That would be unusual for a crossover adapter to swap the 4,5 and 7,8
pairs. Traditionally they swapped 1,2 and 3,6 for the benefit of 10/100
devices that didn't support auto MDI-X. I don't think there's any
context where swapping the spare pairs would have been useful. In
telephony you might encounter a rollover adapter, but that's a horse of
a different color.
What I'm wondering is whether "power pairs" is even a useful term
anymore or just a pointless thing to argue about. I know there's a long
history in WISP-land of the spare pairs on 100BaseT being used for
passive PoE. But, 450b like most modern devices, has gigE. Like all
gigE devices, all pairs carry data. Their official PoE adapter puts
power on certain pairs, but 802.3af/at has multiple power modes where
power could be on different pairs in different polarities.
I think we're seeing more polarity agnostic devices because the gigE
chipsets have to have that. Maybe it's not that Cambium and Ubiquiti
love and protect us, but that Ethernet vendors have to consider the
reality of multiple cabling situations when designing PoE capable
chipsets, and a diode bridge on the DC input is the logical solution
everyone came to independently. So on modern PoE devices there are
pairs carrying power, but there are no more dedicated power pairs. Just
a thought.
On 10/6/2020 10:43 AM, Nate Burke via AF wrote:
Unless they've changed the product in the last couple years, these
cross the power pairs as well. https://www.monoprice.com/product?p_id=5088
On 10/6/2020 9:23 AM, Josh Luthman wrote:
a) cross over cable switches the data pairs, not the power pairs
b) a 450b accepts both polarities for voltage
Josh Luthman
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Direct: 937-552-2343
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On Tue, Oct 6, 2020 at 10:21 AM Matt <[email protected]
<mailto:[email protected]>> wrote:
I just found this:
https://mikrotik.com/product/mqs <https://mikrotik.com/product/mqs>
I assume I can just use a crossover cable to power up a PMP450b.
Anyone used them? I am not sure we need the wifi, our SMs are
pre-programmed to lock on the tower.
On Mon, Oct 5, 2020 at 9:28 AM Matt <[email protected]>
wrote:
>
> What is everyone using to power up an SM for site surveys nowadays?
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