     
© Radiometrix Ltd
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| Issue 2 |
SILRX-UHF data sheet |
19th September 1995 |
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UK Version - SILRX-418-5 / SILRX-418-10
Euro Version - SILRX-433-5 / SILRX-433-10 |
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Top:SILRX-433-5
receiver
bottom: TXM-433-5 transmitter |
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SILRX-418-5 and SILRX-433-5 integrate a complete FM superhet UHF
radio receiver on a small module. Together with the matching TXM-418-5
or TXM-433-5 transmitter a one-way radio data link can be achieved
over a distance up to 200 metres on open ground |
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Typical features
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The SILRX radio receiver and the matching
TXM transmitter are self contained, PCB mounting modules capable of
transferring analogue or digital data up to to a distance of 200m.
The SILRX receiver module is particularly suitable
for battery powered portable applications where it's low power requirements
and small size are of advantage. It may also be used as a lower cost
option to the RXM
in fixed applications where the jam detect and signal strength (RSSI)
output of the RXM are not required.
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Typical applications
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Brief description
The SILRX receiver is a double conversion
FM superhet with a data slicer driven by the AF output. Additionally
a fast acting carrier detect signal is available to indicate to external
circuits that a signal is present. This signal is extremely useful
when implementing duty cycle power save circuits (see fig 4) or to
indicate to external logic that a signal is being received. It is
internally derived from the degree of noise quieting due to the presence
of a receive carrier.
The SILRX is designed to work with the matching
TXM transmitter. With the addition of simple antenna the pair may
be used to transfer serial data up to 200 metres. The range of the
radio link is very variable and depends upon many factors, principally,
the type of antenna employed and the operating environment. The 200m
quoted range is a reliable operating distance over open ground using
1/4 whip antenna at both ends of the link at 1.5 metres above ground.
Smaller antenna, interference or obstacles (e.g. building etc.) will
reduce the reliable working range. Increased antenna height, slow
data or a larger receive antenna will increase the range.
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The following figure shows the receiver's
block diagram.
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 figure
1: Block diagram
figure
2: Test circuit
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Pin Description
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Performance data SILRX-418-5
and SILRX-433-5
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| Parameter
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pin |
Min. |
Typical |
Max. |
Units |
Notes |
| Operating voltage range (Vcc) |
pin 5 |
4.0 |
5.0 |
9.0 |
V |
- |
| Supply current |
pin 5 |
11 |
14 |
17 |
mA |
- |
| Receive frequency |
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- |
418.00/ |
- |
MHz |
- |
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433.92 |
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| Overall frequency accuracy |
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-100 |
0 |
+100 |
kHz |
1 |
| Sensitivity for 20 dB S/N |
pin 1 |
- |
0.5 |
1.0 |
µV |
2 |
| Carrier detect, threshold |
pin 1 |
- |
0.5 |
2.0 |
µV |
- |
| RF input impedance |
pin 1 |
- |
50 |
- |
W |
- |
| IF bandwidth |
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- |
250 |
- |
kHz |
3 |
| AF output level |
pin 6 |
- |
500 |
- |
mVpp |
2, 3 |
| AF bandwidth |
pin 6 |
DC |
- |
5 |
kHz |
3 |
| Frequency/voltage conversion |
pin 6 |
- |
10 |
- |
mV/kHz |
- |
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| Data output, Logic low |
pin 7 |
0 |
0.2 |
0.8 |
V |
4 |
| Logic high |
pin 7 |
4.0 |
4.5 |
5 |
V |
5 |
| Data bit duration |
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0.2 |
- |
20 |
ms |
6 |
| Data Mark:Space |
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20% |
- |
80% |
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7 |
| Data settling time |
pin 7 |
- |
- |
15 |
ms |
8 |
| (minimum preamble duration) |
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| Enable time |
pin 3 |
- |
- |
2.5 |
ms |
3, 9 |
| Signal detect time |
pin 3 |
- |
- |
0.5 |
ms |
3, 9 |
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Absolute maximum ratings:
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Performance data SILRX-418-10
and SILRX-433-10
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Notes:
- over supply and temperature range
- ±25 kHz deviation, 1 kHz tone
- 3 µV input
- 1 mA sink
- 1 mA source
- time between transitions
- (time high / time low) * 100 %, averaged
over any 20 ms period
- time from valid carrier detect to stable
data output
- from application of supply to carrier detect
low (active)
- from application of signal to carrier detect
low (active)
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Absolute maximum ratings:
| Supply voltage Vcc, pin 5 |
- 0.3V |
to |
+ 10 V |
| Operating temperature |
- 10°C |
to |
+ 50°C |
| Storage temperature |
- 40°C |
to |
+ 100°C |
| RF input, pin 1 |
0 dBm |
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| Any input or output pin |
- 0.3 V |
to |
Vcc V, ±10 mA |
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figure
4: Typical performance curves
figure
5: Timing wave forms
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Antenna configurations
The positioning of the antenna is of the
up most importance and is one of the main factors in determining system
range.
The following notes should assist in obtaining
optimum performance:-
- Keep it clear of other metal in the system,
particularly the 'hot' (top) end.
- The best position by far, is sticking out
the top of the product. This is often not desirable for practical/ergonomic
reasons thus a compromise may need to be reached.
- If an internal antenna must be used try to
keep it away from other metal components, particularly large ones
like transformers, batteries and PCB tracks/earth plane. The space
around the antenna is as important as the antenna itself.
- Keep it away from interference sources, bad
interference can easily reduce system range by a factor of 5. High
speed logic is one of the worst in this respect fast logic edges
have harmonics which extend into the UHF band and the PCB tracks
radiate these harmonics most efficiently. Single chip microprocessors
and ground planed logic boards reduce this problem significantly.
