How good is your scope? (problem with capturing offset signals)

Klaus Bahner <Klaus.Bahner@ieee.org> wrote in 
news:4e81ca00$0$56771$edfadb0f@dtext02.news.tele.dk:

> Klaus Kragelund wrote:
> 
>> Hi
>> 
>> So I wanted to check the VCE of a transistor in a small converter
>> running at 100kHz, expected to see about 100mV above ground as the
>> saturation voltage of the NPN, increasing linearely since magnetising
>> current increasing.
>> 
>> I saw nothing like that, debugging and found the scope (Tek DPO5000)
>> somehow saturates with high voltage inputs. The signal is a square
>> wave of 100kHz, 25V peak to peak, offset so low voltage is close to
>> GND (measured by a 10:1 probe)
>> 
>> See plot (green trace):
>> 
>> www.electronicsdesign.dk/tmp/2.jpg
>> 
>> Low value is about 400mV
>> 
>> Ok, changed the scale div from 3V/div to 2V/div then this:
>> 
>> www.electronicsdesign.dk/tmp/1.jpg
>> 
>> Now low value is about 2.4V !
>> 
> 
> Interesting. Just a question of understanding (I'm not a user of Tek 
> scopes, hence apologies if I miss the obvious information): in the 
> screen shots there are different numbers of acquisitions displayed (86 
> vs. 226). Is the scope set into averaging mode? And what is the coupling 
> you selected, AC or DC?
> 
> Besides set I only can tell you that I never ran into this problem with 
> my LeCroy scope and I did that kind of overdrive measurements on an 
> almost daily basis. So, if this is problem is for real, then I dare 
> conclude that not all scopes are affected by it :-)
> 
> Klaus
> 

there's no substitute for the old TEK 7000 series and the 7A13 or 7A22 
differential plug-ins!

-- 
Jim Yanik
jyanik
at
localnet
dot com

Joerg wrote:
>>Besides set I only can tell you that I never ran into this problem with
>>my LeCroy scope and I did that kind of overdrive measurements on an
>>almost daily basis. So, if this is problem is for real, then I dare
>>conclude that not all scopes are affected by it :-)
>>
> 
> 
> Overdrive it past 10x and see. If it can do 100x without flinching then
> they did the amp design about right.
> 
Well, I don't have access to this scope any longer (sigh), so I can't 
check it again - would love to, because before this thread I wasn't 
aware of this overdrive problem at all. And of course I wonder now, 
whether this is because the scope was free of those problem or whether I 
did a bad job on analyzing my results :-(

However, a case I clearly remember was a 2kV pulser design, where the 
major design goal was fast and clean recovery to 0V after the pulse. An 
"offset" voltage in the 1V range was significant, hence I made tons of 
measurements with lots of overdrive (>100x).  Didn't observe any strange 
things during these measurement with that scope (Waverunner 6050).

Please, don't tell me now that this design was just a perceived success 
because overdrive issues acted in the right direction :-(

Well, the pulser worked fine in its intended application, so I take that 
as an argument for that the scope didn't lie. :-)

Cheers,
Klaus

Klaus Bahner wrote:
> Joerg wrote:
>>> Besides set I only can tell you that I never ran into this problem with
>>> my LeCroy scope and I did that kind of overdrive measurements on an
>>> almost daily basis. So, if this is problem is for real, then I dare
>>> conclude that not all scopes are affected by it :-)
>>>
>>
>>
>> Overdrive it past 10x and see. If it can do 100x without flinching then
>> they did the amp design about right.
>>
> Well, I don't have access to this scope any longer (sigh), so I can't
> check it again - would love to, because before this thread I wasn't
> aware of this overdrive problem at all. And of course I wonder now,
> whether this is because the scope was free of those problem or whether I
> did a bad job on analyzing my results :-(
> 
> However, a case I clearly remember was a 2kV pulser design, where the
> major design goal was fast and clean recovery to 0V after the pulse. An
> "offset" voltage in the 1V range was significant, hence I made tons of
> measurements with lots of overdrive (>100x).  Didn't observe any strange
> things during these measurement with that scope (Waverunner 6050).
> 

That would be nice if it had the performance of the good old analog
scopes. What I personally do not like about many LeCroy scopes is the
sluggish Windows interface.


