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參數(shù)資料
| 型號(hào)： | LM1872 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Radio Control Receiver/Decoder |
| 中文描述： | 遙控接收器/解碼器 |
| 文件頁數(shù)： | 9/19頁 |
| 文件大?。?/td> | 371K |
| 代理商： | LM1872 |
Application Hints
A typical application circuit for either 27 MHz or 49 MHz is
shown in Figure 5. Using the recommended antenna input
networks and driving the circuit through the antenna simula-
tion network of Figure 6, a solid decoded output occurs for
10
m
V and 12
m
V input signals at 27 MHz and 49 MHz
respectively.
TL/H/7912–12
FIGURE 6. Antenna Simulation Network
This sensitivity has been determined empirically to be opti-
mum for toy vehicle applications. Less gain will reduce
range unacceptably and more gain will increase susceptibili-
ty to noise. However, should the application require greater
range (
l
50m for a land vehicle, for example), either the
antenna could be lengthened beyond 2
ê
and/or receiver
sensitivity could be improved. There are a number of ways
to alter the sensitivity of the receiver. Decreasing the turns
ratio of input transformer, T3, for example, will couple more
signal into the mixer at the expense of lower tank Q due to
mixer loading. Moving the primary tap on mixer transformer,
T1, further from the supply side and/or decreasing the pri-
mary to secondary turns ratio will also increase gain. For
example, just changing T1 from a 32:1 primary to secondary
ratio to a 5:1 turns ratio (Toko
Y
RMC202202) will double
49 MHz sensitivity (6
m
V vs 12
m
V). Mixer tank Q will be
affected but overall 3 dB BW will remain largely unchanged.
The primary tap on the IF transformer, T2, can also be ad-
justed (further from the supply side) for higher gain, but it is
possible to cause the AGC loop to oscillate with this meth-
od.
Narrow overall bandwidth is important for good receiver op-
eration. The 3.2 kHz 3 dB bandwidth of the circuit in Figure
5 is just wide enough to pass 500
m
s carrier dropout pulses,
t
M
, yet narrow enough to hold down electrical noise and
reject potentially interfering adjacent channels. In the
49 MHz band, the five frequencies available are only 15 kHz
apart. Should only two frequencies be used simultaneously,
these channels could be chosen 60 kHz apart. Should three
frequencies be used, the spacing could be no more than
30 kHz. At four or five frequencies, 15 kHz spacings must be
dealt with, making narrow bandwidth highly desirable. Even
at 27 MHz, where allocated frequencies are 50 kHz apart,
the proliferation of CB stations only 10 kHz away represents
a formidable source of interference. The response of the
circuit of Figure 5 is 34 dB and 56 dB down at 15 kHz and
50 kHz away, respectively (see characteristic curves).
The sync timer should have a timeout, t’
SYNC
, set longer
than the longest channel pulse transmitted, but shorter than
the shortest sync pulse, t
SYNC
, transmitted. Using the com-
ponent values in Figure 5, t’
SYNC
,
e
3.5 ms, which works
well with a transmitted sync pulse, t
SYNC
t
5 ms.
Numerous bypass capacitors appear in the circuit of Figure
5, not all of which may be necessary for good stability and
performance. A low cost approach may eliminate one or
more of the capacitors C1, C9, C10, and C11. The cleaner
and tighter the PCB layout used, the more likely is the case
that bypass capacitors can be eliminated. In the case of
marginal board stability, increasing the size of capacitors
C7, C9, and C10 to 0.1
m
F may prove helpful. If the PCB
layout and parts loading diagram shown inFigure 7 is used,
the circuit will be quite stable up to 72 MHz.
TL/H/7912–13
TL/H/7912–14
FIGURE 7. PCB Layout, Stuffing Diagram and Complete
RX Module for Typical Application Circuit ofFigure 5
9
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM1872N | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Radio Control Receiver/Decoder |
| LM1872N/A+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Remote-Control Receiver/Decoder |
| LM1872N/B+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Remote-Control Receiver/Decoder |
| LM1875 | 制造商:UTC-IC 制造商全稱:UTC-IC 功能描述:20W AUDIO POWER AMPLIFIER |
| LM1875_05 | 制造商:UTC-IC 制造商全稱:UTC-IC 功能描述:20W AUDIO POWER AMPLIFIER |
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