Question 1

I have a similar question to one already on your website. I changed the question to fit our application. Here it is: We are having our cable provider quote our cable channels to be in the clear. Our provider is Charter, and I believe they said they would be converted to ClearQam. This service will be provided by them to one building, and we need to send the Clear QAM signal over our fiber to another location and then reconvert the Clear QAM from fiber to the RF distribution block. We will be doing the same for 3 other locations, all on the same fiber network. Each location has a low TV count: 10 TVs, 7 TVs, 10 TVs, 12 TVs, 17 TVs. What equipment would I need at each location to provide up to 120 channels provided by our cable provider in the clear? 1) They would all be point to point, but not all locations have single-mode. I can dedicate separate fibers just for video and have a separate network with bandwidth control. 2 locations have multimode; the rest are single-mode. Luckily, our runs are rather short. I think the longest distance is 1300 ft. We can replace the multimode fiber with single-mode for the two other properties, or have our cable provider run their fiber to those two locations separately. 2) Can one mini receiver per location split to all the TVs at that location and provide up to 120 channels?

Accepted Answer

1) Are these all point to point with single-mode fiber in place? https://thorbroadcast.com/products/cable-tv-catv-rf-45-900mhz This is our page of dedicated CATV frequency band transmitters and receivers. The rackmount OTx and Mini or Rackmount Receiver sets are the most popular because of their longstanding history of durability. 2 points I need to make off the bat: RF can only be put on single-mode fiber. Putting it on multimode is impossible; the signal deteriorates at a massive level because of the wide core creating reflections. No one in the world makes gear like that because, theoretically, it is impossible. Second, we can use distance to make approximate guesses at what power optical OTx you'll need. If they're short, with minimal patch panels, we can guess. If they are longer runs, I would hope you can get an OTDR reading of the optical loss in the fiber. RF on fiber needs to be dedicated, and optical budget is what we work around to decide what power laser you need. 2) So at this juncture, because of your short runs, I would go with a single high-power OTx; use an optical coupler and mini receivers. This basic diagram shows you a simple layout: single transmitter; optical coupler, which eats a lot of power; and you can run your CATV Clear QAM into the transmitter and get cable everywhere else. Yes, this equipment carries the entire echelon of CATV DVB-C RF modulation; meaning it carries 45-870Mhz or approximately channels 2-135. https://thorbroadcast.com/product/1-x-2-to-1-x-128-fiber-optic-couplers.html/224 This page shows you how optical couplers eat power. The chart at the bottom is what we use with our units; other companies might vary. The coupler essentially dictates how powerful an OTx you need. What I suggest you do is make sure of exactly how many end locations you have; then we work backward. Couplers come in 1x2, 1x4, 1x8, etc., so if you have 4 runs and then need to add a 5th, it really isn't simple. So planning ahead is crucial if you want to future-proof and not need to replace the coupler and OTx.

Question 2

We've got a Dish Smartbox that we distribute mostly over coax (QAM16) throughout our hospital. We've started to extend this to other remote buildings on the same campus, and our current system is very limited. I think what I need is these three items, but I'd love to know if I'm off in left field a bit. At the moment, I only need to get this into two buildings, but we're building more down the road, so I figured the 16x splitter made the most sense. I'm pretty sure I've got the right receiver, but I wasn't sure about the 1310 vs 1550 transmitter, as well as the transmit power...some of the SMF runs are as short as 1200ft, but others could be up to 2 miles. Any input is appreciated. F-RF-1550-TX-16mW transmitter F-RF-RX-RM receiver F-PLC-1x16-LC/APC or SC/APC optical splitter

Accepted Answer

So you're on the right track. Right now, you're only required to send the signal to two buildings, but you will need to expand to 16 buildings? If you think the run might be about 2 miles at most, then hopefully the fiber installed has very mild loss. You should be fine with a 1310nm 32mW OTx. 1550nm is only recommended with the use of an EDFA that is used to distribute the signal to dozens of end locations. In your case, having a maximum of 16 endpoints with minimal distance is not a good reason to use 1550nm. I would suggest this as a BOM: F-RF-1310-TX-32mW transmitter F-RF-RX-RM receiver https://thorbroadcast.com/product/catv-rf-fiber-receiver-high-rf-power-rack-8230.html F-PLC-1x16-SC/APC optical splitter https://thorbroadcast.com/product/1-x-2-to-1-x-128-fiber-optic-couplers.html/227 Since the transmitters and receivers all use SC/APC, I would make sure the PLC coupler follows suit to minimize any reflections.

