Arduino Controlled Direct Conversion Receiver.

Project Description – Good introduction to Arduinos, code easily modified, easily built in stages. An excellent, stable amateur band vfo will be built as part of the project. Good training in filter construction and tuning for best bandwidth. An introduction to spectrum analysers will be given.
Project Champion – Tex
Project Status – Prototypes under construction, initial tests encouraging.
Likely Cost – Not determined yet.
Complexity – Not for beginners unless partnered by an experienced ham.

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PSK Mini Transceiver

Project Description – A simple, no frills introduction to digital transmissions, PSK31, RTTY and others. This could be your first transceiver.
Project Champion – Richard
Project Status – Design being finalised, prototype planned to be built using veroboard.
Likely cost – Circa £10
Complexity – Good for a first time builder with guidance. Success almost guaranteed!!

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Computer to Rig Interface

Project Description – A general purpose interface for your transceiver to PC; enabling the transmission and reception of digital modes, PSK31, CW etc. Provide electrical
Project Champion – Paul/Tex
Project Status – Printed circuit board being finalised, components ordered, ready to be built soon!
Likely cost – Less than £10
Complexity – Good second project or for a first time builder with guidance. Success almost guaranteed!!

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Morse Code Sounder – Version 1

Project Description
Project Champion – Paul (keep it simple s…..)
Project Status – Designed, Board built, Parts obtained and ready for first time builders it all fits into a Marks and Spencer mint tin!
Cost – About £3
Complexity – Dead easy, very small circuit board so careful soldering using a magnifier is needed, guidance given as necessary. Success guaranteed.

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Morse Code Sounder – Version 2

Project Description – A pure sine wave oscillator and transistor amplifier with wave shaping, ‘easier on the ear’!
Project Champion – Paul
Project Status – Designed, Board built, Parts obtained and ready for first time builders. it all fits into a Marks and Spencer mint tin!
Cost – About £4
Complexity – Dead easy, very small circuit board so careful soldering using a magnifier is needed, guidance given as necessary. Success guaranteed.

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Iambic Keyer for Morse Paddle – K1EL Design

Project Description - Uses a microprocessor PIC chip, this will be programmed in the Club and guidance will be given on doing this. Great as an introduction to using PIC chips…. DON’T BE PUT OFF, IT’S EASY!
Project Champion – Paul
Project Status – In design phase, it will fit into a Marks and Spencer mint tin!
Cost – About £4
Complexity – Dead easy, very small circuit board so careful soldering using a magnifier may be needed, guidance given as necessary. Success guaranteed.

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Frequency Counter – VK3BHR Design

Project Description - Uses a microprocessor PIC chip and 2 x 16 LCD display to show Frequency direct from an oscillator and can handle an IF offset either plus or minus. Will count up to 40Mhz
Project Champion – Paul
Project Status –  In design phase. A small 2 board kit.
Cost – Likely to be less than £10
Complexity – Easy. We will have to load a program to the PIC chip; guidance and support will be given.

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Crystal Calibrator

Project Description - Uses 2-3 integrated circuits, a crystal and a few other components.
Project Champion – Paul
Project Status –  On demand. A simple single board kit.
Cost – Likely to be less than £4
Complexity – Easy. Success guaranteed.

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Field Strength Meter

Project Description - Uses a handful of components. A very useful test instrument for the experimenter. Really easy to build and use.
Project Champion – Paul
Project Status –  On demand.
Cost – Likely to be less than £10
Complexity – Easy. Success guaranteed.

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Audio Amplifier

Project Description – A great addition to any experimenters shack, test out that newly built receiver, add to a simple regenerative receiver, add your morse audio oscillator…… A full description below.
Project Champion – Tex
Project Status – On demand.
Cost – Likely to be a couple of pounds, less if you have a plentiful ‘junk box’.
Complexity – Fairly easy.

