BiM1H

VHF NARROW BAND FM 500mW TRANSCEIVER

The BiM1H transceiver modules offer a 500mW RF output VHF data link in Radiometrix transceiver standard pin-out and footprint. This makes the BiM1H ideally suited to those low power applications where existing wideband transceivers provide insufficient range.

 

 

Figure 1: BiM1H-151.300-3

Features

  • Standard frequency 151MHz band
  • Other frequencies from 120MHz to 180MHz
  • Data rates up to 3kbps for standard module
  • Usable range over 10km
  • Fully screened
  • Feature-rich interface (RSSI, analogue and digital baseband)
  • Low power requirements
  • The BiM1H is a half duplex radio transceiver module for use in long range bi-directional data transfer applications at ranges up to 10kilometres.

Applications

  • Tracing and asset tracking systems
  • Meter reading systems
  • Industrial telemetry and telecommand
  • Data loggers
  • In-building environmental monitoring and control
  • Social alarms
  • High-end security and fire alarms
  • DGPS systems
  • Vehicle data up/download

Technical Summary

  • Operating frequency: 151.300MHz
  • Supply range: +5V regulated supply
  • Current consumption: 290mA transmit, 8mA receive
  • Data bit rate: 3kbps max. (standard module)
  • RSSI output with >60dBm range
  • -120dBm sensitivity (for 12 dB SINAD)
  • Size: 33 x 23 x 12mm

Evaluation Platform: Narrow Band Evaluation Kit


Figure 2: BiM1H block diagram

BiM1H transceiver contains a 500mW BiM1HT transmitter circuit and BiM1R receiver circuit with their RF output and input connected to a common RF pin via an internal RF switch.

Functional description

The transmit section of the BiM1H consists of a frequency modulated Voltage Controlled Crystal Oscillator (VCXO) feeding a frequency doubler with two stage amplifier and RF filter. Final Power Amplifier stage is factory pre-set to appropriate band power level. A Tx Select line controls the operation; the transmitter achieves full RF output typically within 8ms of this line being pulled low. The RF output is filtered to ensure compliance with the appropriate radio regulations and fed via a fast Tx/Rx changeover switch to the 50Ω antenna pin.

The receive section is a double conversion FM superhet with IF at 21.4MHz and 455kHz fed by a Low Noise Amplifier (LNA) on the RF front-end. The receiver is controlled by RX Select line and will power up typically <2ms. Quadrature detector output is available as Audio Frequency (AF) output and transmitted digital data is regenerated from AF using adaptive data slicer. A Received Signal Strength Indicator (RSSI) output with some 60dB of range is provided.

User interface


Figure 3: BiM1H pin-out and dimension

Pin Name Function
1, 3 RF GND RF ground pin; internally connected to the module screen and pin 5, 9, 10, 18 (0 Volt).
2 RF IN/OUT 50Ω RF input/output from the antenna
17 Vcc +5V regulated DC power supply
16 RX select Pull low to enable Receiver
15 TX select Pull low to enable Transmitter
14 TXD DC coupled input for 5V CMOS logic. Rin = 100kΩ
13 AF 500mV pk-pk audio. DC coupled, approx 0.8V bias
12 RXD 2.5V pk-pk logic output of data slicer. Suitable for Biphase codes
11 RSSI DC level between 0.5V and 2.4V. 60dB dynamic range
9, 10, 18 0V Supply ground connectio

NOTES:
1. RX select and TX select have (10kΩ approx.) pullups to Vcc
2. Avoid RX select and TX select both low: undefined module operation (but damage will not result)
3. A regulated +5v rail must be used
4. Pinout is as stanadrd BiM1 and BiM2. On RF connector end only pins 1, 2, 3, 9 are present.

Absolute maximum ratings

Exceeding the values given below may cause permanent damage to the module.

Operating temperature: -10°C to +60°C
Storage temperature:    -30°C to +70°C

RF in (pin 1):               ±50V @ <10MHz, +13dBm @ >10MHz
All other pins:              -0.3V to +16.0V

Performance specifications

(Vcc = 5V / temperature = 20°C unless stated)

