In telecommunications and signal processing, frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency (contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant). In analog applications, the difference between the instantaneous and the base frequency of the carrier is directly proportional to the instantaneous value of the input signal amplitude. Digital data can be sent by shifting the carrier's frequency among a set of discrete values, a technique known as frequency-shift keying.
Frequency modulation can be regarded as phase modulation where the carrier phase modulation is the time integral of the FM modulating signal.
FM RECEIVERS
Radio receiver design is a complex topic which can be broken down into a series of smaller topics. A radio communication system requires two tuned circuits each at the transmitterand receiver, all four tuned to the same frequency. The term radio receiver is understood in this article to mean any device which is intended to receive a radio signal and if need be to extract information from the signal.
TYPES OF RADIO RECEIVER
Basic crystal set.
A T.R.F. Receiver.
A Superhetrodyne Receiver.
the Reflex Receiver.
Mainly f.m. receivers are of the superhetrodyne variety.
An a.m. receiver relies upon the original carrier signal (station frequency) having been amplitude modulated. This means the original amplitude (strength) varies at an audio rate. Looking at figure 1 we can see an unmodulated carrier signal as it might be seen on an oscilloscope.
Fig 1. an unmodulated carrier signal
as you can see the amplitude of the carrier signal is unvarying, it remains constant in height looking from the top of the figure to the bottom of the figure. This carrier is common to both a.m. and f.m. signals.
Perhaps the a.m. carrier signal repeats each cycle from point (a) to point (b) - "blue" - in figure 2 below at the rate of 810,000 times a second, this represents a frequency of 810 Khz and would be in the a.m.radio band.
Figure 2. one complete cycle of signal
If the signal were varied at 101,700,000 cycles per second then it would be 101.7 Mhz and located in the f.m. radio band.
Now if the signal of figure 1 is amplitude modulated it looks like the signal in figure 3 below.
Figure 3. - an a.m. modulated signal
Here you will notice that the audio modulating signal which is depicted in red has varied the strength of the carrier signal which is depicted green for purposes of this illustration.
You will note my skills as a graphic artist leave much to be desired (hint: anyone able to contribute oscillograghs in .jpg or .gif formats?) but you should be able to see the carrier sine wave envelope is being varied in strength by the red audio signal. In the receiver circuit a diode detector can convert that envelope above back into the original audio signal for later amplification although some distortion does result.
It was to an extent this distortion property that people sought a better means of transmission. More important it was discovered that noise (either man made QRM or natural noise QRN) was amplitude in its properties.
I have depicted two blue lines in the diagram above, these represent noise impulses caused perhaps by automobile ignition, nearby fluorescent lighting, your computer or atmospheric noise such as a distant storm. Note the blue lines extend beyond the amplitude envelope, they could be many times the magnitude of the received signal.
Nearly everyone has experienced static crashes through an a.m. radio when nearby lightning strikes.
For these reasons frequency modulation evolved. Instead of varying the amplitude of the carrier signal, which remains constant, we vary the carrier frequency more or less by the audio frequency.
If a carrier signal is frequency modulated (fm) it looks like one below in figure 4
Fig 4 frequency modulated carrier
You should immediately note that the carrier frequency is varying yet the amplitude has remained constant.
Construction of one transistor FM radio
Introduction
AM radio circuits and kits abound. Some work quite well. But, look around and you will find virtually no FM radio kits. Certainly, there are no simple FM radio kits. The simple FM radio circuit got lost during the transition from vacuum tubes to transistors. In the late 1950s and early 1960s there were several construction articles on building a simple super regenerative FM radio. After exhaustive research into the early articles and some key assistance from a modern day guru in regenerative circuit design, this is a simple radio kit. It is a remarkable circuit. It is sensitive, selective, and has enough audio drive for an earphone.
Adjustment
If the radio is wired correctly, there are three possible things you can hear when you turn it on: 1) a radio station, 2) a rushing noise, 3) a squeal, and 4) nothing. If you got a radio station, you are in good shape. Use another FM radio to see where you are on the FM band. You can change the tuning range of C3 by squeezing L1 or change C1. If you hear a rushing noise, you will probably be able to tune in a station. Try the tuning control and see what you get. If you hear a squeal or hear nothing, then the circuit is oscillating too little or too much. Try spreading or compressing L1. Double check your connections. If you don't make any progress, then you need to change R4. Replace R4 with a 20K or larger potentiometer (up to 50K). A trimmer potentiometer is best. Adjust R4 until you can reliably tune in stations. Once the circuit is working, you can remove the potentiometer, measure its value, and replace it with a fixed resistor. Some people might want to build the set from the start with a trimmer potentiometer in place
Basic designs
Crystal radio
A crystal set receiverconsisting of an antenna, a variable inductor, a cat's whisker, and a capacitor.
