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LM1819N
Air-Core Meter Driver
National .
Semiconductor
General Description
The LM1871 is a complete six-channel digital proportional
encoder and RF transmitter intended for use as a low pow-
er, non-voice, unlicensed communication device at carrier
frequencies of 27 MHz or 49 MHz with a field strength of
10,000 uV/meter at 3 meters. In addition to radio controlled
hobby, toy and industrial applications, the encoder sectiOn
can provide a serial input of six words for hard wired, infra-
red or fiber optic communication links. Channel add logic is
provided to control the number of encoded channels from
three to six, allowing increased design flexibility. When used
with the LM1872 RC receiver/decoder. a low cost RF linked
encoder and decoder system provides two analog and two
ON/OFF decoded channels.
LM1871 RC Encoder/Transmitter
Features
a Low current 9V battery operation
a On-chip RF osciilator/transmitter
One timing capacitor for six proportional channels
Programmable number of channels
Regulated RF output power
External modulator bandwidth control
On-chip 4.6V regulator
Up to 80 MHz carrier frequency operation
Block and Connection Diagram
" " 16 15
ADD LDEII
cm cns CHE Hm Vcc
Dual-m-Line Package
M00 M00 RF
OUT FILTER OUT BIAS
" 13 12 " 10
CHANNEL REGULATOR
FRAME 'tMt
TMER TIMER
1 2 3 a s 1 s 9
cu: ca: cm 4.6V 3 am:
CHANNEL
A00 tonic
TL/H/7B11-1
Top Vlew
Order Number LM1871N
See NS Package Number N18A
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llBI-W'l
LM1871
Absolute Maximum Ratings
If MllltaryfAeroapaes specliled devices are required,
please contact the National Serttleortduetor Sales
Offlca/Dlstrlbutors for avallablllty and apettmttatlurtts.
Package Dissipation (Note I)
Pin 4 Externally Forced
Operating Temperature Range
1600 mW
-25'C to + 85"C
Supply Voltage ' 16V Storage Temperature Range -65'C to + 150°C
DC Current Out of Pin 4 10 mA Lead Temperature (Soldering, 10 sec.) 260°C
DC Current Out of Pin 13 25 mA
Electrical Characteristics TA = 2S'C, Vcc --- + 9V, see Test Circuit and Waveforms
Symbol Parameter Condltlons Mln Typ Max Units
Encoder Section, Close m, S2, S4 Open S3
V14 Supply Voltage 4.5 9 15 V
I14 Supply Current Encoder Only 10 14 22 mA
V4 Reference Voltage 4.1 4.8 5.4 V
tf Frame Time tf --- RFCF + 0.63RMODCT 8 9.5 10.5 ms
trn Mod Time tm = 0.63RMODCT 0.4 0.5 0.6 ms
tch Channel Time teh = 0.63RCHCT 0.4 0.5 0.6 ms
ts Sync Time, Tx Channels 1-6 Close S1, Close S2 3.5 ms
ts Sync Time, T, Channels 1-5 Open SI, Close S2 4.5 ms
ts Sync Time, Tx Channels 1-4 Close SI, Open S2 5.5 ms
ts Sync Time, Tx Channels 1-3 Open SI, Open Sg 6.5 ms
Atn Supply Rejection, tm + tty., AVCC = 6V to 12V 0.1 %/V
AV13 Encoder Output Swing 3.8 Vp-p
AV12 Mod Filter Output Swing 3.8 VP-p
I12 Mod Filter Source/Sink Current 0.5 i mA
RINGS) Pulse Timer Input Resistance 27 Mn
'TH(7) Frame Timer Threshold Current 0.1 p
'LEAK(15) Mod Timer Leakage Current Pin 15 to 0V 0.01 1 p.A
VSAT(15) Mod Timer Saturation Voltage I15 = 2 mA, (V4-V15) 120 240 mV
'LEAK(CH) Channel Timer Leakage Current Pins 1, 2, 3, 16, 17, 18 to 4.6V 0.06 1 pA
VSAT(CH) Channel Timer Saturation Voltage ICH = 2 mA 120 240 mV
RF Oscillator Section, Collector Pin It, Base Pln 10, Emitter Pln 9 Open S4
VOUT RF Output Level Use RF Voltmeter Close S3 400 mVRMs
I14 Supply Current Open sa, S4 30 mA
h Transistor VCE = +5V, k; = 10 mA 520 MHz
VSAT(11) Transistor Saturation Voltage fo = 49 MHz 800 mV
HFE Transistor BC Beta Ito = 10 mA 75 150 350
LVCEO k: -- 10 M 16 20 V
Note 1: For operation in ambient temperatures above 25'C, the device must be derated based on a ISO‘C maximum iuncllon temperature and a package thermal
resistance of 75°C/W junction to ambient.
