Hello,
There is one more issue to consider. Long lines give delays. Once
I wanted to measure the loss of a coaxial cable on a vna. Was an
interesting experience: no response. Until I realized the receiver
had already traveled higher up in frequency at the time the
response was back. You need to consider a delay in between
frequency steps, long enough so as to give the receiver time to
read the response. This is a documented feature (of course).
Good luck,
Harke, PA0HRK
On 26/05/2022 20:09, Tom Lee wrote:
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Hi Karin,
"Upper limit" is not as hard a cliff as your question presupposes.
Whether or not a given length of cable is too much depends on your
acceptance criteria. What are you trying to measure, and to what
accuracy do you need to measure it?
When you add cable, you get loss, so that loss subtracts directly
from your dynamic range. For example, if you are making
meaurements at a gigahertz or so, with RG-213 you can expect to
lose about 10dB in each direction, roughly speaking. If you aren't
trying to measure small deviations from an exquisitely
well-matched load, you'll be fine. If you're trying to resolve
small changes in the vicinity of a -60dB S11 null, then you may
find the measurement challenging.
The other factor to consider with a long length of cable is that
it isn't rigid, so stability of your measurement can be affected.
And if you are doing a lengthy set of measurements, temperature
effects can come into play as well. Whether these are "don't
cares" or showstoppers depends on what you can tolerate. If you
can tolerate large error bars, your measurement problems become
much less severe. If you're trying to make publication-quality
measurements, you may find that difficult.
Good luck!
--Cheers,
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
On 5/26/2022 09:45, Karin Johnson
wrote:
Hello Group:
I have an 8753C and am wondering what the upper limit on cable
length would be if I place the cal standards at the end of a
cable to do remote measurement of S11.?? In other words I am
using SOL, with the cal standards placed at the end of a 100
foot length of RG-213.? Theoretically placing the measurement
plane at the end of the cable.? I have already done this and the
results seem to be accurate relative to an actual measurement at
the that physical place.
I hope I have explained this issue sufficiently.?
Regards,
Karin Johnson??
BTW: I have had an account on the Keysight forums in the past
and have recently tried to login to that site, but It won't let
me.? Possibly password have changed, and I cannot create a new
account.? I have posted with Keysight support and hope they
return the email.?