Advantages
Simple, easy to make. This is the classic design for a clandestine receiver in a POW camp.
Disadvantages
Insensitive, it needs a very strong RF signal to operate.
Poor selectivity, it often only has only one tuned circuit.
Direct amplification
The directly amplifying receiver contains the input radio frequency filter, the radio frequency amplifier (amplifying radio signal of the tuned station), the detector and the sound frequency amplifier. This design is simple and reliable, but much less sensitive than the superheterodyne (described below).
Reflectional
The reflectional receiver contains the single amplifier that amplifies first radio, and then (after detection) sound frequency. It is simpler, smaller and consumes less power, but it is also comparatively unstable.
Regenerative
The Regenerative circuit has the advantage of being potentially very sensitive, it uses positive feedback to increase the gain of the stage. Many valved sets were made which used a single stage. However if misused it has the great potential to cause radio interference, if the set is adjusted wrongly (too much feedback used) then the detector stage will oscillate so causing the interference.
Regenerative Receiver Schematic
Tuned radio frequency
the RF interference that the local oscillator can generate can be controlled with the use of a buffer stage between the LO and the Detector, and a buffer or RF amp stage between the LO and the antenna.
Direct conversion
In the Direct conversion receiver, the signals from the aerial pass through a band pass filter and an amplifier before reaching a non-linear mixer where they are mixed with a signal from a local oscillator which is tuned to the carrier wave frequency of an AM or SSB transmitter. The output of this mixer is then passed through a low pass filter before an audio amplifier. This is then the output of the radio.
For CW morse the local oscillator is tuned to a frequency slightly different from that of the transmitter to make the received signal audible.
Advantages
Simpler than a superheterodyne
Better tuning than a simple crystal set
Disadvantages
Less selective than a superhet with regard to strong in-band signals
A wider bandwidth than a good SSB communications radio, this is because no sideband filtering exists in this circuit.
Superheterodyne
The FM design is a cheap design intended for a broadcast band household receiver.
A schematic of a superhet AM receiver. Note that the radio has a AGC loop.
For single conversion superheterodyne AM receivers designed for mediumwave and longwave the IF is commonly 455 kHz.
A schematic of a simple cheap superhet FM receiver. Note that the radio lacks a AGC loop, and that the IF amplifier has a very high gain and is driven into clipping.
For many single conversion superheterodyne receivers designed for band II FM (88 - 108 MHz) the IF is commonly 10.7 MHz. For TV sets the IF tends to be at 33 to 40 MHz.
Since we have covered Superheterodyne receivers in our syllabus and my research showed that, it is the most widespread FM receiver used. So, I will be elaborating on this further..
What Heterodyning is
To heterodyne means to mix to frequencies together so as to produce a beat
frequency, namely the difference between the two. Amplitude modulation is a
heterodyne process: the information signal is mixed with the carrier to produce the side-bands. The side-bands occur at precisely the sum and difference frequencies of the carrier and information. These are beat frequencies (normally the beat frequency is associated with the lower side-band, the difference between the two).
What Superheterodyning is
When you use the lower side-band (the difference between the two frequencies), you are superheterodyning. Strictly speaking, the term superheterodyne refers to creating a beat frequency that is lower than the original signal. Although we have used the example of amplitude modulation side-bands as an example, we are not talking about encoding information for transmission. What superheterodying does is to purposely mix in another frequency in the receiver, so as to reduce the signal frequency prior to processing. Why and how this is done will be discussed below.
The received RF-signals must transformed in a videosignal to get the wanted informations from the echoes. This transformation is made by a super heterodyne receiver. The main components of the typical superheterodyne receiver are shown on the following picture:
Figure 1: Block diagram of a Superheterodyne
The superheterodyne receiver changes the rf frequency into an easier to process lower IF- frequency. This IF- frequency will be amplified and demodulated to get a videosignal.
