Small Wonder Labs Retro-40 Manuel utilisateur

‘Retro-40’ Instructions July 11, 2011 Page 1

‘Retro-40’ AM Transceiver

Board Kit Instructions

For illustrative purposes only- do not use as a reference.

Thanks for purchasing a Small Wonder Labs "Retro-40" transceiver kit!

Please take a few moments to look over the sections entitled "First Things First" before

you dive in. This section contains information which is key to your success with this kit.

TABLE OF CONTENTS:

Tools/Basic Info 2,3

Component Identification 4

Retro -40 Description 5,6

Parts List 7, 8

Schematics 9-10

Pictorial Drawing 11

Building instructions 12

Wiring Up the ‘Retro-40’ 14

Alignment 15-16

Troubleshooting the "Retro-40 " [under construction]

‘Retro-40’ Instructions July 11, 2011 Page 2

THE FINE PRINT:

There are lots of small parts in this kit. I strongly

recommend a magnifying glass or close-up

glasses to check all solder joints and component

codes.

THE OTHER FINE PRINT:

If you encounter conflicts between various

sections of this document, contact me for a

resolution. The following order of precedence

applies:

•

Schematic (most trustworthy)

•

Parts list

•

Pictorial

TOOLS:

You'll need the following tools:

-Soldering iron- ~25W

- 60/40 solder, small diameter

-Diagonal cutters

-Needle-nose pliers

-Small slot screwdriver

TEST EQUIPMENT:

- Multimeter

- 50-ohm dummy load

RETRO-40 Power Requirements

The RETRO-40 is designed to operate with a

minimum supply voltage of approximately 10V. A

power supply capable of delivering a minimum of

1 Amp at 12-14 Volts DC is recommended.

Maximum recommended supply voltage is

16VDC.

A low-cost supply suggestion: Jameco's #319920,

15V regulated 'wall-wart'. They're at

www.jameco.com. Note: the less expensive

unregulated 'wall-warts' will not provide

adequately filtered DC- don't waste your

money! 'Filtered' is not sufficient- you need to

see the word ‘Regulated' on the description.

FIRST THINGS FIRST -

-Stuff worth knowing!

COLOR CODES:

Resistor color codes are given in the parts list.

Radio Shack's Color-Code Guide, #271-1210, or

the ARRL Handbook will help. If you're not sure,

verify the resistor values with a multimeter before

installing.

For what it's worth, roughly 8% of the male

population is red/green color-blind. If you're one of

these, you should be verifying all resistors with a

multimeter before installing them.

The RETRO-40 board is double-sided and all

holes on the board are plated-through. This

means that you do not need to solder on the top

side of the board.

SOLDERING SKILLS

Hopefully this isn't your first experience with a

soldering iron. If it is, though, or this is your first

solid-state project, here are some tips to ensure

your success:

- Soldering Iron:

Use a small iron in the 25-watt class (such as a

Radio Shack #64-2070) and keep the tip clean.

Use a moistened sponge or paper towel to clean

the tip periodically as you work.

Apply only as much heat as is needed to get a

good joint. A small vise to hold the printed-circuit

board may make soldering easier.

Touch the soldering iron tip to the PC board

trace and the component lead simultaneously.

Within a second or two, apply solder and you'll

see the solder flow onto the junction. Withdraw

the solder and then the soldering iron.

Avoid the temptation to load solder onto the joint

until no more will fit! This is an invitation for

trouble, as solder bridges may form across the

closer trace separations. Here's what the correct

and incorrect joint treatments look like:

‘Retro-40’ Instructions July 11, 2011 Page 3

PLEASE READ THE SECTION BELOW

BEFORE REMOVING ANY PARTS FROM THE

BOARD

Uh-oh! Sooner or later, you may need to remove

a part installed in the wrong location, or perhaps

pull a component for troubleshooting purposes.

