[Amps] Amps Digest, Vol 142, Issue 35
Isaac Weksler
iweksler at bezeqint.net
Sat Oct 18 13:23:22 EDT 2014
Jeff.
Regarding the PWM type solid state amps. Why not consider EER D-Class solid
state amps? They are quite linear and 90% efficient.
Isaac 4Z1AO
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Subject: Amps Digest, Vol 142, Issue 35
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Today's Topics:
1. Re: Solid State Amps (Chris Wilson)
2. Re: HV Diodes (Carl)
3. Re: Solid State Amps (jeff millar)
----------------------------------------------------------------------
Message: 1
Date: Sat, 18 Oct 2014 17:25:40 +0100
From: Chris Wilson <chris at chriswilson.tv>
To: Manfred Mornhinweg <manfred at ludens.cl>, amps at contesting.com
Subject: Re: [Amps] Solid State Amps
Message-ID: <111338750.20141018172540 at chriswilson.tv>
Content-Type: text/plain; charset=us-ascii
Hello Manfred,
On Saturday, October 18, 2014, you wrote:
<BIG SNIP of fascinating musing>
> Here I agree with you. My FT-736's display is old, tired and very
> dark. The radio has about 130,000 hours on it. Almost all of the time
> the display was kept dimmed, but still it wore out and now I can't
> read it when dimmed, and only barely when undimmed. Guess what? That
> display is a vacuum tube, a fluorescent display. Instead my TS-450's
> display, which is even older and has seen roughly the same amount of
> use, is still perfect. That one is an LCD. But it's special too, and
> the day it fails, I either find a parts donor, or I can operate the
> radio only via computer. I would certainly prefer radios that use
> industry-standard parallel input dot matrix displays, which are made by
many companies, and will remain available for a long time.
> Manfred
Hams should insist that the more exotic and costly new rigs have some means
of using an external monitor instead and as well as the built in display
panel. Personally I think trying to see a waterfall and RF spectrum on the
rigs displays is pretty useless, they need viewing on, at the very least, a
small computer monitor to be worthwhile. With my HP8568B spectrum anaylser
the display tube is obsolete and it's getting harder to find good used
replacements. However it also has a monitor socket to run a separate, (and
much bigger, if desired) display, so all is not lost as it slowly darkens.
The industry standard dot matrix display is a great idea, but what chance
manufacturers agree to such a selfless act of kindness to us end users? ;)
Individuality has its costs...
Chris Wilson 2E0ILY
--
Best regards,
Chris mailto:chris at chriswilson.tv
------------------------------
Message: 2
Date: Sat, 18 Oct 2014 12:27:57 -0400
From: "Carl" <km1h at jeremy.qozzy.com>
To: "Jim Thomson" <jim.thom at telus.net>, <amps at contesting.com>
Subject: Re: [Amps] HV Diodes
Message-ID: <A12EF2B45DB44FB7AD38CDD78A2EE7B7 at computer1>
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reply-type=original
Ive been told by several diode manufacturers that adding all that parallel
resistor and capacitor crap, as they usually called it, could actually be
bad for the circuit.
It took decades before the ARRL finally got with it and removed all their
antiquated drivel once they acquired a team of real engineers to volunteer
and review the HB for serious updating across the board. I dont know if
thats finished yet as I dont buy a HB very often and only then one a few
years old at a hamfest for $5 or so.
FWB flatpacks, at least in the LV category, do generate hash that can be
heard in audio circuits and seen on a scope of course. A .01 across each leg
takes care of that. I suspect they havent changed the technology in them
since the 60-70's as the same part # are still around.
Carl
KM1H
>
> ## You wont see avalanche diodes used in commercial HV
> rectifier assys...used by broadcast. Check out the diode tech notes
> by the diode makers. Even they don?t recommend using super fast diodes
> for 60 hz use....so the super fast types are not required. You wont see eq
> resistors
> across diodes either. The diodes are in series, so they are already
> equalized. The current through em is the same.
> Adding eq resistors will make it worse. The peak dc v is
> equal to the B+. Its 1.41 x the xfmr sec AC voltage.
> A 1 kv ac sec is 1414 vdc. Its not 1414 x 1.41
> Putting a .01 uf cap across each diode is a waste of time.