The Figure shows a block diagram of a typical superheterodyne receiver. The RF-carrier comes in from the antenna and is applied to a filter. The output of the filter are only the frequencies of the desired frequency-band. These frequencies are applied to the mixer stage. The mixer also receives an input from the local oscillator. These two signals are beat together to obtain the IF through the process of heterodyning. There is a fixed difference in frequency between the local oscillator and the rf-signal at all times by tuning the local oscillator. This difference in frequency is the IF. this fixed difference an ganged tuning ensures a constant IF over the frequency range of the receiver. The IF-carrier is applied to the IF-amplifier. The amplified IF is then sent to the detector. The output of the detector is the video component of the input signal.
Image-frequency Filter
A low-noise RF amplifier stage ahead of the converter stage provides enough selectivity to reduce the image-frequency response by rejecting these unwanted signals and adds to the sensitivity of the receiver. The borders of the bandwidth of this amplifier are choosen to eleminate the image frequencies.
Many older radar receivers do not use a low-noise pre-amplifier (RF stage) as the receiver front end; they simply send the echo signal directly to a crystal mixer stage. This has any disadvantages. It is possible for these receivers to receive two different stations at the same point of the dial.
Mixer Stage
The mixer stage is used to increase the received frequency to an intermediate frequency. The mixer also receives an input from the local oscillator. These two signals are beat together to obtain the IF through the process of heterodyning.
fIF = frx - flocal oscillator
fIF = flocal oscillator -frx
There aren't any components which can distinguish a negative frequency of a positive frequency. therefore we can measure the magnitude of the frequency only: fIF = | flocal oscillator - frx |
The result is a second reception frequency as a „mirror image" around the intermediate frequency.
Assuming an intermediate frequency of 60 MHz, the local oscillator will track at a frequency of 60 MHz higher than the incoming signal. For example, suppose the receiver is tuned to pick up a signal on a frequency of 1030 MHz. The local oscillator will be operating at a frequency of 1090 MHz. The received and local oscillator signals are mixed, or heterodyned, in the converter stage and one of the frequencies resulting from this mixing action is the difference between the two signals, or 60 MHz, the IF frequency. This IF frequency is then amplified in the IF stages and sent on to the detector and audio stages.
Any signal at a frequency of 60 MHz that appears on the plate of the converter circuit will be accepted by the IF amplifier and passed on.
So on a receiver with no RF amplifier, the input to the converter is rather broadly tuned and some signals other than the desired signal will get through to the input jack of the converter stage. Normally these other signals will mix with the local oscillator signal and produce frequencies that are outside the bandpass of the 60 MHz IF amplifier and will be rejected. However, if there is a station operating on a frequency of 1150 MHz, and this signal passes through the rather broad tuned input circuit and appears on the input jack of the converter stage, it too will mix with the local oscillator and produce a frequency of 60 MHz (1150 - 1090 = 60). This signal will also be accepted by the IF amplifier stage and passed on, thus both signals will be indicated on the screen. This is known as image-frequency interference.
IF Filter
This filter must filter the desired intermediate frequency out from the mixture frequencies arisen in the mixer stage. It is designed as one or more bandpasses.
Normally, the bandpass is as narrow as possible without affecting the actual signal energy. When a selection of pulse widths is available, such as short and long pulses, the bandpass must be able to match the bandwidth of the two different signals.
IF- Amplifier
The IF amplifier has the capability to vary both the bandpass and the gain of a receiver. After conversion to the intermediate frequency, the signal is amplified in several IF- amplifier stages. Most of the gain of the receiver is developed in the IF amplifier stages. The overall bandwidth of the receiver is often determined by the bandwidth of the IF stages. Gain must be variable to provide a constant voltage output for input signals of different amplitudes.
Detector
Envelope
RF-frequency
Figure 2: Scan from a screen of an oszilloscope
The detector in a microwave receiver serves to convert the IF pulses into video pulses.
Figure 3: a simple detector
The simplest form of detector is the diode detector. It detects the pulse envelope:
The condenser has got the function of a lowpass and blocks the IF- frequency.
In addition to the shown Amplitude Modulation there are possible other types of modulation too.
