Ramsey Electronics STC1 Manuel d'instructions télécharger pdf (Page 21)

FM25B • 21

board. With an operating frequency of 107.9 MHz programmed into the DIP

switches, there should be around 9.0 volts (+- 0.2 volts or so) at TP1. If there

isn’t, adjust L1 until you read 9.0 volts. The LED lock indicator (D1) should

now glow brightly. If not, you may need to SLIGHTLY tune the control voltage

up or down from the expected standard in order to compensate for building

tolerances.

Now let’s verify the other end of the band at 88.1 MHz. Set the DIP switches

for 88.1 MHz and you should see the tuning voltage drop to about 0.8 volt (+-

0.3 volts or so) at TP1. Do not readjust L1 if the tuning voltage varies from that

of the expected value. The most important setting is at 107.9 MHz.

Remember that if you have adjusted the FM25B outside of 88 MHz to 108

MHz range it will default to 88.1 MHz. This means that if you can’t hear any-

thing on the radio near the frequency you are trying to transmit at, go to 88.1

MHz and see if it is there.

If you can’t get either reading even close, see the troubleshooting section.

2. Audio Connection

Adjust both Left and Right level potentiometers (R27, R28) to about half of

their rotation. This is a good starting position. The best audio input for both

testing and general operation are the stereo "line-level outputs" of a cassette

deck or CD player. Most stereo systems have a variety of auxiliary output

jacks of which one or more are line-level outputs.

Hooking up an audio source to your FM25B is really quite simple. However,

there are some general rules:

• A terribly distorted sound is a sign of too much audio level. Simply rotate

the level potentiometers R27 and R28, CCW to reduce the level. Make

sure you rotate each one about the same amount to maintain proper ste-

reo balance.

• NEVER connect the FM25B audio inputs to speaker outputs of a high

power stereo system; such a connection will destroy the IC chip.

• Consider using a mike mixer for professional "radio station" sound. It will

allow you to easily fade, mix and switch between various audio sources.

USING THE FM25B WITHIN THE HOME

Typical use for the FM25B would be to connect it to a personal computer

within a large home so that whatever MP3 or other audio files are playing can

also be tuned-in on portable FM radios in other rooms, the garage or out in the

yard. The provided whip antenna should cover a typical home’s boundaries

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Ramsey Electronics STC1 Manuel d'instructions Page 21