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Crystalcontrolled147.460MHzFMtransmitter

作者:dolphin时间:2016-09-30

Crystal controlled 147.460 MHz FM transmitter

The XFM1 transmitter is a crystal controlled tone modulated FM transmitter designed for model rockets but suitable for wildlife, balloons and many other applications requiring a small, frequency stable FM transmitter. Use this transmitter with a scanner or 2 meter amateur radio receiver. Transmitter ground range is approximately 400 yards (5 feet above ground) . Field tests were done with a ICOM IC-W32A transceiver with 0.16 micro volts of receiver sensitivity through the standard 8 inch antenna. Air to ground transmissions can improve range significantly as will a directional high gain antenna or a more sensitive receiver.General Specifications:
Frequency: 147.455 to 147.460
Mode: FM
Size: 2 .75 "x 0.5"
Weight: 8 grams (.3 oz) including battery
Range (ground): 400 yards with counterpoise
Frequency control: Crystal
Battery life: 3 days (two CR1632 batteries in series)
Receiver Type/requirements: FM, 144.455 - 147.460 MHz., 0.16microvolts sensitivity or better
Receiver Antenna: directional antenna recommended but not required.
Other: Knowledge of radio direction findingTRANSMITTER
The transmitter is a crystal controlled 147.460 MHz FM transmitter. The transmitter is tone modulated by a 12F675 microprocessor approximately every two seconds. A Morse code call sign ID is transmitted approximately every 30 seconds. If a call sign has not been specified it will transmit “XFM1”. The transmitter is turned off between tone bursts which greatly extends the battery life. The circuit is designed to use a low cost “computer crystal” 49.39 Mhz (3rd over tone), However, custom crystals can be used if other frequencies are desired. If other frequencies are desired a 3rd overtone series crystal can be ordered from a crystal manufacture. Microprocessor
The transmitter is controlled by a program running border=0>



Directional Beam antenna:A “beam” or “Yagi” antenna is probably the simplest and best all around choice for a directional antenna. A simple 3 element antenna can be built for about 10.00 using common materials. The sensitivity pattern shown below is when both the transmitter and receiving antenna is polarized vertically (the elements are pointing up and down). If the antenna of the transmitter are not vertical then the pattern will be different unless the receiving antenna is orientated to match the transmitter antenna. Since the transmitter antenna’s orientation is not always known some experimentation must be done with the receiving antenna. (Note that the patterns are not always as shown. They can vary depending border=0>

Receivers

To achieve adequate performance you will need a receiver with at least 0.16 micro volts of sensitivity. Most 2-meter Amateur (ham) radios are at least this sensitivity. Scanners may or may not be sensitivity enough.

Component Side View



reversed foil side

2" x 0.65"

foil side

Transmitter parts

Resistors

Value

Part number

Supplier

Comments

R1

10K 1/8 watt

299-10K

Mouser

R2

100K 1/8 watt

299-100K

Mouser

Capacitors

C1

.001uF

21RX510

Mouser

C2

22pF

21RD722

Mouser

C3

15pF

80-C315C150J1G

Mouser

two C3 (15pF caps) may be needed (see text)

Semiconductors

Q1

NTE107

526-NTE107

Mouser

Q2

NTE108

526-NTE108

Mouser

Crystal

xtal

147.460

815-ABLS-49.152-B2

Mouser

49.152MHZ 3rd overtone crystal

Inductors

L1

0.68 uH

434-22-R68

Mouser

L2

4 turns #22 magnet wire tightly wound on 1/8"dia.

278-1345B

Radio Shack

Enamel-coated magnet wire

Miscellaneous

Battery

CR1632 or BR1632

658-BR1632

Mouser

PCB

See foil pattern

antenna Counterpoise

12 inch

#20 to #24 solid conductor wire

Just about any type of “hook-up” or phone wire

J1

Jumper wire

Use trimmed off lead

source codetele147_1.asm


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