For a system to oscillate you need positive feedback and a bit of phase
shift.

Our dogs oscillate ! The new 16 week old puppy 'hears something' makes a
very gentle 'almost bark' but really a growl, big sister responds with a
proper bark, to which puppy responds thinking 'well there MUST be something
out there'. So big sister, now hearing a proper bark responds again, and the
pair go off into a crescendo of woofing and barking which can be very
amusing, but not when you're on the 'phone. Anyone else have this ?

Andrew

ps lucky the nearest neighbour is half a mile away

Must be someone else prowling then......:-)

Jim K

Andrew Mawson wrote:
For a system to oscillate you need positive feedback and a bit of phase
shift.

Our dogs oscillate ! The new 16 week old puppy 'hears something' makes a
very gentle 'almost bark' but really a growl, big sister responds with a
proper bark, to which puppy responds thinking 'well there MUST be
something out there'. So big sister, now hearing a proper bark responds
again, and the pair go off into a crescendo of woofing and barking which
can be very amusing, but not when you're on the 'phone. Anyone else have
this ?

On a larger scale you can wake a whole district. When camping in a very
quiet and sparsely populated valley dale or glen, I have sometimes let
the dogs accompany me outside for a **** in the middle of the night. A
butterfly flaps its wings in a nearby bush and the dogs start up. Half a
mile down the valley the outdoor farm dogs take up the cry, and you can
sometimes hear it relayed right down to the town, where further racket
probably ensues.

Bill

On Wed, 16 Apr 2014 21:00:52 +0100
"Andrew Mawson" wrote:

For a system to oscillate you need positive feedback and a bit of
phase shift.

Our dogs oscillate ! The new 16 week old puppy 'hears something'
makes a very gentle 'almost bark' but really a growl, big sister
responds with a proper bark, to which puppy responds thinking 'well
there MUST be something out there'. So big sister, now hearing a
proper bark responds again, and the pair go off into a crescendo of
woofing and barking which can be very amusing, but not when you're on
the 'phone. Anyone else have this ?

Andrew

ps lucky the nearest neighbour is half a mile away


Maybe that Rhea on the loose is in your area?

--
Davey.

It can also happen with just on(possibly slightly dim)dog and his or her own
echo from houses across the field from us. grin.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Andrew Mawson" wrote in message
...
For a system to oscillate you need positive feedback and a bit of phase
shift.

Our dogs oscillate ! The new 16 week old puppy 'hears something' makes a
very gentle 'almost bark' but really a growl, big sister responds with a
proper bark, to which puppy responds thinking 'well there MUST be
something out there'. So big sister, now hearing a proper bark responds
again, and the pair go off into a crescendo of woofing and barking which
can be very amusing, but not when you're on the 'phone. Anyone else have
this ?

Andrew

ps lucky the nearest neighbour is half a mile away

It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of phase
shift.

Our dogs oscillate ! The new 16 week old puppy 'hears something' makes a very
gentle 'almost bark' but really a growl, big sister responds with a proper
bark, to which puppy responds thinking 'well there MUST be something out
there'. So big sister, now hearing a proper bark responds again, and the pair
go off into a crescendo of woofing and barking which can be very amusing, but
not when you're on the 'phone. Anyone else have this ?

Yes, we have an 18month old BC, and her 9 year old big brother. She
seems to deliberately triggers him, just for the hell of it.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On 17/04/14 22:20, Harry Bloomfield wrote:
It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of
phase shift.


negative feedback and enough phase shift/delay works better.
positive feedback just leads in the end to going to infinity...



Our dogs oscillate ! The new 16 week old puppy 'hears something' makes
a very gentle 'almost bark' but really a growl, big sister responds
with a proper bark, to which puppy responds thinking 'well there MUST
be something out there'. So big sister, now hearing a proper bark
responds again, and the pair go off into a crescendo of woofing and
barking which can be very amusing, but not when you're on the 'phone.
Anyone else have this ?

Yes, we have an 18month old BC, and her 9 year old big brother. She
seems to deliberately triggers him, just for the hell of it.



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On Thursday, April 17, 2014 10:31:08 PM UTC+1, The Natural Philosopher wrote:
On 17/04/14 22:20, Harry Bloomfield wrote:
It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of
phase shift.

negative feedback and enough phase shift/delay works better.
positive feedback just leads in the end to going to infinity...

or Vcc


NT

On 16/04/2014 21:00, Andrew Mawson wrote:
For a system to oscillate you need positive feedback and a bit of phase
shift.