> Please, don't tell me now that this design was just a perceived success
> because overdrive issues acted in the right direction :-(
> 
> Well, the pulser worked fine in its intended application, so I take that
> as an argument for that the scope didn't lie. :-)
> 

Who knows, but the main thing is that your circuit works and that the
firefighters did not have to come out there :-)

Sometimes such situations can be remedied by using a separate amplifier
in front of the scopes. An amp from the good old days when they still
knew how to design them well. This is one of the reasons why I have an
HP dual amp with 20dB each here. Small, so I can carry that to clients
where it is likely that I have to do pulse measurements and they only
have "modern" analyzers. Fits easily into my carry-on bag but the
security folks sometimes want to know what it is.

-- 
Regards, Joerg

http://www.analogconsultants.com/

On Sep 27, 10:13=A0am, Joerg <inva...@invalid.invalid> wrote:
> Klaus Kragelund wrote:
> > On 27 Sep., 08:25, Jon Kirwan <j...@infinitefactors.org> wrote:
> >> On Mon, 26 Sep 2011 16:28:18 -0700 (PDT), Klaus Kragelund
>
> >> <klausk...@hotmail.com> wrote:
> >>> <snip>
> >>> Seems I should throw out the 10k USD scope and bring my 1k USD Hameg
> >>> to work for some real measurements....
> >> Somehow this reminds me of the old Sorcerer in Aladdin crying
> >> out, "New lamps for old. =A0New lamps for old," trying to
> >> recover that special, magic lamp.
>
> >> (Replace lamp with oscilloscope....)
>
> >> :)
>
> >> Jon
>
> > Hmm, just found an app note from Tektronix on this:
>
> >http://cp.literature.agilent.com/litweb/pdf/5989-0068EN.pdf
>
> Quote "There is a misconception that some oscilloscopes can tolerate
> overdrive conditions, whereas others cannot."
>
> Tell Tektronix that this is not a misconception but it is true. Or
> better yet, tell them to visit some nursing homes around Beaverton
> during lunch time and ask anyone who was an engineer at Tektronix to
> raise their hand. Then they should ask them how it's done right :-)
>
> I just tried it out. I have to send my Instek GDS-2204 (digital scope)
> into 10x overdrive until it distorts. It shouldn't even distort there
> but, oh well, this is a <$2k digital scope. And as expected, the Tek
> 7704 has none of those problems at all, remains true all the way to
> 5mV/div. This is why I was saying all along, Tektronix should operate a
> nursing home for very old engineers and their wifes on their campus.
> Kind of like the Japanese way, where older generations teach the younger.
>
> >http://www.kemt.fei.tuke.sk/predmety/KEMT434_RM/_materialy/Doplnkove%...
>
> > Overdrive seems to be the problem
>
> It shouldn't be. There are risetime limits, of course, but it should not
> suddenly and drasticaly alter the waveform or lose the offset. If I had
> designed ultrasound frontends that way they'd have fired me. Those are
> expected to remain true even in a +40dB overdrive situation.
>
> > However it is typically specified as less than 20ns, i am seeing a lot
> > more. But perhaps thats due to excessive overdrive. Funny enough the
> > DPO5034 does not mention anything about that in the datasheet
>
> > I have been in contact with Tek, and they keep telling me to update
> > the SW of the scope :-)
>
> That's the standard answer I guess. Like when you call your telco
> because the broadband went out. "Sir, please re-install the software".
> Yeah, right :-)
>
> --
> Regards, Joerg
>
> http://www.analogconsultants.com/- Hide quoted text -
>
> - Show quoted text -

Well my cheap TEK 1001B has a recovery time of 2-3 us.  With anything
more than 2 volts on the 200mV/div scale.  It craps up the top of the
pulse too!  My pulser won't do much more than 10V peak so I can't
check the 500mV/div scale beyond that.

My Rigol DS1052 is even worse... again it craps out at 200mV/div...
but it takes like 10 ms to recover!

George H.

