Ah ok, I was (wrongly) assuming Khalid just leaves the TX port
virtually open.
Greetings,
Marcus
On 01/06/2015 08:21 PM, Marcus D. Leech
wrote:
On 01/06/2015 02:17 PM, Marcus Müller
wrote:
>Is the input impedance of your scope
1Mohm or 50 ohms?
Yes, it is 1 Mohm,
Well, in that case, your power consideration is not really
correct; the LFTX is designed for 50 Ohm load impedance; so, for
meaningful measurements, you'd have to measure the voltage over
50 Ohm.
I'm not really sure how much current the opamp on the LFTX is
designed to source, but I think adding a 50 Ohm load would
reduce the current through the negative feedback resistors R4/R7
(and in turn reduce the bias over R33-R3/R35-R6) , which might
change your measurements significantly.
Greetings,
Marcus
The AD8047 is designed for a max of 50mA drive current. If you do
the math, that's plenty.
I believe that Khalid was terminating in 50Ohms resistive, so with
a 1Mohm impedance across that, the scope input impedance will
hardly make any
difference at all--it should "see" the voltage developed across
that 50Ohms, without noticeably changing it.
On 01/06/2015 08:09 PM,
khalid.el-darymli wrote:
Yes, it is 1 Mohm, and my probe is set to 1X.
Khalid
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