The concept of a broadcast range
Rare people think, hearing the announcement about the FM radio, which means that phrase. According to the FM, the term by convention means broadcasting on a carrier frequency, fit into the interval from 87.5 to 108 MHz with FM modulation. But this does not exhaust the variety of entertainment programs transfer methods. Digital radio with extended range are designed to fill the gap.
The most common things we are talking about increasing the boundaries of VHF. Most products are receiving at frequencies from 64 to 108 MHz, favorite pattern, for example, Mason R411, stretch out to the hand of the mark 233 MHz. Such a broad scope covering entertainment broadcasting stations, completely cover the standard values adopted for aviation negotiations.
We mention that, within the countries of the Commonwealth of the described hardware capabilities hardly useful - the transmission is not carried out above 137 MHz - but in the territory of the other state option will be very useful.
The origin of FM and AM terms
Every country has its own broadcast standards. FM is considered accepted in Western countries called VHF-2 and FM-3. AM understood under long wave (LW), all short-wave (HF) occur in SW1-SW11 share.
FM term derived from the English notation modulation type, referred to as frequency. Information is put in deviation - the frequency deviation of the value carrier. In contrast, the AM involves changing another parameter of an electromagnetic wave - amplitude.
Summarizing, we say that in the upper region of the VHF band used FM modulation (FM), and HF, MW and LW - AM. This is the origin of their English names. To distinguish the MW and LW from HF, the latter referred to as SW.
It remains to add that the SW 11 is divided into subbands below FM region is denoted OIRT (VHF and UHF-1), named after the modulation method - polar.
The main principles of expanding the range of the received
All-wave digital radio works with most broadcasting stations. Said quality is ensured by a number of special measures.
By what has been said to add that the frequency of the received wave depends on antenna design. For HF (3-30 MHz) are optimally suited to use ferrite core varieties for VHF appropriately telescopic structure.
receiver preselector configured to change capacitance values of the carrier, at least the inductance of the input filter. Of course, cover the entire range of single resonant circuit is not under force to resolve difficulties in handy range shifter. It throws antenna input signal between circuits with different scopes.
To better understand the described, we form an idea of the bandpass filter. It noted two main characteristics:
- The resonant frequency.
the filter acts like a gate, through which can pass only the desired part of the signal, and the gate can move in different directions, flowing to the output of the queue station. Handle continuously adjustable and regulated movement.
For a long time there is a struggle for the reduction in the size and cost of the equipment, but how to extend the range of the radio without casualties - it is not clear to this day. Swapping the conventional technology is considered received signal between filters.
The width of the filter passband equals the width of the spectrum of the useful signal emitted by the radio station, and the resonance frequency - the center of the target - is configured on a carrier. With strict observance of these conditions the best reception quality.
Continuing the analogy, let's say that AM and FM stations are too "far" from each other, so the device adjusts the position of the gate, there "does not reach." Circuitry resonant circuits operate in a similar manner. Range switching allows another circuit "reach" to the station, which is currently lacking.
At the same time there is a change of type of the receiving antenna. Similarly, the advanced functionality is achieved.
Combined antennas and refinement of the input filter is not limited to - each band uses its own type of signal modulation. Schematic diagram distinguishes the sound of waves oscillations for different case.
It called modulation parameter change carrier according to the law, describing the transmitted message. On the receiving side, there is the opposite effect - the detection. Advantageously, modulation types used at broadcasting:
In the first case the amplitude of the carrier undergoes a change, in the second - the frequency. Features of wave propagation in air and operation of the electronic components of the performance considerations make use known types of modulation.
Described embodiments the diversity of technical solutions is not limited to, share the terms SSB and polar modulation. The need for methods of complexity; appears as necessary to convey a conventional stereo channel width to conserve transmitter power, reducing harmful to human health factors.
Digital radio is a VHF band to work with KV is required to provide the type of detector switches from the frequency (FM) to the amplitude (AM).
Technically, there is no difficulty. To take all radio stations should be:
- Have a number of antennas and input filters for different frequencies.
- Include detector circuit for different modulation types.
- Perform switching between said elements appropriately.
Radio receiving equipment Gryundik
The use of multiple antennas and completion of e-filling described above make it possible to take an extended wavelength range. Here's how to implement the principle of digital radios Grundig (Satellit 750) for professional use:
- digital tuner covers all possible ranges and broadcast talks permitted frequencies;
- 100 preconfigured channels provide instant selection of a desired station;
- shock-resistant housing, borrowed from the measuring devices with protective handles reliably protects the device against damage;
- possibility of working with the pilot signal and the single sideband modulation is implemented for professional use;
- digital signal processors provide maximum sensitivity at a minimum level of distortion;
- remote antenna with the possibility of turning 360 degrees is set in place the best reception;
- further increase in sensitivity achieved by reducing resistance to the external antenna connector gilded.
A more modest pocket radio digital G6 Aviator differs from the model described small size, lack of impact resistant shell and a remote antenna less sensitive. However, the device is located in the upper segment of compact household products. So as not to accidentally press the extra button is present the lock button HOLD.
Grundig digital radios are equipped with numeric keys for the frequency set with the keyboard, line outputs for speakers and headphones, as well as multiple antennas for reliable reception in all bands. All products are targeted at high-quality radio reception is not entertainment equipment.
Applicability of devices with extended range
From the foregoing, it is clear that digital radio receivers with extended range is of limited use. The explanation is simple: most popular stations located in the FM band.
However, the long waves at large distances are caught better, especially in bad weather, there is a demand for digital-wave radios. Tourists, residents of remote villages, working construction sites - these people are interested in the work stations of HF and lower frequency range.