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'In Practice' homepage
GM3SEK's Amateur Radio Technical
Notebook
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'Good-enough' ways to assemble DIN and D connectors
'In Practice' for April and May 2004, now available as PDF
downloads.
Part 1 (April, 6.5MB PDF)
Part 2 (May, 5.6MB PDF)
The most useful tool for antenna and RFI investigations! Here are G0SNO's
original article and some further construction ideas.
The easiest way to remove harmonics from your VHF/UHF transmitter output...
practical solutions from G4SWX.
RFI-proof your TV and FM receivers - and your neighbours' too! More
practical, proven solutions from G4SWX.
Information for constructors in Europe
Most 'bricks' are capable of much more linear operation if you upgrade
the bias circuit. Here's how to do it.
© PowerWerx, Inc.
How to use Heil microphone inserts with Icom transceivers... without
shouting!
Takes the nasty surprises out of power supply design.
- How to speed-up your antenna relays, to avoid RF arcs caused by
'hot switching'.
- How to measure switching time with an ordinary non-storage 'scope.
The real inside story about SWR meters and directional wattmeters,
from the classic QST article by Bruene.
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N2PK's 50kHz-60MHz Vector
Network Analyser
A professional-quality VNA that amateurs can build... but
it's definitely not a beginner's project.
Radcom article (2 pages,
6MB PDF)
N2PK has produced a large number of documents about all
aspects of his VNA. Paul has already answered almost every question you could
imagine, so please read
the documentation - all of it!
Also there is a world-wide
User Group where you
can get information, help and advice.
Windows software
VNA4win
- features and download
Buying Parts from Europe
Very important: use the parts list in
N2PK's "Part 2" PDF document
!
- You can obtain ready-made PC boards for the VNA and
bridge from Gian Moda, I7SWX.
- N2PK gives part numbers from
Digi-Key or
Mouser in the USA, and these companies
will also ship to Europe. You can also buy many of the parts from
European suppliers.
- Analog Devices will generously supply the AD9851BRS
DDS IC to serious amateur experimenters as free samples. First download
the Datasheet,
and then click
Price, Packaging and Availability to order the samples. If this is
the first time you have ordered samples from AD, you will need to register
(nothing to worry about).
- Buy the Mini-Circuits parts direct from Mini-Circuits
Europe. Check the technical details on their
US website, and then phone +44/0
1252 832600 to order.
The three transformers will cost £14.50, but the minimum order is £25 (plus
VAT and postage). To make up the difference, I strongly recommend that
you buy a KARN-50 or similar 50-ohm reference load - you're going to need
it.
- Any ICs and other components that are not available from local European
sources will have to come from the US sources in N2PK's parts list.
- The Valpey-Fisher master oscillator is still the highest-performance
commercial MO module that we know about. The Fox JITO module is much poorer,
and phase noise and jitter will limit your low-level measurements (eg skirts
of crystal filters).
The Valpey-Fisher module is obtainable direct from the manufacturer at
a very reasonable price of $35 each (but that is for US customers only,
minimum order quantity of $1000, ie 29 units). Group buys are often being
organised through the
User Group.
- Some of the other components are also only available in multiples of
10 or more, so it will reduce costs if you form a group of friends to buy
components. Also you can share good ideas as you build and use your VNA.
Please check here regularly for further updates.
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Powerpole connectors
(May, November 2001)
Anderson Powerpole connectors
use a clever 'genderless' design that needs no separate 'male' or 'female'
parts - they just click together in the correct polarity. The same basic
idea works for a whole range of sizes and current capacities, all the way
from 15A up to 320A and more.
The 30A size is ideal for amateur solid-state transmitters and amplifiers,
and is now recommended by ARRL as a standard for 13.8V DC power connections
in amateur radio.
The
Powerpole
wiring standard for 13.8V DC connectors
©
PowerWerx, Inc.
Viewed from the open end, contacts down:
RED on the
LEFT, BLACK on the RIGHT.
Note: Powerpole connectors have no separate 'male'
and 'female' versions. All Powerpole connectors
must be wired exactly the same, as shown
above. Any pair will then connect with the
right polarity,
Following ARRL's lead, 30A Powerpoles are becoming a world standard.
They are used in the RIGrunner™ 13.8V distribution strips
supplied by West Mountain Radio
(USA) and Waters & Stanton (UK).
For data and assembly details, see
Torberry Connectors (the UK importers)
and PowerWerx (USA).
In the UK, Powerpole connectors are available from amateur radio retailers,
Farnell or RS, or direct from
Torberry Connectors.
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Microphone
preamps for Icom transceivers (October 2001)
The preamp is the portion to the left of the dotted line
- the other components are part of the transceiver (component numbers
in the transceiver vary according to the model).
Design notes
The inspiration for this simple preamp was an article by
Michael Covington, N4TMI in QST for June 2000. I added a few extra
components for passband shaping and RF immunity. In N4TMI's design the
transistor was an MPS3904, which I changed for European semi-equivalents.
In the conventional (through-hole) board, you could use either the MPS3904
or the BC109C as available. The BC849C is a surface-mount transistor (I
don't know a US equivalent). The DC bias conditions depend slightly on
the current gain of TR1. You may need to change R2 in order to get about
4V DC at the collector of TR1.
To make PCBs, right-click on a track image to save it,
then print at actual size on UV-transparent tracing paper and
follow instructions
here.
Conventional board: actual size is 0.75 x 0.80in
Single-sided board, view from component side with 'x-ray' view of tracks.
Print track image at actual size and then expose with ink side contacting
UV-sensitive PC board.

