Sensitivity vs selectivity for a beginner
- Thread starter mikes84
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Sensitivity is how "good" a scanner can pluck a weak signal out of the air.
Selectivity is how "good" the scanner is at isolating that signal against adjacent signals on nearby frequencies.
Think of it as sitting in a crowded room full of people talking. Sensitivity is how good you can hear someone on the other side of the room when they whisper. Selectivity is how good you can make out what they're saying when 15 other people are talking at the same time.
This can be VERY important if you're in a major metropolitan area where there's lots of activity on adjacent frequencies to the target frequency you're monitoring. If your scanner/receiver has poor front-end filtering, strong off frequency signals can "bleed" and cause what's referred to as "intermod" interference. Commercial equipment (Motorola/Kenwood/Etc.) is usually substantially better filtered, confined to a single band (VHF Hi, UHF, 800, etc.) which makes their receiver much more selective and sensitive, and isn't affected as much as a wide band scanner/receiver is.
If you're interested in monitoring weak signal stuff (Satellites, systems that you're on the fringe of) then sensitivity is important to a degree, because obviously weaker signals require a much hotter receiver to sniff out.
As you've likely gathered, a receiver with good sensitivity but poor selectivity is a recipe for disaster. In an RF rich environment, I'd much rather have superior selectivity than sensitivity. In suburban areas, or remote areas, sensitivity is the name of the game. You'll also note some scanners have built in switchable attenuators that can help with these RF rich / intermod situations.
Selectivity is how "good" the scanner is at isolating that signal against adjacent signals on nearby frequencies.
Think of it as sitting in a crowded room full of people talking. Sensitivity is how good you can hear someone on the other side of the room when they whisper. Selectivity is how good you can make out what they're saying when 15 other people are talking at the same time.
This can be VERY important if you're in a major metropolitan area where there's lots of activity on adjacent frequencies to the target frequency you're monitoring. If your scanner/receiver has poor front-end filtering, strong off frequency signals can "bleed" and cause what's referred to as "intermod" interference. Commercial equipment (Motorola/Kenwood/Etc.) is usually substantially better filtered, confined to a single band (VHF Hi, UHF, 800, etc.) which makes their receiver much more selective and sensitive, and isn't affected as much as a wide band scanner/receiver is.
If you're interested in monitoring weak signal stuff (Satellites, systems that you're on the fringe of) then sensitivity is important to a degree, because obviously weaker signals require a much hotter receiver to sniff out.
As you've likely gathered, a receiver with good sensitivity but poor selectivity is a recipe for disaster. In an RF rich environment, I'd much rather have superior selectivity than sensitivity. In suburban areas, or remote areas, sensitivity is the name of the game. You'll also note some scanners have built in switchable attenuators that can help with these RF rich / intermod situations.
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Typically this is what separates scanners from communication receivers. Think ICOM R8600 vs Uniden BC125AT.
Very different hardware but can accomplish similar tasks; however, they just go about it in different ways.
It's not a way to decide which is better, as that's dependent upon the user's listening needs/goals.
prcguy
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Sensitivity is good but not expensive to achieve. There are different levels of selectivity from adjacent channel 12.5 to 25KHz away that can be addressed at moderate cost with ceramic or crystal filters. For a receiver to survive in a high RF environment like high power transmitters, cell phone towers, etc, within the same band or even different bands it costs more $$ to get good performance using a more elaborate design using switchable or tunable band pass filters, higher level rated mixers, etc.
A lot of cheap radios like a Baofeng UV-5R test very well in sensitivity on a service monitor or signal generator with just one signal and can easily beat a multi thousand $$ Motorola in that category. But connect that same $25 radio to an antenna with thousands of signals of varying levels hitting it and it fails miserably and its cheap design becomes obvious. A higher cost quality radio that tested worse in sensitivity than a Baofeng on a service monitor can easily pick out weaker signals than the Baofeng when connected to the same antenna because the selectivity, both adjacent channel and out of band are terrible on the cheaper radio and it drowns in all the interference.
A lot of cheap radios like a Baofeng UV-5R test very well in sensitivity on a service monitor or signal generator with just one signal and can easily beat a multi thousand $$ Motorola in that category. But connect that same $25 radio to an antenna with thousands of signals of varying levels hitting it and it fails miserably and its cheap design becomes obvious. A higher cost quality radio that tested worse in sensitivity than a Baofeng on a service monitor can easily pick out weaker signals than the Baofeng when connected to the same antenna because the selectivity, both adjacent channel and out of band are terrible on the cheaper radio and it drowns in all the interference.
I wrote this a while ago and updated it a few days ago: https://vk7aal.blogspot.com/2026/09/sensitivity-vs-selectivity-for-radio.html
That's a great way of describing what receiver selectivity means.
To the OP...if you're really interested in getting deep into it, paying for an AARL membership allows you access to receiver test data of amateur transceivers, as well as some wideband receivers and scanners.
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