Marriage is under fire!!

[legg]

On Sat, 28 Aug 2004 10:36:21 +0100, Paul Burridge
<pb@notthisbit.osiris1.co.uk> wrote:

On Fri, 27 Aug 2004 17:43:34 -0700, John Larkin
jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:

Have you actually built a class C linear RF power amp? Tell us how it
works.

It depends on how you define "linear" basically. But the term is a
total misnomer in RF amp terminology and very misleading. I can't
understand how it got there. :-/

I'd always understood that it refered to an operating frequency range
with a wide bandwidth, therefore suited to FM or frequency hopping.

RL

 

[Ken Smith]

In article <1$so5AEWzMMBFw6N@jmwa.demon.co.uk>,
John Woodgate <noone@yuk.yuk> wrote:
[...]

With a **tuned load**, the output power also depends more or less
linearly on the supply voltage, so amplitude modulation can be achieved
by varying the supply voltage.

Small quibble:

you need to add "for a large enough drive" to the above. For small drive
levels the drive and the device gm control the output power.

--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <1$so5AEWzMMBFw6N@jmwa.demon.co.uk>,
John Woodgate <noone@yuk.yuk> wrote:
[...]

But with a **tuned load**, 'linearity' can be achieved even with Class C
biasing. This is why linearity in this case is defined as output power
being proportional to input power.

I think this is right:

If this isn't the slow modulation case, for a single device RF output
stage to work as a linear you need to bias it to about the point where gm
is 1/2 the "mid current" gm. This makes the stage class AB.

If you want to go towards class B or C there are things you can do in the
slow modulation case. Basically as the RF input increases, you move into
class C and as it decreases you move back towards AB. Moving to class C
lowers the output power for large signals a bit so the AB class's standing
current can be reduced by some amount.


--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <5z5Yc.3257$6o3.2610@newsread2.news.atl.earthlink.net>,
Ralph Mowery <rmowery28146@earthlink.net> wrote:
[...]

Any class ( A, B , C ) of amp can be plate modulated for AM. It is then
not really an amplifier.

I disagree with this. If the stage puts out more RF than it takes in, it
is an amplifier even if the purpose of the stage is to be a modulator.


--
--
kensmith@rahul.net forging knowledge

 

[Lord Garth]

"Dubs" <dubspam@yahoo.com> wrote in message
news:e3d356cd.0408281943.5dd6bcb0@posting.google.com...

Hello, I'm not very good with basic electricity, but I'm interested in
running a 200 - 250 ft cable, probably Underground UFB cable as
opposed to an extension cord. I want to run a 17" monitor, a desktop
computer, and 2 or 3 flourescent bulbs. I'm not really to concerned
about the lifespan of my computer's power supply or my monitor. That
stuff is next to free for me. What I'm more worried about is the
money to buy the cable. Is 12 guage cable acceptable? Do I have to
use 10 guage? Are there any fire risks involved if this is all
plugged into a circuit breaker? Does anybody know about any good
deals on cable?

Thanks Folks

The computer power supply, as well as the monitor, should have a label
that lists the acceptable minimum for the applied voltage.

The equipment you list seems like a fairly light load however, use should
uses large gauge wire for long runs. You can also use a double run of
smaller gauge wire. Further, insure you use cable rated for direct burial
or use electrical conduit. If you opt for conduit, slope it and provide a
sump.

Will you be adding a breaker to your service panel to supply this line?

 

[John Woodgate]

I read in sci.electronics.design that Tim Wescott
<tim@wescottnospamdesign.com> wrote (in <10j2acioqmafqec@corp.supernews.
com&gt about 'How to bias a MOSFET amp?', on Sat, 28 Aug 2004:

A system S is linear if and only if for any two input signals x1 and x2
that generate the output signals y1 = S(x1) and y2 = S(x2), and for any
two real constants A1 and A2, the output signal y = S(A1*x1 + A2*x2) is
equal to A1*y1 + A2*y2.

This condition is approached with a properly adjusted RF linear
amplifier, even one operated class AB or B. It is _not_ approached with
a class C amplifier.