SMD board: actual size is 0.35in square!
SMD board, components and track are all on the same side.
Note that track image is 'flipped' -
print at actual size, and then expose with ink side contacting UV-sensitive
PC board.
Reverse side of SMD board can be either bare, or full copper for maximum
RFI immunity
(countersink around input and output pins, but solder ground pin both sides).
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PSU Designer
software (August
2001)

The PSU Designer main screen, simulating
3kV Bridge.psu
Cursor has just been double-clicked on the transformer to
change its properties.
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Relay speed-up circuit
(April 2002)

Correction: TR1 should be ZVN3306A
and TR2 should be ZVN4306A
(and the same in the PDF file, Fig 3).
This circuit will help reduce RF arcing in most power amplifiers that
use open-frame antenna relays. It should work with the fast (solid-state)
PTT output of any transceiver. TR1 and TR2 could also be NPN bipolar switching
transistors with appropriate voltage/current ratings.
Original references:
K1KP,
K6XX
Measuring relay switching times with an ordinary 'scope - how to become
a "human storage 'scope" (May 2002)
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Inside a directional wattmeter
(September 2002)
From the classic article by Warren Bruene, in QST, April 1959:
Download.
Notes on the 'In Practice' article:
Thanks to Ron Barker, G4JNH, for pointing out that
the equations for SWR and |rho| should both have been described
in terms of EV and EI as vector quantities - in
other words, it is necessary to take account of their phase relationship.
This means that SWR is not given simply by (EV / EI)
as I had claimed in the article, except at a voltage maximum where the
vectors line up.
Ron has prepared an Excel spreadsheet which
gives a superbly clear step-by-step analysis for any value of SWR and
phase angle of reflection: Download.
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RS232-Transceiver
interfaces
ARRL interfaces - from QST February 1993,
or recent ARRL Handbooks.
A
PDF
file is accessible online to ARRL members, but
PCB layouts
are public.
DF4OR's Icom CI-V pages
- Ekki's CI-V Test program is an excellent link debugger
K6XX's IC-706 interface
DK7IN - opto-coupled
interfaces
IK2BCP - opto-coupled interfaces
- click Projects
How
to get power from the RS-232 port
RS-232 connections
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Attenuator design
programs
WINATT.EXE - GM4PMK's standalone
Windows version of ATT.
ATT.BAS (QBASIC source code, contains
design equations)
ATT.EXE (Ready-to-run in a DOS box.
You may need to experiment with screen sizes and fonts to display the ohm
and pi symbols correctly.)
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Drilling templates (July
2007)
CAUTION - these are not precise engineering
drawings!
They are only meant as templates for marking-out panels for drilling
and filing.
Remember to print the PDF page at 100% size ("Page
Scaling = None")
Download templates
(only 40 KB)
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Recommended
tools (July 2007)
See the
UK Component and Tool Suppliers
page for lists of suppliers. Most of them now have web catalogues that
you can browse.