As specified by the _Bark_hausen stability criterion:
http://en.wikipedia.org/wiki/Barkhau...lity_criterion

Our dogs oscillate ! The new 16 week old puppy 'hears something' makes a
very gentle 'almost bark' but really a growl, big sister responds with a
proper bark, to which puppy responds thinking 'well there MUST be something
out there'. So big sister, now hearing a proper bark responds again, and the
pair go off into a crescendo of woofing and barking...



--
Graham Nye
news(a)thenyes.org.uk

On 18/04/14 00:00, Tim Streater wrote:
In article , Harry
Bloomfield wrote:

It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of
phase shift.

Our dogs oscillate ! The new 16 week old puppy 'hears something'
makes a
very gentle 'almost bark' but really a growl, big sister responds
with a proper bark, to which puppy responds thinking 'well there
MUST be something out there'. So big sister, now hearing a proper
bark responds again, and the
pair go off into a crescendo of woofing and barking which can be
very amusing,
but not when you're on the 'phone. Anyone else have this ?

Yes, we have an 18month old BC, and her 9 year old big brother. She
seems to deliberately triggers him, just for the hell of it.

Yapping bloody dogs, what's the point of them.

Burglars dont like em, and they bark at anything unusual.



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

In article ,
"Andrew Mawson" writes:
For a system to oscillate you need positive feedback and a bit of phase
shift.

Our dogs oscillate ! The new 16 week old puppy 'hears something' makes a
very gentle 'almost bark' but really a growl, big sister responds with a
proper bark, to which puppy responds thinking 'well there MUST be something
out there'. So big sister, now hearing a proper bark responds again, and the
pair go off into a crescendo of woofing and barking which can be very
amusing, but not when you're on the 'phone. Anyone else have this ?

I think that's simply amplification feedback, rather than oscilation.

In many countries, it's common for office workers to bring their dogs
to work every day. In the Sun offices in California, lots of the
offices had a dog curled up under the desk, and normally so quiet and
well behaved, you never noticed it. Once in a while, one would start
barking, and in a few seconds, the whole office block was barking like
mad. It was very difficult to stop once you have several hundred dogs
barking.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In message , The Natural Philosopher
writes
On 17/04/14 22:20, Harry Bloomfield wrote:
It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of
phase shift.


negative feedback and enough phase shift/delay works better.
positive feedback just leads in the end to going to infinity...


Either something hits a limit - or the whole thing explodes.

Our dogs oscillate ! The new 16 week old puppy 'hears something' makes
a very gentle 'almost bark' but really a growl, big sister responds
with a proper bark, to which puppy responds thinking 'well there MUST
be something out there'. So big sister, now hearing a proper bark
responds again, and the pair go off into a crescendo of woofing and
barking which can be very amusing, but not when you're on the 'phone.
Anyone else have this ?

Yes, we have an 18month old BC, and her 9 year old big brother. She
seems to deliberately triggers him, just for the hell of it.




--
bert

In message , Andrew Gabriel
writes
In article ,
"Andrew Mawson" writes:
For a system to oscillate you need positive feedback and a bit of phase
shift.

Our dogs oscillate ! The new 16 week old puppy 'hears something' makes a
very gentle 'almost bark' but really a growl, big sister responds with a
proper bark, to which puppy responds thinking 'well there MUST be something
out there'. So big sister, now hearing a proper bark responds again, and the
pair go off into a crescendo of woofing and barking which can be very
amusing, but not when you're on the 'phone. Anyone else have this ?

I think that's simply amplification feedback, rather than oscilation.

In many countries, it's common for office workers to bring their dogs
to work every day. In the Sun offices in California, lots of the
offices had a dog curled up under the desk, and normally so quiet and
well behaved, you never noticed it. Once in a while, one would start
barking, and in a few seconds, the whole office block was barking like
mad. It was very difficult to stop once you have several hundred dogs
barking.

Bit like PMQs as John Bercow would tell you.
--
bert

On Thu, 17 Apr 2014 22:31:08 +0100, The Natural Philosopher
wrote:

On 17/04/14 22:20, Harry Bloomfield wrote:
It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of
phase shift.


negative feedback and enough phase shift/delay works better.
positive feedback just leads in the end to going to infinity...