A Handy Audio Amplifier

One of the most useful items out of the legion of 'bits' that come in handy for anyone building bits and pieces of their own equipment is a 'universal' audio amplifier. This is one that will perform quite well, but will not break the bank. The circuit is shown in the circuit diagram on these pages. It consists of a complimentary pair (though they don't need to be matched absolutely) of transistors in the output (Tr3 & 4), driven by another complementary pair of transistors Tr1 & 2.

You may find the way that Tr1 & 2 are connected, in a rather strange or unusual way. But in this way, it's possible to minimise the voltage losses, in a comparatively low voltage supply. Although shown as a nominal 12V (13.5V from {PSUs) the circuit will still work down to around 6V with somewhat reduced output volume and quality. The overall voltage gain of the circuit is generally decided by the ratio of two resistors, R4 and R6, in that the voltage gain is around 30:1 as shown (1000/33). If we say that the peak to peak output voltage is around 10V (probably nearer 8-9V) then the input needs to have around one thirty-third of this – or some 300mV or around 100mV RMS. By shorting out resistor R4, with a smaller value resistor the gain will increase, but the audio quality and background noise will also increase.  It's difficult to give definitive figures for gain under these circumstances, but with R4, = short, it could be a voltage gain of several hundred, giving a useable output from a simple diode detector circuit.

So, how does the circuit work theoretically as shown (don't worry it's not going to be too technical)! The two resistors R1 and R2 work to give a voltage of just half the level of the power supplies value when taken into account with R5. Let's assume that the PSU is 13.5V so the voltage at the base of Tr1 is some 6.25V. The emitter of Tr1 connected directly to R6 R4 will around 0.6V less than that at around 5.65V.  

The small current passing through Tr1 is also fed directly into the base of Tr2, which amplifies it to flow through R7 and D1 & D2.  Resistor R8 is in parallel with the loudspeaker, and takes a proportion of the audio output, but helps to give better quality overall. Capacitor C4 helps to reduce the high frequency hiss that many simpler audio circuits can have. The two diodes D1 & D2 set up a small forward voltage to bias transistors Tr3 and 4 slightly into a more linear mode. If you left these out the amplifier would still work, but would sound very rough and 'gritty' due to a type of distortion called 'Crossover Distortion'. As the sound level gets smaller the proportion of distortion and 'grittyness' gets apparent.

All that the transistors Tr3 and 4 do is act as a double-emitter follower circuit to match the output of Tr2 into the lower impedance of the loudspeaker.  The positive voltage feedback though C5 to the resistor R8 and across the loudspeaker, gives a better gain linearity to the circuit. It does this by apparently increasing the gain linearity of Tr1 and Tr2's linear gain.

The circuit can be adapted (built) for differing output conditions. Transistors Tr1 & 2 are simple 'small-signal' devices that that can have maximum currents of only a few milliamps. Though Tr2 must be able to deal with a peak of around 25-30mA, while Tr1 should have good gain at under a milliamp. For use with headphone output only, you really could use the same transistor types for Tr1 and 3 and similarly for Tr2 and 4. Transistors Tr1 & 3 need not have a maximum power capability of greater than around 300-500mW in this case

If however, you're intending driving a loudspeaker to rather more output, then transistors Tr3 and 4 should have good gain at around at least 1A (preferably higher) and with at least a 5W capability and may even need some heatsinking in some cases. I've outlined some possible transistor types in the tables, with some pictures of pin identifications for those types.

Anyone interested in making one can get suitable transistors from me (costing only a small donation to club funds).

Tex

Transistors                Headphone / Loudspeaker

Q1                                 2N3904, BC108/9, BC182, BC184, BC548    

Q2                                 2N3906, BC212, BC214, BC558 BFY81

Q3                                 2N2218, BC640                           

Q4                                 BC635, BFY81

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Variable Voltage Power Supply

Project Description – Will use a mains transformer, fuse, metered voltage and current (these will be ordered from China, lead time up to 1 month). Separate outputs for 0-15v (-ish), 12v and 5 v.
Project Champion – Paul
Project Status – Will be designed if requested and can be tailored to requirements.
Cost – Unknown as yet, probably less than £15 as I have some available mains transformers (somewhere)!
Complexity – Relatively straight-forward, safety considerations as dealing with 240volts ac Easy. A most useful piece of equipment for any radio amateur

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Anything Else YOU Suggest

If you’d like to build something I haven’t shown above and you need some help, let’s chat about it. We can discuss sourcing the parts; possible circuit building techniques; adapting the circuit for your requirements; enclosing it in a presentable case….