Get yourself a roll of desoldering braid (Radio

Shack #64-2090B). Lay the end of the braid

down on the joint to be cleaned and press the

soldering iron tip over the braid. Within several

seconds you'll see the braid begin to wick up

solder from the joint. Remove the braid and

reapply a new section as needed until the joint is

clean. It may be necessary to pull the component

out from the top side of the board while heating

the joint. Leave the iron tip on the board only as

long as necessary to do the job- the PC-board

traces will eventually delaminate (peel off) if

overheated.

If that still doesn't do the job, it may be necessary

to cut the offending part off on the top side and

pull the remaining leads through with pliers.

If you need to remove a transistor, I'd highly

recommend sacrificing the part by snipping it off

on the top side of the board. The leads are best

pulled out singly to minimize the risk of lifting

pads. Contact me for replacement parts if

necessary.

After removing a component from the board, the

through-hole will probably still be blocked with

solder. Use a dissecting needle or dental probe

(explorer), apply heat to the probe and the board

trace simultaneously until the tool pushes through.

Lacking either of these tools, a round wooden

toothpick works well also!

WINDING TOROIDS:

-Count as you go. Draw each turn snug against

the core to ensure a trim and tight winding

-Double-check the turns count when you're

finished. Use your fingernail or small screwdriver

to "bump" over each turn as you count- this is

easier than counting by eye.

- Trim the excess wire off to about 3/8" (1cm) and

strip the insulation off the ends with a knife-edge

Counting the turns:

If the wire passes through the toroid center

hole, it counts as a turn. Here's an example:

MATERIALS-

You'll find the following items with your Retro-40

kit:

1- bag of parts, miscellaneous

1- antistatic bag (contains semiconductors)

1- poly bag (resistors/capacitors)

1- printed circuit board

- (these instructions )

GOOD

SOLDER FILLET IS CONCAVE AND 'WETS'

SMOOTHLY TO COMPONENT LEAD

BAD

SOLDER FILLET IS CONVEX OR DOES NOT

ADHERE TO COMPONENT LEAD

This toroid is wound with 8 turns

Turns must be uniformly distributed around

the circumference of the toroid.

‘Retro-40’ Instructions July 11, 2011 Page 4

REFERENCE DESIGNATORS:

Each component is uniquely identified with a

reference designator. Bypass capacitors are

identified as C101 and up. Reference

designators are shown in blue on the schematic

pages. Component values are shown in magenta.

OMPONENT IDENTIFICATION

•

Resistors and RF chokes

This manual describes the color coding for all

resistors. Only the first three bands are described,

the fourth band is a tolerance code, typically gold

(=5%) and is not listed. All resistors are 1/4W 5%

carbon film types, RF chokes are also an axial

(leads on each end) component but are shaped

differently.

•

Capacitors:

Electrolytic caps. The black band

denotes the negative end of the capacitor.

•

NPO Disk Caps

NPO disk caps may be distinguished from

other types of disk caps- they have a black

band at the tip of the ceramic disk.

•

Extra information on components

There's often extraneous information marked on

components. Examining a sample IC, I find

"MC1458P1 KKJK 8949". You care only about

the '1458' or other markings I've specified If I've

specified a capacitor '104' and you find the

correct number of parts, but marked "104M', for

instance, those are them!

Here's the general rule for capacitor

nomenclature:

If 3 digits are printed on the capacitor, the first two

are significant figures and the third is a multiplier.

Examples:

'471' = 47 x 10

1 =

470 pF

'103' = 10 x 10

3 =

10,000 pF = .01 uF

Letter suffixes: J=5%, K=10%, M=20%.

Please: If you're looking for a '104' monolithic

cap, be sure to inspect both sides of the caps

before concluding we gave you the wrong value!

Monolithic caps.

