N connector intermod causes:
What comes to mind is connector contact resistance. All metals, including
silver have some resistance. The larger the center pin and shield
connection, the lower the resistance. Type N connectors have the same small
diameter
center pin as a BNC connector.
With the high peak power associated with digital signal transmission, there
will be a small amount of heat generated in the contact resistance. This
heating will cause a very small instantaneous change in the loss of the
connection as the peak power of the complex waveform increases and descreases.
A change such as this would introduce a non linearity which is very small
but present. This non linearity then is the root of inter modulation of the
multiple signals/carriers present in the complex waveform.
This contact resistance is also the root of most failures of N connectors
in amateur service. With elevated vswr, peak currents are much higher than
low vswr and heat losses are related to current squared. As a center pin
heats up, the base metal resistance increases on the order of 20 parts per
million per degree C and the whole process can begin a thermal runaway toward
destruction.
Center pin sockets are not very robust and are easily bent if the center
pin is not well centered. The usual socket has four slits to allow some
flexure for pin mating. When damaged, you can end up with only one interface
instead of the intended four contact points. That makes contact resistance
four times as much which increases the current density four X at the contact
point. That increases heat loss 16X.
Larger pins have lower contact resistance. The 7/16 style connector is an
example that has lower IM performance.
73,
Gerald K5GW
In a message dated 11/14/2013 2:14:45 A.M. Central Standard Time,
wlfuqu00@uky.edu writes:
The cellular industry like them, as they generate less intermodulation
distortion than N, though the IMD generated by N is not significant
for amateur radio.
Dave
What property of N connectors generate IMD?
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