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Frequency-division multiplexing (FDM) is a way to send multiple signals over one shared transmission medium at the same time by assigning each signal its own frequency band. At the receiving end, filters separate those bands so each signal can be recovered.
How frequency-division multiplexing works
A basic FDM system turns separate inputs into distinct frequency channels, combines them for transmission, then separates them at the receiver. The shared medium may be a cable or another communications channel.
- Limit each input’s bandwidth. The transmitter restricts each signal to the frequency range it needs, helping prevent unnecessary spillover into neighboring channels.
- Assign each signal a band. The signal is modulated onto a distinct carrier or otherwise placed in its allotted frequency range.
- Combine the channels. The band-limited signals are added together into one composite signal and sent over the shared medium.
- Separate and recover them. At the receiver, frequency-selective filters isolate the channels; demodulation then recovers their source signals. ScienceDirect’s overview of FDM describes this general transmit-and-receive process.
What guard bands do
Adjacent channels may be separated by guard bands: unused ranges of frequency between them. Guard bands help limit interference between neighboring signals and give real-world filters room to distinguish one channel from another. The trade-off is that wider gaps make filtering easier but leave less of the available spectrum for carrying information. ScienceDirect’s FDM reference and IEEE’s FDM reference describe this spacing trade-off.
FDM compared with TDM and OFDM
| Method | What separates the signals | How signals share the medium | Key design consideration |
|---|---|---|---|
| Conventional FDM | Different frequency bands | Signals are transmitted simultaneously | Frequency-selective filtering and, in many implementations, guard bands |
| TDM (time-division multiplexing) | Recurring time slots | Signals take turns using the shared channel | Timing and synchronization are central to assigning and recovering the slots |
| OFDM (orthogonal frequency-division multiplexing) | Orthogonal subcarriers | Multiple subcarriers carry data together | Subcarriers can overlap in frequency while remaining separable when the orthogonality condition is maintained |
The central distinction between FDM and TDM is the resource used to separate channels: frequency for FDM, time for TDM. OFDM is a related digital multicarrier method, but it should not be treated as identical to conventional FDM: its subcarriers rely on orthogonality and may overlap spectrally rather than being separated by conventional guard-band spacing. See IEEE’s multiplexing reference for FDM and TDM and IEEE’s OFDM reference for the distinction.
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#1 Best Overall
Elebase USB to USB C Adapter for iPhone 18 Pro Max,USBC Car Charger Adapter
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
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Where FDM is used
Broadcast radio, cable television, DSL, and carrier telephony are examples of applications associated with FDM. The particular implementation matters: these examples do not mean every modern radio, cable, or mobile system uses the same conventional FDM arrangement. IEEE’s FDM reference and ScienceDirect’s overview identify these application areas.
Quick Recap
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Anker USB C Hub, 5-in-1 USBC to HDMI Splitter with 4K Display
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UGREEN USB to USB C Adapter Combo 4-Pack, 10Gbps USB C Converter Space Gray
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Anker USB C Hub, 7in1 Multi-Port USB Adapter, 4K@60Hz USBC to HDMI Splitter
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Anker USB-C Hub, 5-in-1 USB Hub for Laptops, 4K HDMI Multiport Adapter
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
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