Learn how to design a 33 TV CATV RF over fiber system using a 1310 nm transmitter, PLC splitters, and mini optical receivers.
When designing a CATV RF over fiber system, the first product a customer asks about is not always the best final solution. In this real-world application example, the customer originally asked for a complete end-to-end CATV distribution architecture using a multi-output EDFA optical amplifier. After reviewing the actual system requirements, Thor Broadcast determined that a simpler 1310 nm RF over fiber system was a better fit.
This article explains the full process: what the customer requested first, what questions needed to be answered, why the original EDFA approach was not necessary, and how the final 33 TV CATV RF over fiber solution was designed.
Table of Contents
The customer initially asked for a complete end-to-end system architecture or schematic for a CATV distribution network using Thor Broadcast products. The specific product they referenced was:
F-EDFA-33-1X16 - Multi-Output EDFA Optical Amplifier
https://thorbroadcast.com/product/edfa-with-2-to-64-multi-output-optical-amplifier.html
The customer wanted to understand the complete layout and how all components would connect together. They also noted that this was for a federal project and requested formal confirmation for compliance requirements such as TAA and BABA.
The first important point was to explain that the EDFA is not the complete CATV distribution system by itself. The EDFA is an optical amplifier. It does not take RF coax directly. It requires an optical CATV signal from a 1550 nm CATV optical transmitter.
A typical 1550 nm EDFA CATV system works like this:
CATV RF coax input - 1550 nm CATV RF optical transmitter - EDFA optical amplifier - Passive optical splitters - CATV optical receivers - RF coax output to TVs or local coax distribution
For large systems, this can be an excellent architecture. A 1550 nm transmitter with EDFA amplification is normally used for large optical CATV networks feeding many receivers, long fiber distances, or deep passive splitter networks.
Before choosing the final equipment, the following system design questions were asked:
The customer replied with the following important details:
At this point, the application became much clearer. This was not a large 512-point CATV optical distribution system. It was a much smaller 33 end-point system with very short fiber distance.
At first, an EDFA-based system was considered. This would have used:
A typical transmitter for that kind of system would be:
1550 nm Externally Modulated CATV RF Transmitter
https://thorbroadcast.com/product/1550nm-externaly-modulated-catv-rf-transmitter-analog-or-qam-8230.html
This type of system is more appropriate when the network needs higher optical power, larger split ratios, or many more receiver locations. For example, a 16-output EDFA feeding multiple 1x32 splitters could support up to 512 optical receiver locations, assuming the optical budget is correct.
After reviewing the real requirement, Thor determined that a 1550 nm transmitter with EDFA was not required. The customer only needed 33 TV locations, and the maximum fiber distance was only around 200 ft. For this type of system, a high-power 1310 nm RF optical transmitter with passive optical splitters is simpler, cleaner, and more cost-effective.
The recommended transmitter became:
F-RF-1310-TX-32mW - 32 mW CATV RF Over Fiber Transmitter, 45-870 MHz
https://thorbroadcast.com/product/32-mw-catv-rf-over-fiber-tx-45-870-mhz.html
During the design review, one important detail was corrected. The F-RF-1310-TX-32mW has one optical output. If only a 1x32 splitter is used, the system can feed only 32 receivers, but the customer needs 33 end points.
To solve this, the optical output from the transmitter should first feed a 1x2 passive optical splitter.
One output from the 1x2 splitter feeds one receiver directly for receiver location #33. The second output from the 1x2 splitter feeds a 1x32 splitter, which then feeds the other 32 receiver locations.
Analog CATV RF coax input - F-RF-1310-TX-32mW 1310 nm optical transmitter - F-PLC-1x2 passive optical splitter Branch 1: - Direct fiber to 1 x F-RF-RX-MN receiver - RF coax output to TV / RF drop #33 Branch 2: - F-PLC-1x32 passive optical splitter - Fiber to 32 x F-RF-RX-MN receivers - RF coax output to 32 TVs / RF drops
| Qty | Part Number | Description | Product Link |
|---|---|---|---|
| 1 | F-RF-1310-TX-32mW | 1310 nm 32 mW CATV RF optical transmitter, 45-870 MHz. Converts RF coax to optical fiber. | View Product |
| 1 | F-PLC-1x2 | Passive 1x2 optical splitter. Used first because the transmitter has only one optical output. | View Product |
| 1 | F-PLC-1x32 | Passive 1x32 optical splitter. Feeds 32 receiver locations. | View Product |
| 33 | F-RF-RX-MN | Mini CATV RF optical receiver. Converts optical fiber back to RF coax output. | View Product |
| As needed | F-ATT Series | Inline optical attenuators for balancing optical power, especially on the direct receiver branch. | View RF Over Fiber Products |
The 1x2 splitter is necessary because the transmitter has only one optical output, but the system needs 33 receiver locations. A 1x32 splitter alone would only provide 32 outputs.
By adding the 1x2 splitter first, the system creates two branches:
This creates a total of 33 receiver locations.
The receiver connected directly from the 1x2 splitter may receive more optical power than the 32 receivers connected after the 1x32 splitter. This is because the 1x32 splitter adds significantly more optical loss than the direct branch.
For that reason, the direct branch may require an inline optical attenuator. The attenuator reduces the optical power to a safe and balanced level for the F-RF-RX-MN receiver.
The correct attenuator value should be selected after measuring the optical power at the receiver input.
For this type of CATV RF over fiber installation, two test tools are recommended:
An optical power meter is used to measure optical level at the transmitter output, after the 1x2 splitter, after the 1x32 splitter, and at each receiver location.
A CATV RF signal level meter is used to measure the RF coax output after each optical receiver. This confirms that each TV or local coax drop receives the correct RF level.
The original F-EDFA-33-1X16 approach still makes sense for larger CATV optical networks. It is usually used when the system requires:
For example, a 1550 nm transmitter feeding a multi-output EDFA can be designed to feed hundreds of optical receivers when properly engineered.
This project started as a request for a multi-output EDFA CATV fiber distribution system. After asking the right questions, the requirement was clarified: 33 TVs, approximately 200 ft maximum fiber distance, and analog CATV RF.
Because the system was relatively small and the fiber distance was short, Thor Broadcast determined that a 1550 nm transmitter with EDFA was not necessary. The better solution is a high-power 1310 nm transmitter with passive optical splitters and 33 mini CATV optical receivers.
The final recommended design is:
1 x F-RF-1310-TX-32mW 1 x F-PLC-1x2 1 x F-PLC-1x32 33 x F-RF-RX-MN Optional optical attenuator for receiver #33
This is a practical example of why CATV RF over fiber systems should always be designed around the real number of end points, fiber distance, RF level requirement, and final coax distribution. The most expensive or largest optical amplifier is not always the correct solution. The correct solution is the one that fits the actual application.
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