 20 metres with heavy QRM, to VHF contesting
with rock-crunching local signals, to two metre moonbounce work with
infinitesimal signals. Each piece of gear is subject to continual testing,
update and improvement. Building simple gear for casual operating and
cross- town ragchews is a fine way to get started in homebrewing and to gain
design experience. I soon discovered, however, that achieving
state-of-the-art, contest-grade performance is a totally different ball game.
The rig is
shown in the title photo. All the gear is built on 19-inch black rack
panels. The large heavy amplifiers are stacked in the six-foot rack.
The transceiver and smaller items are installed on adjustable pine shelving, to
allow easy access and rearrangement. No attempt is made at
miniaturization; ample space is allowed in each item for thorough shielding and
filtering, and for uncountably many future modifications and improvements.
With hinged boards and other devices, provision is made for instant
accessibility to allow easy servicing and experimentation. I did receive
some essential help in building this gear: one difficult problem was in laying
out the panels to achieve a pleasing appearance. Luckily, my XYL Lisa is a
professional artist, and most of the panels were designed with her assistance.
There is also
another, more rigorous, conception of homebrewing. Some truly amazing hams
also design and build their mikes, keys, headphones, CW memory keyers, paddles,
voice recorders, towers, antennas, rotators, RF power meters, DSP filters - even
test gear and vacuum tubes! To leave ample time for my job, and for
working DX and contests, I had to compromise. All those accessory items I
buy ready-made. I like building the major items on the rack panels, and
find the RF and circuit work intriguing.
Lack of test
gear is often thought to be an insurmountable hurdle to homebrewing, but it
needn't be. I built and aligned the entire station using inexpensive WWII
surplus and Heathkit test gear. Some of the Heath gear I built and some I
bought for a song at flea markets. WWII surplus and Heath test gear can
still be found at hamfests. Formal training is not required, either.
I've never taken any courses in electronics, but the handbooks have all the
required information. Nor are fancy computer programs needed.
Homebrewing for serious DX and contest work is not like advanced development
work. All the required formulas are found in the handbooks; they involve
no more than the simplest high-school algebra. No one calculates by hand
nowadays; the formulas are easily entered into a small programmable calculator,
conveniently situated next to the soldering iron. (In earlier days, we
used slide-rules, and a few wonderful sliding cardboard nomographic rules.)
station come out on top in every contest? No, hardly ever. Devoting
so much effort to building the rigs leaves little time for planting a ‘big gun’
antenna farm. I am quite content to be one of the ‘little pistols’ and
just have fun. A contest is a merciless test of the equipment; I feel like
a winner if none of the homebrew gear breaks down during a contest, and in 50
years it never has. The June VHF contest is my favourite; I held the
division record for five years, put up the top nationwide six metre score
several times, and once blasted through the eastern monopoly to win a place in
the top ten. On HF, my best effort was a division sticker for the ARRL SSB
DX contest, way back when it was a 96 hour two-weekend marathon. Lately, I
can always win an HF single-band DX certificate - provided no one else in my
area competes in the same category. In the moonbounce contest, with only a
single two metre yagi aimed at the horizon for moonrise and moonset, being in
the top ten would be an absurd dream, but last year I finally achieved my
long-standing goal and got out of the bottom ten.
Ham radio and
homebrewing greatly influenced my career choice. At a very early age I
built a battery-operated one-tube receiver; it was beautiful, but it didn't
receive anything. I looked for information on receivers at the local
library, but found the formulas in the electronics books bewildering. That
kid sure wanted that receiver to work, so he had to teach himself algebra.
Thus ham radio, contesting and homebrewing were crucial steps to college, three
years at sea as a deck officer in the U.S. Navy, graduate school, a PhD,
and a university research career as a professor in pure mathematics.
provided a serious challenge to high-school kids in the 1940s. Young
people need serious challenges to capture their enthusiasm and steer them in
worthwhile directions. The ham radio challenge in the 1940s was technical;
no easy paths were obligingly laid down. The exams were tough and required
schematic diagram drawing; entry level was 13 words per minute. A ham
ticket required a serious effort, and was considered a highly-valued
Are there more
projects planned for the K5AM workbench? A few possibilities, perhaps.
But for now, planned improvements to the existing gear will keep me busy for
several years. Also, I've recently come down with a bad case of boatanchor
fever. My HRO, Super-Pro, 75A-4, BC-348, KWM-2, Harvey-Wells, ART-13,
Ranger, DX-100, Goony-Bird, and several other wards all need time and TLC.
I've also been
spending much time setting up a new VHF contest station at 7900 feet on the
north slope of Horse Mountain (grid locator DM54wa). The heavy, bulky
homebrew gear stays home; it would take a week to move it for each contest.