Not necesshairily. You gotta have some form of AGC. Remember the Wein
bridge oscillators? They used a tiny light bulb for the purpose IIRC.
Its resistance changed with the temperature it reached. Nifty.

On Saturday, April 19, 2014 1:12:14 AM UTC+1, Cursitor Doom wrote:
On Thu, 17 Apr 2014 22:31:08 +0100, The Natural Philosopher
wrote:
On 17/04/14 22:20, Harry Bloomfield wrote:
It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of
phase shift.


negative feedback and enough phase shift/delay works better.
positive feedback just leads in the end to going to infinity...
Not necesshairily. You gotta have some form of AGC. Remember the Wein
bridge oscillators? They used a tiny light bulb for the purpose IIRC.
Its resistance changed with the temperature it reached. Nifty.

You need pfb at the resonant frequency, but no pfb at dc.


NT

"Cursitor Doom" wrote in message
...

On Thu, 17 Apr 2014 22:31:08 +0100, The Natural Philosopher
wrote:

On 17/04/14 22:20, Harry Bloomfield wrote:
It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of
phase shift.


negative feedback and enough phase shift/delay works better.
positive feedback just leads in the end to going to infinity...

Not necesshairily. You gotta have some form of AGC. Remember the Wein
bridge oscillators? They used a tiny light bulb for the purpose IIRC.
Its resistance changed with the temperature it reached. Nifty.


Still got a Wein Bridge oscillator that I built when I was 19 - 44 years
ago. The standard design used an R53 thermistor for AGC

Andrew

On 19/04/14 01:12, Cursitor Doom wrote:
On Thu, 17 Apr 2014 22:31:08 +0100, The Natural Philosopher
wrote:

On 17/04/14 22:20, Harry Bloomfield wrote:
It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of
phase shift.


negative feedback and enough phase shift/delay works better.
positive feedback just leads in the end to going to infinity...

Not necesshairily. You gotta have some form of AGC. Remember the Wein
bridge oscillators? They used a tiny light bulb for the purpose IIRC.
Its resistance changed with the temperature it reached. Nifty.

Er that is negative feedback.

And a wein bridge oscillator doesn't use 'positive' feedback, just
negative shifted by 180 degrees at the correct frequency of oscillation.

It will still oscillate at the right freq without the bulb, but the
output will be approximately a square wave.

The trick the bulb is to trim the gain to exactly one, so that only the
sinewave is just enough gain to cause oscillations at all.



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On 19/04/14 02:27, wrote:
On Saturday, April 19, 2014 1:12:14 AM UTC+1, Cursitor Doom wrote:
On Thu, 17 Apr 2014 22:31:08 +0100, The Natural Philosopher
wrote:
On 17/04/14 22:20, Harry Bloomfield wrote:
It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of
phase shift.


negative feedback and enough phase shift/delay works better.
positive feedback just leads in the end to going to infinity...
Not necesshairily. You gotta have some form of AGC. Remember the Wein
bridge oscillators? They used a tiny light bulb for the purpose IIRC.
Its resistance changed with the temperature it reached. Nifty.

You need pfb at the resonant frequency, but no pfb at dc.


You need to understand that pfb at the resonant frequency is nfb,
delayed by half a cycle.


NT



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On Sat, 19 Apr 2014 13:26:45 +0100, The Natural Philosopher
wrote:

On 19/04/14 01:12, Cursitor Doom wrote:
On Thu, 17 Apr 2014 22:31:08 +0100, The Natural Philosopher
wrote:

On 17/04/14 22:20, Harry Bloomfield wrote:
It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of
phase shift.


negative feedback and enough phase shift/delay works better.
positive feedback just leads in the end to going to infinity...

Not necesshairily. You gotta have some form of AGC. Remember the Wein
bridge oscillators? They used a tiny light bulb for the purpose IIRC.
Its resistance changed with the temperature it reached. Nifty.

Er that is negative feedback.

And a wein bridge oscillator doesn't use 'positive' feedback, just
negative shifted by 180 degrees at the correct frequency of oscillation.

It will still oscillate at the right freq without the bulb, but the
output will be approximately a square wave.