Poly Cap

D5- MV1662 Diode

‘Retro-40 Instructions July 11, 2011 Page 5

‘Retro-40 ‘ Description

Note: The text which follows describes the original (75M) Retro version. For the 40M

version , the IF is changed from 6 MHz to 4.915 MHz, and tuned circuits and the output

low-pass filter values are changed. The operating frequency is in the 7.0-7.3 MHz range.

Inspirations:

I’ve long been intrigued by relatively simple voice radios. The BC-611/SCR-536 [at right] was widely used

during WW II as a platoon-level radio. It had a ‘bare-bones’ crystal-controlled superhet receiver and an

AM transmitter with 350 milliwatts of output power. It had an effective range of about a mile with its built-

in whip antenna. Although pressed into service in the postwar years by enterprising hams, its lack of

selectivity limited its usefulness under crowded band conditions. As I extrapolated from this radio’s

highly inefficient whip antenna to a full-sized dipole, I realized that the effective range would be upwards

of 50 miles. In my book, that’s a usable communications distance for keeping in touch with friends! That

served as a challenge and as the inspiration for this project.

Although AM has long been supplanted by more effective modes of communication, AM activity is largely

channelized into ‘watering hole’ frequencies

See www.AMwindow.org . It’s therefore pretty easy to find

activity on the air. 7290 kHz is the standard ‘hot spot’ for 40M; this may vary by Region.

Receiver:

The receiver front end is entirely conventional. A series L-C T-R switch and bandpass transformer feed the SA612 first

mixer. The SA612’s internal oscillator is used to save component count by eliminating the need for a separate local

oscillator (LO) transistor. The varicap diode-tuned LO covers about 50 kHz of the 75M band. It operates at approximately

2.1 MHz and the 1

mixer up-converts to the Intermediate Frequency (IF).

In the interest of tradition, I initially used 455 kHz IF transformer in an IF design. A double-tuned filter using these

transformers proved woefully inadequate in keeping close-by SSB stations out of the detector stage. In light of the BC-

611’s lack of selectivity, this was largely a case of ‘reinventing the wheel’. Rather than wrestle with more stages of

filtering or the use of ceramic filters, I reverted to a tried-and-true crystal filter. I chose an IF of 6.00 MHz to keep both the

filter bandwidth and the LO frequencies reasonable. With the filter values shown on the schematic, pass bandwidth is 3.5

kHz with adequate skirt characteristics. I found it necessary to ground the case of crystal Y3 to eliminate pickup of strong

AM signals from the 49M shortwave broadcast band.

The IF amplifier uses the so-called ‘cascode’ configuration. Although the MC1350 IC is often used here, it’s been around

for an uncomfortably-long number of years. Parts cost was a factor, too- the discrete cascade amp has a parts cost of

about 15 cents. This amplifier is terminated by R6, whose value was chosen as a compromise between stage gain and

consistently stable operation.

The following stage is a peak detector which serves to recover the modulation envelope from the received signal. Q3 is

an ‘infinite-impedance detector’- a JFET biased near cutoff. I’d always wanted to say I’d used one- the phrase has a

nice ‘Hitchhiker’s Guide’ ring to it. I found it more sensitive in practice than an unbiased 1N34 Germanium diode.

U3- an LM386, is a widely-used AF Amp IC, and provides plenty of speaker volume. The transistors around it serve

several functions, Receiver audio needs to be firmly shut off during transmit. The transistor switch in series with the

LM386 output is important. That IC’s output voltage is dependent on supply voltage. As the power supply ‘pulls’ on voice

peaks, it yields an unwanted feedback path to the speaker.

The audio output waveform is also peak-detected by D6 and C20 and applied back to the gate of Q4 as a form of

Automatic Gain Control (AGC). Without it, nearby ‘Big Gun’ stations are easily capable of saturating this amplifier stage,

yielding harsh-sounding clipped audio. The AGC threshold is nominally 6 volts peak-peak, depending on the individual

characteristics of Q4. With this feedback path in place, even the strongest of stations sounds fairly clean in the receiver.

courtesy of N6GCE

www.prc68.com

‘Retro-40 Instructions July 11, 2011 Page 6

Transmitter:

The RF strip consists of a crystal-controlled Colpitts oscillator, a FET-driver IC, and a MOSFET Power Amplifier stage.