Thus the mountain station uses the latest modern, factory-built, store-bought
gear. Yes, all the bells and whistles are great fun. Then why am I
always so happy to get back home and operate the old-fashioned homebrew gear?
It performs a whole lot better!
Selected articles by the
High S.W.R. Protection for
Transceivers and Amplifiers, CQ, May, 1980, 63-65.
ALC for Class AB1 Amplifiers,
QST, July, 1986, 38-39, 47.
Antenna Relay Sequencing, Ham
Radio, October, 1987, 17-26.
A Sensitive Integrating
Squelch, QST, August, 1988, 27-29.
Amplifier Cool-Down Circuits,
QST, March, 1989, 35-36.
Protecting Power Tetrodes, QST,
November, 1989, 22-25.
A Low-Drive, High-Power
All-Band Tetrode Linear Amplifier, CQ, July, 1990, 60-65.
Evasive Noise Blanking, QEX,
August, 1993, 3-6.
An Automatic, Remote
Antenna-Tuning Controller, QST, September, 1995, 46-49.
A High-Performance AGC System
for Home-Brew Transceivers, QEX, October, 1995, 12-22. [Corrections in QEX,
Jul/Aug 2000, p.59.]
The AMSAFID: An Automatic
Microphone Switcher Amplifier Filter Integrator Distributor, QST, November,
A Luxury Linear, QEX, May,
1996, 3-12. (Photos also in QST, Jul 1996, p.19.)
Design Notes for "A Luxury
Linear" Amplifier, QEX, November, 1996, 13-20.
A Homebrew Contest Station, NCJ,
July/August, 1998, 12-13. (Photo also in QST, February 1999, p.84.)
A High-Performance Homebrew
Transceiver: Part 1, QEX, Mar/Apr, 1999, 16-24. [General plan] http://www.arrl.org/members-only/tis/info/pdf/990304qex016.pdf
A High-Performance Homebrew
Transceiver: Part 2, QEX, Sept/Oct, 1999, 3-8. [IF board; notes in QEX,
Nov/Dec 2000, p.60.] http://www.arrl.org/members-only/tis/info/pdf/990910qex003.pdf
A High-Performance Homebrew
Transceiver: Part 3, QEX, Nov/Dec, 1999, 41-51. [RF board; corrections in
QEX, Jul/Aug 2000, p.59, and in QEX, Nov/Dec 2000, p.60.] http://www.arrl.org/members-only/tis/info/pdf/991112qex041.pdf
A High-Performance Homebrew
Transceiver: Part 4, QEX, Jan/Feb, 2000, 47-56. [AF board] http://www.arrl.org/members-only/tis/info/pdf/000102qex047.pdf
A High-Performance Homebrew
Transceiver: Part 5, QEX, Mar/Apr, 2000, 23-37. [Logic board, etc;
corrections in QEX, Nov/Dec 2000, p.60.] http://www.arrl.org/members-only/tis/info/pdf/000304qex023.pdf
HF Circuits for a Homebrew
Transceiver, QEX, Nov/Dec, 2001, 20-42.
Information about obtaining
copies of QEX and QST articles may be found at http://www.arrl.org/qex/#copies,
http://www.arrl.org/members-only/artcopies.html and firstname.lastname@example.org.
K5AM contest station block diagram. To obtain very high dynamic range and
to minimize spurious responses, the rig uses an overall total of only two mixing
conversions on each band from 1.8 to 144 MHz. This configuration differs
from common practice, so there are some semantic problems in describing it.
The ‘transceiver’ proper consists only of the IF panel, tuning 40 to 39 MHz,
with a 9 MHz second IF. The front-end section for MF/HF is on a separate
panel. The separate front-end panels for six metres and two metres, also
with 40-39 MHz output, were formerly called ‘transverters’. Each
front-end section employs high-side local oscillator injection, virtually
eliminating images and spurious responses.
the cleanest signal possible, the station uses class A transistor stages up to 2
watts, and then only tubes - class AB1 tetrodes. The diagram indicates the
power (in watts) available from each unit and also the (lesser) power required
by the next. The resulting headroom yields the best IMD performance.
Overall gain is controlled at the milliwatt level in each front-end. To
prevent splatter, ALC runs from each driver and each high-power amplifier back
to the corresponding front-end panel, with ALC metering at the transceiver.
There are no diodes in the signal path at any point in the station.
The 8072 is
a conduction-cooled tetrode, identical to the well- known 8122 except that the
8072 (with no air-cooling fins) clamps onto a heat sink. The (neutralized)
8072 driver amp for two metres has 26 dB gain.
4-400A bottles used in push-pull on six metres are the originals - only 37 years
old and still running at full output!
UKSMG Six News issue