Various Topics on Electronics - Misc

.... ..n ..r ..ld..

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 bandp*** is 300HZ to 3KHZ.
> Or would it be better to just use an High P*** 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/

....

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

Thanks.

.... ..el..

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 bandp*** is 300HZ to 3KHZ.
>Or would it be better to just use an High P*** 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

.. ..a..

"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 bandp*** is 300HZ to 3KHZ.
> Or would it be better to just use an High P*** 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 bandp***
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

.... ..rk..

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 bandp*** is 300HZ to 3KHZ.
>> Or would it be better to just use an High P*** 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 bandp***
>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

..nda.. .. ..wt..

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 bandp*** is 300HZ to 3KHZ.
>Or would it be better to just use an High P*** 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 highp***
and lowp*** filters to tailor your overall bandp*** 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

.... ..rti..

"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 bandp*** is 300HZ to 3KHZ.
> Or would it be better to just use an High P*** 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 p*** 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

.... ..llia..

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 p***band.

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

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

..fau..

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 bandp*** is 300HZ to 3KHZ.
>Or would it be better to just use an High P*** 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.


-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

.. ..a..

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. Bandp*** 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