>>Message imported from previous forum - Category:Trio Data Radios<<
User: joelw, originally posted: 2018-10-17 22:55:36 Id:124
This is a re-posting from the obsoleted (October 2018) "Schneider Electric Telemetry & SCADA" forum.
The text below was written by Matthew Del Vecchio of Schneider Electric in response to a customer. Matt is a Trio radio systems expert._**
My understanding of your problem is that you want to co-locate (i.e. on the same physical site) multiple QH radios [also applies to QB's] and share a common Tx and Rx antenna between them. This can be achieved with RF multi-coupling, but generally requires specialist RF knowledge to design the multi-coupler. The design will depend on the exact frequencies used by each QH.
To help answer some of your questions, I have created a simplified diagram to show how multi-couplers are generally used with our full-duplex radios. [Attached as "Multicoupling Example.jpg"]
Tx = Transmitter
Rx = Receiver
- Each of the radio's transmitters are interconnected into a Tx Multi-coupler which is constructed from mechanical RF filters & specific lengths of coaxial cable. I have attached a datasheet as an example.
- Each of the radio's receivers are interconnected into an Rx Multi-coupler which is normally a multi-port splitting low noise RF amplifier. I have attached a datasheet as an example.
To prevent the transmitters from desensitizing the receivers, isolation (filtering) between the transmitter and receiver must be designed into the multi-coupling. This can be achieved by using:
- A bandpass filter between the receive antenna and the input to the Rx multi-coupler.
- Physical separation of the Tx and Rx antennas on the tower.
To prevent the transmitters from generating RF noise on the receive frequencies, the transmit multi-couplers need to be implemented with bandpass filters.
The required level of Rx/Tx isolation (for broadband noise/desensitization) for radio products can differ, however, the specification for the Trio Q can be found within the QB/QH Data sheet (UHF = 70dB isolation).
Another important aspect when co-locating radios is to have all transmit frequencies and all receive frequencies selected to provide the same site sense. "Same site sense" means that all transmit frequencies for all co-located radios are at one end of the band. Separation between the Tx and Rx frequency groups of approximately 10 MHz is recommended, though can be made to work with approximately 5 MHz.
!((see attachments below) 1i/ynqwil6i3hh1.png "")
By ensuring all radios have the same site sense, the filtering (for broadband noise/desensitization) will work for all radios, regardless of who is transmitting or receiving.
To answer your specific questions:
- **If we use such a combiner, can we use a collinear antenna?**
Multi-coupled systems can use any types of antenna, the required type of antenna depends on the coverage requirements.
Yagi antennas have a very narrow pattern, and are generally only used in point to point links or, remote sites pointing back to a master in a point to multi point system.
Coaxial Collinear is often used on master stations when 360 degree coverage is required. Other Omni-directional antennas like phased dipoles are preferred when the majority of coverage is biased in one direction.
- **Do you usually install with Combiners and duplexers?**
Multi-coupled systems are designed using bandpass filters, the same sort of filter found in a duplexer. If two antennas can be provided, transmit will go to one and receive to the other. However, if all of the Tx frequencies are sufficiently closely grouped, and all the Rx frequencies likewise closely grouped, the two can be connected to a single antenna with a duplexer.
Note that radios connected to multi-coupling systems must have separate Tx and Rx ports. (i.e. you cannot use a QR450 with a single antenna port in a multi-coupling system).
- **What supplier do you use to buy?**
We have a supplier in Australia, however, these multi-couplers must be tuned to specific frequencies, and installed by professionals. Normal practice is to use a local company to determine the filters/multi-couplers/antennas required along with a professional installation. We can recommend a hardware manufacturer, and in-country Schneider staff may be able to assist with selecting an installation company.
!((see attachments below) bh/wxxv2h657x8x.jpg "")
Attached file: (editor/1i/ynqwil6i3hh1.png), Multicoupling Table.png File size: 8933
Attached file: (editor/bh/wxxv2h657x8x.jpg), Multicoupling Example.jpg File size: 69053
Attached file: (editor/uu/8bdwof2pscnq.pdf), Tx Multi-coupler.pdf File size: 1206685
Attached file: (editor/0p/8lefjqxil6l3.pdf), Rx Multi-coupler.pdf File size: 286928