FM Transmitter Antenna 88-108 MHz

Introduction
Antenna is final device for sending any information from your transmitter. In fm transmitter you need signal transmitted to any direction so you need antenna type that transmitted with polarized circularly.  Antenna gain -3.2 dB, bandwith 500 KHz with maximum power handling 500 Watts. In order to use antenna on 88-108 MHz, broadband antenna type must be designed with no tune involved.




Signal Amplification
Amplification of signal to transmit based on antenna gain in Decible. Signal from transmitter be able to doubled, tripled or even become more power. The value is called ERP (Emmittion Radiating Power). For Doubled your transmitter power to be ERP Power need stacked 4 antennas (3.12 dB gain antenna), 6 antennas (5.12 dB), 8 antennas (6.4 dB).
ERP = Transmitter Power x Antenna gain.



Below is picture of the antenna dimension .

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A Small FM Transmitter With Loop Antenna

This small Low Power FM transmitter with Onboard Magnetic Loop Antenna that designed by Radio Morningstar. It's suitable for home fm broadcasting. As seen on YouTube Page.

This is the PCB board layout for a small LPFM transmitter that i'l showed on Youtube. This new design is even more powerfull, using 4 instead of 2 transistors. The range will go up to 2 kilometers or even 4 - 7 km using een external twinlead fed 300 ohm folded dipol antenne. Or use just 2 transistors for less range using a 100 Ohm Emitor resister instead of the 33 Ohm for lower battery consumption.

Take good notice by placing the transistors , for the BF 199 the connections are 1 Basis 2 Emittor 3 Collector. One set transistors is placed 180 degrees backward , be sure all the collectors are connected at the antenna loop. Visit Radio MorningStar

PCB Layout with components :



The PCB Layout , print this 10 x 15 cm on your printer to get the right printfolie for exposing your PCM material:



The component's silkscreen:

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How To Stack FM Broadcast Antenna

Stacking your broadcast antenna will make your antenna have more gain. If your antenna have more gain, more ERP (Emmittion Radiating Power).

What do you need for stacking antenna?

- More antennas that identical each others.
- Power divider to distribute your RF power to each antenna.
- Jumper cables to connect antennas

Stacking for 4 Antennas

Antenna :
Prepare 4 identical antenna. Tune the antenna for Matching on the working frequency.


Power Divider :
Prepare 1 power divider with 1 port input and 4 ports output.

Jumper Cables :
any length of coax cable with 2 N connectors to connect between power divider and antennas.

Determine Range between Antennas

When you install the antennas in collinear system, you must observe the distant “D” (see drawing of follow page) between two antennas.
The formula for calculate “D” is :

D = 0.75 x λ

Where :
0.75 = is the multiplicative coefficient;

300
λ = -----------
F(MHz)

SWR reading on the frequency 94.4 Mhz <1.25

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