| Issue 3 |
BiM-UHF
data sheet
|
21st October 1997
|
UK Version - BiM-418-40
Euro Version - BiM-433-40
The
BiM-418-40 and BiM-433-40 are miniature UHF radio modules capable
of half duplex data transmission at speeds upto 40 kbit/s over distances
of 30 metres "in-building" and 120 metres open ground.
The module integrates a low power UHF FM transmitter
and matching superhet receiver together with the data recovery and
TX/RX change over circuits to provide a low cost solution to implementing
a Bi-directional short range radio data link. The high data rates
(upto 40kbit/s) and fast TX/RX changeover ( <1ms ) make the BiM
transceiver ideal for high integrity one to one links / multi-node
packet switch networks. Rapid RX power up ( <1ms ) allows effective
duty cycle power saving of the receiver for battery powered applications
(eg. 15µA average @ 1ms ON : 1sec OFF).
figure
1: Block diagram
Click on the image for EXPANDED VIEW
figure
2: mechanical dimensions
Click on the image for EXPANDED VIEW
| pin 1 & 3 |
RF GND |
These pins should be connected to the
ground plane against which the integral antenna radiates . Internally
connected to pins 9,10,18 .
|
| pin 2 |
Antenna |
RF input / RF output for connection
to an integral antenna. It has a nominal RF impedance of 50W
and is capacitively isolated from the internal circuit.
|
| pin 9, 10, 18 |
Vss |
0 volt connection for the modulation
and supply.
|
| pin 11 |
CD |
Carrier Detect - When the receiver
is enabled, a low indicates a signal above the detection threshold
is being received. The output is high impedance (50kW)
and should only be used to drive a CMOS logic input.
|
| pin 12 |
RXD |
This digital output from the internal
data slicer is a squared version of the signal on pin 13 (AF).
This signal is used to drive external digital decoders, it is
true data (i.e. as fed to the transmitters data input). The 10kW
output impedance is suitable for driving CMOS logic.
Note: this output contain squared noise when
no signal is being received.
|
| pin 13 |
RX Audio |
This is the FM demodulator output .It
has a standing DC bias of approximately 1.5Volts and may be used
to drive analogue data decoders such as modems or DTMF decoders.
Output impedance is 10KOhm. Signal level approx. 0.4V pk to pk.
We recommend this signal always be available on a convenient test
point for diagnostic purposes.
Note: unlike the RXD output which is always true data, this
output is true data on the BiM-418 and inverted on the BiM-433.
|
| pin 14 |
TXD |
Should be driven directly by a CMOS
logic device running on the same supply voltage as the module.
Analogue drive may be used but must not drive this input above
Vcc or below 0V. This input should be held at <0.5V when the
TX is not selected to prevent current leak (see block
diagram).
|
| pin 15 |
TX select |
Active low transmit / receive selects
with 10kW internal.
|
| pin 16 |
RX select |
pull-ups. They may be driven by open
collector or CMOS logic
|
All states are valid.
| Pin 15 TX |
Pin 16 RX |
Function |
| 1 |
1 |
power down (<1µA) |
| 1 |
0 |
receiver enabled |
| 0 |
1 |
transmitter enabled |
| 0 |
0 |
self test loop back |
Note - loop
test is at reduced TX power.
| pin 17 |
Vcc |
positive supply, supply voltages from
+4.5V to +5.5V may be used. Reverse polarity will destroy the
module. Supply is internally decoupled. Maximum ripple content
50mV pk to pk. |
figure
3: test circuit BiM-UHF
Click on the image for EXPANDED VIEW
Warning:
Don't be tempted to adjust the trimmer
on the module, it controls the receive frequency and can only be correctly
set-up with an accurate RF signal generator.
