Sunday, December 22, 2013

FM Radio Station Part 2 Assembly

Flipped reverse side photo to match component side
MINI FM RADIO STATION  Note top side component placement. Top two holes are for the 9-volt battery clip leads with ground on the left side. The left bottom hole and the bottom right hole are for the antenna connection.
Connections are easily seen when the printed circuit board is back lit, showing the circuit board traces on the reverse side. This makes it easier to match component locations to the schematic diagram.
Schematic diagram for a two stage transistor FM transmitter. Features microphone driven audio input, with tunable frequency range with L1. Operates on a 9-volt battery. Range tests are yet to be determined but the frequency appears to be around 100MHz on the FM band.

Rotated left to right view for component placement

Work is progressing on the electronic construction of the Lab's two stage exampling FM radio station. Stay tuned to this series of blogs as we supply the details of going on the air, as well as technical info so you can roll your own in-house radio station for fun.

The test transmitter printed circuit board has 17 components mounted and ready for soldering. This blog details the component placement and the circuit traces on the printed circuit board and includes transistor placement guides and a schematic for assembly. Note the two transistor identifications in the illustration showing keyed emitter, base and collector locations. 

The power board uses two transistors, a C1675 K6YC at the right side of the board (see photo above) and a C9013 H049 nearest the microphone. The circuit has one electret microphone input for voice operations and includes one coil, two transistors, two electrolytic capacitors, five ceramic disc capacitors, and five resistors. Not shown is a 9-volt battery clip and the antenna.
Verified leg identification ok
The antenna is only a few inches of wire which minimizes the range for initial testing, and limits use and range of reception to inside the lab room. The electronic project goal is an exampling in-house educational fully functional radio station. More tests will determine the range characteristics more precisely.
Note that some countries and municipalities allow short range transmitters of this type and some do not. Be sure to first check local laws and regulations before proceeding with the project.

The copper printed circuit side of the board with through hole leads ready for hot soldering
Ok to Use: MICRO Data/Japan data
The coil in combination with the parallel capacitor tunes the circuit to a frequency within the FM band.

Frequency trimming is accomplished by stretching or compressing the coil or modifying the value of the ceramic parallel 10 pF capacitor.

Initially the frequency should be in the range of 88 to 108 mHz on the FM band.

Warning - do NOT use USHA India/LGE leg positions
The radio station will have an identical twin backup system for service or parts to remain up and running as necessary.

The cost of the first set of parts is NT$132 (US$4.42) and the backup duplicate parts are NT$120 (US$4.00). Thus far, combined cost is US$8.42 for the hardware.

The transistor leg identification does not agree from one data sheet to the next. See diagrams.

Careful with data sheets for the 2sc1675 transistor as there are discrepancies between the TO92 and TO92b case versions. For example, the equivalent Panasonic 2sc 829 equal to 2sc 1675 as a substitute is in agreement with the transistor placement of emitter, collector, base, therefore this is the arrangement to use.

FM Radio Station Part 5 Index