On Fri, 3 Dec 2004 20:25:26 +0100, "Meindert Sprang"
wrote:

"beryl george" wrote in message
...
Looking at different manufactures units they are quoting their
receivers sensitivity as

.35uV at 12dB SINAD
1uV at 20dB SINAD
-5dBu for 20dB SINAD

Let's convert the uV's to dBuV's first (= referencing all values in dB
compared to 1uV).
0.35uV is -9dBuV
1uV is 0dBuV
-5dbuV is, well, -5dBuV

Now let's add 8 dB on both sides to get the same S/N ratio on the first
line. This results in:
-1dBuV at 20dB SINAD
0dBuV at 20dB SINAD
-5dBuV at 20dB SINAD

It is now clear that the last receiver requires the least signal to reach
20dB signal to noise ratio.

Meindert


That doesn't work. Receiver input level is not linear with sinad
change. At the threshold (near 12db sinad) it takes very little signal
increase for a large sinad increase. At a higher sinad level (near 20
db) it takes much more of an increase in signal level to make a small
change in sinad level. Some receivers may not go much past 20 db sinad
no matter how much signal is applied.

Sinad is comparing signal noise and distortion. At low levels the
distortion is very high. At 12 db it is around 33%. At 20 db
distortion is about 12%. 30 db is around 3% distortion.

The only way to compare is to measure all receivers at the same sinad
level.

You also need to know what the receiver bandwidth is too. If it is not
the same on all receivers that will give different sinad readings.

Also be sure they are operating in the same mode.

Regards
Gary