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BHI Noise Eliminating Speaker

Hi All,

Following Andy G0FTD' comments about the cost and short comings of these little LS units. Many people have commented to me that the Noise Reduction seems very good compared to other more expensive add on DSP units or DSP systems in rigs etc. Make our own mind up. Here is the bulletin I sent 2 years ago, and some mods to do to the cheaper one to make it more usable.

I also went to a ham club talk where one of the 3 man company gave a talk on it's development and the trials and tribulations of getting the product out. It was interesting to learn that the dedicated IC used was designed for noise elimination on car microphones and not on Rx noise. They have also just released a new model that may be more useful with Phono and 3.5mm Jack connections. The control-less NES-CB version meant "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 and 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!) and 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) and 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 and input impedance seen below. In the ON mode there is software AGC as well as the effective noise and tone eliminating function.

Here are some performance figures I measured from my one...

AUTOMATIC NOISE and 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 and 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 unhelpful as the DSP retraining time for the noise change causes the noise to jump on and fade off. The only problem using it at maximum 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 and 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 and 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 and the recovered speech is more like normal. With extremely noisy weak signals (0dB S/N) the recovery process starts to fail and 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 response to 15KHz, but the artifacts became quite noticeable. However with 32MHz clock a reasonable 9KHz treble 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 and 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 and 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 and 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 or company, this is just my personal experiences of the units, that I hope others may be interested in.

Modifications to BHI's NESCB
I have done 5 modifications in one upgrade to make a more enhanced model than the top of the range NES10-2:

A/ Add centre speaker 10 way noise processing level and in/out control switch.
B/ Add dual Green ON and Red through mode dual LED.
C/ Add no power LS only mode.
D/ Improve LF LS O/P, change 100u for 470u
E/ Add External LS socket

Tools needed: 10mm Punch (10mm drill body and a metal hole) LED and 3.5mm Jack holes can be made with soldering iron/drill. Anti Static earthed soldering iron. Use Anti Static handling precautions.

Parts Needed:
RS BCD Switch 327-938.
Small shrouded skirt knob.
5" of 5 way coloured ribbon wire.
Dil 11V C/O reed Relay, and metal screen.
Dual colour LED (-ve common).
Small PNP transistor.
3.5mm surface mounting jack socket.
Small 470uF 10V cap.
Several colours of thin connecting wire.

Method
1/ Remove the warranty label, these mods will invalidate it anyway!

2/ Unscrew case and carefully remove LS and PCB.

3/ Remove front Grill and cloth, punch out central switch hole in grill and cloth.

4/ Cut off switch legs to not foul speaker. With a hot iron quickly wire up the switch tag remains to the ribbon, forming the ribbon from next to the grill. brown-D, red-B, orange-I, yellow-J, green-E-F-M

5/ Make LED whole in top RH corner of plastic baffle (in one of the moulding weakness), and make hole for LED common to go to green switch common and wire up.

6/ Make ribbon recess slot in LS baffle bottom, reassemble LS front checking LS is not fouled, glue ribbon into slot.

7/ Wire ribbon to PCB pad brown on RHS, red next left, orange next left, leaving spare pad on LHS. Connect green to any of the 3 pad grounds. Yellow wire take to component side and wire to the bottom connection of J2 with a 10K resistor in the hole as well.

8/ Power up and connect a noisy source and test the function of switch, making sure you don't short out anything. There should be fully anti-clockwise max noise reduction function with 8 steps to min, the ninth step is no noise reduction, step 10 is max reduction again. Then disconnect supply.

9/ Connect a bare solid wire to pin 14 of the LM380 IC (+12V reg) glue the DIL relay on top of this IC. Wire thick lead to relay coil, the other end of the coil wire to a PNP transistor emitter and also a diode anode. Wire the PNP base to the free end of the 10K (step 7). (Note step 13 when wiring to the relay.)

10/ Change the LS cap C23 from 100uF to 470uF. Make sure it does not foul the pillar hole.

11/ Wire up the PNP collector to the red LED and wire up the diode cathode to the green LEDs respectfully. Retest, the Red LED should only light on step 9 function, green otherwise.

12/ Wire up the LS live connections via the relay to switch to through on power off. Picking up external I/P on bottom of I/P attenuator P1 rhs R. (Note step 13 when wiring to the relay.) Test that the relay puts LS signal though when the power is off and unit functions correctly when powered.

13/ Assemble and checking nothing fouls. Test for LS magnet - relay interaction. If there is (eg not switching audio on power on/off) make a magnetic shield for the relay, eg cut and bend a steel lamination to rap around the LS side of the relay. Also try a lamination strip taped to the LS magnet.

14/ Make whole for an external LS 3.5mm jack socket on the LHS by the upper pillar leaving just enough room to clear the pillar but still clear the LS! Wire up and test again.

73 de John G8MNY @ GB7CIP

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