Richard (Rick) Karlquist wrote:
> Jim Brown wrote:
>> Not as ideal as you might think. The problem is that most coax is
>> shipped on reels with access to only one end. To make a transmission
>> loss measurement, you must unreel it to get a connector on both
> No, see below
>> Now, if you happen to own instrumentation that allows you to measure
>> that loss on a 1,000 ft spool from only one end, that's another
>> story. :)
> See below
>> Jim K9YC
> I happen to own instrumentation that allows me to measure loss from
> one end; it's called an MFJ-259B. Cable loss is a built in function.
> As long as the far end is open, cable loss is half of return loss.
> You can also calculate loss from VSWR. For example, 3:1 means your
> loss is 3 dB.
And a fancier widget that does some computation and actually does vector
detection can do even better (e.g. measure the length of the cable).
The question I would have is how much precision is needed? If you're
measuring 1000 foot spools, then a 1 dB measurement precision will give
you 0.1 dB/100 ft kinds of precision. Measuring 1dB out of, say, 10-20
dB seems doable.
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