> All those caps are in series, so total C is minimal. 10 x .01uf
> caps in series = .001 uf..or 1000 pf. You are better off to put
> a .047uf cap... (4700 pf @ 10-15 kv) across each leg of the
> fwb. I wouldnt even do that. Put 1-2 x 4700 pf @ 10-15kv
> disc ceramic bypass caps from output of FWB.....to chassis.
>
> ## On a side note, I measured 506 pf across a 6A10 diode on my lcr
> meter. If you are going to put anything across each diode, a MOV
> would work better. I tested the movs..and I believe they were 910 pf
> each. The movs will conduct well b4 the piv is ever reached. You will
> see movs across diodes on commercial broadcast rect assys.
> You can also put fused movs across the xfmr primary. You can
> also wire several 1 kv rated movs in series, across the sec of the xfmr.
> You can series movs for more V...and parallel em for more joules.
>
> ## You need to do a re-write on your note below. A lot of water has
> passed
> below the bridge. Nobody ever blew out a string of 1N5408s..and that?s
> with nothing
> across em. Just use enough of them... like double or triple the B+
> value..per leg.
> Most commercial ham amps will only use 50% more piv vs B+..and even
> they don?t blow up.
> Take the $$ wasted on eq resistors + .01uf caps..and spend it on more
> 1N5408s...
> or better yet... 6A10s.
>
> Jim VE7RF
>
>
>
>
>
> This really makes one wonder how many times a subject can be covered, in
> detail, over and over.
>
> Let's do this. Here is a little ditty I wrote a long time ago concerning
> rectifiers. At this point it probably is outdated. Still, it might offer
> some insight and some real engineers to come forth and correct it.
>
> I have read many statements, in this thread, that are nothing but
> guessing
> and speculation. The bottom line is we are talking a small difference in
> price to do it right and/or over do it. I always vote for over do myself.
>
> The question of transients is solved using more modern rectifiers or
> avalanche diodes.
>
> Paul
> WD8OSU
>
>
> *What About Those Series Rectifiers?*
>
>
> The use of several rectifier diodes in a series string is often required
> to achieve the Peak Reverse Voltage (PRV) or Peak Inverse Voltage (PIV)
> required for building a High Voltage Power Supply (HVPS). It makes no
> matter if you are talking about a half wave up to and including a full
> wave
> bridge, one needs to be aware of peak voltages involved and required
> component specifications.
>
> Think about that B+ supply for your dream linear. What are we talking
> about here, 2 to 5 or even 6,000 volts DC for that 4-1000A? Woof! That?s a
> hugh amount of PIV that can burn up an improperly designed string in a
> nanosecond. Having personally experienced a string failure I can tell you
> it is not a pretty sight. There is a lot of noise and many projectiles
> flying about. I can give you a couple options in your design and you can
> decide which will achieve the level of operational reliability and
> financial burden you can endure.
>
> Remember, we are talking about ?PEAK? voltage. If you are shooting for
> 3000 volts DC to your plate the ?PEAK? would be 1.41 times this amount or
> 4230 volts! And, this doesn?t count what they call ?mains over voltage?
> typically 5%. That brings us to a grand total of 4441.5 volts. That is
> what
> your poor little rectifier string has to be capable of handling.
>
> Traditionally, normal, everyday, rectifier, diodes were and are used at
> the output of the HV transformer to whip out more or less DC to the filter
> network. The first requirement is the current that is going to be drawn by
> your favorite tube. Don?t forget we are talking about ?peak? current too.
> So, your tube specifications say 1000 milliamps or 1 amp is the maximum
> current your tube likes. Guess what? That?s average not peak current.
> Instantaneous current can be quite a bit higher. No worries, diodes are
> cheap now days and they have relatively high peak current capabilities. I
> like to use a factor of 3 and this is really safe. If you think your tube
> is going to draw 1000 milliamps during normal operation then a 3-amp
> rectifier will be more than enough to cover the load. They can handle peak
> currents much higher than your 4-1000A could stand. Hey, we?re only
> talking
> about maybe 7 cents a piece for the old, reliable, 1N5408.