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Solder sucker / De-soldering braid

£6

A soldering iron and solder, ideally a temperature controlled iron with several bits.

$40

Wire cutters, Long nose pliers and similar tools. Small 4-5” tools are great.

(Try InExcess shop in Parkstone, Wilkos do a set for £5  or 6)

£8

A bench magnifier and source of light (unless your eyes are better than mine…., component marking and colour codes can be VERY small!)

£12

B&Q etc

Use fine grade 600 / 1000…..

£6

Helping Hands these are terrific for holding small printed circuit boards and/or components while you solder them.

£5

Copper laminate board.

Probably get single sided board to start with, either fibre glass (more expensive) or paper resin type (cheaper, just as good)

£Various

‘Dremel’ drill

(needn’t be Dremel, there are others that will be just as good and cheaper, watch out for ‘shaft wobble’ you want  a drill that will keep a small drill bit straight without shifting from side to side!)

£25

Drill stand

(Best to try before buying, You want one with no ‘wobble’ as small drills can break easily!)

£25

A selection of small drills 1.5mm, 1mm, 0.8mm

£Various

Etchant  chemical

Ferric Chloride (or Ammonium Persulphate, Potassium Persulphate). Ferric Chloride stains easily, GREAT CARE needed!!!! Read the MSDS for any chemical chosen.

£Various

Optional – Brasso, Fine tipped permanent marker, Spray Lacquer

Brasso gives the board a quality shine, pens for marking component positions on the board and the lacquer ensures it stays there!

£5

There are so many and each has its own advantages and devotees! A few are listed here:

1. Making your own printed circuit boards.

a). Using chemical etching

- By photoetching.

- By painting tracks and etching.

1. Find a board layout diagram that matches the circuit you want to build.

2. Make a photocopy if you don’t want to destroy the original. Ensure the copy is to scale.

3. Cut out the layout and glue or selotape it to some copper laminate board.

4. Using your hobby drill, drill through the component holes.

5. Remove the selotaped paper and clean up the copper (very fine sandpaper).

6. Using the original board layout as a guide, paint the tracks on your copper board with a fine hobby paint brush and some enamel model paint. I find the stuiff nylon bristle brushes are best.

7. When dry, place the copper board in a suitable plastic container with a small amount of etching solution.

8. Gently agitate the solution but be careful NOT to get it on your skin or clothes.

9. You will see when the copper is etched away a change in colour as the board is exposed.

10. At this stage remove the board and thoroughly wash away any etchant solution.

11. Dry the board and using a suitable solvent (the wife’s nail polish remover is good. To be removed from its normal location with great care, cunning and dexterity as this stage can be more dangerous than the etching solution; death by irate wives is not unheard of! Replace the remover when the coast is clear).

12. Gently sand (clean) the board again, polish with Brasso, spray with a light coat of clear lacquer to protect the copper from tarnishing.

b). Using computer aided design

- By cnc machines!

1. Either, buy your own machine and spend weeks learning how to use it.

2. or, offer a suitable incentive to someone who has one!

3. These machines are great but there is a huge learning curve before you become proficient and of course to justify the cost you will need to be a prolific builder!

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2. Manhattan Island techniques.

The circuit above was built by PA1ED using Manhattan Island techniques; note also the wise use of separate modules for the different stages of the BITX20 transceiver design. No chemical etching, components either soldered to pcb ground plain or soldered to small pcb islands….look carefully at the .2” by .2” pieces of pcb superglued to the main pcb to provide isolated soldering points. Needs careful layout, can be very quick to construct.

To the right is a plan for a 2N2-40 transceiver by K3PEG using Manhattan Island techniques.