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The next diagrams (fig 6) show three different
antenna configurations wich can be used on both the transmitter and
the receiver. Additionally a coax fed external dipole or 1/4 wave
ground plane antenna may be considered if system range is paramount.
figure
6: Antenna configuration
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Module Mounting considerations
- The module may be mounted vertically or bent
horizontal to the motherboard.
- No conductive items should be placed within
4 mm of the modules' component side to prevent detuning.
- Observe RF layout practice between the module
and it's antenna i.e. < 10 mm unscreened track, use 50 W microstrip or coax for >10 mm
- It is desirable, but not essential, to earth
plane all unused area around the module.
- Mount as far as possible from high frequency
interference sources, Microprocessors with external busses are totally
incompatible with sensitive radio receivers and must be kept at
least 1 m from the receive antenna. Single chip micros are not a
problem.
- In some applications it is advantageous to
remote the receiver and it's antenna away from the main equipment.
This avoids any interference problems and allows flexibility in
the sighting of the receive antenna for optimum RF performance.
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Using
the DETECT output
Pin 3 of the module may be used in several ways:-
- Pulled up to pin 5 (Vcc) with a 47 kW resistor
unmutes the AF and DATA outputs for normal operation.
- Pulled down to 0 Volts with a 47 kW mutes
the AF and DATA Outputs (both go to 0 V).
- To drive the base of a PNP transistor (see
fig 2) to derive a logic compatible carrier detect. The data detect
output on pin 3 may be used for duty cycle power saving control
in portable equipment where battery life is a problem. By pulsing
the receiver on/off the average supply current may often be reduced
by a factor of 20 or more depending upon the system requirements
the data detect output is valid 1.5 ms (2.5 ms worst case) after
application of the supply and is used to inhibit the power saving
while data decoding is done.
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Internal data slicer
A CMOS compatible data output is available on
pin 7, this output is normally used to drive a digital decoder IC
or a microprocessor which is performing the data decoding. The data
slicer in the receive module is designed to accept data with a wide
range of pulse widths and mark:space ratio's, see specification table
for limiting values. The data slicer has a 10 ms transient response
time this is the settling time of the adaptive comparator, i.e. the
first 10 ms of signal may be corrupt at the data output.
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System coding
The transmit and receive modules have no internal
digital coding/decoding thus allowing the flexibility to send many
types of data. Encoder and decoder IC's are required to give the system
a high degree of protection from false triggers due to noise/interference/neighbouring
systems and often for security reasons. There are wide range of suitable
encoder/decoder IC's which may be used with the modules, including
:-
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MM57C200, MM57410,National Semiconductor
UM3750, UMC
HT12 series, Holtek
MC145026 series, Motorola
AS2787, Austria Mikro Systeme International GmbH
Additionally IR. remote control, DTMF, Selcall
and modem IC's can be easily interfaced to the modules.
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AF output
This output is the FM demodulator's output
after buffering and filtering. Since it is taken before the data slicer
in the module, it may be used to drive external data slicers / demodulator's
in cases where the internal data slicer is not suitable. This is the
case where an analogue subcarrier is being employed e.g. 2 tone AFSK
or DTMF tones. In these cases the AF output is used to drive the FSK
/ DTMF decoder directly.
The AF output is also a very useful test point
for monitoring signals or interference. The AF output is DC coupled
to the FM demodulator thus the DC level Varies with the frequency
of the incoming signal.
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Supply requirements
The module requires a clean supply. Noise and
'hash' in the 5 to 500 kHz band and 16 MHz ±1 MHz must be less than
2 mV, We recommend a 10 µF capacitor to ground on pin 5 (Vcc) and
a 10 W series feed resistor in cases where the cleanness of the supply
is in doubt.
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Additional Reading
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Applications note
Four Channel Receiver with battery saver
Fig 7 shows a simple single channel paging receiver
with 256 setable codes. The CMOS 555 timer provides a duty cycle power
save circuit which latches ON when a signal is present. The values
used in the example give 4 ms ON; 400 ms OFF, i.e. 1:100 duty cycle.
The total quiescent current is less than 200 µA, thus a 9 V alkaline
battery (500 mA/hr) will give a power up settling time (3 ms worst
case) + any tolerance of the duty cycle oscillator. The OFF time is
controlled by R8 in the circuit and should be selected to suit the
application depending upon the required response time and any limits
imposed upon the duration of the transmission. It is recommended that
the OFF time be no longer than 1/2 for the transmission preamble duration.
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figure
7: Four Channel Receiver with power save
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Limitation of liability
The information furnished by Radiometrix Ltd is believed
to be accurate and reliable. Radiometrix Ltd reserves the right to make
changes or improvements in the design, specification or manufacture
of its subassembly products without notice. Radiometrix Ltd does not
assume any liability arising from the application or use of any product
or circuit described herein, nor for any infringements of patents or
other rights of third parties which may result from the use of its products.
This data sheet neither states nor implies warranty of any kind, including
fitness for any particular application. These radio devices may be subject
to radio interference and may not function as intended if interference
is present. We do NOT recommend their use for life critical applications.
The Intrastat commodity code for all our modules is: 8542 6000.
R&TTE Directive
After 7 April 2001 the manufacturer can only place
finished product on the market under the provisions of the R&TTE
Directive. Equipment within the scope of the R&TTE Directive may
demonstrate compliance to the essential requirements specified in Article
3 of the Directive, as appropriate to the particular equipment.
Further details are available on The Office of Communications (Ofcom)
web site:
Licensing
policy manual
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