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mtest001
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[SXT LTE6] Explain to me this PoE mystery

Mon Oct 18, 2021 1:05 am

Hi all,
I am currently in the process of deploying an SXT LTE6 antenna. I am trying to connect and power my SXT from a DLINK DGS-1008p, switch that can do 802.3af and 802.3at.

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If I connect the SXT directly to the switch via a long 25m Cat6 ethernet cable then it does not boot up. It seems it's not getting any power from the switch. BUT if I keep the same long cable, but instead of connecting it directly to the switch, I connect it to the power injector that came in the box of the SXT and then the power injector connected into a PoE port of the same switch then it works. I do not plug the power supply into the injector so the injector is getting the power from the switch.

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I understand from the specs that the SXT is passive PoE(https://mikrotik.com/product/RBSXT5nDr2), so in fact it's normal that it does not work when directly plugged into the port of the switch because it cannot negotiate voltage, is this correct ? But what I don't understand is that the power injector is capable of delivering the power from the PoE port. Is this normal ?

Thanks a lot for your help !
 
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Hominidae
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Re: [SXT LTE6] Explain to me this PoE mystery

Fri Oct 22, 2021 11:10 am

I understand from the specs that the SXT is passive PoE(https://mikrotik.com/product/RBSXT5nDr2), so in fact it's normal that it does not work when directly plugged into the port of the switch because it cannot negotiate voltage, is this correct ? But what I don't understand is that the power injector is capable of delivering the power from the PoE port. Is this normal ?
...don't know if this electrically correct, but as far as I understand, since the Switch does not power on the port does not imply that the "wires" are not connected.
To my knowledge in the switch this is not a physical connect/disconnect of the wires, but rather a resistor based thing, from where the electric/power flow is routed.

The "proper" solution to your problem ist using this: https://mikrotik.com/product/rbgpoe_con_hp on the switch port to then power the SXT with it.
I do have some of these on DGS1005PD switches...this works well.
 
holvoetn
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Re: [SXT LTE6] Explain to me this PoE mystery

Fri Oct 22, 2021 1:31 pm

I have an SXT LTE device powered by a TP-Link TL-SG105PE. It can provide a bit more power then your Dlink device from what I see.
That same switch also powers a cAP AC and cAP Lite.
No power injector or whatsoever needed with 20m cable as longest.

Maybe stating the obvious but are you sure you plugged the cable in an PoE OUT port of the DLINK ? I've made that mistake already myself, hence my question.

If simply plugging the power injector in between without any other external power source and then it works, something definitely is wrong.
Am I correct in seeing there is no sort of management interface with that DGS-1008p device where you can change PoE settings ?
Already tried another (shorter) cable just to check ? Also there: been there, done that ... (and had to throw away a couple of cables because of such issues).
 
mtest001
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Re: [SXT LTE6] Explain to me this PoE mystery

Fri Oct 22, 2021 1:47 pm

Thank you for your feedback. I believe my low quality 25m cable might be the culprit. I am assuming the power loss are such that the very low current used during the PoE probing and negotiation are lost on the line. By inserting the injector between the switch and the long cable that goes to the antenna I believe then the PoE negotiation is done between the switch and the injector, or something along those lines.
The real surprise to be is the fact that the injector also let PoE pass through, I was not expecting that.
Anyway I need to do more tests, starting by removing this long cable to confirm it's indeed the root cause of the problem.
 
mtest001
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Re: [SXT LTE6] Explain to me this PoE mystery

Fri Oct 22, 2021 1:50 pm

Maybe stating the obvious but are you sure you plugged the cable in an PoE OUT port of the DLINK ?
Yes, I'm using the PoE ports.

Am I correct in seeing there is no sort of management interface with that DGS-1008p device where you can change PoE settings ?
Correct these are unmanaged switches unfortunately

Already tried another (shorter) cable just to check ? Also there: been there, done that ... (and had to throw away a couple of cables because of such issues).

I'll do that as soon as I can. Unfortunately I cannot go to the installation site at the moment, but I hope in a week or so.
 
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mkx
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Re: [SXT LTE6] Explain to me this PoE mystery

Fri Oct 22, 2021 3:04 pm

Personally I'd stop trying to power the RBSXT5nDr2 from your 802.3 af/at PoE switch because RBSXT5nDr2 is certified to work with supply voltages between 8V and 32V while 802.3 af/at specifies 48V. It can kill your SXT.

That is if the link is actually about your SXT (you wrote SXT LTE6, which probably corresponds to RBSXTR&R11e-LTE6 ).
 
mtest001
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Re: [SXT LTE6] Explain to me this PoE mystery

Fri Oct 22, 2021 6:08 pm

Thanks for the advice, the specs says: PoE in input Voltage 12-57 V

https://mikrotik.com/product/sxt_lte6_kit

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