Question 3

What are the typical losses in the fiber? How do you calculate the optical budget when the transmitter outputs +15dBmV and the optical receiver has a 0dBmV receiver sensitivity?

Accepted Answer

There are several types of losses that can occur in fiber optic cables, including: Insertion loss: This is the loss of signal power that occurs when light is transmitted through the fiber. It is typically caused by imperfections in the fiber itself, such as bends, scratches, or impurities. Splice loss: This occurs when two fibers are joined together, typically through a splicing process. Losses can occur due to imperfections in the splicing technique, as well as the difference in the refractive index between the fibers being spliced. Connector loss: This occurs when light is transferred between two fibers through a connector. Losses can occur due to imperfections in the connector itself, such as dirt or damage. Absorption loss: This is caused by impurities in the fiber that absorb light, reducing the signal strength. The main cause of absorption loss is the absorption of water molecules in the core of the fiber. Scattering loss: This is caused by microscopic variations in the refractive index of the fiber, which cause light to scatter and be absorbed. Macrobending Loss: This is caused by the fiber being bent in a radius of curvature that is too large. This causes the light to be reflected back into the cladding and is lost. The use of passive optical splitters results in each splitter having its own insertion loss. For example, the F-FOS-1x2 1x2 splitter has a 4.5dB insertion loss These losses can be mitigated by using high-quality fiber optic cables, connectors, and splicing techniques, as well as by regularly inspecting and maintaining the fiber optic network. Insertion loss in fiber refers to the loss of signal power that occurs when light is transmitted through a fiber optic cable. In single mode fiber, insertion loss is typically measured at 1310nm and 1550nm wavelengths, which are the most commonly used wavelengths for long-distance telecommunications. The insertion loss at 1310nm is typically higher - 0.35dB/km than at 1550nm -0.25dB/km, due to the fact that the attenuation coefficient at 1310nm is smaller than at 1550nm. However, the use of 1550nm allows for a larger transmission window and can support higher bandwidths, making it more suitable for high-speed data transmission. Insertion loss can also occur at the connections and splices within a fiber optic cable. These losses are caused by imperfections in the connectors and splicing techniques, as well as by the difference in the refractive index between the fibers being spliced. To minimize these losses, high-quality connectors and splicing techniques must be used. This loss should not exceed 0.1dB per connection . Additionally, insertion loss can occur at connections and splices due to imperfections in connectors and splicing techniques. To minimize these losses, high-quality connectors and splicing techniques must be used, This loss should not exceed 0.1dB per connection -- To calculate the optical budget, you need to take into account all of the losses that occur in the fiber optic link, including attenuation, connector loss, and splice loss. The optical budget is calculated by subtracting the total losses from the transmitter output power. In this case, the transmitter outputs +15dBmV and the receiver has 0dBmV receiver sensitivity. To calculate the optical budget, you would subtract the receiver sensitivity from the transmitter output power: Optical budget = Transmitter output power - Receiver sensitivity Optical budget = +15dBmV - 0dBmV Optical budget = 15dB It's important to note that the receiver sensitivity is usually given in negative dBmV. So, in this case, the receiver sensitivity of 0dBmV is equivalent to -0dBmV. It's also important to note that the optical budget should be greater than the receiver sensitivity to ensure that there is enough power to reach the receiver and also to take into account any other losses that may occur in the link. Additionally, depending on the application, the optical budget should be designed with a margin of safety, to account for changes in the link such as temperature, aging, or unexpected loss.

Question 4

1) Have a project where the local cable company brought in coax, and we need to transition to fiber into our treatment plant. We are looking for technical advice on making sure your product is the correct solution. 2) We will need option 2. Can we buy direct from you? Do you offer a second option for multimode?

Accepted Answer

1) Okay, we certainly have the gear available that you need, but to narrow it down, I just have a couple of basic questions. What is the distance of your single-mode fiber? Do you already have SC/APC terminations on the singlemode? Do you need bidirectional, or is this application going unidirectionally? If this is unidirectional transmission (Cable TV video only) you can use those TX/RX units. 1 single-mode fiber is required. SC/APC fiber connects F-RF-TX-MN-2mW https://thorbroadcast.com/product/thor-optical-mini-catv-rf-transmitter-45-1000mhz.html F-RF-RX-MN-2 https://thorbroadcast.com/product/thor-fiber-optical-mini-ftth-rf-catv-cable-tv-receiver-8230.html If this is bidirectional (Cable TV + Internet) You can use this unit. 2 single-mode fibers are required. SC/APC fiber connects F-RFoF-TX/RX https://thorbroadcast.com/product/coax-cable-bi-directional-catv-rf-transmitter-and-receiver-over-fiber-8230.html 2) Unfortunately not, because it is impossible to put RF on multimode; no company offers such a product because it simply won't work. It's absolutely mandatory to use singlemode fiber

