Scanner sensitivity and path loss?
 

I was wondering what's an accurate estimate for scanner sensitivity?
I've got a Uniden BC180, and the owner's manual doesn't list that
information. I was wondering what a good value would be to use in
order to do some path loss calculations. I've heard 1.0 uv is a good
conservative estimate. Is this too low?

As a second question, what's the approximate margin needed to make out
audio? I've heard for data 20dB margin has a link reliability of
99.9%, and 30dB margin yields 99.99%. I imagine to make out audio
without too much difficulty, it'd be much less.

Thanks in advance for any insight!
Dave

"David Harper" wrote in message
om...
I was wondering what's an accurate estimate for scanner sensitivity?
I've got a Uniden BC180, and the owner's manual doesn't list that
information. I was wondering what a good value would be to use in
order to do some path loss calculations. I've heard 1.0 uv is a good
conservative estimate. Is this too low?


The 1 uv is fine for the calculations. You may even be able to go as low as
..5 uv . The lower the number the more sensitive the receiver . Not sure
what you mean about the margin to make out audio. For FM singnals .5 uv
should give you good audio with a trace of noise and at 1 uv it should be
almost full quietning (for FM that is all the hissing noise should dissapear
out of the audio ) .

"Ralph Mowery" wrote in message hlink.net...

Not sure
what you mean about the margin to make out audio. For FM singnals .5 uv
should give you good audio with a trace of noise and at 1 uv it should be
almost full quietning (for FM that is all the hissing noise should dissapear
out of the audio ) .

First of all, thanks for the info!

What I mean by margin is:

Transmit strength (dB) + Receiver sensitivity (dB) - path loss (dB) =
margin (dB)

If I understand what you're saying correctly, with a margin of 0 you
can still make out decent audio? I thought there'd still be too much
S/N ratio or not enough "signal" for the amp to work with in order to
get "hearable" audio at 0 margin?

Thanks again!
Dave

"Ralph Mowery" wrote in message hlink.net...
"David Harper" wrote in message
om...
I was wondering what's an accurate estimate for scanner sensitivity?
I've got a Uniden BC180, and the owner's manual doesn't list that
information. I was wondering what a good value would be to use in
order to do some path loss calculations. I've heard 1.0 uv is a good
conservative estimate. Is this too low?


The 1 uv is fine for the calculations. You may even be able to go as low as
.5 uv . The lower the number the more sensitive the receiver . Not sure
what you mean about the margin to make out audio. For FM singnals .5 uv
should give you good audio with a trace of noise and at 1 uv it should be
almost full quietning (for FM that is all the hissing noise should dissapear
out of the audio ) .

I just did some reading based on what you said. The sensitivity is
actually based on a minimum S/N ratio... and if I understand
correctly: if an audio signal comes in with a strength of 1.0uV and
the receiver sensitivity is 1.0uV, it will be understandable?

Thanks again!
Dave

I just did some reading based on what you said. The sensitivity is
actually based on a minimum S/N ratio... and if I understand
correctly: if an audio signal comes in with a strength of 1.0uV and
the receiver sensitivity is 1.0uV, it will be understandable?

If you are using FM then you will see a specification of say .5uv sinad or
..7 uv for 20 db quieting. Usually that is about the same real world
sensitivity unless I have it backwards for sinad and quieting. This level
is for understandable audio. FM has a threshold level in that you get a
bunch of noise with the audio comming out of the receiver tuil you hit the
threshold point and then just a small aditional ammount of signal will clear
up the audio. Any more signal will sound the same. You should hear the
audio just fine at the above levels.

As far as the fade margin goes, the 0 level is what you get for the above
sensitivity. YOu will need some ammount above this level to get a good
signal all the time. At vhf and above for a distance of say 30 miles you
will have a signal of so much for maybe 70 % of the time. To get to the 99
% or more you may need 20 or 30 db of fade margin. Maybe 2 % of the time
you will have a stronger signal . All this is due to the way the atmosphere
bends the signals.