[TowerTalk] Measuring Coax Loss

[Roger (K8RI)]

jimlux wrote:
> Mike Besemer (WM4B) wrote:
>   
>> How, it the real world of ham radio, do you experience hearing the
>> difference of 3dB daily?
>>
>> I'm not talking about a lab.
>>
>>
>>
>>     
> Yes..
> 3dB is the difference between unreadable and barely readable against the 
> noise floor.  The difference between the 3kHz and 2.4kHz IF filter on 
> SSB is a lot less than 3dB and readily audible on a weak signal (on HF).
>
>    It's probably the difference between somewhat noisy and full quieting 
> on a FM rig.
>
> At threshold, 3dB is important.
>
> At S9 or 60 over, 3dB is irrelevant.
>   
Not if that's your noise floor, which isn't all that uncommon up here in 
snow country when the wind blows. <:-))
It was S7 last night and very steady, well...night before last now.
> Now, if you start talking 1dB... 1dB is very close to a "just noticeable 
> difference" in audio levels.. 
That is the definition of 1 db (just barely detectable)  It just so 
happens our hearing is logarithmic so to us, the change sounds linear.  
If it's under 6 KHz I'll probably be able to detect the difference.  If 
it's below 120 Hz I will detect it. If it's 8 KHz and above I won't hear 
anything to be able to detect the difference. At that frequency my 
hearing is 80db down.  IOW, it's a good low pass filter, except for some 
reason screaming kids in the grocery aisle can hit a note that resonates 
in my ears that is actually painful...very painful.

73

Roger (K8RI)
> that is, if you have two tones that are 
> 0.5dB apart in level, you'll have a hard time telling the difference 
> between them.  (see, e.g. Weber-Fechner law, etc.)
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