ambient temperature: 20 °C
supply voltage: +5.0V, unless noted otherwise
Data applies to all frequency versions, except
where noted
| Parameter |
Min
|
Typ
|
Max
|
Units
|
Notes
|
| DC parameters |
|
|
|
|
|
| Operating supply range, Vcc |
4.5
|
-
|
5.5
|
V
|
-
|
| Supply current, transmit (standard) |
8
|
12
|
15
|
mA
|
-
|
| transmit (HP version) |
15
|
17
|
21
|
mA
|
|
| receive |
10
|
12
|
16
|
mA
|
-
|
| loop test |
-
|
20
|
25
|
mA
|
-
|
| stand-by |
-
|
-
|
1
|
µA
|
-
|
| Parameter |
Min
|
Typ
|
Max
|
Units
|
Notes
|
| RF Parameters - Transmit |
|
|
|
|
|
| Radiated power (ERP) (standard) |
-10
|
-6
|
-3
|
dBm
|
1
|
| (-HP version) |
+3
|
+6
|
+10
|
dBm
|
1
|
| Transmit frequency (Frf) BiM-418-40 |
-
|
418.000
|
-
|
MHz
|
-
|
| Transmit frequency (Frf) BiM-433-40 |
-
|
433.920
|
-
|
MHz
|
-
|
| Initial frequency accuracy |
-75
|
0
|
+75
|
kHz
|
-
|
| Overall frequency accuracy |
-95
|
0
|
+95
|
kHz
|
-
|
| Spurious radiation |
|
meets
|
ETS
|
300-
|
220
|
| FM deviation (+/-) |
15
|
20
|
30
|
kHz
|
2
|
| Distortion |
-
|
5
|
10
|
%
|
3
|
| Modulation response @ -3dB |
DC
|
-
|
32
|
kHz
|
-
|
| Parameter |
Min
|
Typ
|
Max
|
Units
|
Notes
|
| RF Parameters - Receive |
|
|
|
|
|
| Receive frequency (Frf) BiM-418-40 |
-
|
418.000
|
-
|
MHz
|
-
|
| Receive frequency (Frf) BiM-433-40 |
-
|
433.920
|
-
|
MHz
|
-
|
| Receiver sensitivity |
-100
|
-107
|
-
|
dBm
|
-
|
| AF bandwidth @ -3dB |
0.1
|
-
|
22
|
kHz
|
-
|
| AF output level, pin 13, pk to pk |
-
|
400
|
-
|
mV
|
-
|
| Local Oscillator leakage, pin 2 |
-
|
-57
|
-
|
dBm
|
-
|
| IF Bandwidth |
-
|
200
|
-
|
kHz
|
-
|
| AFC lock range (5µV signal) |
-
|
200
|
-
|
kHz
|
-
|
| Parameter |
Min |
Typ |
Max |
Units |
Notes |
| Timing |
|
|
|
|
|
| RX select low to valid CD |
- |
- |
1 |
ms |
- |
| RX select low to valid RXD |
- |
- |
3 |
ms |
- |
| Transmit to Receive delay |
- |
- |
1 |
ms |
- |
| RF input (5µV) to valid CD |
- |
- |
0.5 |
ms |
- |
| RF input (5µV) to stable AF |
- |
- |
0.5 |
ms |
- |
| Parameter |
Min
|
Typ
|
Max
|
Units
|
Notes
|
Base Band transfer function
(through a pair of transceivers) |
|
|
|
|
|
| Linear drive (4V pk to pk,
sine) |
|
|
|
|
|
| AF response @ -3dB |
0.1
|
-
|
17
|
kHz
|
-
|
| Analogue distortion |
-
|
5
|
10
|
%
|
-
|
| Parameter |
Min |
Typ |
Max |
Units |
Notes |
| Digital drive |
|
|
|
|
|
| Data rate ( 50:50 ) |
- |
- |
40 |
kbits/s |
4 |
| Time between transitions |
25 |
- |
2000 |
µs |
5 |
| Average Mark:Space ratio |
30 |
50 |
70 |
% |
6 |
| preamble duration (10101010) |
3 |
- |
- |
ms |
- |
| data delay (TXD to RXD) |
- |
25 |
- |
µs |
- |
| Parameter |
|
Min
|
Typ
|
Max
|
Units
|
Notes
|
| Interface levels |
- inputs
|
|
|
|
|
|
| TX & RX select, |
Vhigh
|
Vcc-0.5
|
|
Vcc
|
V
|
-
|
|
Vlow
|
0
|
|
1
|
V
|
-
|
| Source current |
@Vlow = 0
|
0.5
|
|
1
|
mA
|
-
|
| TXD |
Vhigh
|
Vcc-0.5
|
|
Vcc
|
V
|
-
|
|
Vlow
|
0
|
|
0.5
|
V
|
-
|
| Parameter |
|
Min
|
Typ
|
Max
|
Units
|
Notes
|
| Interface levels |
- outputs
|
|
|
|
|
|
| RXD & CD |
V high
|
|
Vcc-0.6
|
Vcc
|
V
|
-
|
| (no load) |
V low
|
|
0.2
|
1
|
V
|
-
|
Notes:
- module on 50mm square ground plane , 16cm whip antenna
- Standard modulation : 2kHz square wave, 0 to Vcc
- 1kHz, 4V pk to pk, Sinewave centred on +2.5V at pin 14 (TXD)
- Digital drive, 50:50 mark:space (over 4ms) data pattern.
