400HZ Notch Filter how to.

[Dana]

Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.
The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.
Problem with that is getting the inductors locally.
Up here In Fairbanks our choices are very limited.

Thanks.

 

[Joop van der Velden]

Dana wrote:

Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.
The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.

There is a chance that filtering the 400Hz tone will not be sufficient,
and that there are several harmonics present in the audio signal (800,
1200Hz etc).

Find this out first, by comparing the hum you hear with a clean sine
wave of 400Hz. http://members.lycos.nl/audiofriends/testsignalen/

--
Joop van der Velden
pe1dna@amsat.org
-- A DIY GPS receiver: http://www.gpskit.nl/

 

[John Fields]

On Mon, 29 Sep 2003 17:51:36 -0800, "Dana" <dana.raffaniello@gci.net>
wrote:

Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.
The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.
Problem with that is getting the inductors locally.
Up here In Fairbanks our choices are very limited.

You might want to try this:

http://www.national.com/ms/LB/LB-5.pdf

--
John Fields

 

[Al Clark]

"Dana" <dana.raffaniello@gci.net> wrote in news:vnho0p7j179of7
@corp.supernews.com:

Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.
The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.
Problem with that is getting the inductors locally.
Up here In Fairbanks our choices are very limited.

Thanks.

This is an easy application for one of our small DSP boards. Our DSP-8300
is flash programmable, and has a stereo 16 bit audio codec. You could
program the board with a 400 Hz notch and also a very good bandpass
filter if you want. We can help you with the code.

Details are on our web site.

--
Al Clark
Danville Signal Processing, Inc.
--------------------------------------------------------------------
Purveyors of Fine DSP Hardware and other Cool Stuff
Available at http://www.danvillesignal.com

 

[Harvey White]

On Mon, 29 Sep 2003 17:51:36 -0800, "Dana" <dana.raffaniello@gci.net>
wrote:

Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.

Try a notch filter with an active amplifier, op amp would do well.
Look for the National Semiconductor application notes for some
formulas, circuits, etc. Go find out what you can snag at RS, then
go look for the ap notes. You want a notch filter.... not high
pass... You don't need inductors.

Harvey

The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.
Problem with that is getting the inductors locally.
Up here In Fairbanks our choices are very limited.

Thanks.

 

[John Larkin]

On Tue, 30 Sep 2003 03:00:32 GMT, Al Clark <dsp@danvillesignal.com>
wrote:

"Dana" <dana.raffaniello@gci.net> wrote in news:vnho0p7j179of7
@corp.supernews.com:

Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.
The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.
Problem with that is getting the inductors locally.
Up here In Fairbanks our choices are very limited.

Thanks.



This is an easy application for one of our small DSP boards. Our DSP-8300
is flash programmable, and has a stereo 16 bit audio codec. You could
program the board with a 400 Hz notch and also a very good bandpass
filter if you want. We can help you with the code.

Details are on our web site.

Or use three capacitors and three resistors in a twin-tee notch. The
software is somewhat easier.

John

 

[Randall R. Gawtry]

In article <vnho0p7j179of7@corp.supernews.com>, "Dana" <dana.raffaniello@gci.net> wrote:

Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.
The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.
Problem with that is getting the inductors locally.
Up here In Fairbanks our choices are very limited.

Thanks.

Dana,

We have two products that have built-in notch filters - the DSP-599zx and the
DSP-8100c Noise Filters. Both units have an automatic notch filter and a
manual tunable notch filter. No programming is necessary. Just push a button
and/or dial in the notch frequency you want. They also have tunable highpass
and lowpass filters to tailor your overall bandpass to meet your specifc
requirements. Check them out on our website - http://www.timewave.com.

http://www.timewave.com/dsp599zx.html

http://www.timewave.com/Datasheets/8100data.html

Both units are in stock for immediate shipment anywhere in the world.


Thank you,

Randy Gawtry
Timewave Technology Inc.
St. Paul, Minnesota

 

[John Fortier]

"Dana" <dana.raffaniello@gci.net> wrote in message
news:vnho0p7j179of7@corp.supernews.com...

Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.
The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.
Problem with that is getting the inductors locally.
Up here In Fairbanks our choices are very limited.

Thanks.

If the tone is pure 400 Hz, you should be able to use a twin T filter.

By themselves Twin Ts have a very low Q, but if you "activate" them they
can be made to provide a pretty sharp filter.

The advantage is that no inductors are required.

I won't try to draw one using ASCII which would probably be very confusing,
but if you need a circuit diagram, e-mail me and I can send you one.

On the other hand, if you use a high pass filter, the problem is going to be
building a filter which has a sharp enough cut off to eliminate the 400Hz
while leaving the rest of the signal relatively unattenuated. You can use a
multi-stage Sallen and Key filter, but the complexity and the tight
component values required make this a difficult solution to achieve in
reality.

All in all, the Twin T seems your best bet.

John

 

[Tony Williams]

In article <Vteeb.19884$pe7.6456@twister.nyroc.rr.com>,
John Fortier <jfortier@rochester.rr.com> wrote:

By themselves Twin Ts have a very low Q, but if you "activate"
them they can be made to provide a pretty sharp filter.

I won't try to draw one using ASCII which would probably be very
confusing,

ASCII dwgs are ok if viewed in a fixed width font.

C C
+----||---+---||---+
| | |
| \ |
| /R/2 | Fo= 1/2.pi.R.C.
| \ |
| | |
| --+--0v |
In --+ +--Out.
| R R |
+--/\/\---+--/\/\--+
|
===2C
|
--+--0v

That's the basic Twin-T, suffers from a not very sharp notch.

Bootstrapping can steepen the sides of the notch and gain
a flatter response in the passband.

+-------+ ______
| | | |
+-|-\ +--|Twin-T|----|+\
| >--+ |__ ___| | >--+----Out
In---|+/ | +-|-/ |
| | |
| +-------+
| |
| \
+----->/ <--Bootstrapping adjust
\
|
--+--0v

--
Tony Williams. Change "nospam" to "ledelec" to email.

 

[default]

On Mon, 29 Sep 2003 17:51:36 -0800, "Dana" <dana.raffaniello@gci.net>
wrote:

Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.
The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.
Problem with that is getting the inductors locally.
Up here In Fairbanks our choices are very limited.

Thanks.

I don't know how useful this reply will be . . . forgot where the

schematic got to. The basic circuit is a single transistor amp common
emitter with collector load and emitter resistors the same value.

The input has a twin T filter that attenuates all but the notch
frequency, so you accentuate the frequency you want to notch out.
Emitter and collector are sampled via individual caps and combined.
At the twin T frequency, the emitter and collector are 180 out of
phase and cancel providing a very sharp notch.

I saw the circuit some 30 years ago and built it and fooled with it.
The notch attenuation was impressive and sharp. Perhaps someone
following one of your cross posts has the schematic.


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[Al Clark]

An analog notch filter may be fine for this application if the following
conditions are actually true:

1. Temperature is stable, so that the filter will not drift.
2. The interfering signal is actually 400 Hz. My guess is that it has a
fundamental at 400 Hz and also some significant harmonics. The harmonics
may be a bigger problem than the fundamental, since hearing is more
sensitive at higher frequencies (1-2kHz).

I would look at the signal with an FFT analyzer (You can probably find a
PC program on the web). This information will suggest an appropriate
solution.

These might be:

1. A simple notch filter as discussed.
2. Multiple notch filters.
3. Automatic notch filters using adaptive filtering.
4. Comb filters.
5. Bandpass Filters.

All of these solutions are easily addressed with a DSP and I have used
each of these methods for similar noise problems. The best solution
depends on the specifics.

--
Al Clark
Danville Signal Processing, Inc.
--------------------------------------------------------------------
Purveyors of Fine DSP Hardware and other Cool Stuff
Available at http://www.danvillesignal.com

 

[Baphomet]

"Dana" <dana.raffaniello@gci.net> wrote in message
news:vnho0p7j179of7@corp.supernews.com...

Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.
The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.
Problem with that is getting the inductors locally.
Up here In Fairbanks our choices are very limited.