Question 5

Can you please explain how a CMTS system works? I'm trying to understand how it is possible to connect 500 or even 1,000 cable modems on the same network. I understand that modems receive RF, but they also transmit upstream - so how are they synchronized so they don't interfere with each other? If the return path is using standard QAM in the 5-45 MHz range, and hundreds of modems are transmitting data back, how is that data kept organized and readable? Is there some form of multiplexing or time-sharing involved? Also, since each modem has a 10/100/1000 Ethernet interface, how is that data packaged and converted into RF for upstream transmission? How does one modem's transmission avoid interfering with others?

Accepted Answer

Great question — this is the core of how DOCSIS / CMTS systems actually work, and once you see it, it all clicks. I’ll break it down step-by-step in a practical way (not textbook). ???? Big Picture You’re thinking: “If 500–1000 modems are all transmitting RF back on the same cable… why don’t they collide?” ???? Short answer: They DO NOT transmit at the same time. The CMTS acts like a traffic controller and strictly schedules who is allowed to talk and when. ???? Downstream (Easy Part) From CMTS → Modems: Continuous broadcast (like TV) Uses QAM modulation (e.g., 64-QAM / 256-QAM) All modems receive everything Each modem only reads its own data ???? This is simple — like IPTV or RF broadcast. ???? Upstream (This is the Key Part) From Modems → CMTS: ???? This is NOT continuous QAM like downstream ???? It is time-controlled burst transmission ???? Think of It Like This Imagine 1000 people sharing one microphone Instead of everyone talking at once: ???? The CMTS says: “Modem #1 → talk for 2 microseconds” “Modem #2 → now you talk” “Modem #3 → your turn next” This is called: ???? TDMA (Time Division Multiple Access) ???? How Modems Stay Synchronized This is where DOCSIS is very smart: 1. Ranging (Distance Measurement) Each modem: Measures how far it is from CMTS (signal delay) CMTS tells it: ???? “Transmit slightly earlier/later” ? So all signals arrive aligned at the CMTS 2. Power Control CMTS adjusts modem power: Far modem → transmit stronger Close modem → transmit weaker ? So all signals arrive at similar levels 3. Timing Slots The upstream channel is divided into: ???? mini time slots (microseconds) Each modem is assigned: exact time exact duration ? No overlap → no collisions ???? What Modulation is Used Upstream? Not always the same as downstream. Typical: QPSK 16-QAM 64-QAM (clean systems) ???? Lower modulation = more robust for noise ???? How 1000 Modems Share One Channel Example: Let’s say: 1 upstream channel = ~30 Mbps usable 1000 modems connected ???? Not all are transmitting at once Real behavior: Most modems are idle Only active ones get time slots Bandwidth is dynamically assigned This is called: ???? Statistical multiplexing ???? Data Flow (Ethernet → RF) Inside each modem: Step 1 – Ethernet Input User traffic enters: Netflix, browsing, etc. Step 2 – Packet Processing Modem: buffers data waits for CMTS permission Step 3 – CMTS Grants Transmission CMTS sends: ???? “You can transmit now (time slot X)” Step 4 – Burst Transmission Modem: converts data → RF burst sends during assigned time slot Step 5 – CMTS Receives & Reassembles CMTS: collects bursts from all modems reconstructs data stream ???? Why Signals Don’t Interfere Because of 3 controls: ? 1. Time separation Only one modem transmits per time slot ? 2. Power leveling All signals arrive at similar strength ? 3. Timing alignment All bursts arrive perfectly aligned ???? Important Concept ???? The upstream is NOT continuous RF ???? It is short bursts from many devices This is why your RF over fiber system works: ? It just transports RF ? It doesn’t care what’s inside ? CMTS logic still controls everything ???? Real-World Example Let’s say: 100 modems active each needs small bursts CMTS schedules: Modem A → 10 µs Modem B → 5 µs Modem C → 20 µs This happens thousands of times per second. ???? Why This Scales to 1000+ Modems Because: Users are not always transmitting Traffic is bursty CMTS dynamically allocates bandwidth ???? Simple Analogy (Best One) ???? It’s like a Wi-Fi network — but fully controlled and scheduled Instead of random collisions (Wi-Fi): ???? CMTS enforces strict order ???? Key Takeaways Upstream is time-shared, not continuous CMTS controls EVERYTHING Modems never “talk over each other” RF channel is shared efficiently Fiber transport doesn’t change behavior 1. System Diagram (CMTS → Fiber → Nodes → Modems → Return) Here’s a clean logical diagram of your setup:                            HEADEND                     ?????????????????                     ?     CMTS      ?                     ? (Down + Up RF)?                     ?????????????????                            ? RF (Coax)                            ?                  ????????????????????????                  ? 1310nm TX (Forward)  ?                  ????????????????????????                            ? Fiber (SM, SC/APC)                            ?                   ?????????????????????                   ? Optical Splitter  ?                   ?   (1x8 / 1x32)    ?                   ?????????????????????                       ?    ?    ?         ???????????????    ?    ???????????????                           ?                 FIELD / DOCK AREAS (xN)         ?????????????????????????????????         ?   Mini Node (Optical → RF)    ?         ?   F-MININODE-2RP-HP           ?         ?????????????????????????????????                     ? RF (Coax)                     ?           ??????????????????????????           ? Splitters / Cabling    ?           ??????????????????????????                       ?          ????????????????????????????          ?        Cable Modems      ?          ?   (Boats / Users)        ?          ???????????????????????????? ================= RETURN PATH ================= Cable Modems (Upstream RF 5–45 MHz)                     ?                     ? RF         ?????????????????????????????????         ? Mini Node (RF → Optical)      ?         ?????????????????????????????????                     ? Fiber (DEDICATED)                     ?            HEADEND RETURN RECEIVERS         ????????????????????????????????         ? 4ch Return RX (F-RF-RP4RX)   ?         ????????????????????????????????                     ? RF Combined                     ?                  ?????????                  ? CMTS  ?                  ?????????   ???? 2. What’s REALLY Happening (Over Fiber) Now let’s connect this with the DOCSIS behavior you asked about. ???? KEY IDEA ???? Your fiber system is NOT doing any routing, switching, or packet handling ???? It is ONLY doing: RF → Optical conversion Optical → RF conversion So: ? CMTS still controls everything ? Modems behave exactly the same as coax network ???? Forward Path (CMTS → Modems) Flow: CMTS generates RF channels (downstream QAM) RF goes into F-RF-1310-TX Converted to optical (1310 nm) Split (1x8 / 1x32) Sent to all nodes Each node converts back to RF RF distributed to modems ???? This is identical to coax — just longer distance ???? Return Path (THIS IS THE IMPORTANT PART) Flow: Modems transmit upstream (burst mode) RF enters mini node Mini node converts RF → optical Each node sends back on its OWN fiber Headend receivers convert optical → RF RF combined → fed into CMTS ???? WHY THIS WORKS PERFECTLY Because your system preserves: ? Timing DOCSIS timing slots stay intact ? Power levels Nodes + CMTS control levels ? Burst structure Nothing changes — still time-based bursts ???? IMPORTANT INSIGHT (This is GOLD for you) ???? The fiber system behaves like: “A very long, very clean coax cable” ???? No Collisions Still Even over fiber: Only one modem transmits per time slot CMTS schedules everything Fiber does NOT change this behavior ???? Why You NEED Separate Return Fibers This is critical: Forward: ? Can split (broadcast) Return: ? Cannot combine optically Why? Because: Upstream is burst-based RF If you combine optical signals passively → signals mix → noise So instead: ???? Each node = dedicated return fiber Then: ???? Combine in RF domain at headend (controlled) ???? Real Example (Your Harbor) Let’s say: 8 nodes 100 modems per node 800 total modems What happens: CMTS schedules all 800 modems Each modem transmits in micro time slots Signals travel: modem → node → fiber → receiver → CMTS ???? No collisions ???? No overlap ???? Fully controlled ???? Why This Is BETTER Than Coax In coax system: Signal degrades over distance Many amplifiers Return path becomes messy In your fiber system: ? No distance issue ? No RF noise buildup ? No amplifier cascade ? Much cleaner return path ???? VERY IMPORTANT (For your design thinking) The ONLY thing you must ensure: 1. Optical levels Node input ≈ 0 dBm 2. RF output from node ~45 dBmV → enough for local distribution 3. Return levels Balanced so CMTS sees ~0 dBmV ???? Simple Way to Explain to Customer You can say: “We are extending your CMTS over fiber — the system behaves exactly like coax, just without distance and noise limitations.” ???? Bonus Insight (Why This Is Perfect for You) Your application (harbor + boats): ? Fiber backbone already exists ? Coax needed at dock ? WiFi unreliable ???? This solution = BEST FIT