The trick the bulb is to trim the gain to exactly one, so that only the
sinewave is just enough gain to cause oscillations at all.

Yeah, I mean you gotta have negative feedback as a component of the
positive feedback loop, in order to ensure that the fed-back signal is
of the correct (pos) phase and doesn't hit the supply rails once the
oscillator gets up to speed. Naturally it needs to allow the
oscillations to build up from the initial switch on. That's why it was
such an elegant solution. Somebody above said it was a thermistor
rather than a lamp and I believe he's dead right. I also recall that
there was only one type which really did the trick beautifully and
that was sadly discontinued years ago.

"Cursitor Doom" wrote in message
...

On Sat, 19 Apr 2014 13:26:45 +0100, The Natural Philosopher
wrote:

On 19/04/14 01:12, Cursitor Doom wrote:
On Thu, 17 Apr 2014 22:31:08 +0100, The Natural Philosopher
wrote:

On 17/04/14 22:20, Harry Bloomfield wrote:
It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of
phase shift.


negative feedback and enough phase shift/delay works better.
positive feedback just leads in the end to going to infinity...

Not necesshairily. You gotta have some form of AGC. Remember the Wein
bridge oscillators? They used a tiny light bulb for the purpose IIRC.
Its resistance changed with the temperature it reached. Nifty.

Er that is negative feedback.

And a wein bridge oscillator doesn't use 'positive' feedback, just
negative shifted by 180 degrees at the correct frequency of oscillation.

It will still oscillate at the right freq without the bulb, but the
output will be approximately a square wave.

The trick the bulb is to trim the gain to exactly one, so that only the
sinewave is just enough gain to cause oscillations at all.

Yeah, I mean you gotta have negative feedback as a component of the
positive feedback loop, in order to ensure that the fed-back signal is
of the correct (pos) phase and doesn't hit the supply rails once the
oscillator gets up to speed. Naturally it needs to allow the
oscillations to build up from the initial switch on. That's why it was
such an elegant solution. Somebody above said it was a thermistor
rather than a lamp and I believe he's dead right. I also recall that
there was only one type which really did the trick beautifully and
that was sadly discontinued years ago.


R53 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Andrew

On Sat, 19 Apr 2014 17:57:31 +0100, "Andrew Mawson"
wrote:

"Cursitor Doom" wrote in message
.. .

On Sat, 19 Apr 2014 13:26:45 +0100, The Natural Philosopher
wrote:

On 19/04/14 01:12, Cursitor Doom wrote:
On Thu, 17 Apr 2014 22:31:08 +0100, The Natural Philosopher
wrote:

On 17/04/14 22:20, Harry Bloomfield wrote:
It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of
phase shift.


negative feedback and enough phase shift/delay works better.
positive feedback just leads in the end to going to infinity...

Not necesshairily. You gotta have some form of AGC. Remember the Wein
bridge oscillators? They used a tiny light bulb for the purpose IIRC.
Its resistance changed with the temperature it reached. Nifty.

Er that is negative feedback.

And a wein bridge oscillator doesn't use 'positive' feedback, just
negative shifted by 180 degrees at the correct frequency of oscillation.

It will still oscillate at the right freq without the bulb, but the
output will be approximately a square wave.

The trick the bulb is to trim the gain to exactly one, so that only the
sinewave is just enough gain to cause oscillations at all.

Yeah, I mean you gotta have negative feedback as a component of the
positive feedback loop, in order to ensure that the fed-back signal is
of the correct (pos) phase and doesn't hit the supply rails once the
oscillator gets up to speed. Naturally it needs to allow the
oscillations to build up from the initial switch on. That's why it was
such an elegant solution. Somebody above said it was a thermistor
rather than a lamp and I believe he's dead right. I also recall that
there was only one type which really did the trick beautifully and
that was sadly discontinued years ago.


R53 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Andrew

Er, excuse me?

On 19/04/14 18:39, Cursitor Doom wrote:
R53 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Andrew
Er, excuse me?

R53 was THE thermistor to use.


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On Sat, 19 Apr 2014 19:22:15 +0100, The Natural Philosopher
wrote:

On 19/04/14 18:39, Cursitor Doom wrote:
R53 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Andrew
Er, excuse me?

R53 was THE thermistor to use.

Oh right. What a bloody shame they're unobtainable now. An effective
alternative is neither simple nor cheap.

