The Best Of 'In Practice'

Archives and 'extras' from GM3SEK's monthly RadCom column

Also see
Cumulative Index, 1993-2010
indexed by subject


CONTENTS	Click the links for more details.
Back to: 'In Practice' homepage GM3SEK's Amateur Radio Technical Notebook	Attenuator design programs Blowers: estimating performance from dimensions Chokes: Toroidal and other chokes Clamp-on RF current meter The most useful tool for antenna and RFI investigations! Here are G0SNO's original article and some further construction ideas. Connectors: '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) Connectors: Powerpole connectors © PowerWerx, Inc. DC injector/extractor for coax feedlines This simple "Bias-Tee" handles 1kW+, 1.8-50MHz. Directional Wattmeters Inside a Directional Wattmeter: the real inside story about SWR meters and directional wattmeters, from the classic QST article by Bruene. Drilling templates Driving earth rods Filters: Harmonic notch filters The easiest way to remove harmonics from your VHF/UHF transmitter output... practical solutions from G4SWX. FM and UHF-TV interference filters RFI-proof your TV and FM receivers - and your neighbours' too! More practical, proven solutions from G4SWX. High voltage power supplies Essential information about safety, circuits and components Microphone preamps for Icom transceivers How to use Heil microphone inserts with Icom transceivers... without shouting! Also an IC-746 mod requiring no preamp. Noise levels - data from ITU At most sites, there is at least 30-40dB difference in external noise level between Top Band and VHF. Many ITU technical reports are now free to download in several languages (no more need to open an account). PSU Designer software Take the nasty surprises out of power supply design! Recommended tools Relay speed-up circuit 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. Rotating Centre for Wire Dipoles RS232 interfaces for transceiver control Small Mains Power Supplies Also see separate mini-series on High Voltage Power Supplies. Switch-mode power supplies How to modify computer and other switch-mode PSUs for amateur use (not 'In Practice' articles, so not included in the Cumulative Index) Tools and techniques for SMD soldering Transistor PA bias circuits Most 'bricks' are capable of much more linear operation if you upgrade the bias circuit. Here's how to do it.

Back to: Contents list 'In Practice' homepage	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, RS or direct from UK importers Torberry Connectors (also trading on eBay as Racebolts).

Back to: Contents list 'In Practice' homepage	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). IC-746 mod requiring no preamp.

Back to: Contents list 'In Practice' homepage	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. Duncan Amplification main site Download PSU Designer from Duncan's site (855 KB) Extra files - download these into the same directory as PSU Designer. Fig1.psu LV20A.psu 3kV Bridge.psu 3kV Doubler.psu

Back to: Contents list 'In Practice' homepage	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)

Back to: Contents list 'In Practice' homepage	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 E_V and E_I 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 (E_V / E_I) 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.

Back to: Contents list 'In Practice' homepage	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

Back to: Contents list 'In Practice' homepage	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.)

Back to: Contents list 'In Practice' homepage	Drilling templates (August 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)

Back to: Contents list 'In Practice' homepage	Recommended tools (August 2007) 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. Sliding set-square - the sliding type is the most adaptable. 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. 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. Very sharp scriber - sharp enough to draw blood. 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. 6mm and 3mm centre-drills - the best way to start holes accurately in the right place, and also doubles as a countersink. 12mm hand reamer - Halls make lots of nice sharp tools of this kind, including a tiny version that is useful for PC boards. 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. 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. 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. 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. Hacksaw - needs to keep the blade tensioned and accurately parallel with the frame. This Stanley model is a good one. Assorted flat and round files - over the years, you will acquire these like stray cats. Wood rasp - for quick-and-dirty removal of metal, wood and flesh. Not shown - vice, small electric drill, hand drill, 13mm pillar drill. Those are another story...

Back to: Contents list 'In Practice' homepage	Driving earth rods (October 2007) Before you begin, always check for buried cables and pipes! *Read G0GRI's letter in November Radcom, page 93.* High-quality earth rods: Most electrical trade counters stock the 14mm (5/8in) rods made by Furse. TLC Direct supply the same rods and accessories by mail order. See item No TL ER58. 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. 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. 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) Smooth trigger-operated speed control - especially at low speeds, for starting holes in precise locations Reverse rotary option Hammer-only option ('rotary stop') for chiseling and light concrete breaking Facility to lock the chisel at a selection of fixed angles 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. Makita HR2450 - I recommend this highly from personal experience... but expect to pay about £110. 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.