General pin min. typ. max. units notes
DC supply
Supply voltage
17
-
5
-
V
TX Supply current
17
-
290
-
mA
RX Supply current
17
-
8
-
mA
Antenna pin impedance
2
-
50
-
Ω
RF centre frequency (100mW)
-
151.300
-
MHz
Channel spacing
-
25
-
kHz
Number of channels
1
Transmitter
RF
RF power output
2
+26
+27
+28
dBm
1
Spurious emissions
2
-
-
-36
dBm
Adja. channel TX power
-37
dBm
Frequency accuracy
- 2.5
0
+2.5
kHz
2
FM deviation (peak)
±2.5
±3.0
±3.5
kHz
3
Baseband
Modulation bandwidth @ -3dB
0
-
2.5
kHz
8
Modulation distortion (THD)
5
%
TXD input level (logic low)
14
-
0
-
V
4
TXD input level (logic high)
14
-
5.0
-
V
4
Dynamic timing
TX select to full RF
-
8
-
ms
Receiver
RF/IF
RF sensitivity @ 12dB SINAD
2, 13
-
-120
-
dBm
RF sensitivity @ 1ppm BER
2, 12
-
-115
-
dBm
5
RSSI threshold
2, 11
-
-127
-
dBm
5
RSSI range
2, 11
-
60
-
dB
Blocking
2
-
88
-
dB
Image and other Spurious emission
2
-
-70
-
dBm
Adjacent channel rejection
2
-
-70
-
dBm
LO leakage,re-radiated
-
-60
-
dBm
Baseband
Baseband bandwidth @ -3dB
13
-
5
-
kHz
AF level
13
-
500
-
mVp-p
6
DC offset on AF out
13
-
0.8
-
V
Distortion on recovered AF
12
5
%
Dynamic timing
Power up with signal present
Power up to valid RSSI
16, 11
TBA
ms
Power up to stable AF outpu
16, 13
-
2
-
ms
Power up to stable RXD output
16, 12
-
10
-
ms
Signal applied with supply on
Signal to valid AF
2, 11
TBA
ms
Signal to stable data
2, 12
TBA
ms
Time between data transitions
12
-
-
0.3
ms
7
Mark : space ratio
12
20
50
80
%

Notes:

  1. Measured into 50Ω resistive load.
  2. Total over full supply and temperature range.
  3. With 0V - 5.0V modulation input.
  4. To achieve specified FM deviation.
  5. See applications information for further details.
  6. For received signal with ±3kHz FM deviation.
  7. For 50:50 mark to space ratio (i.e. squarewave).
  8. A Wide bandwidth (0-5kHz) version, which supports 10kbps data rate, is also available as special.

Application Information

RX Received Signal Strength Indicator (RSSI)

The BiM1H wide range RSSI which measures the strength of an incoming signal over a range of 60dB or more. This allows assessment of link quality and available margin and is useful when performing range tests.

The output on pin 11 of the module has a standing DC bias of up to 0.5V with no signal, rising to 2.4V at maximum indication. DVmin-max is typically 1V and is largely independent of standing bias variations. Output impedance is 56kΩ. Pin 11 can drive a 100mA meter directly, for simple monitoring.

Typical RSSI characteristic is as shown below:


Figure 4: RSSI level with respect to received RF level at BiM1H antenna pin

Expected range

Predicting the range obtainable in any given situation is notoriously difficult since there are many factors involved. The main ones to consider are as follows:

  • Type and location of antennas in use
  • Type of terrain and degree of obstruction of the link path
  • Sources of interference affecting the receiver
  • "Dead" spots caused by signal reflections from nearby conductive objects
  • Data rate and degree of filtering employed

Antennas

The choice and positioning of transmitter and receiver antennas is of the utmost importance and is the single most significant factor in determining system range. The following notes are intended to assist the user in choosing the most effective antenna type for any given application.

Integral antennas

These are relatively inefficient compared to the larger externally-mounted types and hence tend to be effective only over limited ranges. They do however result in physically compact equipment and for this reason are often preferred for portable applications. Particular care is required with this type of antenna to achieve optimum results and the following should be taken into account:

1. Nearby conducting objects such as a PCB or battery can cause detuning or screening of the antenna which severely reduces efficiency. Ideally the antenna should stick out from the top of the product and be entirely in the clear, however this is often not desirable for practical/ergonomic reasons and a compromise may need to be reached. If an internal antenna must be used try to keep it away from other metal components and pay particular attention to the "hot" end (i.e. the far end) as this is generally the most susceptible to detuning. The space around the antenna is as important as the antenna itself.

2. Microprocessors and microcontrollers tend to radiate significant amounts of radio frequency hash which can cause desensitisation of the receiver if its antenna is in close proximity. The problem becomes worse as logic speeds increase, because fast logic edges generate harmonics across the VHF range which are then radiated effectively by the PCB tracking. In extreme cases system range may be reduced by a factor of 5 or more. To minimise any adverse effects situate antenna and module as far as possible from any such circuitry and keep PCB track lengths to the minimum possible. A ground plane can be highly effective in cutting radiated interference and its use is strongly recommended.