George Herold wrote:
> On Sep 27, 10:13 am, Joerg <inva...@invalid.invalid> wrote:
>> Klaus Kragelund wrote:
>>> On 27 Sep., 08:25, Jon Kirwan <j...@infinitefactors.org> wrote:
>>>> On Mon, 26 Sep 2011 16:28:18 -0700 (PDT), Klaus Kragelund
>>>> <klausk...@hotmail.com> wrote:
>>>>> <snip>
>>>>> Seems I should throw out the 10k USD scope and bring my 1k USD Hameg
>>>>> to work for some real measurements....
>>>> Somehow this reminds me of the old Sorcerer in Aladdin crying
>>>> out, "New lamps for old.  New lamps for old," trying to
>>>> recover that special, magic lamp.
>>>> (Replace lamp with oscilloscope....)
>>>> :)
>>>> Jon
>>> Hmm, just found an app note from Tektronix on this:
>>> http://cp.literature.agilent.com/litweb/pdf/5989-0068EN.pdf
>> Quote "There is a misconception that some oscilloscopes can tolerate
>> overdrive conditions, whereas others cannot."
>>
>> Tell Tektronix that this is not a misconception but it is true. Or
>> better yet, tell them to visit some nursing homes around Beaverton
>> during lunch time and ask anyone who was an engineer at Tektronix to
>> raise their hand. Then they should ask them how it's done right :-)
>>
>> I just tried it out. I have to send my Instek GDS-2204 (digital scope)
>> into 10x overdrive until it distorts. It shouldn't even distort there
>> but, oh well, this is a <$2k digital scope. And as expected, the Tek
>> 7704 has none of those problems at all, remains true all the way to
>> 5mV/div. This is why I was saying all along, Tektronix should operate a
>> nursing home for very old engineers and their wifes on their campus.
>> Kind of like the Japanese way, where older generations teach the younger.
>>
>>> http://www.kemt.fei.tuke.sk/predmety/KEMT434_RM/_materialy/Doplnkove%...
>>> Overdrive seems to be the problem
>> It shouldn't be. There are risetime limits, of course, but it should not
>> suddenly and drasticaly alter the waveform or lose the offset. If I had
>> designed ultrasound frontends that way they'd have fired me. Those are
>> expected to remain true even in a +40dB overdrive situation.
>>
>>> However it is typically specified as less than 20ns, i am seeing a lot
>>> more. But perhaps thats due to excessive overdrive. Funny enough the
>>> DPO5034 does not mention anything about that in the datasheet
>>> I have been in contact with Tek, and they keep telling me to update
>>> the SW of the scope :-)
>> That's the standard answer I guess. Like when you call your telco
>> because the broadband went out. "Sir, please re-install the software".
>> Yeah, right :-)
>>
>> --
>> Regards, Joerg
>>
>> http://www.analogconsultants.com/- Hide quoted text -
>>
>> - Show quoted text -
> 
> Well my cheap TEK 1001B has a recovery time of 2-3 us.  With anything
> more than 2 volts on the 200mV/div scale.  It craps up the top of the
> pulse too!  My pulser won't do much more than 10V peak so I can't
> check the 500mV/div scale beyond that.
> 
> My Rigol DS1052 is even worse... again it craps out at 200mV/div...
> but it takes like 10 ms to recover!
> 

What on earth are they doing wrong? 10msec sounds like they screwed up
majorly, with some supply rail going out of whack. 2-3usec might be the
use of wrong clamping diodes. Someone should teach those engineers, and
soon. Anyhow, I'd send those two scopes back for a full refund unless
you are past the time limit for that. Then buy something better.

My Instek scope does distort a bit if I go past 10x. It is fairly minor
saturation which isn't nice but at least I cannot see any recovery time.
It's instant. If I go beyond 100x the trigger "loses it".

Of course, the trusty old Tex 7704 and its 7A26 insert sail through all
that without flinching. I don't know whats so difficult about that. In
ultrasound we build amplifiers that must listen to microvolts and they
get hit with pulses of up to 200V. Takes some time but I didn't find
such designs particularly difficult to do. It's not rocket science.

-- 
Regards, Joerg

http://www.analogconsultants.com/

On 27 Sep., 15:05, Klaus Bahner <Klaus.Bah...@ieee.org> wrote:
> Klaus Kragelund wrote:
> > Hi
>
> > So I wanted to check the VCE of a transistor in a small converter
> > running at 100kHz, expected to see about 100mV above ground as the
> > saturation voltage of the NPN, increasing linearely since magnetising
> > current increasing.
>
> > I saw nothing like that, debugging and found the scope (Tek DPO5000)
> > somehow saturates with high voltage inputs. The signal is a square
> > wave of 100kHz, 25V peak to peak, offset so low voltage is close to
> > GND (measured by a 10:1 probe)
>
> > See plot (green trace):
>
> >www.electronicsdesign.dk/tmp/2.jpg
>
> > Low value is about 400mV
>
> > Ok, changed the scale div from 3V/div to 2V/div then this:
>
> >www.electronicsdesign.dk/tmp/1.jpg
>
> > Now low value is about 2.4V !
>
> Interesting. Just a question of understanding (I'm not a user of Tek
> scopes, hence apologies if I miss the obvious information): in the
> screen shots there are different numbers of acquisitions displayed (86
> vs. 226). Is the scope set into averaging mode? And what is the coupling
> you selected, AC or DC?
>

