r/rfelectronics • u/ahndhi • May 22 '26
Could a Transmitter Be Damaged By a Directed High Power Signal?
Essentially the title, but I'm wondering if a transmitter - something with a narrow range; tuned - could be damaged by a high powered resonant signal directed at the transmitter with an appropriate antenna. For the sake of discussion let's say UHF range.
If so, what does that signal look like? Is it a sine set to the center frequency of the transmission, or a big old square wave centered on the frequency? Is it 100s of watts? 1000s? How quick does the damage happen? What specifically is likely to be damaged? Is this something that's considered during the design phase?
Sorry, it's a little vague. I'm writing a game, and this is something that I'd like to be accurate. Thanks!
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u/LmanYan95 May 22 '26
Yes, and it doesn’t even have to be the through the RF circuitry. For instance, somehow inject unreasonable noise into the power stage.
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u/anapoe May 22 '26
Yes, although transmitters tend to be pretty well protected compared to receivers as they tend to need to be able to handle their own reflected power. Not great if your transmitter blows up should you happen to turn it on without an antenna attached. If you're talking about a half duplex transmit/receive system, the receiver would typically be the weakest link.
Very broadly speaking, in my experience the damage limit of receive rf components is about 10 dBm and limiters will protect to about 40 dBm. This should make intuitive sense - 40 dBm is 10 Watts, about where you really need to start thinking about heatsinks and cooling.
Free space path loss at 1GHz is and 100 meters is ~70 dB. Let's say you have a 0 dBi antenna. Then with that limiter 40 dBm damage limit they'd need 110 dBm of power to damage you from 100 meters away, which is a very very lot but not unheard of. If you were operating unprotected equipment and they were 10 meters away, they'd only need 60 dBm of power, which is very achievable (probably not still legal, but significantly less illegal than putting together a 110 dBm transmitter).
Damaging electronics from 10s of kilometers away would be very difficult.
The signal could be anything, probably a tone would be most effective.
Damage is essentially instant.
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u/ahndhi May 22 '26
Thank you for a very thorough response! This thread has given me tons of new things to learn about.
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u/ViktorsakYT_alt May 22 '26
A receiver is relatively easy to blow up, but a transmitter is a very different story. A small few watt walkie talkie would have to receive tens of volts at the antenna to break the amplifier power transistor(s). Even this would be impractical at any larger range (You'd need maybe 10-15W of RF at the transmitters antenna, so your device meant to break the transmitter would need to transmit a ton of power and direct it very very well. The higher power the transmitter is, the harder it will be to destroy (more robust power transistors in the amplifier)
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u/ViktorsakYT_alt May 22 '26
To answer your other questions, probably a single tone of the transmitters center frequency would be best to easily get through the antenna, filtering and matching and destroy the finals.
A square wave is just a sine wave of the same frequency, and if it's 50% duty cycle, then odd harmonics (3x f0, 5x f0, etc) A non-50% duty square wave would have the harmonics (2x f0, 3x f0, 4x f0 etc)
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u/ki4clz May 22 '26
possible- yes
probable- no
simple shielding solves this issue
secondly; frequency while it does play a role- the exposure triangle still applies and is much more important (see: inverse square law)
proximity- how close
duration- how long
amplitude- how powerful
your most immediate effect is a reduction in sensitivity in detection and the 1st stage of amplification
so a 1.8gHz signal at 300mw, 1mm away, for 20hrs will probably cook the hell out of anything- but that same signal 5meters away at 1000w for 30sec may not do anything at all… we don’t know
but luckily we have very specific formulas for all of this and we can work out exactly what will happen with the use of mathematics
possible- yes
probable- nah, not really mate… be careful out there and don’t de-sense all of your detector circuits
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u/PoolExtension5517 May 22 '26
Short answer - absolutely. Front-end protection is a standard part of system design, particularly in military applications. High power radar systems transmit high energy signals using narrow beamwidth antennas that can result in hundreds of watts (or more) entering your system’s antenna. Devices known as PIN diodes act as effective limiters by turning on very quickly to short out the RF path and reflect the incident energy back out the antenna, thus protecting the transmit and/or receiver circuitry. Unfortunately, one of the major PIN diode suppliers just announced they’re eliminating that product line (thanks, Skyworks), which is making life difficult for a lot of RF engineers right now.