The PA stage runs class-C to keep the transmitter efficiency reasonably high. Generating an amplitude-modulated output

is done using one of the oldest tricks in the book: the transmitter’s supply voltage is varied by superimposing audio on it

through transformer T3. This is an inexpensive 48Ω:3.2Ωaudio output transformer. In this application, the transformer is

run ‘in reverse’ to step up the voltage output from U6. With no audio applied, the transmitter outputs a steady carrier. At

full (100%) modulation, the PA supply voltage swings to a minimum of 0V and to a maximum of twice the nominal supply

voltage.

In theory, this method is simplicity itself. When it’s extended to higher power levels, though, a pitfall becomes evident.

The necessary modulation transformers become rather formidable in size, and they were fondly referred to as ‘Big Iron’ by

the AM fraternity. The more modern term is, invevitably ‘Heavy Metal’. I considered heating in T3 (a maximum specified

output of 475mW) to be a design constraint and elected not to push it too hard. The transmitter runs about 2W of carrier

power and 6-7W peak output. I ran key-down tests of up to a half-hour duration- they showed minimal transformer

warming.

The ‘Big Iron’ approach is still in use, but it sees action mainly in vintage equipment. The necessary transformers have

largely gone the way of the hoop skirt and whale-oil lamps. More recent practice uses pulse-width (class-D) modulation to

directly form a varying power supply voltage, with a resulting improvement in transmitter efficiency, Other modulation

classes improve further on efficiency. The interested reader is invited to see Steve Cloutier- WA1QIX’s web site

www.classeradio.com for a treatment of the topic.

The FET driver, U8, is one of a family of devices with various peak drive-current ratings. The TC1412 can source/sink 2

Amps peak; other versions can supply up to 8 A. Its output is a 3.8 MHz square wave varying between 0V and 6V. I

selected the device for its small (8-pin DIP) footprint, but other builders have used CMOS hex inverters (for instance) with

all gates connected in parallel for higher drive current capability.

The choice of a microphone can often be problematic. I’d initially planned on using an HT speaker/mic to do the job, but

their typical shared mic/PTT line led to considerable complexity in T/R switching and AGC ‘gating’. I reverted to the classic

approach - a manually-operated switch- to do the job. This is more in line with the relaxed AM ‘ethos’ and lends more

flexibility to the choice of microphones. I settled on a Radio Shack

dynamic microphone, largely because of its modest

cost and wide availability.

U6 is a 10-Watt automotive AF amplifier in a 5-pin package. This device was attractive both for its output power capability

and for its ‘beefy’ heat sink tab. Voltage gain (40dB) and frequency response are established by the R-C networks

between pins 2 and 4 of this device.

A sample of the AF Amplifier’s output is peak-detected and applied back to an attenuator at the stage’s input. The

attenuator is formed by the series resistor between AF stages and a shunt to ground provided by Q10. The series diode,

LED and turn-on voltage of Q10 provide a fairly consistent AGC threshold at about 75% modulation. The 3.3K resistor in

the path is there to slow the AGC response time for ‘pop-free’ operation. . The AF amplifier is easily capable of

overmodulating the carrier, so it was gratifying to ‘close the loop’ and observe its effect on modulation percentage.

Transistor Q9 is turned on during receive intervals to mute the transmit audio strip.

