interesting design for a cheap tdr. thanks!
On Sat, 7 Jul 2018, 16:16 Michael A. Terrell, <mike.terrell@...>
wrote:
Both parts are 5% but that isn't important.
The time required for a pulse to travel to the discontinuity isn't
affected by the error in the pulse width. If it bothers you, use a crystal
time base instead of a simple one gate oscillator.
I have another schematic with multiple pulse widths that you can select
from, but like this design, it is built with 5% parts. That one also allows
you to select 50, 75 or 100 ohm output impedance by adding a 22 ohm, or a
50 ohm resistor in the output path.
Even temperature has some effect on the frequency, along with the
propagation delay on the gate.
Michael A. Terrell
-----Original Message-----
From: n4buq <n4buq@...>
Sent: Jul 7, 2018 9:03 AM
To: [email protected]
Subject: Re: [TekScopes] Kludging together a TDR or similar?
Looking at that schematic, it appears the frequency is determined by C3
and R1. If I'm not mistaken, the exact values of those components would
result in a frequency of 3.129 kHz; however, the oscilloscope images appear
to show 4.81 kHz. Is that difference due to component tolerances or is
something else at work here?
Thanks,
Barry - N4BUQ