The point that the discussion has reached is that the term 'linear' IS
used in a different sense that includes Class C, whether we like it or
not.

So if you define "linear" the way electronics engineering professionals
define "linear" a class A, AB or B amplifier can be made to act
linearly, more or less, and a class C amplifier cannot. So the term
isn't a misnomer, and its use is obvious.

These are the 'electronic engineering professionals' who have 49
different definitions of 'level' in the International Electrotechnical
Vocabulary? (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Winfield Hill]

Robert Baer wrote...

Say you used 12 AWG, that would be about 0.8 ohms; at 2 amps
current (crudely 250 watts) that would give a drop about 1.6 volts
- which is not enough to worry about.

BUT, most computer and monitor power supplies are not PFC, not
power-factor corrected, and draw their current in a short pulse
in the middle of the sine wave. With a stiff source impedance
they draw about 10x the rms current, so that'd be 20A and a 16V
drop. Of course we'd not call 0.8 ohms a stiff source, so the
pulse wold be spread out some and the drop a bit less severe.


--
Thanks,
- Win

(email: use hill_at_rowland-dotties-org for now)

 

[Paul Burridge]

On Sun, 29 Aug 2004 00:48:51 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <5z5Yc.3257$6o3.2610@newsread2.news.atl.earthlink.net>,
Ralph Mowery <rmowery28146@earthlink.net> wrote:
[...]
Any class ( A, B , C ) of amp can be plate modulated for AM. It is then
not really an amplifier.

I disagree with this. If the stage puts out more RF than it takes in, it
is an amplifier

By that definition, it could also be an oscillator!
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[John Woodgate]

I read in sci.electronics.design that Winfield Hill
<Winfield_member@newsguy.com> wrote (in <cgscqi02hbc@drn.newsguy.com&gt
about 'How much Voltage Drop is acceptable for computers? Outdoor
Desktop', on Sun, 29 Aug 2004:

Robert Baer wrote...

Say you used 12 AWG, that would be about 0.8 ohms; at 2 amps
current (crudely 250 watts) that would give a drop about 1.6 volts
- which is not enough to worry about.

BUT, most computer and monitor power supplies are not PFC, not
power-factor corrected, and draw their current in a short pulse
in the middle of the sine wave. With a stiff source impedance
they draw about 10x the rms current, so that'd be 20A and a 16V
drop. Of course we'd not call 0.8 ohms a stiff source, so the
pulse wold be spread out some and the drop a bit less severe.

Considerably less severe. I don't have data for 120 V mains, but this

issue is important for IEC 61000-3-2 and -3, and 0.8 ohms strongly tends
to turn 'rapacious' rectifier loads into pussy-cats.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Paul Burridge]

On Sun, 29 Aug 2004 00:46:11 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

If this isn't the slow modulation case, for a single device RF output
stage to work as a linear you need to bias it to about the point where gm
is 1/2 the "mid current" gm. This makes the stage class AB.

If you want to go towards class B or C there are things you can do in the
slow modulation case. Basically as the RF input increases, you move into
class C and as it decreases you move back towards AB. Moving to class C
lowers the output power for large signals a bit so the AB class's standing
current can be reduced by some amount.

Can't agree. If you're running any amount of standing current, then it
ain't class C.
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Paul Burridge]

On Sun, 29 Aug 2004 02:10:52 GMT, legg <legg@nospam.magma.ca> wrote:

On Sat, 28 Aug 2004 10:36:21 +0100, Paul Burridge
pb@notthisbit.osiris1.co.uk> wrote:

On Fri, 27 Aug 2004 17:43:34 -0700, John Larkin
jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:

Have you actually built a class C linear RF power amp? Tell us how it
works.

It depends on how you define "linear" basically. But the term is a
total misnomer in RF amp terminology and very misleading. I can't
understand how it got there. :-/

I'd always understood that it refered to an operating frequency range
with a wide bandwidth, therefore suited to FM or frequency hopping.

