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Franzis Do-it-yourself User Manual

Vhf retro radio
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Do-it-yourself
VHF Retro Radio

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Summary of Contents for Franzis Do-it-yourself

  • Page 1 Do-it-yourself VHF Retro Radio...
  • Page 2 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. © 2014 Franzis Verlag GmbH, Richard-Reitzner-Allee 2, 85540 Haar, Germany All circuits and programs depicted in this book are developed and tested with utmost care.
  • Page 3 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.
  • Page 4 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.
  • Page 5 Components • pre-assembled PCB with TDA7088 • rod antenna • speakers 8 , 0.5 W Ω • volume control 22 k Ω with switch • tuning control 22 k Ω • insulated wire • battery compartment with connection wires • T1 PNP transistor BC557B •...
  • Page 6 • D1 varactor diode 1SV101 • R1 4.7 k Ω (yellow, violet, red) • R2 220 k Ω (red, red, yellow) • R3 1 k (brown, black, red) Ω • R5 330 k Ω (orange, orange, yellow) • R6 33 Ω...
  • Page 7 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...
  • Page 8 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.
  • Page 9 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.
  • Page 10 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.
  • Page 11 Winding the coils Installation of the coils Insert the resistors R1 (4.7 k Ω , yellow, violet, red), R2 (220 k Ω red, red, yellow) close to the connections to potentiometer PT2. The resistors R3 (1 k Ω , brown, black, red), R5 (330 k Ω...
  • Page 12 the AF amplifier on the other side of the board. The resistor R4 (5.6 k Ω ) is already soldered as an SMD component. Now bend the connecting wires so that they are suited for vertical assembly. The resistors Solder the D1 varactor diode (1SV101 in the flat transistor housing with two connections, imprint V101), following the direction shown on the PCB marking.
  • Page 13 Now solder in the electrolytic capacitor C15 (100 µF). Observe the mounting direction. The positive terminal is marked on the board. The negative terminal – which is marked with a white line – points towards the IC. Afterwards install the ceramic disk capacitor C17 with 100 nF (print 104).
  • Page 14 Next, solder on the appropriate wire pieces to the two potenti- ometers. For length refer to the wiring diagram. Now you can either pass the wire ends through the holes and solder them like the other components or, alternatively, you can solder them flat on the solder pad.
  • Page 15 The wiring diagram The complete wiring...
  • Page 16 Initial testing and settings Insert two 1.5V mignon alkaline batteries. Turn on the radio and set the volume control to maximum. Turn the frequency knob, and you will quickly find a station coming loud and clear from the speaker. Now you have to adjust the frequency. Use a radio at hand for comparison.
  • Page 17 Reception practice When fine-tuning a station, the receiver’s AFC (Automatic Fre- quency Control) will lock on to the exact frequency. Then the station can be heard in a certain range of the frequency control- ler. Position the controller as exact as possible in the middle of this range.
  • Page 18 Explanations on the wiring diagram Most VHF superhet receivers use an intermediate frequency of 10.7 MHz. The receiving frequency is first converted to the in- termediate frequency and then filtered, amplified and demodu- lated. The VHF retro radio is a superhet, too, which converts the received signal to an intermediate frequency.
  • Page 19 The board is designed in a way that its components are all as- sembled in SMD technique around the actual TDA7088 re- ceiver. That makes construction easy. You can exchange some of the wired components you have soldered yourself to modify certain properties of the radio.

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