- High or Low pulse.
- Averaged over any 4ms period
Absolute maximum ratings
| Supply voltage Vcc, pin 17 |
-0.1
|
to
|
+6 V
|
| All input / output pins |
-0.1
|
to
|
Vcc + 0.1 V
|
| Operating temperature |
-20°C
|
to
|
+55°C
|
| Storage temperature |
-40°C
|
to
|
+100°C
|
figure
4: signal to noice curve
Click on the image for EXPANDED VIEW
figure
5: timing waveform
Click on the image for EXPANDED VIEW
Three types of integral antenna are recommended and approved for
use with the BiM transceiver :
| A) |
Helical: |
Wire coil, connected directly to pin
2, open circuit at other end. This antenna is very efficient given
it's small size (20mm x 4mm dia.). The helical is a high Q antenna,
trim the wire length or expand the coil for optimum results. The
helical de-tunes badly with proximity to other conductive objects.
|
| B) |
Loop, |
A loop of PCB track tuned by a fixed
or variable capacitor to ground at the 'hot' end and fed from
pin 2 at a point 20% from the ground end. Loops have high immunity
to proximity de-tuning.
|
| C) |
Whip |
This is a wire, rod, PCB track or combination
connected directly to pin 2 of the module. Optimum total length
is 17cm (1/4 wave @418MHz). Keep the open circuit (hot) end well
away from metal components to prevent serious de-tuning. Whips
are ground plane sensitive and will benefit from internal 1/4
wave earthed radial(s) if the product is small and plastic cased.
|
figure
6: Antenna configuration
Click on the image for EXPANDED VIEW
Antenna selection chart
|
A
helical |
B
loop |
C
whip |
| Ultimate performance |
** |
* |
*** |
| Easy of design set-up |
** |
* |
*** |
| Size |
*** |
** |
* |
| Immunity proximity effects |
** |
*** |
* |
| Range open ground to similar antenna
|
80m |
50m |
120m |
The antenna choice and position directly controls the system range.
Keep it clear of other metal in the system, particularly the 'hot'
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.
The BiM-418-40 is type approved in the UK to MPT1340
for use in Telemetry, Telecommand and In-Building alarm applications.
CONFORMANCE to MPT1340 REQUIRES THAT:
- The transmitting antenna must be one of the
3 variants given in the data sheet. Antenna structures which yield
ERP gain are not permitted.
- The module must be directly and permanently
connected to the transmitting antenna without the use of an external
feeder. Increasing the RF power level by any means is not permitted.
- The module must not be modified nor used outside
it's specification limits.
- The module may only be used to send digital
or digitised data.Speech / Music are not permitted.
- The equipment in which the module is used must
carry an inspection mark located on the outside of the equipment
and be clearly visible. The minimum dimensions of the inspection
mark shall be 10 x 15 mm and the letter and figure height must be
no less than 2mm. The wording shall read: " MPT 1340
W.T. LICENCE EXEMPT ".
