It is indeed interesting to slow the sweep speed down to about 0.5s or more and watch the readout written after the sweep completes. I had not seen that before today.
Thanks,
Barry - N4BUQ
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----- Original Message -----
From: "Jim Ford" <james.ford@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 6:52:39 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
1) AKA Chop mode, 2) AKA Alt mode.? ?Both useful but at different sweep speeds.
? ? ? Jim FordSent from my T-Mobile 4G LTE Device
-------- Original message --------From: Harvey White <madyn@...>
Date: 12/30/21 7:46 AM (GMT-08:00) To: [email protected] Subject: Re:
[TekScopes] 7704A - Noise on sine-wave traces Do not do anything.There is one
beam.? It has to be "borrowed" to write the readouts.There are two ways:1)
Borrow the beam when it's needed.? This chops tiny holes in the trace.? it's
going to be obvious at some sweep speeds, but will work on slow sweeps.2)
refresh the readouts on the sweep retrace.? This eliminates the "noise" but for
slow sweep speeds, you will get a flickering readout.There's generally a switch
on the readout board to control this behavior.HarveyOn 12/30/2021 10:14 AM,
n4buq wrote:> When displaying a sine-wave where several cycles/division are
present, when the READOUT is switched on, there is noticeable "noise" (for lack
of a better definition) in the trace.? It appears as tiny blank spots in the
trace that move rapidly along the trace.? The noise is not in sync with the
triggering and appears at many points along the trace.? Switching the readout
off stops the effect.>> The power supply has fresh filter caps as well as the
horizontal board and the HV board so I don't think this is PS ripple and more
likely digital noise from the READOUT circuitry but that's just a guess.>> I've
looked for places in the READOUT board and/or interface board where there might
be bypass filtering components that might have been designed to eliminate this
but I don't see anything.? I do note that switching on the READOUT connects it
to the +15V rail and possibly that's the source of the noise.>> I've mostly
observed this with sine-waves but it might be present with other waveforms.? As
a side note, with mostly square-waves, with the GRATICULE ILLUMINATION turned
up, I can see a much smaller presentation of similar noise in the trace.? This
is much less noticeable but could be related.>> Any ideas what I can look for
as a cause for this?>> Thanks,> Barry - N4BUQ>>> >>>
