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From: Jan Panteltje on 13 Dec 2009 13:14
On a sunny day (Sun, 13 Dec 2009 18:04:22 +0000) it happened Martin Brown
<|||newspam|||@nezumi.demon.co.uk> wrote in
<B0aVm.68146$de6.1720(a)newsfe21.iad>:
>
>Reminds me. Anyone have any thoughts on why the fifth harmonic on UK
>mains at 250Hz is so strong these days?

Global warming?
From: Martin Brown on 13 Dec 2009 16:50
Jan Panteltje wrote:
> On a sunny day (Sun, 13 Dec 2009 18:04:22 +0000) it happened Martin Brown
> <|||newspam|||@nezumi.demon.co.uk> wrote in
> <B0aVm.68146$de6.1720(a)newsfe21.iad>:

>> Reminds me. Anyone have any thoughts on why the fifth harmonic on UK
>> mains at 250Hz is so strong these days?
>
> Global warming?

I suspect switched mode PSU's but I can't see why the 5th harmonic is
now so strong or for that matter where the roughly 623+/-3Hz component
in my local electrical interference is coming from.

There is a heck of a lot of crossover distortion on our local mains - it
doesn't look all that much like a sine wave!

I can see other higher frequencies from CFLs but the 5th harmonic of
mains remains a bit odd. Some days it is the strongest harmonic component.

Regards,
Martin Brown
From: Jan Panteltje on 13 Dec 2009 17:01
On a sunny day (Sun, 13 Dec 2009 21:50:07 +0000) it happened Martin Brown
<|||newspam|||@nezumi.demon.co.uk> wrote in
<8kdVm.46713$cd7.8799(a)newsfe04.iad>:

>Jan Panteltje wrote:
>> On a sunny day (Sun, 13 Dec 2009 18:04:22 +0000) it happened Martin Brown
>> <|||newspam|||@nezumi.demon.co.uk> wrote in
>> <B0aVm.68146$de6.1720(a)newsfe21.iad>:
>
>>> Reminds me. Anyone have any thoughts on why the fifth harmonic on UK
>>> mains at 250Hz is so strong these days?
>>
>> Global warming?
>
>I suspect switched mode PSU's but I can't see why the 5th harmonic is
>now so strong or for that matter where the roughly 623+/-3Hz component
>in my local electrical interference is coming from.

In my place I think there are signals send superimposed to switch between day and night metering.
At night the electricity is cheaper.
But I do not know how many Hz that is, and it is likely not an harmonic,
maybe 623?



>There is a heck of a lot of crossover distortion on our local mains - it
>doesn't look all that much like a sine wave!

Looks nice and clean here...



>I can see other higher frequencies from CFLs but the 5th harmonic of
>mains remains a bit odd. Some days it is the strongest harmonic component.
>
>Regards,
>Martin Brown
From: john jardine on 13 Dec 2009 21:32

"Harold keller" <haroldkeller(a)quantum.com> wrote in message
news:4b2491c4.5812453(a)news.tpg.com.au...
> Can anyone provide information on implementing a 50Hz notch filter for
> data acquisition that operates without phase distortion?
>
> This could be a circuit or dedicated linear phase filter IC.
>
> Harold Keller
>
>

This any help? ...
http://i48.tinypic.com/zsv4nc.jpg

(From Ebay, I'd bought a defunct research institute's complete collection of
that EE magazine. The above circuit was one of about 100 items that were
begging to be scanned to a printable PDF, for light bedtime reading :)






From: miso on 13 Dec 2009 23:11
On Dec 13, 6:32 pm, "john jardine" <zen177...(a)zen.co.uk> wrote:
> "Harold keller" <haroldkel...(a)quantum.com> wrote in message
>
> news:4b2491c4.5812453(a)news.tpg.com.au...
>
> > Can anyone provide information on implementing a 50Hz notch filter for
> > data acquisition that operates without phase distortion?
>
> > This could be a circuit or dedicated linear phase filter IC.
>
> > Harold Keller
>
> This any help? ...http://i48.tinypic.com/zsv4nc.jpg
>
> (From Ebay, I'd bought a defunct research institute's complete collection of
> that EE magazine. The above circuit was one of about 100 items that were
> begging to  be scanned to a printable PDF, for light bedtime reading :)

That is just a notch filter implemented in a different manner. You get
no phase shift at the center frequency, so the subtractor makes a
notch. Really is it no better than building a notch filter in the
first place.

What the original poster failed to mention is over what bandwidth does
he need linear phase. Far away from the notch, the phase error is
small.
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