On Sat, 19 Apr 2014 22:59:34 +0200, Cursitor Doom
wrote:

On Sat, 19 Apr 2014 19:22:15 +0100, The Natural Philosopher
wrote:

On 19/04/14 18:39, Cursitor Doom wrote:
R53 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Andrew
Er, excuse me?

R53 was THE thermistor to use.

Oh right. What a bloody shame they're unobtainable now. An effective
alternative is neither simple nor cheap.

The alternative lamp filament method is just as effective but it
needs more drive from the oscillator circuit for this to work (that's
the method used by the Thorens TD125 oscillator - you can even see the
lamp filament glowing a dull yellow!).

I couldn't find a suitable thermistor when I was making a test
sinewave oscillator (1, 10 and 18.5 KHz spot frequencies at 0 and
-20dbmW balanced/ unbalanced outputs) 30 odd years ago so I used a 6v
40mA indicator lamp. The only other candidate I had a ready supply of
were 12v 20mA lamps but I think the higher voltage requirement
precluded its use in a circuit powered from a PP3 battery[1]).

As it was, I needed a dark room and night adapted vision to detect
the very dim orange filament glow in that PP3 powered oscillator. The
6v 40mA lamp is right on the edge of usability as a feedback gain
stabiliser in this case.

[1] I also made a mains powered variable frequency Wein bridge
oscillator where I may have taken advantage of the higher DC voltage
bias rails to make use of the 12v 20mW lamp. It's been many years now
since I last saw the circuit diagram I drew up for this project so I
really can't recall which lamp type I'd elected to use.
--
Regards, J B Good

On 20/04/14 00:47, Johny B Good wrote:
On Sat, 19 Apr 2014 22:59:34 +0200, Cursitor Doom
wrote:

On Sat, 19 Apr 2014 19:22:15 +0100, The Natural Philosopher
wrote:

On 19/04/14 18:39, Cursitor Doom wrote:
R53 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Andrew
Er, excuse me?

R53 was THE thermistor to use.

Oh right. What a bloody shame they're unobtainable now. An effective
alternative is neither simple nor cheap.



http://www.ebay.co.uk/itm/R53-BEAD-T...R/181386986139


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

In article , Cursitor Doom
scribeth thus
On Sat, 19 Apr 2014 19:22:15 +0100, The Natural Philosopher
wrote:

On 19/04/14 18:39, Cursitor Doom wrote:
R53 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Andrew
Er, excuse me?

R53 was THE thermistor to use.

Oh right. What a bloody shame they're unobtainable now. An effective
alternative is neither simple nor cheap.

I think theres on in the junk box .. somewhere;!...
--
Tony Sayer

On Sun, 20 Apr 2014 13:18:04 +0100, tony sayer
wrote:

In article , Cursitor Doom
scribeth thus
On Sat, 19 Apr 2014 19:22:15 +0100, The Natural Philosopher
wrote:

On 19/04/14 18:39, Cursitor Doom wrote:
R53 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Andrew
Er, excuse me?

R53 was THE thermistor to use.

Oh right. What a bloody shame they're unobtainable now. An effective
alternative is neither simple nor cheap.

I think theres on in the junk box .. somewhere;!...

And yet with much higher frequencies like in the RF spectrum it's not
a problem; tuned circuits take care of it!

On Saturday, April 19, 2014 1:27:53 PM UTC+1, The Natural Philosopher wrote:
On 19/04/14 02:27, wrote:
On Saturday, April 19, 2014 1:12:14 AM UTC+1, Cursitor Doom wrote:
On Thu, 17 Apr 2014 22:31:08 +0100, The Natural Philosopher
wrote:
On 17/04/14 22:20, Harry Bloomfield wrote:
It happens that Andrew Mawson formulated :
For a system to oscillate you need positive feedback and a bit of
phase shift.


negative feedback and enough phase shift/delay works better.
positive feedback just leads in the end to going to infinity...
Not necesshairily. You gotta have some form of AGC. Remember the Wein
bridge oscillators? They used a tiny light bulb for the purpose IIRC.
Its resistance changed with the temperature it reached. Nifty.

You need pfb at the resonant frequency, but no pfb at dc.

You need to understand that pfb at the resonant frequency is nfb,
delayed by half a cycle.

which is pfb at that frequency


NT