Receiver ‘Test’ function:

One of the impediments to building an L-C oscillator (here used as the receiver LO) is that component tolerances make

the resulting operating frequency somewhat uncertain. CW/SSB projects can usually count on a borrowed signal from a

‘big rig’ in the shack to locate and adjust the local oscillator to frequency. With AM, though, there’s no ‘beat note’, and

you’ll probably hear an ‘in-shack’ AM signal everywhere you tune. The circuit block labeled ‘Test’ provides a built-in

frequency adjustment tool. At its heart is an 8-pin microcontroller coded as a frequency discriminator. It outputs a duty-

cycle modulated waveform which a digital multimeter will interpet as a DC voltage. Based on the DC reading, the builder

can compensate with a ‘select’ capacitor to bring the oscillator on frequency. See the ‘Alignment’ section of these

instructions for further details.

‘Retro-40 Instructions July 11, 2011 Page 7

‘Retro-40’ Parts List

Qty. Ref. Designator Description Identification

2 C3-A,C22 22 pF NPO disk ‘22’

C3 6-30 pF trimmer Green

C8-C11 33 pF NPO disk ‘33J’

3 C1,C2,C3-B 47 pF NPO disk ‘47J’

1 C3-C 68 pF NPO disk ‘68J’

7 C3-D, C4,C12,C13,C34-C36 100 pF NPO disk ‘101J’

1 C3-E 120 pF NPO disk ‘121J’

1 C3-F 150 pF NPO disk ‘151’ or ‘151J’

2 C38,C41 270 pF mono. cap ‘271’ or ‘271J’

1 C26 330 pF disk ‘331’ or ‘331J’

2 C39,C40 680 pF mono. cap ‘681’ or ‘681J’

1 C15 .001 uF poly ‘102J’, or ‘1n0’

2 C6,C7 2200 pF mono

. cap

‘222’

1 C5 6800 pF mono. cap ‘682J’

10 C14,C23,C101-104,106,109,C113,C114 .01 uF disk ‘103M’

1 C25 .015 uF poly ‘153’ or .’015’

1 C16 .033 uF poly ‘333’ or ‘333J’

9 C18,C24,C29,C31,C37,C108,C111,115,116 .1 uF mono. ‘104’

4 C21,C27,C28,C32 1 uF electrolytic ‘50 v 1 uF’

2 C17,C20 10 uF electrolytic ’35 v 10 uF’

3 C33,C107, C110 100 uF electrolytic ’16 v 100 uF’

3 C19,C105,C112 220 uF electrolytic ‘25V 220 uF’

1 C30 470 uF electrolytic ‘470 uF 10v’

10 D1-D4, D6-D9, D11,D12 1N4148 diode glass body

1 D5 MV1662 varicap diode 2 leads, banded

1 D10 LED red plastic, 2 leads

1 D13 1N5818 rectifier diode ‘1N 5818’

1 L1 10 uH RF choke btown-blk-blk-gold

1 L2 T68-6, add 32 turns #24 wire

Use 30” (75cm) of wire to wind

yellow toroid, large

1 L3 FT37-61, add 10 turns #24 wire

Use 8” (20cm) of wire to wind

dark grey toroid

2 L4, L6 T44-2, add 16 turns #24 wire

Use 12” (30 cm) of wire to wind

red toroid

1 L5 T44-2, add 18 turns #24 wire

Use 14” (35 cm) of wire to wind

red toroid

6 Q1,Q2,,Q7,Q8, Q10, Q11 2N4401 transistor

1 Q3 2N5485 transistor

4 Q4-Q6,Q9 2N7000 transistor

1 Q12 IRF530A power transistor

1 R26 1 ohm resistor brn-blk-gold-gold

2 R8, R25 2.2 ohm red-red-gold-gold

2 R9, R17 10 ohm “ brn-blk-blk-gold

2 R5, R23 47 ohm “ ylw-viol-blk-gold

1 R24 220 ohm “ red-red-brn-gold

4 R11, R14, R33, R36 1K ohm “ brn-blk-red-gold

2 R2, R16 1.5K ohm “ brn-grn-red-gold

2 R29, R30 2.2K ohm “ red-red-red-gold

1 R27 3.3K ohm “ org-org-red-gold

5 R3, R4, R6, R17-A R21 4.7K ohm “ ylw-viol-red-gold

3 R18, R19, R22 10K ohm “ Brn-blk-org-gold

‘Retro-40 Instructions July 11, 2011 Page 8

‘Retro-40’ Parts List (cont’d)

