I just gotta get into this analogy story telling.
When I was studying electronics we had to study all this, frequency, wavelength,
impedance matching.
I remember a tutor telling us this story.
In a country with a less then honest government an outside company was asked to
build an
electric railway/tramway.
For some reason this
system involved an AC supply instead of DC.
The
system was built and ready for commissioning when the government said " We're not going to pay you what we owe. And we are going to kick your engineers out of the country"
Deciding on revenge one of the engineers cut the wires on the
system so that they were exactly cut in multiples of the wavelength. At this
point if the load is mismatched more energy is returned down the
line to the source. Ie for simplicity say wavelength = 3 units long then he cut the wires so they = 9 units long. Wavelength in metres = 1 / frequency in
Hertz.
Then comes the big the day, brass bands, politicians
etc.
They haven't got the train connected to the wires yet. The top guy turns on the
power. The
power goes rolling down the wires and when it gets to the end there is no load to take it. ( no matching
impedance). So the
power says I am out of here and heads back to the
power generator. Because there is now more
power at the generator then it was designed for it blows a
fuse. So some bright spark puts in a heavier
fuse and they try again. Same thing happens then a bigger
fuse. They try again but now there is no protection and the generator destroys itself. Last laugh to the engineer.
In your case with a 150ohm instead of 120
ohm nothing will blow up. It just means that some of the signal can
bounce back down the
line mixing in with the
dmx signal coming out of the
DMX source. It may do nothing or it may just change the value of a chanels data by a couple of bits thus causing a flicker or something unexpected.
As has been said it might have little
effect on short
dmx runs but on longer runs with more
dmx devices connected problems might start appearing.
But I definitely would loose sleep over it.
Ham radio operators do worry over this. They have meters that show how much energy sent from the transmitter is not going out the antenna due to mismatched
impedance. If too much
power is being wasted because of a mismatched
impedance (anntena load) you may need a bigger transmitter. The bigger transmitters is needed to
send the radio signal the same distance as a smaller transmitter that has a better matched
impedance ( antenna load).
Some one just to go and add some science to this. He.. He..