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G8MNY > TECH 22.01.03 04:17l 126 Lines 6246 Bytes #999 (0) @ WW
BID : 40563_GB7CIP
Read: GUEST OE7FMI
Subj: Noise Eliminating Speaker
Path: DB0MRW<DB0PV<DB0ZKA<DB0KFB<DB0CZ<F6KFG<DB0GE<F6KFT<LX0PAC<LX0HST<
HA3PG<7M3TJZ<ON0AR<IK1ZNW<GB7CRV<GB7CIP
Sent: 030121/1227Z @:GB7CIP.#32.GBR.EU #:40563 [Caterham] $:40563_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
Hi All,
I recently bought a BHI NES 10-2 after reading the 2002 December Radcom
Article by G4HCL, and hearing actually demonstrated at a rally. The demo is
what really sold it to me.
I also went to a ham club talk where one of the 3 man company gave a talk on
it's development & the trials & tribulations of getting the product out. It was
interesting to learn that the dedicated IC used was designed for noise
elimination on car microphones & not on Rx noise. They have also just released
a new model that may be more useful with Phono & 3.5mm Jack connections. The
control-less NES-CB version ment "Commercial Businesses" not "Citizen's Band",
which goes to show how much they knew of the market, now to be renamed NES-5!
The units have quite amazing performance, don't be fooled by the little
amplified speaker box & it's relatively high cost, it really is the state of
the art surface mount 64 pin Digital Signal Processing noise reduction unit
running at 16MHz.
It has 8 levels of noise reduction set up on DIL switch on the rear, as well as
an I/P volume control (does same as Rig Volume!) & a noise reduction on/off
switch that also lights a red/green LED visible through the speaker grill. The
unit is power by the usual 2.3mm DC connector (+ in the middle) & it has a
series idiot diode for protection. In the OFF mode the unit is just an
amplified speaker, with the time delay, frequency response & input impedance
seen below. In the ON mode there is software AGC as well as the effective noise
& tone eliminating function.
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 averaging analogue meter.
At setting 8 MAX there is no need to use a SQUELCH on FM, in fact a chopping
squelch is unhelpfully as the DSP retraining time for the noise change causes
the noise to jumps on & fade off. The only problem using it at max under noisy
conditions, is knowing when an over has occurred as you are left with almost
silence, just the DSP remnants musical tones peaking at -33dB.
FREQUENCY RESPONSE (external Hi Z connections) 25Hz - 4.5KHz @ -3dB. Which
makes it quite acceptable for non HiFi Broadcast Radio signals.
INPUT IMPEDANCE is 10K Ohms. (20K on NES-CB)
TIME DELAY was 27mS, which I guess is the time to go from Analogue to Digital &
back to Analogue.
In the off mode the audio still goes Analogue-Digital-Analogue 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. The
processor clocks at 16MHz. Higher clock rates (I tested up to 55MHz) give
proportional higher frequency responses, but after about 32MHz (-3dB @9MHz)
much of the improvement was lost in unwanted musical effects.
IN USE, I found that you soon get used to the musical artifacts (like digital
cellphones) that the highest level of DSP gives you on very noise signals, as
these are much preferred to normal very noisy audio. At moderate eliminating
levels, 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 who
have computer birdies etc. on channel. 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, although the tone will slightly reappear on speech
peaks.
ON CW as long as the wanted signal is stronger than others in the Rx passband
normal CW will be heard noise free. Slow Morse having longer than 1 second CW
elements will be attenuated are the DSP action tries 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 in the audio quality just much reduced
background noise. With music there is a tendency to eliminate all but the
loudest instruments.
WITH TV.
On sports commentary the background crowd noise is well reduced, making the
commentator's voice stand out rather than be drowned out, something deaf people
may find very useful. For HIFI use I did try higher clocks up to 55MHz where it
gave flat responce to 15KHz, but the artifacts became quite noticable. However
with 32MHz clock a resionable 9KHz trebble compromise sounded OK to me.
HAM ATV
I have to listen to several channels at a time when using 23cms ATV repeater
GB3HV :- 144.75 FM talkback locally, 5.5MHz subcarrier carrying Engineering
sound 144.75 Rx @ GB3HV, as well as 6MHz subcarrier HiFi Sound. So using
several of the cheaper NES-CB boxes is a option for me. However I understand a
multi-input version may be introduced later.
PROBLEMS
My main gripe with the unit is use of a tiny DIL switch to control the depth of
noise reduction. Although the maker suggest most people leave this set at level
6 (NES-5 & NES-CB models). This should really have been a easy access BCD
switch as off mode is useful in tuning in SSB. I have done this mod to several
cheaper NES-CB models, as well as increased the 100uF LS cap to 470uF & made
the unit operate as a dumb LS when there is no power.
Other problems are slight RFI from the unit if used close to your Rx aerial,
(eg when using Handhelds). And it has slight susceptibility to alternator whine
when /M on Tx, this is down to the series diode & 12V reg not doing anything
as there is no voltage headroom!
For more information on the unit see www.bhinstruments.co.uk or see the RADCOM
article.
P.S. I have no commercial interest in this product/co, this is just my personal
experiences of the units, that I hope others may be interested in.
73 de John G8MNY @ GB7CIP
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