A simple test for interference is to monitor the receiver RSSI output voltage, which should be the same regardless of whether the microcontroller or other logic circuitry is running or in reset.

The following types of integral antenna are in common use:

Quarter-wave whip: This consists simply of a piece of wire or rod connected to the module at one end. At 151MHz the total length should be 471mm from module pin to antenna tip including any interconnecting wire or tracking. Because of the length of this antenna it is almost always external to the product casing.

Helical: This is a more compact but slightly less effective antenna formed from a coil of wire. It is very efficient for its size, but because of its high Q it suffers badly from detuning caused by proximity to nearby conductive objects and needs to be carefully trimmed for best performance in a given situation. The size shown is about the maximum commonly used at 151MHz and appropriate scaling of length, diameter and number of turns can make individual designs much smaller.

Integral antenna summary:

Features
whip
helical
Ultimate performance
***
**
Ease of design set-up
***
**
Size
*
***
Immunity to proximity effects
**
*


Figure 5: integral antenna configurations

External antennas

These have several advantages if portability is not an issue, and are essential for long range links. External antennas can be optimised for individual circumstances and may be mounted in relatively good RF locations away from sources of interference, being connected to the equipment by coax feeder.

Helical: Of similar dimensions and performance to the integral type mentioned above, commercially-available helical antennas normally have the coil element protected by a plastic moulding or sleeve and incorporate a coax connector at one end (usually a straight or right-angle BNC type). These are compact and simple to use as they come pre-tuned for a given application, but are relatively inefficient and are best suited to shorter ranges.

Quarter-wave whip: Again similar to the integral type, the element usually consists of a stainless steel rod or a wire contained within a semi-flexible moulded plastic jacket. Various mounting options are available, from a simple BNC connector to wall brackets, through-panel fixings and magnetic mounts for temporary attachment to steel surfaces.

A significant improvement in performance is obtainable if the whip is used in conjunction with a metal ground plane. For best results this should extend all round the base of the whip out to a radius of 300mm or more (under these conditions performance approaches that of a half-wave dipole) but even relatively small metal areas will produce a worthwhile improvement over the whip alone. The ground plane should be electrically connected to the coax outer at the base of the whip. Magnetic mounts are slightly different in that they rely on capacitance between the mount and the metal surface to achieve the same result.

A ground plane can also be simulated by using 3 or 4 quarter-wave radials equally spaced around the base of the whip, connected at their inner ends to the outer of the coax feed. A better match to a 50Ω coax feed can be achieved if the elements are angled downwards at approximately 30-40° to the horizontal.


Fig. 6: Quarter wave antenna / ground plane configurations

Half-wave: There are two main variants of this antenna, both of which are very effective and are recommended where long range and all-round coverage are required:
1. The half-wave dipole consists of two quarter-wave whips mounted in line vertically and fed in the centre with coaxial cable. The bottom whip takes the place of the ground plane described previously. A variant is available using a helical instead of a whip for the lower element, giving similar performance with reduced overall length. This antenna is suitable for mounting on walls etc. but for best results should be kept well clear of surrounding conductive objects and structures (ideally >1m separation).

2. The end-fed half wave is the same length as the dipole but consists of a single rod or whip fed at the bottom via a matching network. Mounting options are similar to those for the quarter-wave whip. A ground plane is sometimes used but is not essential. The end-fed arrangement is often preferred over the centre-fed dipole because it is easier to mount in the clear and above surrounding obstructions.

Yagi: This antenna consists of two or more elements mounted parallel to each other on a central boom. It is directional and exhibits gain but tends to be large and unwieldy - for these reasons the yagi is the ideal choice for links over fixed paths where maximum range is desired.

Module mounting considerations

Good RF layout practice should be observed. If the connection between module and antenna is more than about 20mm long use 50Ω microstrip line or coax or a combination of both. It is desirable (but not essential) to fill all unused PCB area around the module with ground plane.

Variants and ordering information

The BiM1H transceiver is manufactured in the following variants as standard:

Standard: BiM1H-151.300-3
BiM1H-151.300-3
Special: BiM1H-151.300-10 (10kbps)
BiM1H-151.300-10 (10kbps)

Other variants can be supplied to individual customer requirements at frequencies from 120MHz to 180MHz and/or opitomized for specific data speeds and formats. However these are subject to minimum order quantity (MOQ) and long lead time. Please consult the Sales Department for further information.

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