Question 6

Per our earlier conversation I have included an aerial view of the prison with the locations of our current amps. The location at the bottom noted by the 1 is slightly off screen but is where the mess of receivers and combiners are. We have 49 recievers plugged into 49 modulators that then run into 2 combiners then into a amplifier here in the shop. From there it runs on coax to the numbered locations 2-7 with all locations with the exception of 7 having an amplifier. Each amp takes the signal and feeds it through a splitter into 2 buildings a most buildings have 6 TVs with exception of the 5th location also powering an additional TVs. Currently the 7th location is fed by the amplifier from 6.My thoughts are this I would like to minimize the equipment in my shop and from what I could tell you have equipment that would eliminate our combiners and 49 receivers that we have stacked to provide each tv with independent control of the tv station. My thoughts were that since we already have the endpoints on analog splitters we would just need everything here at the head end to transmit over fiber down to the unit mech rooms then convert back to analog through the existing system. The recreation department also used to have a movie program that they offered movies from however the system went down long before my time and they would like to be able to play ether DVDs or streamed content on an additional channel for educational/movies that are provided for the inmates. This would have to be installed in the 2nd location with access from either my shop or from a remote location inside of the recreation department. We would like to be able to make this system accessible and manageable by recreation as this is their system and ultimately have responsibility for what is on the TVs.Please let me know if you require any further information I will have to step out to run some CAT6 but will be available throughout the day. Thank you again for all your help and I look forward to working with you and Thor Broadcasting.

Accepted Answer

The question is where would you like to put the fiber splitter.  The honest answer is you just need a 1x8 coupler: https://thorbroadcast.com/product/1-x-2-to-1-x-128-fiber-optic-couplers.html/226     At the minimum I would go with an 8mW power transmitter to go with the 1x8 splitter https://thorbroadcast.com/product/8-mw-catv-rf-over-fiber-tx-45-870-mhz.html   Then you have your choice of receivers; they're all on this page: https://thorbroadcast.com/products/cable-tv-catv-rf-45-900mhz   I would say numbers 2 & 3 are the most popular receivers for optical RF.  #9 is the rackmount option.  You don't need any return path configuration for a system like this, it will all be unidirectional, so it's fairly simple.  You just need to figure out where the splitter will go, if it's at your station and you will home run every receiver, or if you want to place the splitter near station 3 or 4, and have runs going to each end point from there.

Availability:	In stock	Condition:	new
Shipping:	starting at $0.00	Warranty:	2Yrs

Model	F-RF-1310-TX-32mW
Wavelength	1310nm
Optical Power	32mW
Frequency Range	45-1000 MHz
Supported Signals	NTSC, PAL, QAM J.83B, ATSC, ATSC 3.0, 8VSB
Laser	High-Linearity DFB

*All Specifications Subject to Change Without Notice
Input	1x Type-F connector - 75 Ohm
Optical Wavelength	1310nm
Line Width:	< 1 MHz FWHM
Extinction Ratio	>20 dB XP
Equivalent Noise Intensity	< -160 dB/Hz
Output Power	32 mW
Return Loss	>55 dB
Optical Connector	SC/APC - Angle Polished IMPORTANT NOTE* (It is very important to interface our unit with an SC/APC - Angle Polished Connector to avoid any light reflections.) If your fiber is terminated with the SC, ST, FC /PC flat connector, you need to use an optical jumper from PC type to SC/APC for proper conversion.**
RF Power Level	11-29 dBmV AGC Managed
Flatness	<+/- 0.75 45 - 862 MHz
SBC Restrain	>17 dBm
CNR	>50 dB @ 10km fiber length
CTB	< -63 dB
CSO	< -57 dB
Dimensions	19 x 10 x 1.75 inch
Weight	2.5 kg
Operating Temperature	0 - 45 ?

32 mW CATV RF Over Fiber Tx 45-870 MHz

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RF over Fiber Tx - 32mW Output 45-1000 MHz

High-Power RF over Fiber Transmitter - 32mW | 45-1000 MHz

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Designed for Large Optical Splits

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Recommended Accessory: F-PLC Passive Fiber Optic Splitter

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Question:
What are the typical losses in the fiber? How do you calculate the optical budget when the transmitter outputs +15dBmV and the optical receiver has a 0dBmV receiver sensitivity?

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