[Test-Equipment] Oscilloscopes

[Edward J White]

Hi John:
What would you recommend for a analog high freq 400 MHz + bench not portable 
scope? 8754?
Ed
WA3BZT
----- Original Message ----- 
From: "J. Forster" <jfor at quik.com>
To: "Edward J White" <wa3bzt at verizon.net>
Cc: "Test Equipment" <Test-Equipment at mailman.qth.net>
Sent: Saturday, March 19, 2005 5:35 PM
Subject: Re: [Test-Equipment] Oscilloscopes


> Apples and oranges.
>
> Digital scopes sample the waveform at intervals. The important spec is the
> sampling rate (samples/second). The sampling theorem applies in that 1 GHz
> sampling rate cannot reproduce a sine wave of more than 500 MHz. In fact, 
> you
> likely cannot tell the difference between a sine and a square 500 MHz 
> waveform.
> There are also problems with 'aliasing' or the folding over of frequency 
> space
> (because sampling is like mixing which causes upper and lower side bands 
> to fold
> into the lower side band and makes a hash of things. Tek introduced 
> 'random'
> sampling to lessen this problem.
>
> Also, sampling often requires a repetitive waveform (a Tek 7S11  and S6 
> cannot
> see a 35 ps 1 shot waveform, despite the spec)
>
> Analog scopes have a 3 dB BW spec and degrade gracefully.
>
> As to RF, scopes are not all that useful above 100 MHz or lower. They 
> really
> don't tell you much, except modulation depth on AM (AM is less common 
> above 30
> MHz). You really want a spectrum analyzer, or if testing components, a 
> scalar or
> vector Network Analyzer.
>
> -John
>
>
>
> Edward J White wrote:
>
>> Hi Gang:
>> Wile on the subject of oscilloscopes what is the difference between the
>> digital and analog scopes? I read  speed or should we say bandwidth of 
>> 1GHz.
>> will this work at 1 GHz RF or are we talking speed of a digital signal of 
>> 18
>> or less v P/P.
>> What is some recommendations for a good RF scope?
>> Ed
>> WA3BZT
>
>
>