Thanks.

http://www.militarymags.com/electronics/NotchFilter.gif . This is a bandpass

filter so you can either use the twin tee feedback circuit as a stand alone,
or you can add an additional op amp to invert the signal. This circuit was
liberally filched from "Network Synthesis" by Charles A. Vergers

 

[Ian Molton]

On Tue, 30 Sep 2003 14:23:51 GMT
Al Clark <dsp@danvillesignal.com> wrote:

I would look at the signal with an FFT analyzer (You can probably find
a PC program on the web). This information will suggest an appropriate
solution.

If you run linux theres a FFTscope on my website. crude but effective.
eats floats for breakfast

--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with
ketchup.

 

[Dana]

<jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote in message
news:bk2invgfeku5396dqvohv0e4abel7eqku3@4ax.com...

On Tue, 30 Sep 2003 03:00:32 GMT, Al Clark <dsp@danvillesignal.com
wrote:

"Dana" <dana.raffaniello@gci.net> wrote in news:vnho0p7j179of7
@corp.supernews.com:

Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.
The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.
Problem with that is getting the inductors locally.
Up here In Fairbanks our choices are very limited.

Thanks.



This is an easy application for one of our small DSP boards. Our DSP-8300
is flash programmable, and has a stereo 16 bit audio codec. You could
program the board with a 400 Hz notch and also a very good bandpass
filter if you want. We can help you with the code.

Details are on our web site.


Or use three capacitors and three resistors in a twin-tee notch. The
software is somewhat easier.

That is more like what I am looking for, as I would prefer a passive device
over an active. I originally came up with an LC notch filter, but cannot
obtain any inducters locally, so I would like to look at just using an rc
filter. But am having problems remembering from school the calculations
needed. That is the problem with technology going to board level and even
box level repair, tend to forget the basics.
So does anyone remember how to determine component values for an rc notch
filter.

John

 

[Dana]

"John Fortier" <jfortier@rochester.rr.com> wrote in message
news:Vteeb.19884$pe7.6456@twister.nyroc.rr.com...

"Dana" <dana.raffaniello@gci.net> wrote in message
news:vnho0p7j179of7@corp.supernews.com...
Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.
The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.
Problem with that is getting the inductors locally.
Up here In Fairbanks our choices are very limited.

Thanks.



If the tone is pure 400 Hz, you should be able to use a twin T filter.

By themselves Twin Ts have a very low Q, but if you "activate" them they
can be made to provide a pretty sharp filter.

The advantage is that no inductors are required.

I won't try to draw one using ASCII which would probably be very
confusing,
but if you need a circuit diagram, e-mail me and I can send you one.

On the other hand, if you use a high pass filter, the problem is going to
be
building a filter which has a sharp enough cut off to eliminate the 400Hz

Yes I tried that, and I found that to reduce the 400hz I needed to have my
cutoff at around 650hz and higher to obtain enough attenuation at 400hz.
The 400hz is the whine of the 400hz power that supplies the remote location
electronics, and as the equipment technology is old, the audio of the
operator is neing swamped out by this noise. Why thye did not go with some
kind of vox circuit like is used in aircraft I do not know.

while leaving the rest of the signal relatively unattenuated. You can use
a
multi-stage Sallen and Key filter, but the complexity and the tight
component values required make this a difficult solution to achieve in
reality.

All in all, the Twin T seems your best bet.

John

 

[John Fields]

On Tue, 30 Sep 2003 07:15:13 -0800, "Dana" <dana.raffaniello@gci.net>
wrote:

That is more like what I am looking for, as I would prefer a passive device
over an active. I originally came up with an LC notch filter, but cannot
obtain any inducters locally, so I would like to look at just using an rc
filter. But am having problems remembering from school the calculations
needed. That is the problem with technology going to board level and even
box level repair, tend to forget the basics.
So does anyone remember how to determine component values for an rc notch
filter.

---
If you'd take a look at the URL I referred you to you'd find that the
equations for everything you want to do are right there, whether you
want to use a passive or an active solution.

