Understanding sesitivity specifications

[silagi]

I need help understanding sensitivity specifications. I am trying to compare specs on 3 radios.
On two of the radios, the sensitivity in the civilian aircraft band is 1.0 uv @ 20 db S/N. The other radio is 3.0 uv but at 10db S/N. Now I know the lower the the number of "uv" the better. But how do you compare when they are at different db S/N. How can I compare that third radio to the first 2?

 

[K9WG]

The db S/N is the ratio of receiver noise open squelch no signal to receiver noise open squelch with an unmodulated signal in (in uV). In the first example the ratio of noise as presented to the speaker with a 1 uV signal is 20 db lower then without a signal. The second one the ratio of noise as presented to the speaker with a 3 uV signal is 10 db lower then without a signal.

 

[silagi]

Thanks for the explination but to tell you the truth a lot of that went over my head Can it be translated into something a non-techie like me can understand? How much better or worse would that 3 radio be at picking up weak am aircraft signals?

 

[ab3a]

The whole story

The s/n ratio is the Signal to Noise ratio. Assuming your radio is making the normal hiss that it would with absolutely no signal, how much stronger is that signal from that usual background Hiss?

A 10 dB signal to noise ratio means that the signal is ten times louder than the background noise.

A 20 dB signal to noise ration means that the signal is one hundred times louder than the background noise.

You tend to hear things on an logarithmic scale, so it is customary to use a log of a ratio to describe performance in easy to understand terms.

The radio with the 1 microVolt at 20 dB signal to noise ratio is therefore considerably more sensitive than the radio with the 3 microVolts for a 10 dB signal to noise ratio.

HOWEVER: That's not the whole story. There is another specification which can appear in several different ways called dynamic range. Having super sensitive hearing isn't going to help you much when you're standing in the middle of a rock concert. Likewise, if you live in a city with lots of signal sources, it could well be that the more "deaf" radio actually may perform better.

It's like someone wearing earplugs at a gun range. You definitely won't hear the super quiet sounds you would hear without earplugs. However, if you don't wear them, your ears may start ringing from gunfire noise and you won't be able to hear what people say next to you anyway.

The subject of how one measures dynamic range is unfortunately quite complex. People literally write books on the subject. However, one easy to understand number is called Blocking Dynamic Range. The higher that number is, the better.

That's the short answer. Hope this helps...

 

[silagi]

Thanks for the explination. I got it now. Thanks