The number is number of aquisitions made, in essense the number of
triggers (screen plots) since you last pressed "Run". I did not use
averaging, but if I had, then you can see by that number how many data
sets the current plot is made from.

> Besides set I only can tell you that I never ran into this problem with
> my LeCroy scope and I did that kind of overdrive measurements on an
> almost daily basis. So, if this is problem is for real, then I dare
> conclude that not all scopes are affected by it :-)
>

It could be interesting to try that with a Lecroy. I will try to see
if we have one in the lab somewhere :-)

Regards

Klaus

On 27 Sep., 16:13, Joerg <inva...@invalid.invalid> wrote:
> Klaus Kragelund wrote:
> > On 27 Sep., 08:25, Jon Kirwan <j...@infinitefactors.org> wrote:
> >> On Mon, 26 Sep 2011 16:28:18 -0700 (PDT), Klaus Kragelund
>
> >> <klausk...@hotmail.com> wrote:
> >>> <snip>
> >>> Seems I should throw out the 10k USD scope and bring my 1k USD Hameg
> >>> to work for some real measurements....
> >> Somehow this reminds me of the old Sorcerer in Aladdin crying
> >> out, "New lamps for old. =A0New lamps for old," trying to
> >> recover that special, magic lamp.
>
> >> (Replace lamp with oscilloscope....)
>
> >> :)
>
> >> Jon
>
> > Hmm, just found an app note from Tektronix on this:
>
> >http://cp.literature.agilent.com/litweb/pdf/5989-0068EN.pdf
>
> Quote "There is a misconception that some oscilloscopes can tolerate
> overdrive conditions, whereas others cannot."
>
> Tell Tektronix that this is not a misconception but it is true. Or
> better yet, tell them to visit some nursing homes around Beaverton
> during lunch time and ask anyone who was an engineer at Tektronix to
> raise their hand. Then they should ask them how it's done right :-)
>
> I just tried it out. I have to send my Instek GDS-2204 (digital scope)
> into 10x overdrive until it distorts. It shouldn't even distort there
> but, oh well, this is a <$2k digital scope. And as expected, the Tek
> 7704 has none of those problems at all, remains true all the way to
> 5mV/div. This is why I was saying all along, Tektronix should operate a
> nursing home for very old engineers and their wifes on their campus.
> Kind of like the Japanese way, where older generations teach the younger.
>
> >http://www.kemt.fei.tuke.sk/predmety/KEMT434_RM/_materialy/Doplnkove%...
>
> > Overdrive seems to be the problem
>
> It shouldn't be. There are risetime limits, of course, but it should not
> suddenly and drasticaly alter the waveform or lose the offset. If I had
> designed ultrasound frontends that way they'd have fired me. Those are
> expected to remain true even in a +40dB overdrive situation.
>


That why I didn't believe my measurements was correct when I first saw
it, seems logical to me that I can do whatever with the gain setting
without the scope representing the data incorrectly. At least such a
scope with a lot of SW whould have waved a flag in front of my nose
that I cannot trust current measurements due to saturation effects.

> > However it is typically specified as less than 20ns, i am seeing a lot
> > more. But perhaps thats due to excessive overdrive. Funny enough the
> > DPO5034 does not mention anything about that in the datasheet
>
> > I have been in contact with Tek, and they keep telling me to update
> > the SW of the scope :-)
>
> That's the standard answer I guess. Like when you call your telco
> because the broadband went out. "Sir, please re-install the software".
> Yeah, right :-)

Today I asked them to find a analog guy from Tektronix, I won't spend
any more time from guesswork by the first line of defence at Tek :-)