>
> Now we run into an area that takes up considerable bandwidth on the
> Internet arguing about compensation and/or equalization resistors and
> suppression capacitors in parallel with the diodes. There is a bit of a
> problem when you start stacking a bunch of diodes in series. Especially
> when you use really fast switching diodes, which even the cheapies are
> pretty quick now. Each diode does have it?s own personality and really
> doesn?t conduct or shut off at the same time as all the others. What does
> this mean? Well, basically, it means that there may be voltage differences
> across each diode and noise induced in the output of the HVPS that you
> don?t want. It can even lead to distortion on your transmitted signal.
>
> Like I said, folks in the industry still argue about this. But, I always
> figure better safe than sorry. You can take care of the unequal voltage
> issue by placing equalization resistors in parallel with each diode. This
> insures that each diode sees the same, or close to the same, voltage as
> all
> the others in series.
>
> Now issue number 2, transient voltages across each diode and all the
> little bits of noise they make. When the diodes turn on and off, at
> different times due to their personalities again, they make a bit of noise
> that you don?t necessarily want. There is an issue of unwanted surges too.
> Transients are the little creatures that can cause all kinds of problems
> and come from any of a number of sources. The bad thing about them is they
> don?t always go with the normal flow of current. They are the things, for
> lack of a better explanation, that can make your life miserable and cause
> your standard rectifiers to give up the ghost. This is what all the
> amplifier-building guys are arguing about all the time. How do you stop
> transients?
>
> One old school answer is placing a capacitor in parallel with the diode
> and
> a resistor to make a happy family. OK, OK, I know, the Handbook says not
> to
> do this anymore. Well, ah, what can I say? If in doubt, look over
> STMicroelectronics application note ?AN443? May 2004 and make up your own
> mind. To me a few cents of parts that is not really going to hurt anything
> might be worth it. Is it really going to make a difference? There?s not a
> whole lot of data out there either way. Some say that their semiconductors
> are so good now that you need not bother.
>
> Now, let me give you the ultimate, modern, answer to all the normal
> diode?s problems. Introducing the grandson or granddaughter of the 1N
> whatever diode family, the avalanche diode. These little guys do what a
> normal diode would never do on purpose and survive. Conduct relatively
> large amounts of reverse currents on command. What a concept! These dudes
> switch on and off on command really quick, don?t introduce noise, and are
> all around our power supply friends. Take a look at Dynex Semiconductor?s
> Application Note ?AN5370? to read all about the little marvels.
>
> Yea, they do cost a bit more but not that much. As a matter of fact, after
> you put the bucks into an equalization network for your favorite 1N5408 it
> works out to about the same. Let me give you an example, Fagor makes a
> little number that will do 3 amps at 1000 PRV for about a quarter a piece
> at Allied Electronics (BYM36E). Not bad!
>
> So, sooner or later we always get to the math of it all. Let me give you
> the basics to get done what you need to do. Remember, it is always PEAK!
> Take the plate voltage you are shooting for and multiply that by 1.41 to
> get peak voltage. This is the minimum PRV your diode string should have in
> a full wave bridge I.E. 3000 VDC X 1.41 = 4230 volts peak. This will work
> for normal rectifier diodes.
>
> Avalanche diodes are a bit different, look out now, a safety factor of 2.4
> to 3 times has to be added to the mix. With that in mind, 3000 VDC X 1.41
> X
> (a minimum of 2.4) = 10152 PIV. That jumped right up there didn?t it? Yes,
> you need more avalanche diodes than normal rectifiers. Now, don?t forget
> about this little thing called ? mains over voltage?. That pumps in
> another
> 1.05% to the equation. Let?s see, we were up to 10152 PIV (10152) X 1.05 =
> 10659.6. So, you get 11 avalanche numbers is each leg and your set to go.
>
> You really didn?t think you were going to get all this great avalanche
> stuff for free did you? There is always a trade off isn?t there?
>
> The bottom line is using the avalanche diode is the best way to go for a
> very dependable HVPS and at the price they are affordable, even if it
> takes
> more to get the job done.