- Products intended for UK commercial application must be notified
to the Radiocommunications Agency (RA) on form RA 249 ( Cat I),
obtainable from the RA's library service, Tel 0171 211 0502/ 0505
OEM Manufacturers incorporating the BiM-418-40
transceiver as a component part of their product are authorised by
Radiometrix Ltd to quote our type-approval provided all the above
conditions are met.
MPT 1340 is the type approval specification issued
by the RA and may be obtained from the RA's library service on 0171
211 0502/ 0505.
Sending and Receiving Digital data
The BiM contains no data coding or decoding functions.
These must be provided by the external controller, usually a single
chip microprocessor, e.g. Arizona Microsystems PIC, Motorola MC68HC05
or similar. Alternatively a dedicated protocol controller such as
CML's FX909 or Echelon's Network chips will work well.
The Radiometrix RPC-000-40
Radio Packet Controller IC provides all the processor intensive
low-level packet formatting and data recovery functions required in
a high speed bi-directional data link/network. The RPC-418-40 and
RPC-433-40 provide a self-contained UHF radio port for a host micro
controller. The board combines a BiM transceiver and a RPC packet
controller. (Data available on request.)
A pair of BiM transceiver's will transmit direct
serial data applied to the TXD input and reproduce direct serial data
at the RXD output of receiving BiM. The BiM may also be used with
linear data e.g. from modem IC's (see test circuit for linear biasing
of TXD input).
figure
7: typical microcontroler interface
Click on the image for EXPANDED VIEW
Direct Digital, TXD > RXD at 5V CMOS Levels
The data path through a pair of BiM's is AC coupled.
This places 3 basic constraints that any serial code must satisfy
for reliable transfer.
1. Pulse width time The receiver
base band bandwidth and the AC coupling determines that the time,
T, between any 2 consecutive transitions in the serial code must satisfy:
25µs < T < 2ms
2. RX settling time The AFC and
data slicer in the receiver require at least 3ms of '10101010' preamble
to be transmitted before the data at the RXD output may be considered
reliable. Increasing this time to 5ms will give increased immunity
to RF interference.
3. Mark:Space ratio The data slicer
in the receiver is optimised for data waveforms with 50:50 Mark:Space
averaged over any 4ms period. The slicer will tolerate sustained asymmetry
up to 30/70 (either way), however, this will result in up to increased
in pulse width distortion and a decreased noise tolerance.
Any serial data waveform satisfying the above criteria
will pass reliably through a pair of BiM's.
figure
8: fully buffered CMOS interface - digital drive
Click on the image for EXPANDED VIEW
"RS232" Serial data
It is possible to transmit "RS232" serial
data directly at 4.8 to 38.4kbps baud between a pair of BiM transceivers
in half duplex. The data must be "packetised" with no gaps
between bytes. i.e. :
The data must be preceded by >3ms of preamble
(55h or AAh) to allow the data slicer in the BiM to settle, followed
by 1 or 2 FFh bytes to allow the receive UART to lock, followed
by a unique start of message byte, (01h), then the data bytes and
finally terminated by a CRC or check sum. The receiver data slicer
provides the best bit error rate performance on codes with a 50:50
mark:space average over a 4ms period, a string of FFh or 00h is
a very asymmetric code and will give poor error rates where reception
is marginal. Only 50:50 codes may be used at data rates above 20kbit/s.
We recommend 3 methods of improving mark:space ratio
of serial codes, all 3 coding methods are suitable for transmission
at 40kbit/s :-
Method 1 - Bit coding
Bit rate , Max 40kbits/s , Min 250bit/s
Redundancy (per bit) 100% (Bi-phase), 200% (1/3 : 2/3)
Each bit to be sent is divided in half, the first
half is the bit to be sent and the second half, it's compliment. Thus
each bit has a guaranteed transition in the centre and a mark:space
of 50:50 . This is Bi-phase or Manchester coding and gives good results,
however the 100% redundancy will give a true throughput of 20kbit/s.
A less efficient, variation of Bi-phase is 1/3 :
2/3 bit coding. Each bit to be sent is divided into 3 parts, the first
1/3 is a low, mid 1/3 is the data bit and final 1/3 is high. This
code is easy to decode since each bit always starts with a negative
transition. This code should not be sent faster than 100µs per bit
(10kbit/s) since the mark/space can vary for 33 to 67%.
