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Context: It frequently happens that when a particular brand of RC transmitter and receiver are too close (within a meter) the two units lose connection. The recommended fix (which works) is to move the two units farther apart, and the explanation usually given is that the signal is "swamped".

What is "swamping" in this context? Is this a commonly observed phenomenon in radio communications?

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  • \$\begingroup\$ its called "blocking the receiver" \$\endgroup\$
    – analogsystemsrf
    Aug 29, 2019 at 18:11
  • \$\begingroup\$ Swamping, I believe, means a signal is dominating a circuit (may even self-limit or clip, too) even though it isn't necessarily the desired signal (selected via some method of tuning a system.) If a nearby signal is strong enough and if the resonant circuit parts and/or wiring are sufficiently imperfect (parasitics), then the resonant circuit will resonate more strongly than the nearby tuned frequency. How this plays out will depend on the exact receiver design. But it just means that the Q is wide and "spread out" and that a nearby signal is swamping out weaker tuned signals. \$\endgroup\$
    – jonk
    Aug 29, 2019 at 18:19
  • \$\begingroup\$ even in high-Q frontends, the arrival of fast edges (impulses) will make the circuitry ring and thus block/swamp the desired signal. Makes radio-on-chip an exciting venture. \$\endgroup\$
    – analogsystemsrf
    Aug 30, 2019 at 14:52

2 Answers 2

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swamp

swɒmp

noun

  • an area of low-lying, uncultivated ground where water collects; a bog or marsh.
    synonyms: marsh, bog, quagmire, mire, morass, fen, quag, sump; More

verb

  • overwhelm or flood with water.
    "a huge wave swamped the canoes"
    synonyms: flood, inundate, deluge, wash out, soak, drench, saturate, immerse "the rain was driving down with great force, swamping the dry ground"

Source: Lexico.

You're using the verb and "overwhelm" is a good alternative. In the context of radios the signal is so strong that the receiver can't see the modulation (AM or FM) any more and reception is lost.

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Figure 1. An AM radio demodulation circuit. Image from What role does the capacitor play in an AM demodulating circuit?.

This is a very crude example but it may help. It should be clear from Figure 1 that the diode and capacitor are demodulating the incoming modulated RF signal. If the demodulator stage was preceded by an amplifier stage then it would be possible for a very strong incoming signal to drive the amplifier into saturation so that (what were) the low amplitude RF cycles are amplified to the same level as the peak amplitude signals. When that happens the modulation has been lost and the demodulation stage will just give a DC output and no audio. In the case of the AM radio one could expect the audio to be distorted as the signal level goes from "acceptable" to "swamped" as the positive peaks get increasingly clamped until eventually the modulation drops to zero.

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  • \$\begingroup\$ See also: "saturation" \$\endgroup\$
    – Shamtam
    Aug 29, 2019 at 18:01
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    \$\begingroup\$ It's in the synonyms. Thanks! \$\endgroup\$
    – Transistor
    Aug 29, 2019 at 18:02
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It's kind of like standing too close to the big speakers at a rock concert. The music is so loud you can't really make out what it sounds like. It's just a painfully loud noise.

The same thing can happen to receivers. They are made to pick up weak signals. If the receiver is too close to the transmitter, then the radio signal is so "loud" that the receiver can't make out what is being "said."

The details vary as to what exactly happens in the receiver when the signal is too strong.

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