OT - PC Oscilliscope Performance

[VK1OO, Mike Walkington]

All,

Just found this PC based oscilloscope http://www.bitscope.com/product/BS310/
and wonder what you think of it. Yes you are limited by needing a PC, but
the  waveform generator, spectrum analyser and logic analyser functionality
seem to be most versatile.

Mike
VK1KCK
K2 #2599

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[Don Wilhelm-4]

Mike,

For that price, one could do better with a used Tektronics analog
'scope.  Check with Bob Garcia (Mr. Scope) to see what he has available
([hidden email]) - you may be surprised at what you can obtain
from him.  I speak only as a satisfied customer of Bob's - he is a real
gentleman to do business with.  I believe he is a retired Tek repair
type and usually has several Tek 'scopes available for sale.  He can be
found at hamfests in the SouthEastern US.

Specificlly responding to your quesion:
The 100 MHz rating is good for most HF use, but for most ham purposes,
one does not need the digital storage features.  Remember that the
probes must also have the frequency rating of the 'scope or greater -
the lowest common denominator is the frequency limit.  The digital
storage qualities are nice when investigating digital circuits or power
supply transient responses, but are seldom used for normal ham purposes,
in most cases, one would want a real time display.  The most common use
of a 'scope for ham radio troubleshooting is to measure RF voltages.  
Yes, my 200 MHz  Tek 475 'scope has dual vertiacal channels and delayed
sweep, but most of the time is is used as a single channel 'scope with
normal sweep.  Only investigations of delay parameters and the relative
timing of digital signals require the use of the delayed sweep and both
vertical channels.

Bottom line - if you are into digital stuff, this 'scope may be a
bargain, but for most ham radio related purposes, one can save a lot of
money with an older Tek 'scope (and HP too).

73,
Don W3FPR

Mike Walkington wrote:

> All,
>
> Just found this PC based oscilloscope http://www.bitscope.com/product/BS310/
> and wonder what you think of it. Yes you are limited by needing a PC, but
> the  waveform generator, spectrum analyser and logic analyser functionality
> seem to be most versatile.
>
> Mike
> VK1KCK
> K2 #2599
>
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> You must be a subscriber to post to the list.
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[Dick Green WC1M]

Mike,

You might want to compare the Bitscope 310 with the Velleman PCSU1000 60 MHz
PC-based scope. Depending on where you buy it, the Velleman is about half
the price of the Bitscope. It doesn't have the eight separate logic channels
and built-in function generator, but it has most of the rest of the features
of the Bitscope, and more. The Velleman software appears to be superior,
too, thought I'm only basing that on the feature lists -- haven't actually
used the Bitscope software.

I'm pretty pleased with the Velleman PCSU1000, but there's one task I
haven't been able to get it to do yet: display the CW envelope. I'm not sure
if this is due to not feeding it a clean trigger signal (I think the output
from my keyer needs to be buffered) or if scope sample rate isn't high
enough.

I don't know the exact technical details of how sample rate figures into
these PC-based scopes, but I imagine like any A/D converter they
periodically sample the waveform. The higher the frequency and resolution,
the higher the sample rate required. The Bitscope 310 lists a 40Ms/s maximum
sample rate, and the Velleman has a max of 50Ms/s. The sample rate used
depends on the sweep rate (lower sweep rate = lower sample rate.) But the
Velleman has a 1Gs/S rate that can be switched on for four of the highest
sweep rates (.2us, .-1us, .05us and .02us.) When viewing a 7MHz signal from
my K3, I found the waveform "wobbled" unless I used the 1GS/s modes. Then it
was rock steady.

When displaying the K3 CW envelope, I fed the signal from my keyer into one
channel and the RF into the other channel (I use a Bird RF sampler between
the K3 antenna port and antenna or dummy load.) The keying signal displays
fine, but the CW envelope doesn't. Depending on the volts/div, the display
is anywhere from a random-looking splotch of dots to the waveform you would
expect, but with gaps and holes. The only way I can display the waveform
properly is to use the software's Persist mode, which keeps all traces on
screen. Eventually, the gaps in the trace fill in and I see the waveform
displayed as it should be. But there are limitations when doing this: it's
hard to line up the waveform with the graticule to estimate time duration,
and the Velleman software Waveform Parameters page, a great feature which
displays many measured and calculated values for the waveform, shows a bunch
of question marks. Obviously, the Vellemen doesn't quite know what to make
of the composite waveform.

I mention stability of the keying signal because even when I do this test on
my old HP 1725A 275 MHz scope, the CW envelope wobbles back and forth. I'm
pretty sure this is due to the keying signal not providing a clean trigger
source. I'm planning on building a little buffer circuit for the keyer to
clean up the signal. If the HP can display a steady CW envelope, it's
possible the Velleman can. Otherwise, it may have something to do with the
sample rate being too low. at the slow sweep speed required to display the
CW envelope.

Hope this is helpful.

73, Dick WC1M

> -----Original Message-----
> From: Mike Walkington [mailto:[hidden email]]
> Sent: Friday, September 12, 2008 10:06 PM
> To: Elecraft-Reflector
> Subject: [Elecraft] OT - PC Oscilliscope Performance
>
> All,
>
> Just found this PC based oscilloscope
> http://www.bitscope.com/product/BS310/
> and wonder what you think of it. Yes you are limited by needing a PC,
> but
> the  waveform generator, spectrum analyser and logic analyser
> functionality
> seem to be most versatile.
>
> Mike
> VK1KCK
> K2 #2599
>

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