Video Amplifier
The video amplifier receives pulses from the detector and amplifies these pulses for application to the indicating device. A video amplifier is fundamentally an RC coupled amplifier that uses high-gain transistors. However, a video amplifier must be capable of a relatively wide Frequency response. The output stage of the receiver is normally an emitter follower. The low-impedance output of the emitter follower matches the impedance of the cable. The video pulses are coupled through the cable to the indicator for video display on the crt.
Local Oscillator
The local oscillator excite a frequency for mixing with the incoming signal to get the intermediate frequency.
Most radar receivers use megahertz intermediate frequency (IF) with a value between 30 and 75 megahertz. The IF is produced by mixing a local oscillator signal with the incoming signal. The local oscillator is, therefore, essential to efficient operation and must be both tunable and very stable. For example, if the local oscillator frequency is 3,000 megahertz, a frequency change of 0.1 percent will produce a frequency shift of 3 megahertz. This is equal to the bandwidth of most receivers and would greatly decrease receiver gain.
The power output requirement for most local oscillators is small (20 to 50 milliwatts) because most receivers use crystal mixers that require very little power.
The local oscillator output frequency must be tunable over a range of several megahertz in the 4,000-megahertz region. The local oscillator must compensate for any changes in the transmitted frequency and maintain a constant 30 or 75 megahertz difference between the oscillator and the transmitter frequency. A local oscillator that can be tuned by varying the applied voltage is most desirable.
The exiting frequency is either higher or lower than the incoming frequency. An RF amplifier stage ahead of the converter stage provides enough selectivity to reduce the image-frequency response by rejecting these unwanted signals and adds to the sensitivity of the receiver.
The companies that build the Superheterodyne receivers are too many, so I shall be covering the one's that actually began making them in the early days.
General Electric Co.: In 1932 the General Electric Co. was awarded a contract by the recently established Civil Aeronautics Authority (known as the FAA today) to provide short-wave (HF in today's terminology) transmitters and receivers to the Government for air safety use in the fledgling airline industry. GE had developed a transmitter but they did not have a receiever. The Western Electric Company had a receiver, but for competitive reasons GE did not want to team with Western Electric and instead approached Millen to have National design and manufacture a suitable receiver. The result was the AGS (for Aeronautical Ground Station). This was the first high performance short-wave receiver made by National and one of the first high performance receivers commerically available. Most of the receivers were sold to the CAA through General Electric Co. A few went into the amateur market along with amateur band-spread coils.
GenRad : The company began manufacturing large amounts of portable wave meters and crystal sets for trench-warfare communications. At this time, another General Radio part played a small role in another historic radio event. Some of the first instruments shipped for use in the war were a number of precision air capacitors, or "condensers." The capacitor was used in an Army laboratory to tune the first super-heterodyne receiver. Today, the same super-heterodyne circuit is used in virtually every television, radar, and communication receiver worldwide.
HammarLund : The Hammarlund Manufacturing Company, founded by Oscar Hammarlund in New York City, New York, USA in 1910, initially designed and produced short wave radio equipment. Hammarlund Mfg. Co., Inc. entered into the shortwave receiver market with the introduction of the "Comet Pro", the first commercial short wave superheterodyne receiver. Within five years, thousands of these receivers were in use at commercial radiotelegraph and radiotelephone stations, aboard ships and at broadcasting stations as well as by amateur radio operators the world over. Professional listening post installations made great use of the Comet Pro, and it was used also on many major exploration expeditions
FM Receivers in Mobile Phones
There is a strong belief among many in the radio industry that FM radio receivers should be incorporated into virtually all mobile devices, including mobile phones. Such a move helps to perpetuate the ubiquitous nature of radio and to provide a communication lifeline during times of crisis or natural disaster. Some may wonder why FM radio receivers are necessary when many mobile devices already have access to radio through internet connections. When radio is needed most it's least likely to be available through an internet connection on a mobile device and only available when a mobile device has an FM receiver built-in.
Radio's Importance in Times of Crisis
In January 2009, parts of the Midwestern United States were struck by a voracious winter storm. Combinations of snow and ice virtually paralyzed many areas. Owensboro, Kentucky was one area struck exceptionally hard and declared a federal disaster area. Residents were without power, land line communication, mobile phone communication and cable television. The only functioning source of information was "over the air" broadcasting. A nearby radio station run by the Cromwell Group was broadcasting. However, residents could only tap into the radio station with a radio receiving device that did not require an external power source (such as a battery-operated or crank radio, or a mobile phone with a built-in FM receiver).
