GB2266028A

GB2266028A - Active two-way radio repeater

Info

Publication number: GB2266028A
Application number: GB9206994A
Authority: GB
Inventors: Brian Alfred Bidwell
Original assignee: USW PCN Inc
Current assignee: USW PCN Inc
Priority date: 1992-03-31
Filing date: 1992-03-31
Publication date: 1993-10-13
Anticipated expiration: 2012-03-31
Also published as: GB2266028B; GB9206994D0

Abstract

The repeater has a port for connection to a system antenna, a port for connection to one or more local antennas and means (4, 5, 9, 10) for amplifying the radio signal in the repeater. Prior to and subsequent to amplification the radio signal passes through a frequency changer (2, 3, 7, 8) so that the signal is amplified at a different frequency to that of the received signal. The repeater comprises separate sections (A, B), each provided with the frequency changing means and the amplification means, the repeater sections being adapted for electrical connection and physical separation. Preferably the sections are constructed as discrete units each in its own housing, for instance with one section adjacent to the local antenna and another section adjacent to the system antenna. The oscillator signals supplied to the mixers in each frequency changer are preferably derived from the same oscillator. There may be one system antenna and two or more local antennas. <IMAGE>

Description

ACTIVE TWO-WAY REPEATER This invention relates to an active repeater for a radio communications system.

Any radio communication system will have problem areas where, for any one of a number of reasons coverage is inadequate. For example, in a cellular radio system, there are often areas of poor coverage in city centres with numerous high rise buildings. Hill and mountain ranges can also cause problems. In these circumstances, it is usual for the master antenna for a particular problem area, to be boosted by one or more system antennae in radio communication with the master antenna and electrically connected to one or more local antennae. The connection to the local antennae may either be passive, ie simply receive and pass the signal from the system antenna or active, ie receive, amplify and broadcast the signal from the main antenna.

If amplification is required, it is usual to include in the connection between the system and local antennae an active on-frequency repeater. For cellular radio systems, typically the gain required for the repeater is in the range 50-90 dB. It has proved difficult to design a repeater capable of producing such a high gain, but active on-frequency repeaters are commercially available for various systems including 900 MHz cellular radio. Although the repeater itself can be made stable, it is difficult to eradicate signal leakage between the input and output ports and such leakage may cause the installation as a whole to become unstable with serious consequences for the system.

The simplest active on-frequency repeater is shown schematically in Figure 1 of the drawings. The signal is received from and transmitted to a suitably placed system antenna, fed via co-axial cable to the repeater and thence by co-axial cable to the local antenna. Stability in the system relies on the path loss between the antennae being substantially greater than the gain of the repeater but is at risk from coupling between the co-axial cables.

A known improvement of this basic design is to include in the repeater and oscillator controlling mixers for incoming and outgoing signals so that the amplification can be achieved with the signal at a lower frequency. This design, which is shown schematically in Figure 2, substantially reduces the risk of signal interference at the amplification stage but does not eliminate the possibility of interference between the high frequency areas of the repeater and in particular between the input and output ports.

Moreover, an increase in the operating frequency of the cellular radio system, eg from 900 MHz to 1800 MHz for example, greatly exacerbates the problem referred to above of designing a stable repeater capable of producing the required gain.

According to the present invention, there is provided an active two-way repeater for a radio communications system including a port for connection to a system antenna, a port for connection to a local antenna, means for changing the frequency of the radio signal entering the repeater prior to amplification thereof, means for changing the frequency of the radio signal leaving the repeater after amplification thereof and means for amplifying the radio signal in the repeater characterized in that the repeater comprises two sections each provided with the frequency changing means and the amplification means, the two repeater sections being adapted for electrical connection and physical separation.

In a repeater according to this invention, the two sections may be constructed as discrete units each in its own housing and located wherever convenient, for example with one section adjacent to each antenna, stability of the system then relies on the separation of the antennas only.

This means for changing the frequency of the radio signal may comprise any suitable arrangement, for example mixers in each section for the incoming and outgoing signals acting under the control of an oscillator. In order to maintain the system frequency accurately for local coverage, it is generally desirable to use the same oscillator for both the up and down mixing. However, it is possible that for certain applications it might be desirable for the operating frequency of the local antenna to differ from that of the system antenna in which case two oscillators would be required. The location of the oscillator(s) as between the two sections of the repeater is not of importance.

It will be understood that there are circumstances in which it would be desirable for a given system antenna to relay signals to more than one local antenna. In this situation a repeater according to the present invention could comprise a correspondingly greater number of sections, ie.

a first section for connection to the system antenna. In this situation, a repeater according to the present invention could comprise a correspondingly greater number of sections, ie., a first section for connection to the system antenna and a second section for connection to each local antenna.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made to Figure 3 of the accompanying drawings which shows schematically, an active repeater according to the present invention.

The repeater includes a first section A for connection by cable C to system antenna 1 and comprising filters 15, 16, mixers 2, 3 and amplifiers 4, 5 for the incoming and outgoing signals and a second section B for connection to local antenna 6, also comprising filters 17, 18, mixers 7, and amplifiers 9, 10 for the incoming and outgoing signals.

In addition, the second section contains an oscillator 11 controlling all four mixers, 2, 3, 7 and 8, so that the accuracy of the system frequency is preserved. The output of amplifier 4 in the first sectionis connection by co-axial cable 12 to the input of amplifier 9 in the second section, as is the output of amplifier 10 in the second section to the input of amplifier 5 in the first section (co-axial able 13). There is an additional connection by co-axial cable 14, between oscillator 11 in the second section and mixers 2 and 3 in theXfirst section.

A signal from system antenna 1 enters the first section of the repeater at the system frequency. It then passes through bandpass filter 15 to mixer 2 under the control of oscillator 11 and emerges at a lower frequency. It is then amplified by amplifier 4, passed down cable 12 to amplifier 9 in the second section, then to mixer 7 where it is transformed back to the system frequency, passed through bandpass filter 17 and passed by cable D to the local antenna 6.

Likewise, radio signals picked up by antenna 6 enter the second section of the repeater, pass through bandpass filter 18 to mixer 8, are converted there to a lower frequency, passed to amplifier 10: and then by cable 13 to amplifier 5 and mixer 3, passed through bandpass filter 16 in the first section and then by cable C to the system antenna.

It will be appreciated that this embodiment includes three co-axial cables connecting the repeater sections. However, since it is possible adequately to separate the three signals by the addition of suitable filtering, it would also be possible to combine the signals on a single coaxial cable and thus simplify installation.

Claims

1. An active two-way repeater for a radio communications system including a port for connection to a system antenna, a port for connection to a local antenna, means for changing the frequency of the radio signal entering the repeater prior to amplification thereof, means for changing the frequency of the radio signal leaving the repeater after amplification thereof and means for amplifying the radio signal in the repeater, characterized in that the repeater comprises separate sections, each provided with the frequency changing means and the amplification means, the repeater sections being adapted for electrical connection and physical separation.

2. An active two-way repeater as claimed in claim 1, characterized in that the sections are constructed as discrete units each in its own housing.

3. An active two-way repeater as claimed in claim 2, characterized in that one section is adjacent to a local antenna and another section is adjacent to the system antenna

4. An active two-way repeater as claimed in claim 1, characterized in that the oscillator signals supplied to the mixers in each frequency changer are derived from the same oscillator.

5. Active two-way repeaters as claimed in any of the preceding claims, characterized in that the repeater is connected to a system antenna and two or more local antennas.

6. Active two-way repeaters as claimed in claim 1 and as herein described.

7. Active two-way repeaters as herein described with reference to, and as shown in, the accompanying drawings.