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300mm/12in ruler - you still need both metric
and inch scales. The 'satin chrome' finish with black engraved markings
has by far the best readability.
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Sliding set-square - the sliding type is the
most adaptable.
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Box of drills, 1.0–9.0mm in 0.5mm steps - this
should be the first set that you buy. Spend a bit of money on good-quality
drills in a metal box.
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Main box of drills, 1.0–4.9mm in 0.1mm steps
- this will be your most frequent choice for small jobs, but the
narrower range of sizes means it shouldn't be the first one that
you buy. Again, good drills and a metal box are worth the extra cost.
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Very sharp scriber - sharp enough to draw blood.
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Centre-punch - sharp enough to find the tiny
pinpricks that the scriber makes. A plain centre-punch that you can
hit with a hammer gives more control than the spring-loaded 'automatic'
type, and it's cheaper too.
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6mm
and 3mm centre-drills - the best way to start holes accurately
in the right place, and also doubles as a countersink.
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12mm hand reamer - Halls make lots of nice
sharp tools of this kind, including a tiny version that is useful
for PC boards.
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Step
drills, - Halls again, though several other makes are now available.
Useful sizes are 4-12mm in 1mm steps, and 6-24mm in 2mm steps. I
prefer the stepped pattern to the plain conical drills, as they give
parallel-sides holes in a range of definite diameters.
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Screw-down hole punches - you probably only
need the 5/8in (16mm) size.
Q-Max is the classic make, but once again
several other makes are available.
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Vitrex 3mm round file. Disaster - after
about 40 years, the manufacturers have have chosen this moment to
stop making them! I'm afraid you'll have to manage with a coarse
3mm needle file.
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Tin-snips - less useful than they seem, because
most of them distort the metal. The pair in the photograph are at
least 70 years old, hand-made in Sheffield.
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Hacksaw - needs to keep the blade tensioned
and accurately parallel with the frame. This Stanley model is a good
one.
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Assorted flat and round files - over the years,
you will acquire these like stray cats.
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Wood rasp - for quick-and-dirty removal of
metal, wood and flesh.
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Not shown - vice, small electric drill, hand
drill, 13mm pillar drill. Those are another story, all on their own.
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Driving
earth rods (October 2007)
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High-quality earth rods:

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SDS Plus drills and accessories:

For general DIY and amateur radio use, look for a
model that has all of the following options and features.
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Choose a mains-powered drill from the '2kg' range. Don't be tempted
by the cheap '4kg' models - they are not as good for these
applications.
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Rotary-only option ('hammer stop') for starting holes in precise
locations, and for occasional drilling of wood or metal (using
appropriate drill bits, of course)
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Smooth trigger-operated speed control - especially at low speeds,
for starting holes in precise locations
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Reverse rotary option
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Hammer-only option ('rotary stop') for chiseling and light concrete
breaking
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Facility to lock the chisel at a selection of fixed angles
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Safety clutch - absolutely essential.
More information is
here - part of the
uk.d-i-y newsgroup
FAQ, a treasure-house of good DIY information.
Before you buy an SDS+ drill, check and read the
small print of the specification very carefully. If you can't find a
drill with all of those features at a reasonable price, keep
looking.
Recommended models:
The links to suppliers are examples only, and I
recommend that you shop around for special offers.
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Makita HR2450 - I recommend this highly from personal
experience... but expect to pay about £110.
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Wickes own
brand - well recommended by users, and probably best value, though I
haven't tried it myself.
The same suppliers also sell drill bits and accessories, eg
the
'nut driver' adapter for 0.5in sq sockets.
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Toroidal and
other chokes (August 2007)
Suppliers for toroids
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GM3SEK's Amateur Radio Technical
Notebook
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