Mobile phones were incapacitated because the mobile phone infrastructure was not working. That means internet access over the mobile phone network was also incapacitated. Access to information using a mobile phone was only possible if the mobile phone contained an FM receiver.
Capacity and Bandwidth: Over the Air Radio Versus Internet-Based Radio
What about cases in which the mobile networks are still functioning? Mobile networks are built assuming that only a percentage of users will use the network at the same time. On occasions in which usage begins to exceed capacity, the networks begin to exhibit stress (we've all experienced the "all circuits are busy" message from time to time). In times of crisis when all other means of communication have been disabled, usage of the network to talk and to access information using a mobile internet connection has been shown to skyrocket. Will networks be able to handle the burden and still be able to support access to critical information from radio broadcasts over mobile internet connections? With FM receivers in mobile devices one would not need to worry about this issue. Essential information would be available from nearby radio stations via "over the air" signals that are unaffected by network burden.
Bud Walters, owner of Cromwell Group, summed it up succinctly after January's Midwestern storm by saying, "If there ever was a case for FM radio receivers in cell phones, this is it. Everyone has a cell phone, now useless. The cell phone would not be useless if it had an FM radio in it."
The Current State of FM Radio Receivers in Mobile Devices
Why not add an inexpensive analog FM radio receiver into all mobile devices? It provides essential access to critical information over the air during times of crisis using a device that consumers will already be carrying.
Broadcom recently announced an integrated circuit device that combines WiFi, Bluetooth and FM on a single "chip," making it easier for manufacturers to integrate essential functionality in one chip.
Verizon Wireless, AT&T and T-Mobile are including FM radio-capable handsets in their offering and the radio industry is working on getting Apple on board as well. In fact, the Apple iPhone 3GS includes the Broadcom chip described above which has FM receiver capability. It is not a current function of the 3GS but can be easily included in a future upgrade since the FM-capable device is already present in the current design.
Nokia has sold more than 700 million devices with built-in FM radio receivers worldwide, demonstrating consumer recognition of the value.
The different FM receivers available in the market along with their features and applications are discussed below.:
Si4702/03
The Si4702/03 extends Silicon Laboratories Si4700/01 FM tuner family and further increases the ease and attractiveness of adding FM radio reception to mobile devices through small size and board area, minimum component count, flexible programmability and superior, proven performance.
Features
Worldwide FM band support (76-108 MHz
Seek tuning
Automatic frequency control (AFC) and automatic gain control (AGC)
Excellent overload immunity
Programmable de-emphasis (50/75 μs)
Adaptive noise suppression
Applications
Cellular handsets
MP3 players
PDAs, notebook PCs
Portable radios
Portable navigation
Automobile applications
Consumer electronics
USB FM radios
Si4704/05
The Si4704/05 enhanced FM receiver is the most advanced portable solution available today offering embedded antenna support, digital audio out, worldwide FM band support and highly flexible, mature and proven FM functionality in a simple API.
Block Diagram
Features
Worldwide FM band support (64~108 MHz)
Supports integrated antenna
Seek tuning
Automatic frequency control (AFC) and automatic gain control (AGC)
Adjustable seek parameters
Adjustable mono/stereo blend
Applications
Cellular handsets
MP3 players
PDAs, notebook PCs
Portable radios
Portable navigation
Automobile applications
Consumer electronics
USB FM radios
Si4708/09
As the world's smallest FM receiver, the Si4708/09 extends Silicon Laboratories' Si4700 FM tuner family and further increases the ease and attractiveness of adding FM radio reception to mobile devices.
Block Diagram
Features
Worldwide FM band support (76-108 MHz)
Automatic frequency control (AFC) and automatic gain control (AGC)
Excellent overload immunity
Signal strength measurement
Digital low-IF receiver
Applications
Cellular handsets
MP3 players
PDAs, notebook PCs
Portable radios
Portable navigation
Automobile applications
Consumer electronics
USB FM radios
The various FM/AM receivers available through the well known American company DENON are:
DRA-697CIHD
Premier AM/FM/FM Stereo Multi-Source/Multi-Zone Stereo Receiver with HD Radio
MSRP $899.00
DRA-697CI
Premier AM/FM/FM Stereo Multi-Source/Multi-Zone Stereo Receiver
MSRP $600.00
DRA-397
AM/FM/FM Stereo Multi-Source/Multi-Zone Stereo Receiver
MSRP $399.00
DRA-297
AM/FM/FM Stereo Receiver
MSRP $299.00
DRA-37
AM/FM/FM Stereo Receiver
MSRP $299.00
Some other FM receievers offered by the Swiss company PHONAK are:
MLxi
A universal Dynamic FM receiver, compatible with virtually all manufacturers behind the ear hearing instruments and cochlear implants.