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Test Circuit and Switching Tlme Waveforms
A 3 EPISODE!
5000 "
on 'fi)
0.1uF i
" 17 15 15 " 13 "
mu m m n. vet mm Ian
I Cl" rrkttt1
' ' uv
A"llth ', : n:nuum
EDEN".
t t l l sun! I rum
_l "Y mum m” ""n
cu: m m u: I IDDLOGIE I an
1 t 3 4 5 a 1 a s d mus
J. tllt
v 0 0 , 7
=rt St S2
m " CT
Rm Nm LI "
v 1000 pF
ro SCOPE
Notc: Test tgrmdt has been ttonfigurtrd tor evaluatlon by oscilloscope, Use 1% Liming components, RM, Ros, RP. Cr
"ll --1
L1: Toko E523LN-7210019 type M6117 w, turns with tap 2% turns from top
Y1: 49.86 MHz crystal 3rd ovenone
Encoder output (pln 13) close 81, 52. $4. 0.5 maldiv sweep
I ' ' y RF use! I I = um svm:
53 " Ct
=t'iF-to I-- "t"s""Cl'?-r11-m-
TL/H/7D11-2
TL/H/7911-3
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ltBHfil‘l
LM1871
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Typical Performance Characteristics
Supply Current
" vs Supply Voltage
114 — SUPPLY CURRENT (MN
V13 - EHCUDER OUTPUT WING N”)
0357911131517 157
1114 -sumv VOLTAGE (ttl
RF Transistor
Input Admittance
" Collector Current
VCE 3 "
Vi. ~1NPUT ADMITTANEE (lnlnhu)
Anubmmuhu
1 5 In " " IN
I; - COLLECTOR CUHREMT FIN " lmA)
Applications Information
The LM1871 has been designed to encode and transmit
27 MHz or 49 MHz carriers for remote radio control (RC) of
up to six independent analog functions. The encoder sec-
tion converts a variable potentiometer setting to a variable
pulse width. The variable pulse widths, each preceded by a
fixed modulation pulse, are added together sequentially and
then followed by a synchronization pulse. Figure 1 shows
the digital proportional control format and how the channel
pulse widths, sync time and frame time are defined.
"tAME''----------;
SYNC(A) irijciiiifieii-'s-iirrFi-,-i, U'UZL
1--ttm _ f---ts--
"’1 l-tn,
'"R"l Fil
TL/H/7911-5
FIGURE 1. (A) Encoder Output (Pin 13)
(B) Transmitted RF Carrier Envelope
(C) Typical Receiver Channel 1 Output
(D) Typical Receiver Channel 2 Output
Encoder Output Swing
" " Supply Voltage
V14 -SUH’LV VOLTAEE (V)
RF Output Voltage Level
vs Supply Voltage
11111511 357911111517
VII - SUPPLY VDLTAGE M
RF Transistor
Output Admittance
' vs Collector Current
It . "
V“ - OUTPUT ADHITTANCE 1mm“)
1 5 Ill tll " IN
I; -CtbiLECTO CURHEIT PHI " imAl
TL/H/7911-4
Figure 1 (A) shows the encoder output waveform. The mod-
ulation time (tm) is fixed while the channel time (U) is the
variable pulse width. In Figure 1 (C. D) the recovered chan-
nel pulse (tn) is the sum of tm and ten at a rep rate set by the
frame time (ti). Because the frame time is fixed, the sync
time (ts) will vary inversely to the variable channel times.
