Ramsey Electronics FM10A - Manual (Page 15)

USING THE FM10A WITHIN THE HOME
A most practical use for the FM10A would be to connect it to the main
stereo system within a large home so that whatever is playing on the main
system can also be tuned-in on portable FM radios in other rooms, the
garage or out in the yard.
This connection consists of using shielded audio cables to connect the
auxiliary "line audio" output of your cassette deck, CD player or other stereo
device to the audio inputs of the FM10A. Consult the literature that came
with your stereo equipment.
Even if you intend only this limited convenience use of the FM10A for your
own home and family, it is still your responsibility, in accord with Part 15 of
the FCC Rules, to ensure that this operation does not cause interference to
your neighbors.
POWER SUPPLY CONSIDERATIONS
The FM10A is designed to operate from a single 9-volt battery mounted on
the PC board. For prolonged operations, note from the schematic diagram
that replacing R8 with a jumper wire will permit operation from a 1.5V or 3.0V
DC source such as D cells. Diodes D1, D2 and D3 regulate the voltage to
U1 at 2.1 volts. Note, however that reduced voltage will also affect the
collector voltage and therefore the output power of Q1.
Whether an alternative AC adapter can be used depends on the quality of
the adapter and its ability to suppress unwanted AC-line hum. Various plug-
in adapters and power supplies in the 6 to 12 volt range may be tried, but
make sure the unit has DC output (positive tip) and is not merely a
transformer relying on rectifier circuitry within the device for which it was
originally supplied as an accessory.
L.E.D. "POWER ON" INDICATOR
Since the transmitter consumes power and emits RF whenever it is turned
on, a visual "on the air" indicator is desirable and is a fun enhancement of
your completed kit. If you are designing the FM10A setup for use by
youngsters, a flashing indicator is easily provided using our BL-1 "LED
Blinky" kit. Voltage for a standard LED is easily taken from the unused top
terminals of S1. The inner pin nearest the red lead of the battery cable is the
+9 volt pin. The ground can be taken from the black battery terminal, or the
case of any of the jacks, but it CANNOT be the antenna. This positive DC
must be connected to the anode (longer wire) of the LED. Use a 1K resistor
in series with either wire of the LED. The cathode lead is connected to the