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Post by wa1fxt on Sept 18, 2007 12:48:06 GMT -5
Bob,
What is the difference between using the OSL Calibate Analyzer method to cancel out the effects of connecting cables and the refer to antenna method? Is the limiting factor the length of the cable? I know the book mentions that the effects of "several" feet of cable can be factored out by the AIM when you are calibrating the analyzer.
73,
Bob WA!FXT
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Post by Bob on Sept 18, 2007 16:34:34 GMT -5
Bob, What is the difference between using the OSL Calibate Analyzer method to cancel out the effects of connecting cables and the refer to antenna method? Is the limiting factor the length of the cable? I know the book mentions that the effects of "several" feet of cable can be factored out by the AIM when you are calibrating the analyzer. 73, Bob WA!FXT Hi Bob, Theoretically the SOL cal procedure could compensate for arbitrarily long stubs but in actual practice, the data at increments of 1/4 wavelength may not be accurate because the Zmag is nearly zero or very, very large. This can result in a glitch in the scan data. It may not be a problem, depending on the application, but the latest version of the program does warn if this condition occurs. The warning can be disable by a flag in the config file. The ref to antenna calibration is accurate for transmission lines that are any length as they are symmetrical. Using resistors that are not close to zero or infinity results in better accuracy. You can see this effect by doing the cable calibration with an open circuit (R_large=1meg ohm) and shorted (R_small=zero ohms). The result with these extreme values is usually not as good as when using real resistors. Calibrating with two resistors assumes the cable is symmetrical, which is fine for a single piece of coax. It takes into account the loss too. However, when the transmission line is made up of more than one cable, such as coax and ladder line, the symmetry condition may not apply. Evaluate the results using some known complex impedance loads. 73/ Bob |
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n2kbe
New Member
Posts: 4
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Post by n2kbe on Sept 18, 2007 17:00:42 GMT -5
Hi Bob,
It seems to me that the software calibrates the analyzer at a fairly fast pace. Do you average the values at all in the calibration routine? If not, do you think it could help, especially at the higher frequencies?
John
N2KBE
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Post by Bob on Sept 18, 2007 20:20:55 GMT -5
Hi Bob, It seems to me that the software calibrates the analyzer at a fairly fast pace. Do you average the values at all in the calibration routine? If not, do you think it could help, especially at the higher frequencies? John N2KBE Hi John, Each reading is averaged 16 times. -- Bob |
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Post by wa1fxt on Sept 19, 2007 7:38:31 GMT -5
Thanks Bob....understood. It helps an awful lot to understand the underlying mecahnics when applying any tet gear.
Like Clint Eastwood says, "A man has to know his limitations".
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