Back to: Contents list 'In Practice' homepage	Estimating blower performance (September 2007) Use this Excel spreadsheet to estimate blower performance from wheel dimensions and RPM (blue line) and compare with airflow requirements of tube (red line and dot). Excel spreadsheet (540KB)

Back to: Contents list 'In Practice' homepage	Toroidal and other chokes (August 2007) W7EL - Baluns: What They Do and How They Do It The original article identifying why feedline chokes can work well in a variety of situations. K9YC - A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing. Excellent reading - print and keep! Contains impedance data for many kinds of toroidal chokes (wound with enameled wire, so chokes wound with coax will resonate slightly lower in frequency). Typical impedance data for air-wound RFCs and strings of beads (same as in the ARRL Antenna Handbook). W8JI - several pages, authoritative and well worth reading. W1HIS - how much ferrite can you pack into one house? Suppliers for toroids Micrometals, Inc - manufacturers of iron-powder toroids etc. Fair-Rite, Inc - US manufacturers of ferrite toroids etc. Amidon, Inc (USA) - 'tier 1' distributor for Micrometals and Fair-Rite Palomar Engineers (USA) - cores, beads, balun kits and RFI kits

	Radio noise levels (January 2008) It makes no sense for any communication receiver to have the same sensitivity across the whole range from 1.8 to 30MHz - and certainly not to be the same at 50MHz as well. For more detail, download ITU-R-P372(1), the International Telecommunication Union's definitive report on world-wide noise levels. Many ITU technical reports are now free to download in several languages (no more need to open an account).

Back to: Contents list 'In Practice' homepage	Tools and Techniques for SMD Soldering (September 2008 and October 2008) Zoom into photograph for extra detail. Key requirements If you don't have ALL of the following, SMD soldering will be much more difficult! 1. Magnifier 2. Good lighting 3. Work-holding for small boards 4. Small-tipped soldering iron 5. Tweezers 6. Thin flux-cored solder wire 7. Desolder braid 8. Flux pen or spray 9. Flux solvent for final cleanup. The links provided here are only to show you what's available. Shop around for best prices. Soldering iron: thermostatically controlled irons are best, but the Antex CS18 isn't bad for under £20. I'm suggesting this model because a sharp pointed tip is available. A sharp pointed tip is an absolute necessity. This short conical shape gives the best heat storage, right behind the point. Don't use the thin pencil-style tips - they chill too easily. Solder wire: Use tin/lead alloy, no larger than 0.5mm diameter, for example any of the 0.5mm or thinner solders here. Avoid unleaded solder - it's more difficult to use, and it is not required for home construction. Rapid Electronics have an SMD rework kit which includes a smaller quantity of 0.4mm (28swg) tin/lead/silver cored solder and jelly flux in a syringe applicator. This very thin solder is easier to use in a traditional way (heat the joint, then apply cored solder) without melting too much solder in one go. Another source of 0.35mm tin/lead/silver cored solder. This 100g reel will go a very long way! Flux pen or syringe - another essential. Some users prefer a free-flowing liquid flux, while others prefer a jelly flux which is more sticky and helps to hold the components in place. Either kind will do - the important thing is to always have a supply of extra flux. Don't rely entirely on the flux in the cored solder. Desolder braid - no wider than 3mm. It often helps to swipe with fresh flux before use. Flux cleaning solvent - once again, essential. The brush dispenser is expensive, but the brush head can be re-used with other less expensive aerosol cans. Magnifier: How to choose a magnifier - a good description of the range available, from a reliable supplier. Also see tools and craft suppliers, along with various eBay shops. Strong 'half-eye' reading glasses - try them on at the drugstore. Boots currently have a nice frameless style. Work light - here is a very good buy from IKEA. Tweezers - drugstore again, or many of the UK Components and Tool Suppliers. ESD mat and wristband - sorry, no room to write about those, but you really do need them. YouTube video of JBC soldering stations. There are more soldering videos on the same page. SMD Soldering Techniques (October) Low Cost SMD Soldering Guide - an excellent extended guide to tools and techniques YouTube videos - start with Surface Mount Soldering 101. More links with thanks to G4UGM via G3SVW Nice tutorial on SMD construction. Soldering with a "conventional" iron - shows how difficult it can be without the right tools! Using a hot air gun Hot air guns available here, here and here for example. Solder paste - a different technique. Here is a nice presentation including more links. Solder paste available here for example.