Features
State-of-the art Dynamic FM receiver
Compatible with all BTEs and cochlear implants
Compatible with all Phonak transmitters
Automatic or Direct Frequency Synchronization
Save to and read information from receiver
Revolutionary antenna design for optimal reception from all angles
No pin orientation required
Sleep mode saves hearing instrument batteries
ML13i
A miniature, design-integrated Dynamic FM receiver for Phonak Ambra microP and SP hearing instruments.
Features
State-of-the-art Dynamic FM receiver
Compatible with Phonak Ambra BTE hearing instruments which use a 13 battery
Automatic Frequency Synchronization (AFS) with
WallPilot
Direct Frequency Synchronization (DFS) with inspiro
or any other Phonak FM transmitter
Intelligent stand-by mode saves power when the transmitter is switched off
Fully programmable with FM SuccessWare 4.5 or later
ML12i
A miniature, design-integrated Dynamic FM receiver for Phonak BTE hearing instruments that use a 13 battery, such as NIOS micro.
Features
State-of-the art Dynamic FM receive
Compatible with all Phonak micro BTEs that use a 13 battery
Compatible with all Phonak FM transmitters
Highly durable
Direct Frequency Synchronization (DFS) with the inspiro or any other Phonak FM transmitter
Intelligent stand-by mode (saves power when the transmitteris switched off)
Fully programmable with FM SuccessWare
ML11i
A miniature, design-integrated Dynamic FM receiver for Naída SuperPower and Milo SuperPower hearing instruments.
Features
State-of-the art dynamic FM receiver
Compatible with all Phonak FM transmitters
Automatic or Direct Frequency Synchronization
Save to and read information from receiver
Revolutionary antenna design for optimal reception from all angles
Sleep mode to save hearing instrument batteries
ML10i
A miniature, design-integrated Dynamic FM receiver for Naída UltraPower and Milo SuperPower hearing instruments.
Features
State-of-the art Dynamic FM receiver
Compatible with all Phonak transmitters
Automatic or Direct Frequency Synchronization
Save to and read information from receiver
Revolutionary antenna design for optimal reception from all angles
Sleep mode saves hearing instrument batteries
ML9i
A design-integrated Dynamic FM receiver, compatible with Phonak's Exelia Art, Exelia, Versáta and Certéna BTE hearing instruments.
Features
State-of-the art Dynamic FM receiver
Compatible with all Phonak transmitters
Automatic or Direct Frequency Synchronization
Save to and read information from receiver
Revolutionary antenna design for optimal reception from all angles
Sleep mode saves hearing instrument batteries
MyLink+
An entry-level Dynamic FM receiver with neck-loop, compatible with all T-coil hearing instruments.
Features
State-of-the art, digital synthesizer, multi-frequency Dynamic FM receiver
Compatible with all hearing instruments with a T-coil
Compatible with all Phonak transmitters
Automatic or Direct Frequency Synchronization
Save to, and read information from, the receiver
Headphone output
iSense Micro
A trendy, Bluetooth-style Dynamic FM receiver for users with normal or near-to-normal hearing.
iSense Classic
An MP3 player-style Dynamic FM receiver for users with normal or near-to-normal hearing.
MLxi Baha
Offers MLxi functionality with an additional connector for Cochlear's Intenso, Divino and Compact Baha instruments.
Features
State-of-the art Dynamic FM receiver
Compatible with all Phonak transmitters
Automatic or Direct Frequency Synchronization
Save to and read information from receiver
Revolutionary antenna design for optimal reception from all angles
Sleep mode saves hearing instrument batteries
MicroLink Freedom
The world's first multifrequency FM receiver, compatible with Cochlear's Nucleus Freedom and all Phonak transmitters.
features
State-of-the art, digital synthesizer, multi-frequency FM receiver
Compatible with all Phonak FM transmitters
Automatic or Direct Frequency Synchronization
Save to and read information from receiver