>
>
> *Col. Paul E. Cater, WD8OSU, is a Cambridge, Ohio native that returned to
> the area in 1994 after retiring from government service. Mr. Cater is a
> veteran and has been a technician, electronics maintenance officer, field
> service engineer, instructor, signals analyst, and the director of
> training
> for a major government contractor. He currently resides at historic
> Prospect Place Mansion in Trinway, Ohio. *
>
>
> _______________________________________________
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> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
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------------------------------
Message: 3
Date: Sat, 18 Oct 2014 12:52:15 -0400
From: jeff millar <wa1hco at wa1hco.net>
To: amps at contesting.com
Subject: Re: [Amps] Solid State Amps
Message-ID: <54429ABF.1040304 at wa1hco.net>
Content-Type: text/plain; charset=windows-1252; format=flowed
See below...
On 10/17/2014 02:24 PM, Manfred Mornhinweg wrote:
> - Heat. Solid state devices simply are very small, and don't tolerate
extreme
> temperature. So, a high power, class AB, solid state amplifier will ALWAYS
be
> problematic in terms of cooling. It will need large heatsinks, fans, heat
> spreaders, and careful design of the thermal aspects, just to start
becoming
> viable.
PC water cooling technology is able to get rid of 150W of CPU heat from a 1
cm
die with only 10-20 degrees of temperature rise. For an RF amplifier,
allowing
70 degrees of rise, the same CPU thermal block should support 1000W of heat
takeaway per transistor. The best water cooling blocks have thermal
resistance
below 0.03 deg C per Watt, for example see
http://skinneelabs.com/v1-swiftech-mcr-320-qp/4/.
Hams need to think more about the difference between thermal mass and
thermal
resistance. The solid state amp people often add a big heat sink with
copper
and aluminum...that's thermal mass. The thermal resistance is set by the
fans
blowing across the fins. There's really no need for thermal mass when a very
thin bit of copper with water cooling is a much lower thermal resistance
from
Silicon die to water.
>
> - Fragility: RF power transistors are usually run very close to their
absolute
> maximum voltage spec, close to their maximum current spec, and at or even
> above their rated thermal capability, with the heat sink system used. Any
> problem like non-perfect SWR, relay glitches, etc, and their survival
depends
> 100% on excellent protection circuitry. Tubes instead are so forgiving
that in
> practice they don't need protection circuits in most cases, or some tubes
need
> simple circuitry to protect against excessive screen or grid dissipation,
but
> not much else.
Modern RF transistors have enough margin to handle 100% VSWR for some
milliseconds (Freescale MRFE6VP1k25, NXP BLF-188) which is achieved by
having
enough Voltage tolerance to handle peak voltage and enough current/thermal
tolerance to give the shutdown circuits enough time to act.
>
> - Poor linearity: Both bipolar and field effect transistors are less
linear
> than tetrodes and pentodes, and while better than triodes, they don't have
> enough gain to use them in grounded base/gate configuration. So, they
depend
> on negative feedback or other external means, to arrive at good IMD specs.
> Many designers still don't grasp this concept well enough, and try
building
> solid state class AB amplifiers without negative feedback, getting
horrible
> IMD performance.
Many VHF and UHF RF power transistors (typically LDMOS) have good linearity
(-40
dB IMD) because the Cellular market demands it. Then amplifier designers
added
additional linearity with digital pre-distort and typically get a system IMD
of
-60 dB for 10 MHz of bandwidth. Practical pre-distort algorithms can
improve
IMD by 15-20 dB, although lab experiments can show 30 dB improvement in any
one
case.
Achieving good linearity of the transistor requires precise control of the
impedance seen by the part around the peaks of the modulation cycle...which
probably can't be achieved with ham antennas that blow in the wind and get
wet.
So the solution is to use active pre-distort which measures distortion in
real
time and controls the input to the amplifier.
I've been working on the design of a system which samples the RF output of
the
amplifier (or transceiver) and adds pre-distort to the microphone audio to
cancel out distortion. The whole SSB signal chain is linear and the output
is
just the frequency shifted input, so it should work. There are some issues:
for
example a pre-distort system like this would work very hard to cancel out
the
audio compression of the transceiver...so audio compression and frequency
response adjustment would have to occur in the MIC path before the
pre-distort.