Back to: Contents list 'In Practice' homepage	Building Small Mains Power Supplies (November 2008) In Europe, most important standard for the safety of electrical products is the Low Voltage Directive 2006/95/EC, which covers the vast majority of electrical products in everyday use. The Low Voltage Directive only applies to products that are "placed on the market" within the narrow legal definition of that term. Equipment constructed for our own use is excused the need for compliance testing and paperwork, but that is no excuse for incompetent and dangerous home construction! We must still meet the applicable standards. The Radcom article shows how this can be done using a combination of approved components and good construction techniques. Here is a useful Guide to the Low Voltage Directive. Try the visual index page where you can click on individual components for more information. Links follow through to manufacturers' catalogues. You can buy these components on the websites of distributors such as Farnell, Rapid Electronics or CPC. Another viewpoint on home-constructed mains supplies is Elektor magazine. This page doesn't have illustrations, but you can see that it follows the same principles as my Radcom article. PSU Designer software by Duncan Munro, M0KGK - highly recommended!

Back to: Contents list 'In Practice' homepage	High Voltage Power Supplies (January, February and March 2009) You can download the three-part Radcom article from the links above. PowerPoint presentation from the RSGB Convention, October 2009 No sound track, but you can click through the slides to follow the presentation. (to download 2MB file, right-click 'Save Link As...' ) High Voltage Power Supplies *M0KGK's PSU Designer* program: Protecting the HV-minus rail and the anode/grid current meters:** Figure 1 in the Radcom articles includes only basic protection for the HV-minus rail. For details of anode and grid current metering in the amplifier itself, see here for example. Step start circuits Another useful reference: High Voltage PSUs by Mark Mandelkern K5AM. 'Industrial scale' HV PSU design with some detailed thought behind it. Read and copy! ###Components: See Component Suppliers page for contact and ordering details. Check catalogue pages for links to individual data sheets. Mains relay - this range of 30A SPNO 'baby contactors' has never let me down. Combined mains switch and thermal circuit breaker. To make a complete thermal-magnetic breaker, you must also order the snap-on magnetic conversion module. 1N5408 rectifier diodes. Reservoir capacitors - example of a catalogue search for 220uF and 330uF 450V electrolytics, sorted by increasing price. 7W metal oxide film resistors for capacitor equalising and bleeder strings. 10 ohm 14W vitreous enameled wirewound resistors - the workhorse of HV surge resistors, featured in March. SHV high voltage connectors - ignore the new prices and look for surplus bargains. Basic safety principles Basic principles (UK Health & Safety Executive): Defence in depth: no single failure shall lead to a direct hazard (eg before working on HV circuits, always switch off and unplug from mains, and short the HV rail to ground) To protect against human error, build safety into the hardware (eg protective covers) where reasonably practicable. Safety in Electrical Testing: Switchgear and Control Gear is particularly relevant. It all looks like obvious common sense... the problem is, we sometimes forget to use it! Other HSE publications

Back to: Contents list 'In Practice' homepage	DC Injector/Extractor for Coax Feedlines (April 2009) Handles 1kW+, 1.8-50MHz - but only if you use the specified components for C1 and RFC1! Components Murata 10nF 1kV capacitors for C1 (3 in parallel req'd), C2 DO NOT SUBSTITUTE FOR C1! (minimum order multiple = 10, but well worth keeping some on hand) RFC1, RFC2 DO NOT SUBSTITUTE FOR RFC1! V24ZA50P varistors (NB minimum order multiple = 5) Diecast box - I'm not very happy with the quality of casting, but they're just about adequate. SO239 (2 req'd) - not critical, eg these. Construction notes To mark out the diecast box for the two SO239 sockets, you can download this template (updated from an earlier column). Print at 100% size and cut out a single piece of paper containing the SO239 outlines A and C. Wrap this template around the underside of the box and use the guide lines to adjust it accurately to position, and then tape it in place and mark through the paper using a sharp scriber. There is just enough space to fit M3 bolts and nuts, although self-tapping screws are quite adequate. To make the lid fit, you will need to file away the flanges on the underside.

Back to: Contents list 'In Practice' homepage	Go 'Over The Top' with a Rotating Dipole Centre (April 2009) Original version at G0IVZ (scroll about half-way down the page) Components Fibreglass tube from Moonraker Dipole Centre from Moonraker - remove all metal parts Stainless steel hardware from Screwfix Wire etc from Moonraker or Westlake.

Back to: Contents list 'In Practice' homepage GM3SEK's Amateur Radio Technical Notebook