Franzis Do-it-yourself User manual

Do-it-yourself

VHF Retro Radio

65228-5 RADIO 160x110_HB+Titelei_Layout 1 11.11.13 11:42 Seite 1

Dear Customers,

This product was developed in compliance with the applicable European directives

and therefore carries the CE mark. Its authorized use is described in the instructions

enclosed with it. In the event of non-conforming use or modification of the product,

you will be solely responsible for complying with the applicable regulations. You should therefore

take care to assemble the circuits as described in the instructions. The product may only be passed

on along with the instruction and this note.

Waste electrical products should not be disposed of with household waste. Please recy-

cle where facilities exist. Check with your local authority or retailer for recycling advice.

All circuits and programs depicted in this book are developed and tested with utmost care.

Nonetheless, it is not possible to rule out all errors in the book or in the software. Publisher and author

are only liable in case of intent or gross negligence according to legal regulation. Beyond that, publis-

her and author are only liable according to the law on product liability concerning hazards to life,

body, and health and the culpable violation of essential contractual obligations. The damage claim

for the violation of essential contractual obligations is limited to the contract-specific, predictable

damage, unless in cases of mandatory liability according to the law on product liability.

part may be reproduced and distributed on paper, on storage media, or in the Internet, especially as

PDF, without the publisher‘s prior written permission. Any attempt may be prosecuted. Hardware and

software product names, company names, and company logos mentioned in this book are generally

registered trademarks and have to be considered as such. For product names, the publisher uses

mainly the spelling of the manufacturer.

Translation and DTP: G&U Language & Publishing Services GmbH

Author: Burkhard Kainka

Art & Design Cover: www.ideehoch2.de

ISBN 978-3-645-65228-5

65228-5 RADIO 160x110_HB+Titelei_Layout 1 11.11.13 11:42 Seite 2

The VHF Retro Radio

This modern VHF radio in vintage style receives FM stations

in the 87.5 MHz to 108 MHz band with good reception per-

formance. You will mainly hear the powerful local stations in

high sound quality. However, the sensitivity of the receiver also

allows you to listen to remote stations at times.

Large-scale introduction of VHF broadcasting began only after

1945. Initially there were still many radios that were able to re-

ceive only the AM ranges – long wave, medium wave and short

wave. Many devices, however, could be upgraded with VHF ret-

roﬁt kits. During the 1950s the tube superhet with VHF range

became widely accepted.

This radio looks very much like a typical portable radio of the

1960s. The invention of the transistor allowed the construc-

tion of radios that consumed less power than valve receivers

and therefore could be operated with batteries. Apart from this,

they technically still resembled the older tube radios.

Thanks to the highly integrated receiver IC TDA7088 building

your own VHF radio has become so easy that anybody will be

successful in soldering this radio together. The single-ended

low frequency ampliﬁer functions pretty much like the his-

torical tube radio. Your nostalgic radio works with a dual-stage

transistor ampliﬁer with medium volume at low battery volt-

age. Now you only need two 1.5-V alkaline batteries for up to

100 hours of radio reception. With your DIY-radio listening to

the radio will become even more fun. Enjoy the diversity of the

VHF stations.

Components

• pre-assembled PCB with TDA7088

• rod antenna

• speakers 8 Ω, 0.5 W

• volume control 22 kΩ with switch

• tuning control 22 kΩ

• insulated wire

• battery compartment with connection wires

• T1 PNP transistor BC557B

• T2 NPN transistor BC547B

• D1 varactor diode 1SV101

• R1 4.7 kΩ (yellow, violet, red)

• R2 220 kΩ (red, red, yellow)

• R3 1 kΩ (brown, black, red)

• R5 330 kΩ (orange, orange, yellow)

• R6 33 Ω (orange, orange, black)

• C15 electrolytic capacitor 100 µF

• C17 100 µF ceramic (104)

Assembly of the control elements

The radio has two rotary controls – one for frequency and one

for volume. The three-port volume controller is equipped ad-

ditionally with the two-port on/off switch. If you turn the axis

all the way to the left, the switch opens. Insert the volume con-

troller into the left mounting hole. A small tab secures correct

insertion. Fix the controller with the ring nut and do not forget

the washer.

The second potentiometer with 22 kΩ is used for frequency

tuning and is mounted on the right. The connections of both

potentiometers should face inwards so that the board can be in-

stalled between them later. Then screw both rotary knobs onto

the axes so that the end stops are aligned with the printed scales.

Volume control (potentiometer) with switch

Insert the speaker by pushing it into the corresponding slot. The

connectors should face upwards to make sure that the connec-

tions to the board will be short. The speaker sits securely in its

slot. You can, however, also add a drop of adhesive or hot glue.

Loudspeaker

Screw the solder lug to the base of the telescopic antenna. Then

slide the antenna from the inside through the housing opening

and push the end into the ﬂat holder which you have to secure

correctly in the housing with the enclosed adhesive tape. Now

the antenna is mounted sufﬁciently ﬁrmly but can still be ﬁxed

with some additional adhesive tape later.

The antenna

Soldering

The board contains a large number of SMD components (sur-

face-mounted device, wireless components) already soldered

on: the receiver IC TDA7088, 15 condensers and one resistor.

You will only need to solder in some components with con-

necting wires. This includes all components of the AF ampliﬁer,

the coils and all components needed for the diode tuning of

the radio.

The SMD components

Now the PCB is to be assembled, please refer to the circuit dia-

gram on the last page of the manual for orientation.

Components on the circuit board

Equip the PCB with the electronic components according to

the layout diagram. First install the coils SP1 and SP2. Both

coils have to be built of the included connecting wire. They

each have three turns with an inner diameter of 5 mm and a

length of approximately 7 mm. Use the electrolytic capacitor

100-µF as winding mandrel. First wind three turns closely ad-

jacent to one another. Then pull the turns apart to reach a total

length of approximately 7 mm. Absolute accuracy is not crucial

here because the coil can still be slightly modiﬁed after instal-

lation. Remove the insulation from the wire ends. Only then

pull off the coil from the winding mandrel. Now solder on the

two wires at the bottom. Then cut off the protruding wires with

sharp pliers approximately 2 mm above the circuit board.

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