The Best Of 'In Practice'

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GM3SEK's Amateur Radio Technical Notebook
 

Clip-on RF current meter

The most useful tool for antenna and RFI investigations! Here are G0SNO's original article and some further construction ideas. 

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.

N2PK Vector Network Analyser

Information for constructors in Europe

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. 

Powerpole connectors

© PowerWerx, Inc.

Microphone preamps for Icom transceivers

How to use Heil microphone inserts with Icom transceivers... without shouting!

PSU Designer software

Takes the nasty surprises out of power supply design.

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.

RS232 interfaces for transceiver control

Inside a directional wattmeter

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.

• 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
  

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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 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.

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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)

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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.

1. 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.

2. Sliding set-square - the sliding type is the most adaptable.

3. 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.

4. 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.

5. Very sharp scriber - sharp enough to draw blood.

6. 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.

7. 6mm and 3mm centre-drills - the best way to start holes accurately in the right place, and also doubles as a countersink.

8. 12mm hand reamer - Halls make lots of nice sharp tools of this kind, including a tiny version that is useful for PC boards.

9. 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.

10. 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.

11. 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.

12. 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.

13. Hacksaw - needs to keep the blade tensioned and accurately parallel with the frame. This Stanley model is a good one.

14. Assorted flat and round files - over the years, you will acquire these like stray cats.

15. Wood rasp - for quick-and-dirty removal of metal, wood and flesh.

16. Not shown - vice, small electric drill, hand drill, 13mm pillar drill. Those are another story, all on their own.

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Toroidal and other chokes (August 2007)

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GM3SEK's Amateur Radio Technical Notebook