After detection by the RC receiver, the channel pulse widths
must now be converted back to the required analog furtty.
tions, which might be a mechanical arm movement, motor
speed control or simply an ON/OFF transistor switch. In the
case of the mechanical arm movement, commercially avail-
able closed loop servo modules can be found in most hobby
shops. The input requirements of these servos will deter-
mine the transmitted frame time and channel pulse width
range. Usually the pulse width for arm at center will be
1.5 ms;torfull left, 1.0 ms; and for full right, 2.0 ms, at a rep
rate of 20 ms. A motor speed control open loop servo can
be designed for the same input pulse widths: 1.0 ms for
maximum forward speed, 1.5 ms with some dead band for
motor OFF and 2.0 ms for maximum reverse speed. In both
servo systems the input pulse width being continuously vari-
able allows full control of arm position, motor speed and
direction. The ON/OFF function could also use the same
input pulse width range (1 ms ON, 2 ms OFF).
The 1.0 ms to 2.0 ms pulse width range required by most
servo modules is a result of transmitted RF spectrum limita-
tions required by the FCC. If the modulation time (tm) and
the channel time were made very short (E10 ps each)
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Applications Information (Continued)
many sidebands 5 kHz apart would be generated on each
side of the center frequency. The amplitude and number of
sldebands are determined by the depth and duration of the
modulation pulse. FCC regulations require that all side-
bands greater than 10 kHz from center frequency be less
than 500 pV/meter at three meters. In the example cited
above, the 100% modulated carrier spectrum would not be
acceptable if the field strength of the carrier was
10,000 pV/meter at three meters. If the modulation and
channel times were made much longer (a 10 ms each) the
transmitted spectrum would be acceptable but now the
frame time would be longer than desirable for optimum ser-
vo designs. When the received channel pulse widths are
t500 "
Note: See Figure 4 for RF components.
between 1.0 ms and 2.0 ms at a frame rate of 20 ms the
modulation time should be between 400 us and 600 he to
insure an acceptable transmitted RF spectrum.
Figure 2 shows the block diagram and a typical application
of the LM1871 utilizing two fully proportional (analog) chan-
nels and two uniquely encoded ON/OFF (digital) channels.
The LM1872 Receiver/Decoder, a companion IC to the
LM1871, has been designed to receive and decode two an-
alog channels and two digital channels. The two digital
channel output states are determined by the number of
transmitted channels rather than by the width of a channel
pulse. Table I shows the digital output format as a function
of the number of transmitted channels.
---MN---
tt " " 15 " " 12 11 10
cu g cm I... rte HOD man up ms - - 52 "
OUT mun out
I S ' IIV MII
fltl%t IC) mum... on "D--- v P 4N
s LtM871
I... TRANSMITTER
Krtrur
[ICUBII
1 1 , VII"! '2iirl
-I (IV cunnnu TIMER YIIII
m m cm us l um um: I arm
1 t J 4 5 6 7 I D
h o 6 ir
Rpt M A tl c2
RC" ".005 "
fig ns
- - . 200k
- - 0.1”;
TL/H/7911-6
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l-LBlW'I
Applications Information (Continued)
RI TT, WHIP
LM1871
T0 MOTORS Mr - A 4
AND LOADS
. l IE“
'I 100 "
I 0.01 ::t T. " p" f -
l. ' CHI
av E 49.405 mm 0.1 0.01 (01mm. OUTPUTS)
J. XI =1 - 1" J7
1 T - 3 a 5 - a 7 a ,
L0 XTAL mun vms MIX m tt' CHA nun can
(COLLECTOR) (EMITTER) (COLLECTOR)
lM1I72 RECEIVERIOECODER
MIX OUT IF IN ABC IF MT 6ND SYNC CH2 CHI (EMITTER)
13 in in -l1-0
L-L. -rl-
(ANALOG OUTPUTS)
TL/H/r911-7
T1 = Toko RMC 202313 } 00 = 110
T2 = Toko RMG 402503
T3, L1 --- Toko KEN 402802
FIGURE 2. Two Channel Analog/Two Channel Dlgltal Trantttttlttermetteltnrr Appllcatlon
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Applications Information (Continued)
LM1871 ENCODER TIMING
Figure 3 shows the two timing circuits and waveforms used
by the LM1871. The frame timer oscillator consists of a high
gain comparator and a saturating NPN transistor switch.