--
John Fields

 

[Dana]

"Al Clark" <dsp@danvillesignal.com> wrote in message
news:Xns94065FEDDE68Caclarkdanvillesignal@66.133.128.150...

An analog notch filter may be fine for this application if the following
conditions are actually true:

1. Temperature is stable, so that the filter will not drift.

Once the site is turned up, the temp remains fairly constant.
Big fear here is latter on this winter when outside temps are -20 and lower,
may take a bit longer to stabilize.

2. The interfering signal is actually 400 Hz. My guess is that it has a
fundamental at 400 Hz and also some significant harmonics.

It is 400hz power that is making the whine. We use 400hz power on the
electronic equipment at the site, except of course the comm gear which is
your basic 120.

The harmonics
may be a bigger problem than the fundamental, since hearing is more
sensitive at higher frequencies (1-2kHz).

I would agree with this outlook in most other situations. But being that
this is the noise of the 400hz power, these harmonics are not so bad.

I would look at the signal with an FFT analyzer (You can probably find a
PC program on the web). This information will suggest an appropriate
solution.

Looked at with a Spec A, as well as one of those level meters that gives
freq's and levels that are used to find rf hotspots to comply with OSHA
regs.

These might be:

1. A simple notch filter as discussed.
2. Multiple notch filters.

For the remote locations these would be best option, as I have restrictions
on electrical supply, being these are very remote locations.

3. Automatic notch filters using adaptive filtering.
4. Comb filters.

Active devices are kind of limited due to the scaricty of electricity at
site.

5. Bandpass Filters.

Cutoff is to high to properly knock down the 400. This was also my first
choice of trying to find a solution for this problem, which has existed
since before I came here.

All of these solutions are easily addressed with a DSP and I have used
each of these methods for similar noise problems. The best solution
depends on the specifics.

I agree, active would be nice, but electrical supply is very limited.

--
Al Clark
Danville Signal Processing, Inc.
--------------------------------------------------------------------
Purveyors of Fine DSP Hardware and other Cool Stuff
Available at http://www.danvillesignal.com

 

[Dana]

Just wanted to say thanks for all the helpful replies.


"Dana" <dana.raffaniello@gci.net> wrote in message
news:vnho0p7j179of7@corp.supernews.com...

Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.
The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.
Problem with that is getting the inductors locally.
Up here In Fairbanks our choices are very limited.

Thanks.

 

[Dana]

"John Fields" <jfields@austininstruments.com> wrote in message
news48jnvcsp26c8dhp0m05ink64i8tbi8gok@4ax.com...

On Tue, 30 Sep 2003 07:15:13 -0800, "Dana" <dana.raffaniello@gci.net
wrote:


That is more like what I am looking for, as I would prefer a passive
device
over an active. I originally came up with an LC notch filter, but cannot
obtain any inducters locally, so I would like to look at just using an rc
filter. But am having problems remembering from school the calculations
needed. That is the problem with technology going to board level and even
box level repair, tend to forget the basics.
So does anyone remember how to determine component values for an rc notch
filter.

---
If you'd take a look at the URL I referred you to you'd find that the
equations for everything you want to do are right there, whether you
want to use a passive or an active solution.

Domo arigato
Thanks.

--
John Fields

 

[Jim Thompson]

On Mon, 29 Sep 2003 17:51:36 -0800, "Dana" <dana.raffaniello@gci.net>
wrote:

Looking to notch out a 400HZ whine from some audio circuits connecting
remote manned sites to a central location.
The audio is microwaved from remote location to the central location.
Would like to know the formula for determing the resistor and capacitor
values.
The overall bandpass is 300HZ to 3KHZ.
Or would it be better to just use an High Pass filter.
Problem with that is getting the inductors locally.
Up here In Fairbanks our choices are very limited.

Thanks.

See the gyrator-based filters shown on the S.E.D/Schematics page of my
website. A notch is just another variation since the gyrator creates
an inductor to ground.

These filters are *very* stable compared to Sallen-Key... component
sensitivities are unity. (In an S-K realization the sensitivities are
a function of Q.)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.