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3. Dead-bug.

Not for me, but preferred by some builders, quick to build, no chemical etching, tricky to make alterations or replace failed components, MESSY, but I’m biased and it does provide a useful quick solution to circuit building.

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4. Veroboard.

Preferred by some constructors, provides secure mounting for components, no chemical etching as tracks already pre-defined, small tracks easily cut, you’ll often need to use jumper wires between tracks, can be messy. QUICK to build. Needs soldering.

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5. Plug board

Very easy to test circuits before committing to pcb design. Quick to change, no soldering, thoroughly recommended for beginners. Although it has limitations when used with high frequency circuits. NOT really for permanent use, but if nobody is looking you might get away with it!!!

Small boards can be bought from China (through AliExpress, Ebay…) for $0.94 which includes postage.

Jumper wires are essential to make connections between various component tracks, you can make your own for ‘nowt’, or buy a set sufficient for most projects for another dollar!

So, how does it work?

1.    The vertical tracks (A) with the red and blue lines at the side of each are all connected and meant for a +ve or -ve connection to the power supply.

2.    The horizontal tracks (B) with numbers to the side are connected together; however horizontal tracks on either side of the central island are separated. So 1a, 1b, 1c, 1d, 1e are all connected to each other, BUT not connected to 1f, 1g, 1h, 1i and 1j.

This sounds complicated, but the example circuit below will help clarify the simplicity!

Now you can see why I advise it’s not for a permanent construction. This took me 5 minutes (ok, 10) to build and test…… no soldering, no etching, dead easy and equally easy to correct my inevitable daft mistakes! The hole spacing (0.1”) is ideal for integrated circuits as well.

Can you spot why the LEDs didn’t flash?

(Answer – the LEDs didn’t flash because the battery wasn’t connected!  Doh!)

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Poole Radio Society has no control over the content of these external web sites many of which will store cookies on your computer. 

Walford Electronics

Web Site - http://www.walfords.net/

Notes – Tim provides a range of kits to suit all skill levels, typically provision of a suitable case is left to the builder. Tim attends several radio rallies and can be found year on year at the Yeovil Radio Rally.

QRP-Labs

Web Site - http://qrp-labs.com/

Notes – A range of excellent value kits using ‘state of the art’ technology, possibly not for the first time builder.

HF Signals

Web Site - http://www.hfsigs.com/

Notes – Produces an excellent SSB Transceiver kit at a terrifically low price, ready built and aligned and just needing a suitable case to your design. Many modifications available.

Elecraft

Web Site - http://www.elecraft.com/

Notes – World class transceiver kits, expensive, but if your pockets are deep take a look!

JUMA Amateur Radio Kits

Web Site - http://www.jumaradio.com

Notes – An excellent range of receiver/transceiver kits, not for the first time builder.

Kit Radio Company

Web Site - http://www.kitradio.co.uk

Notes – A range of simple, suitable-for-beginners, receiver kits.

Radio Kits

Web Site - http://www.radio-kits.co.uk/

Notes – A range of amateur radio kits.

Kits and Parts dot Com

Web Site - http://kitsandparts.com/

Notes – A US supplier of a range of useful amateur radio parts (notably toroid’s) and a few transceiver kits.

Oak Hills Research

Web Site - http://www.ohr.com

Notes – A range of superb, albeit expensive amateur radio transceiver kits.

Vectronics

Web Site - http://www.ohr.com

Notes – A range of basic (beginner) receives and transceivers.

Spectrum Communications

Web Site - http://www.spectrumcomms.co.uk

Notes – A local (Dorchester) supplier of useful amateur radio kits and parts.

Ebay, AliExpress

Web sites -  http://www.ebay.co.uk/  and  https://www.aliexpress.com

Notes – There are a good many very cheap Chinese copies of well known simple transceivers…..they are very cheap indeed but the documentation is in ‘Chin-glish’ so be prepared. Nevertheless they are great for starters and Club help is always available. Use ‘Ham Transceiver kit’ as a possible search criteria.

Common Schematic Symbols