When the NPN transistor is turned OFF the timing capacitor
(CF) will charge up to y, of the VREG voltage. The compara~
tor will then turn ON the NPN transistor, discharging the
capacitor back to ground ending the timing cycle. The pulse
timing circuit is similar in operation except that the timing
capacitor (CT) is charged and discharged between 16 and
% of the VREG voltage. The saturating PNP transistor
switch pulls up the modulation timing resistor (RM) which
charges CT to % VREG and six independently switched NPN
transistors provide the discharge path through the channel
timing resistors (RCH). The tlme constant for both circuits
can be found as follows:
ct, - z n V_1
when V1 = Voltage across timing resistor at end of timing
cycle.
V2 --= Voltage across timing resistor at beginning of
timing cycle.
Vnes o
FRAME TIMER
'Extemal components
In the frame timer circuit the NPN transistor is held on for a
period determined by the modulation pulse (tm). This was
done to insure that the timing capacitor was fully dis-
charged. The frame (ti), modulation (tm) and channel time
(tch) can be calculated as follows:
tt = --dn 4::(RFCF) + tm =1.1RFCF + tm
tm or tch = - l n ?i.%7 (RM Dt RGH)CT
= th69 (RM or RCH) CT
The above calculated time constants will be modified by
transistor saturation resistances and comparator switching
voltages that are slightly different than the y, and % VREG
reference. One time constant should be used for the frame
time (tf) and 0.63 time constant should be used for the mod..
ulation (tm) and channel (ten) times. Because the switching
voltages are a percentage of the VREG voltage the timer
accuracy will not be affected by a low battery condition (Vcc
< 5.6V). High and low temperature (-25°C to +85'C) op-
eration also has little effect on timer accuracy.
to ENCDDER
OUTPUT
SYNC TIME CAP
CHARGE CKT LATCH
PULSE TIMER
TL/H/7911-8
m 7 _/
(C) ttyt - ttttt - ‘CH - t H - t t -
mm b] 1 b:] 2 bl 3 In i tn. , tm git tm svuc
thw-------
(A) Voltage on Cr
(B) Voltage on or
(C) Encoder pulse train output
TL/H/7911-ty
FIGURE 3. Slmpllfled Encoder Tlmlng Circuits and Waveforms
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LM1871
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Applications Information (Continued)
The accuracy and temperature characteristics of the exter-
nal components will determine the total accuracy of the sys-
tam. The capacitors should be NPO ceramics or other low-
drift types.
As an example the following procedure can be used to de-
termine the external timing components required for Figure
Given: Frame time (tf) = 20 ms
Modulation time (tm) = 500 us
Recovered pulse width (tn) range =
2.0 ms with trim capability
Non variable channel pulse width (tn) = 1.0 ms
1. Frame Timer Components
Choose CF = 0.1 pF i10%
RF = ttah ET!“ = i.l.t.Lni-S.:El.e.r..E Ill-,- :Fso ms = 195 m (200 kn)
2. Modulation Time Components
Choose Cr = 0.01 p.F i10%
RM = tm = 500 X10-6
0.6301- (0.63)(1 x 10-8)
3. Non-Variable Channel (3 through 6) Component
tch = tn - tm =.. 1.0 ms - 0.50 ms = 500 "s
t 500 x 10-6
RCH - A = - = 79.36 kn (82k)
1.0 ms to
= 79.36 kn (82 kit)
4. Variable Channel 101) and Channel 2 (t2) Components
When the Ftp wiper arm varies across the full potentiom-
eter range, (AR = on to Rp value) Rs is found for on
and minimum tn pulse width.
- tn -tm _1ms -0.50ms
0.63CT (0.63)(1 x 10-8)
Ftp(AFt) is found for maximum tn pulse width.
Rs = 79.36 kn (82k)
_ 2 ms - 0.50 ms
- (0.63)(1 M 10-6)
= 156 kn
The Rp value could have been chosen first and a CT calcu-
lated. Usually the 270'' to 32ty' angle of potentiometer rota-
tion is inconvenient especially if it is desired to spring return
the control to center, or if lever type knobs are required. A
- 82 ktt
500 kn potentiometer that has 300° of end to end wiper arm
rotation could be used if mechanical stops limit this range.
