On 10/1/2015 4:24 AM, Jeff wrote:

Does your online calculator include cable loss and velocity factor? I
used .0233dB/m and .66 velocity factor with a length of 4.57m. Sorry for
the metric numbers, but that's what my chart uses.

How do any of those things enter into the VSWR calculation? VSWR is
defined solely by the match of the cable and antenna impedances.

I don't know much about the calculator I used, some random online thing.

http://chemandy.com/calculators/retu...calculator.htm


Yes they do have an effect.

Cable loss will improve the VSWR as the cable gets longer and the loss
increases so the VSWR reduces.

You are referring to the VSWR at the ATU rather than at the antenna?
John already mentioned that.


The velocity factor determines how long the cable appears electrically
compared to the physical length.

The calculator that you linked to takes no account of the cable length
and what the mismatch, or vswr, at the load looks like at the other end
of a length of cable.

If the cable impedance matched the system impedance, 50 ohms in this
case, and it were totally lossless then the VSWR at the tx end of the
cable would be the same as at the antenna end, BUT the phase of the
mismatch would change, ie your -j120 could end up as being +j120 or
anywhere in between depending on cable length.

Now if the feeder is an impedance other than 50 ohms it act as a
transformer and both the real and imaginary parts of the impedance seen
at the Tx end will change. Depending on length and what impedance the
feeder is it may or may not improve things.

Jeff




--

Rick