Curious. I have a book (by an author whose name I can't recall off
hand) called "High-Linearity RF Amplifier Design" in which said author
claims that a linear RF amplifier is one in which the transmitted
signal, regardless of however non-linear it may be, is passed through
sufficient filtering to clean it up! Work that one out if you can!
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Paul Burridge]

On 29 Aug 2004 03:57:22 -0700, Winfield Hill
<Winfield_member@newsguy.com> wrote:

Robert Baer wrote...

Say you used 12 AWG, that would be about 0.8 ohms; at 2 amps
current (crudely 250 watts) that would give a drop about 1.6 volts
- which is not enough to worry about.

BUT, most computer and monitor power supplies are not PFC, not
power-factor corrected, and draw their current in a short pulse
in the middle of the sine wave. With a stiff source impedance
they draw about 10x the rms current, so that'd be 20A and a 16V
drop. Of course we'd not call 0.8 ohms a stiff source, so the
pulse wold be spread out some and the drop a bit less severe.

"Stiff source impedance"? I know what you mean, but have never
encountered that curious term before...

--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Anthony]

dude17@sacbeemail.com (~Dude17~) wrote in
news:b959931f.0408290758.2592a92d@posting.google.com:

http://dude17site.tripod.com/printer.html

I suspect it may be the heating coils.

--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

 

[artie]

In article <b959931f.0408290758.2592a92d@posting.google.com>, ~Dude17~
<dude17@sacbeemail.com> wrote:

X-No-Archive: Yes

I've got a laser printer that draws current in spikes and it
makes the lights flicker as well as causing a UPS on the same circuit
to switch over to battery due to excessive dV/dT. Unfortunately, I
don't have a way of putting the printer on its own circuit unless I
want to use a long extension cord.

When it's in sleep state, it draws about 0.22A. When I print
something, it draws about 8A RMS to heat up. After it's done
printing, it stays in "ready to print" state for about ten minutes
before going to sleep and this is where problem starts.

<snip>

heater for the fuser assembly. On the first couple of generations of
laser printers, they didn't even bother to use a zero-crossing switch,
and that really made the lights flicker!

--
Namaste--

 

[John Larkin]

On Sun, 29 Aug 2004 12:49:46 +0100, Paul Burridge
<pb@notthisbit.osiris1.co.uk> wrote:

Can't agree. If you're running any amount of standing current, then it
ain't class C.

Tube class-C amps often self-bias (via grid rectification) when
operating normally. Without drive, they often have high, sometimes
dangerous, idle currents.

John

 

[no_one]

why don't you steal the guts from one of those singing bass fish things;
http://www.howstuffworks.com/singing-fish.htm


"raphihell" <eots@riseup.net> wrote in message
news:13be8fca.0408290818.50f53256@posting.google.com...

Before I begin I should say that we are pretty familiar with most
basic electronics but are really stumped here.

What we are looking for is a circuit that would use very little power-
be battery operated and as small as possible. The idea is to a mic
that would be "listening" to the room it would store a charge relative
to the mic signal- or ideally from the small charge generated by the
mic itself- when this value crossed a certain threshold it would
trigger a serperate circuit- lets say a buzzer. the triggering charge
would be reduced to zero and it would all start over again.

In practice what this would mean is that put on a shelf in an a closed
office- the buzzer might go off once or twice a day assuming the
telephone was used - and if there was an office party it would be
going off all the time.

Now the trick here is that this thing should ideally be able to be
"on" for a few months without draining the battery.

We were thinking of a simple biased capacitor charged by a mic- with
the cap discharging at a certain level- but are having problems.

Any ideas?
Thanks
Raphael and Peter

 

[Paul Burridge]

On Sun, 29 Aug 2004 11:12:18 -0700, John Larkin
<jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote:

Tube class-C amps often self-bias (via grid rectification) when
operating normally. Without drive, they often have high, sometimes
dangerous, idle currents.