(300°)(156 kn)
500 kn
In most applications the resistor and capacitor tolerances
prevent sufficient system accuracy without mechanical or
electricai trimming of the analog channel pulse widths. If a
500k potentiometer is used, two trim methods can be uti-
lized. RS can also be included as part of the potentiometer
resistance.
Required angle of rotation = = 93.6''
Potentiometer Body
far Mechanical Trlm far Electrical Trlm
uecumm
mm 810?!
Eljcitrss" 4 V .
|°3lnsl |Aulsou a mu:
TLfH/7911-10 L,,,,,,', 11
AR ---156kn,Rs = 82 kft
If G = 1.5 ms k30% is required:
iRTRIM = th3-2- + RS = 48 kn
300'' 48k
Required Body Rotation = (300'')_(4isk) 530k ) = 128.8''
Channel Add Logic
Table I shows the number of transmitted channels as a
function of pin 5 and pin 6 conditions. The threshold voltage
for both pins is = 0.7V. When grounded, the pins are sourc-
ing E300 psA from the internal pull up resistors. External
voltages may be applied to these pins but should be below
the VREG voltage by at least one volt and not less than the
pin 9 ground.
Modulator and Crystal Oscillator/Transmitter Circuit
(FIGURE 4)
The modulator and oscillator consist of but two NPN transis-
tors whose operation is quite straightforward. The base of
the modulator transistor is driven by a bidirectional current
source with the voltage range for the high condition limited
by a saturating PNP collector to the pin 4 VREG voltage and
TABLE I. Digital Channel Output Format as a Function of Transmitted Channels
LM1871 Channel Add Logic LM1872 Receiver
Pln Conditions Number ot Channels Dl Ital Out uts
Transmitted g p
Pin 5 (A) Pin 6 (B) A B
OPEN OPEN 3 OFF OFF
GND OPEN 4 ON OFF
OPEN GND 5 OFF ON
GND GND 6 ON ON
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Applications Information (Continued)
low Condition limited by a saturating NPN collector in series
with a diode to ground. A current source of i500 HA was
chosen to provide a means for external modulator band-
width control. When a capacitor is used at this node the
transmitted RF carrier is made to slew ON and OFF at a
time determined by;
Modulation slew time (tms)
- (AV12)(CM) - (3.8V)(0.01 uF) -
- I12 - 500 ps/k -
when AV12 = peak to peak voltage swing of pin 12 = 3.8V
the = source/sink current from pin 12 = 500 ptA
CM = capacitance at pin 12 = 0.01 “F
Figure 5 shows the advantage gained by this capacitor es-
pecially if adjacent channels are 10 kHz to 15 kHz away
trom the desired channel.
The crystal oscillator/transmitter is configured to oscillate in
a class C mode with the conduction angle being approxi-
mately 140° to 160°. Resistor RIO provides the base bias
current from the pin 4 VREG voltage. This resistor value has
been optimized for most RC applications. When the emitter
of the modulation transistor is high (ESBV) the collector
and tank cell are pulled up into the active range of the oscil-
lator transistor. RF feedback to the base is via the series
mode crystal which determines the oscillator frequency. Be-
cause third overtone crystals are used for 27 MHz or
49 MHz applications a tuned Collector load must be used to
guarantee operation at the correct frequency. Tuning the
LC tank, while having little effect on oscillator trequency, will
control the conduction angle and oscillator efficiency. Tun-
ing the LC tank for minimum Vcc supply current while ob-
serving the carrier envelope on an oscilloscope would be
the best alignment method.
For most RC applications the carrier ON to OFF ratio must
be as high as possible to ensure precise pulse width detec-
tion at the receiver. If we were to look at the base of the
oscillator transistor we would see that the crystal is still os-
cillating during the time that the carrier is OFF (tm). This is
because of the high Q characteristic (10k to 30k) of crystals
in this application. We can roughly calculate the number of
cycles required tor a decay or rise in amplitude tor one time
constant (63% of final value) by:
Number of cycles = l-?