>
> Now some people have tried, and are still trying, to solve these problems
by
> brute force methods: Use lots of transistors, on big heatsinks, run them
well
> below their maximum specs, use UHF transistors at HF to get enough gain
that
> allows using lots of negative feedback, and put in complicate protection
> circuits. The results of these efforts can work reasonably well, producing
> amplifiers that are instant-on, no-tune, reliable, and about as large and
> heavy as tube amplifiers - but the solid state ones tend to be more
expensive,
> done that way. And often the implementations are simply wrong and unsafe,
for
> example by relying on an SWR sensor placed between the low pass filters
and
> the antenna.
Agree there is another way to do it.
Protection circuits are not really that complex any more because a $30
Arduino
(or equivalent) can sample the voltages, currents, and RF levels well enough
to
protect the amp. Moore's Law has done it's work. Once a designer commits
to
digitizing and processing many points in the amplifier design for
protection, it
is a relatively short step to increasing the sampling speed and implementing
digital predistortion.
As an aside, what's the problem with a SWR sensor between LPF and antenna?
>
> What we need to do, my dear friends, is something totally different. For
> starters: Forget class AB, because it's too inefficient, and forget
Granberg's
> push-pull configuration, because it has no inherent protection features
and
> needs problematic transformers.
yes
>
> Instead of Granberg's design, we need to place our RF power transistors in
> half bridge or full bridge configurations, with effective antiparallel
diodes.
> This configuration eliminates all risk from overvoltage. Then we need to
run
> our transistors in switchmode, _not_ in any linear mode, to get rid of the
> heat that causes so much trouble. Then we add simple current sensing with
> quick shutdown, to protect against severe overcurrent situations. We need
to
> take the highest voltage transistors we can, up to a level of 400V or so,
to
> get rid of the ultra low impedances that result from low voltage
operation,
> and which are hard to handle. And instead of a broadband transformer (not
very
> easy at the kilowatt level), followed by relay-switched low pass filters,
we
> should use relay-switched resonant matching networks. That's no more
complex
> than the low pass filters, and the resulting Q is low enough to pre-tune
these
> networks to each band and then forget them.
There is an example of these kinds of "amplifiers" from the induction heater
industry. The designs operate IGFETs at line voltage and use pulse width
modulation to generate "RF" at about 50 KHz to drive the heater coil. You
can
get a 1.8 KW hot plate for less than $100. IGFETs don't have the switching
speed to operate at HF frequencies, but we can probably learn from how they
design their systems.
>
> And then, of course we need to add circuitry around the amplifier block,
to
> obtain a linear transfer function despite the switching operation of the
RF
> transistors. This can be done by RF pulse width modulation of the drive
> signal, power supply modulation, bias modulation, a combination of two or
> three of these, or any other method. This is far more complicate than a
> traditional tube amplifier, of course, but it uses cheap, small, widely
> available components, and so it's inexpensive to implement.
A SS high power amplifier consists of a three high power stages; Power
factor
correction, Power Voltage generation, and RF amplification. It's useful to
consider how to use each stage. To some extent, you can consider the power
supply as an RF amplifier operating at HF, the frequencies and design issues
are
similar.
Instead of using PWM for controlling RF output in the RF stage, the
amplifier
can the use the existing PWM in the power supply stage to control the main
power
voltage to the RF amplifier stage. The RF amplifier only sees enough supply
voltage to meet the power output needs of modulation cycle and so operates
at
maximum efficiency at all times with effectively near zero idling current.
Modulating the supply voltage has a hard to predict effect on linearity and
IMD...but we let the digital pre-distort measure and compensate for that in
real
time.
Two other high efficiency techniques from cellular industry should be
considered. Doherty amplfiers and out-phasing. A Doherty amplifier uses a
linear stage and a separate peaking amplifier running in class C.
Outphasing amplifiers modulate the current draw to control RF output (see
"Ampliphase"). The amplifier consists of two output stages in parallel
operating out of phase. When perfectly out of phase the power cancels and
each
amplifier sees a very high impedance load, as the phase shifts to in phase,
the
power output add and the amplifiers see a match load.
The last thing to consider is whether to implement an amplifier or to
implement
a complete transmitter. Power supply modulation and out-phasing techniques
lend
themselves to separating the modulation into amplitude and frequency
components
and it's easier to perform that separation at audio than at RF. The
predistort
system works best on MIC audio so we have control of that part of the
system.
