15W FM Transmitter based BLY88C

Making a quality FM transmitter (88-110Mhz) starts with getting the right schematic. You do not need to understand the precise operating of the transmitter to construct it. But some basic knowledge won’t harm. A transmitter alone is, as you most likely know, is not enough to start your radio-station. Within the simplest form you need four things. First an input device like an amplifiler you also use together with your home-stereo.

You are able to also use a walkman. Details about input-devices in the page: “Input”. Second you need a regulated power-supply. In this case a 14-18 Volts/2,5-3,5 Ampere. 1 of probably the most influencial things you need is antenna and coax-cable. More about this later on. And finally the transmitter itself. You are able to devide the transmitter in two main parts: the oscilator and also the amplifiler. The oscilator converts electric sound info into electromagnetic waves. The amplifiler gives these waves
a larger amplitude.

It is stable and has output of 15-18 watts. This sufficient to terrorize your wide surroundings at the fm-band.

15w fm transmitter copper board

Probably the most often utilized technique to connect the components to one another is soldering them on a double sided copper-board. An additional way is connecting the components floating. It’s less expensive but very tricky. Below you see the copper-board layout(PCB).

To obtain this pattern in copper surface you start using a acid bath. Use a water-resistant permanent marker to paint your own copper-board black within the pattern the shown above. Color the back side ompletely black. The grid-squares are 0,5*0,5 cm each.

Copper bath

When the acid has eaten the non-painted copper away you must eliminate the complet thin layer of black paint with sandpaper. Don’t eliminate too much copper with it.

So, now you’ve the surface to solder the electric components on.

Now a couple of basic rules for great soldering:

  1. Use a special electronics-solderingrod having a slim top.
  2. Use soldering-metal with an anti-oxidant-fluid core.
  3. Do not heat the components! Heat the connection-point on your PCB.
  4. Make sure that the surface isn’t too smooth.
  5. Don’t use an excessive amount of metal.
  6. Do not let the soldering metal form a bridge beetween two copper-surfaces.
  7. If you are intelligent you begin from the middle of your prepaired board.

In this way you will have sufficient space.

The following is the schematic diagram. The yellow lines are pieces of copperboard that devide the transmitter in three parts. This is essential. With out them, internal interferrence will ruin your signal.

Fm transmitter PCB

Fm transmitter parts

Fm transmitter components

There are some parts that need extra attention. Transistors generally have three or four various
wires comin’ out. If you connect these wires in the wrong way the transmitter won’t work. It may even explode. The picture below shows how to prevent from such an event.

Transistor pin layout

You can find the numbers and letters back in the soldering schematic.
Coils also need additional attention. You can buy the coils trough ferrite in the shop, but the other ones have to be created your self. Use 1mm AgCu wire. A coil like 7x/d=10mm/l=15mm, goes round 7 times, has an diameter of 10 millimeter and is long 15 millimeters. The best method to make a coil would be to bend it around a pencil or other cilindrical shaped object tight. The diameter of the object is usually d-coil minus 1 mm. In this case 9mm. As I said: bend the wire round (in this case 7times) with the revolves tight together. To obtain the desired length stretch the coil when still around the pencil.

15W FM Transmitter based BLY88C Source:http://www.sz123.com/15w-fm-transmitteruse-bly88c.html

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