At 49 MHz this will be 15k cycles or 300 ps for a crystal Q of
30k. At 27 MHz this time will be 560 p5 for the same crystal
Q. If long carrier OFF times were required the oscillator start
up time would as a result also be quite long. The shorter
carrier OFF times overcome one problem but do suggest
that the crystal be isolated from the antenna circuit. During
the carrier OFF time the base of the modulator transistor is
held approximately 0.9V above ground such that the emitter
still supplies current to the now saturated collector of the
oscillator transistor. Both ends of the LC tank circuit now
“see” a low impedance to ground. Further isolation is pro-
vided by the split tuning capacitor.
LLBLW'I
Component 27 MHz 49 MHz
Tp 2 Turns 6 Turns T h A _
O O menca
Ts 3 Turns 1 Turn 1250 Feehanvilie Drive
Ll TOKO KXN K4636 BJF TOKO KEN K4635 BJE Mount Prospect, IL 60056
LL MILLER #4511 MILLER #9330-10 (312) 2970070
CA 5.4 pF 6.2 pF
RA 1.150 3.780.
CI 1000 pF 220 pF
C2 680 pF 47 pF
cs 20 pF 33 pF
mo 24k 47k
"it tt
am " o3,,u- lam tit"
"8ttpF 15”,; - A - Cm-an
g a - -ct
27 MHz or 49 MHz ' 'd I Ts =es I cm " m
3rd Dvertone Series "eta I CA
Mode Crystal Cr..' v1 _ear--,'r-l fe -1o nu r, f: +11: m,
' m " I TLfH179t1-13
"ttc-Mtv-t " I n. FIGURE 5. Envelope of Transmitted
$92 " o 'lg/dill",'',',,?)','),'"" 1it1RE Spectrum for Circuit in Figure 2
TL/H/7911-12
FIGURE 4. 27 MHz and 49 MHz RF thtttlllatorfTransmltter
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LM1871
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Applications Information (Continued)
If the printed circuit board shown in Figure 6 is to be repro-
duced, it is recommended that the layout be followed as
closely as possible. The positions of pin 13 decoupling ca-
pacitors and coil components tend to be critical in regard to
undesired harmonic emissions. Short lead ceramic disc ca-
pacitors and short decoupled traces are recommended. A
number of boards with this configuration have successfully
met all requirements of the FCC as perceived only by Na-
tional Semiconductor. Final approval of any unlicensed
transmitter is granted only by the FCC via certified test mea-
surements.
Fleld Strength Measurements
As noted above the maximum radiated RF energy of an
unlicensed transmitter operating in the 27 MHz or 49 MHz
frequency band must not be greater than 10k p.V per meter
at a distance of 3 meters from the transmitting antenna. In
addition to the carrier amplitude requirement, all sidebands
greater than 10 kHz from the carrier and all other emissions
(harmonic or spurious) must be less than 500 WV per meter
at a distance of 3 meters.
The term used for electrical field intensity (V/meter at 3
meters) refers to the open circuit voltage induced at the
ouptut of a resonant halt-wave dipole antenna in a single
dimensional one meter field, 3 meters distant from the
transmitter under test. When making field intensity measure-
ments, the antenna length must be adjusted for resonance
at each frequency of interest and the induced voltage made
proportional to the one meter reference length. The induced
voltage value must not include losses caused by the inser-
M" DIGITAL
ANTENNA GND CHANNEL
tion of a 1:1 balun transformer (-6 dB) or loading (-6 dB)
and mismatch (72tt to 500, --1.7 dB) of the voltage mea-
suring instrument. We can now relate the induced voltage
(VIN) to a measured voltage (VMEA) by:
VMEA = m = (VMEA) (Losses)
Losses L
where: VMEA = Voltage measured by a spectrum ana-
lyzer or calibrated receiver.
VlN = Field intensity (volts/meter).
L = Half-wave length ot antenna in meters.