Lastly, the RF power amplifier has 30 dB of gain and doesn't need a 100W
transceiver driving it. We could include something like a Softrock for the
transmitter (and use the receiver for the RF sampling of the output)
>
> The result would be an instant-on, no-tune, small, lightweight, silent,
highly
> efficient, reliable _and_ inexpensive legal limit amplifier.
yes
>
> Anyone actually developing this concept to market maturity can put all
> existing ham amplifier manufacturers out of business. A scaring thought -
for
> them!
no, the old farts will resist ;-)
>
> Do you notice the logic in this? Going from class AB to a switching mode
> achieves several important advantages:
>
> - Cooling becomes very much simpler, cheaper, and silent.
> - Power supply requirements are drastically cut down, producing advantages
in
> cost, size, weight, etc. A 1700W power supply can power a 1500W amplifier.
> - Power consumption is reduced a lot, an important selling point in many
> countries that have expensive electricity. Maybe not in the US, where it
is
> almost free.
> - The transistors needed are very much smaller and cheaper than those
needed
> for class AB, due to low dissipation requirements.
A niggle, but the die will be the same size, and peak thermal density will
be
the same. So, cheaper only if produced in very high quantity because they
are
used in power suppliers or other applications.
> - A good active linearization circuit can produce far better linearity
than
> class AB with 10dB of negative feedback, and even better than that of
tetrodes.
yes. Another aside. In crowded band conditions, the - 30 dB IMD from many
transmitters across the band is the most significant limitation on
communication. Buying an $8000 transceiver with 100 dB of dynamic range
doesn't
do any good when the splatter from 10 nearby stations raises the noise
floor.
I would be in favor of requiring improved IMD in transmitters and power
amplifiers...say -40 dB for 100W transceivers and - 50 dB for 1000W
transmitters. This would drive the state of the art, improve the bands
dramatically.
>
> And the difficulties involved in this approach:
>
> - Finding ways to get around the limitations of present-day RF power
> transistors, in terms of voltage-dependent internal capacitances, slew
rate
> limitations, and high voltage handling.
Solved at VHF with unmatched LDMOS FET's from Freescale and NXP. Will those
work
at HF?
> - Summonning the determination to do all the detail design work, and break
> free from the idea "if Granberg did it that way, that must be the
best/only way".
>
> Any idea, anyone?
The most complex part might be the linearity management system. But that a
separable component with it's own value. We need a box which samples the
RF on
any HF band with 2KW passing through it. A box which generates predistort
on
the mic audio. And the software to process it.
Second most complex part, building an 90% efficient RF stage based on switch
mode (class C) transistors and a modulated power supply voltage. This would
be
coupled with a separation of amplitude and phase in either RF or audio. The
DC
power supply would put out 0 to 50V (or 0 to 400V) with a bandwidth of 3
KHz.
The modulated power supply would have to run at 1 MHz or greater switching
frequency to achieve this bandwidth. The input to the modulated power
supply
would be 400 VDC from power factor corrected direct line rectification.
Where to put the line isolation transformer? The 400 VDC from line
rectification and PFC is not isolated. The modulated power supply is
simpler if
it doesn't have a transformer (would need 2 KW transformer for 1 MHz). Is
it
cheaper to put the transformer in the RF path?
Radical but scary thought, what about just capacitively coupling the RF
output
and skip the whole line isolation completely? The water cooling loops would
have to isolate the RF transistor case from safety ground, that used to work
for
plate voltages and this would only be a few hundred volts.
> Maybe we should start a collaborative open project, developing this thing!
The
> final goal: A solid state amplifier no larger nor heavier than a typical
HF
> radio, that can produce solid legal limit output in all modes, with no
time
> limit, with good IMD performance and high reliability, a total parts cost
> around $500, and selling to those who are too lazy to build it, for around
$1000.
I'm willing to help. I've wanted to do something like this for a while now.
jeff, wa1hco
>
> I'm just waiting for the right transistors to show up, and then I will do
it
> myself. With the transistors I know right now, I would get up to the 40m
band
> only, or at most to 20m, but not to 10.
>
> Manfred
>
> ========================
> Visit my hobby homepage!
> http://ludens.cl
> ========================
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