What is a maximum length of 50 ohm coaxial cable that can define the calibration plane?
I would like to use SOL at the end of a 100 foot length of 50 ohm coaxial cable to define the calibration plane. This is so I can measure at a remote distance the effective S11 parameter of an antenna. Is there a limit as to how long the cable can be? What issues should I be aware of regarding calibration accuracy, repeatability?
Regards,
Karin
Thanks David,
The lowest frequency is 3.5 MHz the upper frequency is 7.3 MHz. Not very exotic, I know. Using Davis Bury Flex coax.
I should have mentioned I am using 8753C analyzer. I am not looking for super accurate results, just to get in the ball park with a matching network design. What I should have commented about is that I am assuming the calibration values are probably kept in floating point format. I think the processor in the 8753C is a 68000 variety. I was curious as to the limits of how small or big the cal constants would be stored and thus the max length of the cable. Phase stability is not too much of a concern at these frequencies, and the measurement and calibration are done in a matter of minutes.
Best Regards,
Karin
Hello,
You indicated a sweep frequency of 3.5MHz to 7.3MHz. I took a look at the noted Davis Bury Flex cable and their specification for loss per 100' of cable at 10MHz is 0.6dB (http://davisrf.com/buryflex.php). With this low loss (at this low frequency) a mechanical coaxial short - open - load calibration should be achievable. The other issues of concern:
From the description it appears as the 100' cable assembly is intended only to allow access to the end antenna which is the actual device under test (i.e. DUT or AUT). If this interpretation is correct, have you considered the use a 6# battery operated portable Keysight FieldFox combination analyzer? If accessibility is the issue then this may be a very good solution to avoid the 100' 'test port cable'.
Sincerely,
tsilcha.
I think the maximum attenuation that can be tollerated is around 15 dB.If the attenuation of the cable is very high, then you will not get a decent calibration.
I think the biggest issue will be the phase stability of the cable. What frequency is this? If the cable is many wavelengths long, then the slightest change in temperature will cause amplitude and phase shifts. If the cable is only a fraction of a wavelenght, then this will not be a major issue.