Regards

Klaus

On 27 Sep., 19:45, George Herold <gher...@teachspin.com> wrote:
> On Sep 27, 10:13=A0am, Joerg <inva...@invalid.invalid> wrote:
>
>
>
>
>
> > Klaus Kragelund wrote:
> > > On 27 Sep., 08:25, Jon Kirwan <j...@infinitefactors.org> wrote:
> > >> On Mon, 26 Sep 2011 16:28:18 -0700 (PDT), Klaus Kragelund
>
> > >> <klausk...@hotmail.com> wrote:
> > >>> <snip>
> > >>> Seems I should throw out the 10k USD scope and bring my 1k USD Hame=
g
> > >>> to work for some real measurements....
> > >> Somehow this reminds me of the old Sorcerer in Aladdin crying
> > >> out, "New lamps for old. =A0New lamps for old," trying to
> > >> recover that special, magic lamp.
>
> > >> (Replace lamp with oscilloscope....)
>
> > >> :)
>
> > >> Jon
>
> > > Hmm, just found an app note from Tektronix on this:
>
> > >http://cp.literature.agilent.com/litweb/pdf/5989-0068EN.pdf
>
> > Quote "There is a misconception that some oscilloscopes can tolerate
> > overdrive conditions, whereas others cannot."
>
> > Tell Tektronix that this is not a misconception but it is true. Or
> > better yet, tell them to visit some nursing homes around Beaverton
> > during lunch time and ask anyone who was an engineer at Tektronix to
> > raise their hand. Then they should ask them how it's done right :-)
>
> > I just tried it out. I have to send my Instek GDS-2204 (digital scope)
> > into 10x overdrive until it distorts. It shouldn't even distort there
> > but, oh well, this is a <$2k digital scope. And as expected, the Tek
> > 7704 has none of those problems at all, remains true all the way to
> > 5mV/div. This is why I was saying all along, Tektronix should operate a
> > nursing home for very old engineers and their wifes on their campus.
> > Kind of like the Japanese way, where older generations teach the younge=
r.
>
> > >http://www.kemt.fei.tuke.sk/predmety/KEMT434_RM/_materialy/Doplnkove%.=
..
>
> > > Overdrive seems to be the problem
>
> > It shouldn't be. There are risetime limits, of course, but it should no=
t
> > suddenly and drasticaly alter the waveform or lose the offset. If I had
> > designed ultrasound frontends that way they'd have fired me. Those are
> > expected to remain true even in a +40dB overdrive situation.
>
> > > However it is typically specified as less than 20ns, i am seeing a lo=
t
> > > more. But perhaps thats due to excessive overdrive. Funny enough the
> > > DPO5034 does not mention anything about that in the datasheet
>
> > > I have been in contact with Tek, and they keep telling me to update
> > > the SW of the scope :-)
>
> > That's the standard answer I guess. Like when you call your telco
> > because the broadband went out. "Sir, please re-install the software".
> > Yeah, right :-)
>
> > --
> > Regards, Joerg
>
> >http://www.analogconsultants.com/-Hide quoted text -
>
> > - Show quoted text -
>
> Well my cheap TEK 1001B has a recovery time of 2-3 us. =A0With anything
> more than 2 volts on the 200mV/div scale. =A0It craps up the top of the
> pulse too! =A0My pulser won't do much more than 10V peak so I can't
> check the 500mV/div scale beyond that.
>
> My Rigol DS1052 is even worse... again it craps out at 200mV/div...
> but it takes like 10 ms to recover!
>

I saw the same thing with the 12bit USB Picoscope, took forever to
return to the correct level. Really crappy design. It has 12bit
resolution however, so I could zoom in on the vertical axis and get
resonable resolution for low signals

Like Joerg says, this is not rocket science, but I guess it maybe a
test the Scope engineers may omit intentioally to save a buck or
perhaps they are not aware that some engineers/users would like good
performance at such an stimuli.

