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G8MNY > DSP 27.11.02 17:14l 88 Lines 3872 Bytes #-7113 (0) @ WW
BID : 28012_GB7CIP
Read: GUEST DK5RAS
Subj: Noise Eliminating Loudspeaker
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Sent: 021127/1441Z @:GB7CIP.#32.GBR.EU #:28012 [Caterham] $:28012_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : DSP@WW
Hi All,
I recently bought a BHI NES 10-2 after reading the December Radcom Article
by G4HCL, and hearing actually demonstrated at a rally. The demo is what really
sold it to me.
Quite amazing performance, don't be fooled by the little loudspeaker box, it
really is the state of the art Digital Signal Processing noise reduction unit.
It has 8 levels of noise reduction set up on a not very friendly DIL switch on
the rear as well as an I/P volume control & noise reduction on/off switch that
also lights a red/green LED. The unit is power by the usual 2.1mm DC connector
(+ in the middle) & seems to have an idiot diode for basic protection.
Here are some performance figures I measured from my one...
AUTOMATIC NOISE & TONE REDUCTION
DIL SSB 1KHz
SETTING NOISE * TONE
1 Min 9 dB 4 dB
2 11 dB 5 dB
3 12 dB 6 dB
4 13 dB 8 dB
5 16 dB 16 dB
6 19 dB 21 dB
7 24 dB 25 dB
8 Max 33 dB 65 dB
* Noise & Tones was measured on a flat average analogue meter.
At 8 MAX there is no need to use a SQUELCH on FM, in fact a chopping squelch is
unhelpfully as the retraining noise DSP jumps the noise on & off. The only
problem is knowing when an over has occurred as you are left with almost
silence, just the DSP remnance musical tones at -33dB.
FREQUENCY RESPONSE (external connections) 25Hz - 4.5KHz @ -3dB.
which makes it quite acceptable for Broadcast signals.
INPUT IMPEDANCE is 10K Ohms.
TIME DELAY was 27mS, which I guess is the time to go from Analogue to Digital
& back to Analogue.
In off mode the audio still goes A-D-A but without any noise processing, you
still get the frequency filtering due to the 12KHz sample rate, eg a 6KHz
turnover frequency & filtering that gives -3dB @ 4.5KHz.
IN USE, I found that you soon get used to the musical artifacts (like digital
cellphones) that the highest level of DSP give you, as these are much preferred
to normal very noisy comms audio. At moderate level, moderate noise reduction
occurs & the recovered speech is more like normal. With extremely noisy weak
signals (0dB S/N) the recovery process starts to fail & little usable audio
comes though, at these levels straining with the normal signal may just be
better.
The tone reduction feature may be of specific interest to HF/VHF operators how
have computer birdies etc on channel, as this unit can automatically eliminate
carriers by up to 65dB if needed in under a couple of seconds, allowing weaker
Dx to be worked underneath.
ON CW as long as the wanted signal is stronger than others in the Rx passband
normal CW will be heard OK noise free. Slow Morse having longer than 1 second
CW elements will be attenuated are the DSP action trains on this to remove it.
Also strong signals may have clicky starts again as the DSP gets it wrong.
ON AM/SSB/FM there is little difference, just a good cleanup of the audio, with
music there is a tendency to eliminate all but the loudest instrument.
WITH TV. On sports commentary the background crowd noise is well reduced,
making the commentator's voice stand out rather than ne drowned out, something
deaf people may find very useful.
My only gripe with the unit is the DIL switch, as this should really have been
implemented as 10 way switch from OFF (direct to LS), ON 4.5KHz amplified
filter, then 1-8 levels of DSP to be set for the grade of enhancement needed
for that QSO.
For more information on the unit see www.bhinstruments.co.uk or RADCOM.
P.S. I have no commercial interest in this product/co, this is just my personal
experiences of the unit, that I hope others may be interested in.
73 de John G8MNY on 2001-NOV-27 @ 14:41 local time, from an IBM XT.
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