On Mon, Nov 4, 2024 at 09:11 AM, Peter Cimino-K1PCN wrote:
I have a few questions re the cable length function.? Does it measure the actual length or the electrical length?? I know that there can be differences between the published velocity factor for a cable and the actual measured which can cause discrepancies.
The measurement made is the electrical length.? The conversion to physical length is done by using the velocity factor that you entered.? Yes there can be a difference between the actual velocity factor and the published velocity factor.? This is due to manufacturing tolerances.? There can also be considerable difference between different manufactures version of a cable type (like RG-58, RG-213 etc.)
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This brings me into the Cable loss function.? I run the analysis with the open and short measurements say on a 3ft piece of LMR 240.? The reading is 0.6db loss at 450MHZ which I believe is for a 3ft cable which would be a 20db/100ft @450Mhz which is terrible for a not so bad piece of coax.? Am I doing something wrong?
The loss measured is an approximate value and includes losses in the connectors.? PL-259's would be poor at this frequency.? The way it measures attenuation is by using return loss (RL).? If you measure RL with a short at the end and an open at the end the estimated attenuation is (RL-short + RL-open)/4.? The reason why is is only an estimation is discussed by Owen Duffy on his blog....
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Roger
Peter Cimino-K1PCN
Roger Need