2 R31,R32 47K ohm “ Ylw-viol-org-gold

7 R10, R12, R13, R15, R20, R28, R35 100K ohm “ Brn-blk-ylw-gold

1 R34 220K ohm “ red-red-ylw-gold

2 R1, R7 1M ohm “ Brn-blk-grn-gold

2 T1,T2 IF transformer metal can-‘42IF123’

1 T3 Audio transformer ‘TU048-R’

1 U1 SA612AN IC

2 U2, U7 78L06 – 6V voltage regulator IC

1 U3 LM386 IC

1 U4 12C508A IC preprogrammed

1 U5 LM1458/MC1458 IC

1 U6

TDA2003V IC

1 U8 TC1412N IC

3 Y1-Y3 5.185 MHz crystal

1 Y4 7.290 MHz crystal

5 - 8-pin IC socket

2 - 4-40 x ¼” machine screw

2 - 4-40 nut

2 - Heat sink

1 - 4-40x ½” nylon machine screw

1 - 4-40 nylon nut

1 - 4-40 nylon shoulder washer

1 - 6’ (1.8m) #24 magnet wire

‘Retro-40 Instructions July 11, 2011 Page

Dave Benson, K1SWL 7/11/2011

40M AM Transceiver - p.1 of 2

.001

4.7K

2N7000

AF Out

2.2 220 uF

50K

LM386

100K

Vsw

2N7000

10 uF

220 uF

.033

.01 Vr

L1 T1 SA602

1 Mhz

6800

NPO 2200

NPO

(2 pl)

4.7K

.01

1.5K

4.7K

.01

5.185 Mhz

47 10 uH

100

50K

RX TUNE

GAIN

100

100K

10 uF

78L06

.01

1K .01

100K

22 pF

100K

1.5K

TP1

'TEST'

CLK IN Vss

Vdd

12C508A

GP2 GP1

C6 C7

C9 C10

C11

Y1 Y2 Y3

ground case

C12

C102

C103

C104

C13

C14

R6 R7

C15

C16 R8 C105

C17 C18

C19

R10

R11

D8 C20

R12

C22

R14

R16

R13

C23

R15

Q7 Q8

C101

L2: 32 turns #24

on T68-6

n/c

.01

1 uF

C21

C106

C3-A

22 22

150

‘Retro-40 Instructions July 11, 2011 Page 10

7.122

MHz

40M AM Transceiver - p.2 of 2

7/11/2011

.01

MIC

Vsw

ANT.

10K

.1 4

100

Dave Benson, K1SWL

1.38 uH

HDBK

#97

DC power

12-15V ( )

1N5818

330 pF

Pri. Sec.

1.70 uH

270 270

680

78L06

IRF530A

100 uF

Q12

(T)

(R)

R17

R18

C107

C108

C109

C26

C24

L4 L5 L6

C37

C38

C116

C39 C40 C41

1 uF

100K

100 uF V

100K

1 uF

R20 C110 C111

.1 uF

220

2.2

470

4.7K

10K

1 uF

100

100K

(Y5)

47K

100

220K

1412N

1,8

6,7

4,5

Q11

2.2K

.01 .01

C113 C114 D11 D12

C115

3.3K

Q10

220

R19

10K

C25

.015

R21

R22

R23

R24

R25

R26

R27

R28

R29

R30

R32

R31

R33

R34

R35

R36

C27 C28

C29

C30

C31

C33

C32

C34

C35

C36

C112

D10

D13

100 680

1.38 uH

T44-2, 16T T44-2, 16T

T44-2, 18T

R17-A

4.7K

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