Method 2 - Byte coding
Bitrate, Max 40kbit/s , Min 2kbit/s
Redundancy (per byte) 25% (synchronous), 50% (async)
If only a subset of the ASCII code is required (e.g.
0-9 , A-Z and a few control codes) then translate (via. a look up
table) the required ASCII codes into the 8 bit codes below. These
codes all have a 50:50 mark:space when sent serially.
Of the 256 possible 8 bit codes, 70 contain 4 ones
& 4 zeros. The 68 Hex codes below have a 50:50 mark:space and
may either be sent/received from a standard serial port (UART) using
1 start, 1 stop and no parity or as bytes of a synchronous code. Use
for this subset also allows simple byte error checking on reception
as all received codes must contain exactly 4 one's and 4 zero's.
|
17
|
1B
|
1D
|
1E
|
27
|
2B
|
2D
|
2E
|
33
|
35
|
36
|
39
|
3A
|
3C
|
47
|
4B
|
4D
|
|
4E
|
53
|
55
|
56
|
59
|
5A
|
5C
|
63
|
65
|
66
|
69
|
6A
|
6C
|
71
|
72
|
74
|
78
|
|
87
|
8B
|
8D
|
8E
|
93
|
95
|
96
|
99
|
9A
|
9C
|
A3
|
A5
|
A6
|
A9
|
AA
|
AC
|
B1
|
|
B2
|
B4
|
B8
|
C3
|
C5
|
C6
|
C9
|
CA
|
CC
|
D1
|
D2
|
D4
|
D8
|
E1
|
E2
|
E4
|
E8
|
Method 3 - FEC coding
Bit rate , Max 40kbit/s , Min 4.8kbit/s
Redundancy (per byte) 100%
Each byte is sent twice; true then it's logical compliment.
e.g. even bytes are true and odd bytes are inverted. this preserves
a 50:50 balance.
A refinement of this simple balancing method is to
increase the stagger between the true and the inverted data streams
and add parity to each byte. Thus the decoder may determine the integrity
of each even byte received and on a parity failure select the subsequent
inverted odd byte. The greater the stagger the higher the immunity
to isolated burst errors.
A pair of transceivers may also be viewed as a linear analogue channel
with a pass baseband of 100Hz to 17kHz with <10% distortion. The
ultimate S/N ratio being >40dB (see quieting
curves v RF input). The test circuit shows the TXD input biased
for linear operation and a simple digital filter to shape the transmit
data to a raised-cosine wave shape. The 22kW
resistor linear- biases the TXD input. The drive voltage should be
between 3.5 and 5V pk to pk to achieve full modulation (greatest S/N
at receiver)
figure
9: linear drive
Click on the image for EXPANDED VIEW
Raised-cosine shaping may be applied externally to any serial data
stream and will yield better error performance than unshaped data
at high data rates (up to 40kbit/s) for data steams with 50:50 mark:space
(4ms averaging period). Several excellent modem chips (FX 589 &
FX 909) are available for Consumer Microcircuits Ltd (CML tel +44
(0)1376 513833). These chips employ GMSK (shaped data and matched
receive filters) and enable operation up to 40kbit/s.
figure
10: raised cosine generator
Click on the image for EXPANDED VIEW
Digitised analogue data
Linear operation of BiM transceivers will allow
direct transfer of analogue data, however in many applications the
distortion and low frequency roll off are too high (e.g. bio-medical
data such as ECG). The use of delta modulation is an excellent solution
for analogue data in the range 1Hz up to 4kHz with less than 1% distortion.
A number of propitiatory IC's such as Motorola's MC3517/8 provide
CVSD Delta mod/demod on a single chip.
Where the signal bandwidth extends down to DC , such as strain gauges,
level sensing, load cells etc. then V-F / F-V chips (such as Nat Semi
LM331)
provide a simple means of digitising.
Packet data
In general, data to be sent via a radio link is
formed into a serial "packet" of the form :-