Losses = All mismatch, loading and Insertion
losses. (In this case = 13.7 dB = 4.87)
The length of a half-wave dipole antenna is found by:
-- E meters
where: C = Speed of light in a vacuum.
k = A constant related to antenna length to width
ratios, end effects and surface effects. Use
k = 0.96 for practical antenna rods 'As" in
diameter.
f ..-- Frequency of interest.
meters
. ... - 144
Simplified) fMHz
R92; Lin; I
TLlH/7911-15
TL/H/7911-t4
FIGURE 6
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Applications Information (Continued)
Now that we have a way in interpreting the field strength
measurements we must deal with the technique used In
making these measurements. Usually all measurements are
done outside on a flat area away from trees, buildings, bur-
ied pipes or whatever. The test transmitter is placed on a
wooden steel or table approximately 3 feet high such that
the vertical antenna is in a vertical position, The receiving
dipole is adjusted for the frequency of interest and oriented
to the same plane as the transmitter and placed 3 meters
from the transmitter. The dipole may be mounted on a
wooden pole or ladder such that the height of the antenna
can easily be changed. The antenna length must always be
symmetrical about the center tapped balun transformer. The
operator and his test equipment must be "behind" the di-
pole by some 3 or more feet. It it is desired to have the
operator at a much more distant location the transmission
line must be characterized for additional losses. A number
of measurements should be made at each frequency for
difterent heights and orientations of both the transmitting
and receiving antennas. The highest reading should be con-
sidered the correct reading. In addition to fundamental,
sidebands and harmonic emissions, the frequency spectrum
from 25 MHz to 1000 MHz should also be scanned for spuri-
Ous emissions greater than 50 pV/meter at 3 meters.
Additional Applications
Figure 2 shows a typical application of the LM1872 Receiv-
er/Decoder. The LM1872 consists of a crystal controlled
local oscillator, IF amplifier, AGC, detector, decoder logic
and digital channel output drivers. The supply voltage range
of 2.5V min to 7V max was chosen to allow battery opera-
tion by four "C" or "D" cells.
Figure 7 shows how the LM1871 encoder can be used to
frequency shift a 200 kHz carrier that is transmitted over the
110V AC line in a home or office. Figure 8 shows how ON/
OFF carrier modulation is also possible. An LM1872 could
be used as a receiver/decoder for the Figure t? transmitter
circuit. When using an LM1872 the carrier trequencies
should be 50 kHz or greater to insure proper detector opera-
Figure 9 shows the LM1871 configured for six analog chan-
nels with a TTL compatible output. The VREG voltage at pin
4 has been shorted to Vcc. This allows a VCC(MlN) of 3V
and VCC(MAX) of 6V. The encoder output could be used for
a fiber optic transmitter/receiver link, infra-red, tone keying
or transducer carrier modulation. If the encoder output is
hard wired to the Figure to serial input we can recover the
six analog channels. From Figure " we see that the data
input will appear during the sync time which Is always longer
than any channel tlme (tn). Inverter Xt wlll discharge C1
each time the input goes high. During the longer sync tlme
Cl will charge up to the y, Voc threshold of X2 and via X3
provide the data input. The R and C components are calcu-
lated by:
tdatadelay = 0.565 R1 C1
It large values of CI (>0.01 JuF) are required the diode D1
should be replaced by e PNP transistor with the base on X1
output, emitter to X2 input and collector to ground.
In applications requiring ON/OFF decoding of a channel
pulse width the circuit shown below could be used.
ttmint in output LO
t(m) in output HIGH
cu, iuvut
rnnn FIGURE "
TL/H/7911-tt)
It the recovered channel pulse width is short (t(min)) R2 and
G2 are selected such that the input to inverter X4 does not
rise to the y, Vcc threshold. The output of X4 will be high
and the output of X5 will be low. A longer input pulse (t(max))
will allow the output of X4 to go low pulling the input of X5
low. R3 and C3 are selected such that the input to X5 wlll
not rise past the % Vcc threshold during the remainder of
the frame time. The R and C values are found by:
Given: ttmin) = 1.0 ms, C2 = 0.01 HF
ttrams = 20 ms
0.565n202 = t(min) + -tim-axitims = 1.5 ms
1 .5 ms
= =.. 7
0.565C2 2 0 kn
= ttreme =
0.56503 360 kn
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LLBIW'I
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LM1871
5.1II 5.1K
115 VAC
IIII‘KH
0.1 uF
CI‘AIIII
IUD l 0G":
Hllmlllml
PNZZZZA VA" 60027"
UM!“ TOP VIEW
DEVIATION
l .00 LOGIC l
Capacitor values in pF
Resistor values in n
TSeled for carrier freq.
fc C4 C7
onal Applications (Continued)
200 kHz 82 1000
100 kHz 160 3900
Note: See AN-146 to: additional infatuation.
