[TenTec] NR Impact on Signal Level

[Merle Bone]

Grant /NQ5T said:

"With NR on, I have to run the AF gain on 2.059 way up on CW.  Listening to
the same signal on both v2/Orion-II radios at the same time, the II AF level
is about 40$% while the v2 AF level is way up -- 80-90% to get the same
output level (with NR on) through the internal speakers.   If you then hit
SPOT on the v2, it busts an eardrum.  Even without NR, SPOT is too hot on
the v2."

I used "Spectrum Lab" to look at the impact of NR on the audio signal level using a signal generator on 40M.
I saw the following impact on the signal level:
NR OFF Sig Level = -35Db
NR On 1 Sig Level = -38Db
NR On 2 Sig Level = -38.6Db
NR On 3 Sig Level = -39 Db
NR On 4 Sig Level = -39.5Db
NR On 5 Sig Level = -40.4Db
NR On 6 Sig Level = -41.6Db
NR On 7 Sig Level = -42.9Db
NR On 8 Sig Level = -45.7Db
NR On 9 Sig Level = -50.3Db
There are probably more digits here then accuracy but the overall trend and magnitudes are good approximations.

It does look like a bandpass filter is being formed that is about 3db down at 400Hz and 1600Hz. It isn't clear that the shape of that filter changes much from a setting of 1 to 9. However, there is about a 15Db reduction in the signal audio level from NR (Noise Reduction) Off to NR = 9. 

Merle - W0EWM