Toobz? I was talking of transistors. Many tranny designs for Class C
RF utilize self-bias, too, but there is still no quiescent current!
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[John Larkin]

On Sun, 29 Aug 2004 19:34:57 +0100, Paul Burridge
<pb@notthisbit.osiris1.co.uk> wrote:

On Sun, 29 Aug 2004 11:12:18 -0700, John Larkin
jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote:

Tube class-C amps often self-bias (via grid rectification) when
operating normally. Without drive, they often have high, sometimes
dangerous, idle currents.

Toobz? I was talking of transistors. Many tranny designs for Class C
RF utilize self-bias, too, but there is still no quiescent current!

What makes an amp Class C is a low conduction angle while operating.
When it's not operating, is has no class at all.

John

 

[Robert C Monsen]

"raphihell" <eots@riseup.net> wrote in message
news:13be8fca.0408290818.50f53256@posting.google.com...

Before I begin I should say that we are pretty familiar with most
basic electronics but are really stumped here.

What we are looking for is a circuit that would use very little
power-
be battery operated and as small as possible. The idea is to a mic
that would be "listening" to the room it would store a charge
relative
to the mic signal- or ideally from the small charge generated by the
mic itself- when this value crossed a certain threshold it would
trigger a serperate circuit- lets say a buzzer. the triggering
charge
would be reduced to zero and it would all start over again.

In practice what this would mean is that put on a shelf in an a
closed
office- the buzzer might go off once or twice a day assuming the
telephone was used - and if there was an office party it would be
going off all the time.

Now the trick here is that this thing should ideally be able to be
"on" for a few months without draining the battery.

We were thinking of a simple biased capacitor charged by a mic- with
the cap discharging at a certain level- but are having problems.

Any ideas?
Thanks
Raphael and Peter

One approach would be an analog 'integrator' circuit to keep track of
the charge. Unfortunately, integrators are usually built with
capacitors, and its pretty hard to keep a capacitor charged with tiny
amounts of charge over a long period of time like hours or days; the
cap will leak.

Another way would be to count how many times the microphone went over
a particular input excitation, and use that count as the trigger. You
could do this with CMOS logic chips; perhaps a counter chip activated
by some kind of analog level meter circuit on the microphone. Once a
particular bit on the output went high, fire off the buzzer for a bit
using a C555.

A tiny microcontroller, like a PIC 12F675 or ATTiny would also be a
good choice for this kind of circuit; you could use the internal
comparator to wake it up when the mic was active, and keep track of
the count in its eeprom. It could output the 'buzz' as well, so you
could use a cheap piezo disk rather than a buzzer. Thus, it might be a
single chip solution. It would be very low power, but would require
you to write the software for it. Keeping the microphone powered would
probably take the most of your energy budget. However, you might be
able to power the thing using a small solar panel charging a little
rechargable cell. Offices usually have pretty good light.

This is going to be a fairly complex circuit to pull off, I'm
guessing. Good luck!

Regards,
Bob Monsen

 

[Ian Stirling]

In sci.electronics.design Rich Webb <bbew.ar@mapson.nozirev.ten> wrote:

On 29 Aug 2004 08:58:37 -0700, dude17@sacbeemail.com (~Dude17~) wrote:

X-No-Archive: Yes

I've got a laser printer that draws current in spikes and it
makes the lights flicker as well as causing a UPS on the same circuit
to switch over to battery due to excessive dV/dT. Unfortunately, I
don't have a way of putting the printer on its own circuit unless I
want to use a long extension cord.
snip
At the start of cycle it draws 26A RMS for about 32mS or two cycles
and tapers down to 8.5A RMS after 550mS. Between the start and 550mS,
there's two spikes of about 8mS where current is only drawn from half
of the cycle. After 550mS, the current draw drops to 0.22A RMS, then
starts this whole cycle again after 15 seconds.
snip
it's the heating element for the fuser, maybe a halogen lamp element
inside the fuser cylinder. You're seeing a resistive current draw from
the 60 Hz mains that tapers off as the element heats up and increases
resistance. Your 26 amp initial draw is reasonable for a cold
(relatively) element resistance of around 5 ohms.

One 'easy' way might be to find an appropriate NTC thermistor, and put
it in series with the lamp.

Maybe several small ones for their lower thermal mass.