TL/H17911-17
FIGURE 7. LM1871, LM566 200 kHz Line Carrier Tranamltter wllh FSK Carrier Modulation
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5.“: 5.":
EMMIEI
IUD LDGIC
KKGUIIVDI
UM!“ TOP VIEW
EICOOII
FIGURE 8. LM1871, LM566 200 kHz Llne Carrier Transmitter wlth ONIOFF Carrler Modulation
crunch
A Annumc I
"“002 3D VET
PN2222A
YAN-EMZTN
Capacitor values in pF
Resistor values in :1
Select for carrier freq.
200 kHz
100 kHz
115 VAC
Additional Applications (Continued)
TL/H/7911—18
llBlW'I
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LM1871
5.“ 11k
seam m
TRANSMISSION
“EDI UM
ENCOOER
OUTPUT
IIGUIIIOI
(CLOCK)
SERIAL SHIFT REGISYEH
LM1I11 TOP VIEW
6111 1:112 8113 1:1"
& LII loill.‘ I
(DATA)
Wm = 0.565 RC
N010: See Fpgwa I1 10r‘l1ming Wavefm
FIGURE 9. LM1871 SIX Analog ChanHEI Encoder W111! 'ITL Compatible Ou1pu1 FIGURE 10. 81! Analog Channel Detector
Additional Applications (Continued)
TUH/7911-19
Additional Applications (Continued)
(EHCODEB OUTPUT)
SERIALIM‘UT I I I I I I I I I I I I
- svuc TIME -
‘dm dun, -
(DATA) I I I
WI I I I I
cu: m |__.l
cm I-I i-n
ounurs
q cl".-,...-..;-'', F'-"-l_.,
Mili i-l I I
cus r-, r '
TL/H/7911-20
FIGURE 11. Six Analog Channel Detector Waveforms
LM1871 Component Selection Guide
Component Mln Typ Max Comments
RF 2 kn 180 kft 1M Pin 7. Frame timer resistor used with CF to set frame time (tr).
tt = HFCF + tm.
CF 500 pF 0.1 " 0.5 pF Pin 7. Frame timer capacitor used with RF.
RM 2 kn 150 ktl 1M Pin 15. Modulation timing resistor used with Crto set mod time
(tm). tm = 0.63 RMCT.
RCH 2 kn 150 kn 1M Channel pins l, 2, 3, 16, 17, 18. Variable or fixed resistor used
with CT to set channel pulse widths IU). tch = 0.63 RCHCT.
CT 500 pF 0.1 " 0.5 pu' Pin 8. Pulse timer capacitorused with RM and HCH.
CM 0.01 p.F Pin 12. Modulation slew time (tms) capacitor used to decrease
modulator bandwidth. Reduces sideband emissions.
(AV12)(CM)
ms = T = 7600 CM
C4 0.1 p.F Pin 4. 4.6V regulator decoupling capacitor.
C13A 1500 pF Pin 13. Modulator output RF decoupling capacitor. Improves
C138 2700 PF carrier ON to OFF ratio.
C14 0.1 p.F Pin 14. Vcc decoupling capacitor.
R10 24 kn/51 kn Pin 10. RF oscillator/transmitter bias resistor.
Note: See Figure 4 for RF components. All timing capacitors should be Iow-drih (NPO) Iypas.
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llBl-W'I
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LM1871
CHAIN! l MID
SDI 13!
Schematic Diagram
DRIVER
FEEDIICK m m
ml“ fl IOU
TIER W0 FILTER
TUH/7911—21
FIGURE 12
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National Semiconductor was acquired by Texas Instruments.
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This file is the datasheet for the following electronic components:
LM1819N - product/lm1819n?HQS=TI-nu|I-nu|I-dscatalog-df-pf-null-wwe