Regards

Klaus

On 27 Sep., 02:15, Joerg <inva...@invalid.invalid> wrote:
> Klaus Kragelund wrote:
> > Hi
>
> > So I wanted to check the VCE of a transistor in a small converter
> > running at 100kHz, expected to see about 100mV above ground as the
> > saturation voltage of the NPN, increasing linearely since magnetising
> > current increasing.
>
> > I saw nothing like that, debugging and found the scope (Tek DPO5000)
> > somehow saturates with high voltage inputs. The signal is a square
> > wave of 100kHz, 25V peak to peak, offset so low voltage is close to
> > GND (measured by a 10:1 probe)
>
> > See plot (green trace):
>
> >www.electronicsdesign.dk/tmp/2.jpg
>
> > Low value is about 400mV
>
> > Ok, changed the scale div from 3V/div to 2V/div then this:
>
> >www.electronicsdesign.dk/tmp/1.jpg
>
> I believe you set it from 3V/div to 600mV/div for channel 4.
>
> > Now low value is about 2.4V !
>
> Can't follow that but I think it's 400mV. Which is weird, assuming you
> haven't changed the offset (or the scope didn't do that because it
> thought you might have wanted to ...).
>
>
>
>
>
> > I checked it was not my setup and all is fine.
>
> > So I then hooked up the HP33120A function generator, with a BNC
> > directly to the scope, now the problem still exists, but just at
> > another volt/div setting (probably since the probe P500 has internal
> > scaling etc). The signal, square wave, 9Vpp, 4.5V offset, 100kHz) (a
> > levelshifted 9Vpp signal above GND)
>
> > My suspicion is that the input stage of the scope is saturated since
> > the top level of the signal is way out of bounds. If I reduce the
> > frequency to 1kHz, then the signal starts to look good again, which
> > tells me the input stage of the scope has settled and recovered from
> > the overdrive.
>
> > Then for a sanity check I hooked up a Tek TDS3032B and it showed the
> > correct signal all the way down to 20mV/Div setting
>
> > Then I took a Tek DPO4000 scope, and it had the same fault, allthough
> > at a different volt/div setting
>
> That is rather surprising.
>
> > Tried with a TDS220 (low end scope), it has the fault beginning at
> > below 2V/div
>
> I've never trusted those things.
>
> > Tried a PicoScope 3000 series, had the fault at below 2V/div
>
> > Tried a Agilent DSO 4000 series, had the fault at AFAIR 5V/div
>
> > Then dusted off my first scope, the Hameg 205-3, it worked all the way
> > down to 100mV/div :-)
>
> Well, good old German quality :-)
>
> > To the question, do any of you guys know the front-ends of scopes and
> > if so is my assumption that the input stage is saturated correct (so
> > the amp takes time to recover)?
>
> > Seems I should throw out the 10k USD scope and bring my 1k USD Hameg
> > to work for some real measurements....
>
> In a nutshell, yes. Maybe not throw out the $10k scope though but I'd
> send this info to Tektronix support. If they can't answer I'd ask the
> sales rep who sold it to you to come out there.
>
> I can't count the times where I've had to ask clients "Do you have a
> real scope?" and out came a big old Tektronix boat anchor where people
> took a step back when I pulled the power switch handle ... bzzzt ...
> TUNGGGG ... blueish green traces showed up and ... tada ... fuzz could
> be seen that the DSO simply was unable to show.
>
> Here I have a Tektronix 7704, a Telequipment D66 and I also still have
> my old Hameg that I had as a highschool student (but that doesn't get
> used much anymore). I would not want to be without a real scope. They
> don't make them like that anymore. So if your workplace does not have
> something like a Tek 7000 series or a Tek 2465 I'd ask them to go on
> Ebay and get one :-)
>
> --

Hey, its even cheap, goes for 200 USD at ebay, has a geek factor too

If it breaks, you can just buy a new one :-)

Regards

Klaus

Klaus Kragelund wrote:
> On 27 Sep., 02:15, Joerg <inva...@invalid.invalid> wrote:
>> Klaus Kragelund wrote:
>>

[...]


>> Here I have a Tektronix 7704, a Telequipment D66 and I also still have
>> my old Hameg that I had as a highschool student (but that doesn't get
>> used much anymore). I would not want to be without a real scope. They
>> don't make them like that anymore. So if your workplace does not have
>> something like a Tek 7000 series or a Tek 2465 I'd ask them to go on
>> Ebay and get one :-)
>>
>> --
> 
> Hey, its even cheap, goes for 200 USD at ebay, has a geek factor too
> 
> If it breaks, you can just buy a new one :-)
> 

Keep in mind that any 7000 series scopes are back-breakingly heavy so
the shipping charges will be high. The fact that it has a handle does
not mean it is portable :-)

The flat R-versions are probably less heavy but also much more expensive.

-- 
Regards, Joerg

http://www.analogconsultants.com/