I installed Condition Monitoring System (CMS) that uses an Ethernet to communicate to a MAX BR1 MK2 cellular router. The router is installed in a metal building with few windows. We are using two proxicast ANT-124-SMA and we tried to aim for the cell towers (6.5-8dBi 12.6" external magnetic load coil antenna). If there a better antenna that can push the signal out (On our cell phones we have 2-3 bars) or are we looking at getting cable extensions to reach the outside? How long can your cell antenna cable be before it starts to become an issue?
Compare your cell phone carriers and what bands they are using. If Peplink supports/its the same then position the inside antennas in the same area?
“2-3 Bars” doesn’t really mean anything given the scale is not really known or any kind of fixed value.
What are the actual stats you get from the Peplink for RSSI/RSRQ/SINR?
As mystery suggests perhaps check what bands the Peplink is connecting via, a lower frequency will generally offer better signal indoors, often at the expense of outright performance but bear in mind that the metalwork will do more than just attenuate the signal.
Signal strength (RSSI) is not the only metric that matters, quality (RSRQ/SINR) are also important when you are considering the quality of a connection.
Honestly, yes that would probably be the best option if you can manage it.
The shorter the better. The type of cable the antenna is connected with has a bearing on how much attenuation over length it will cause, but generally I aim to keep anything within 10m of the modem as a maximum, ideally much shorter - typically I will aim for ≤5m and that is with a good antenna and LMR400 type cable.
Have you got any option to relocate the Peplink if it were a case of keeping the antenna cables as short as possible?
There are plenty of ways to remotely mount a Peplink in a NEMA type enclosure and feed it with POE… 
+1 on keeping cables short.
There is a formula which addresses this. For every yard/meter you extend the antenna cable its performance is degraded X-amount. After a certain amount of cabling you’re now degrading it beyond a point of what shorter cables with less optimal antenna placement may have provided.
Better to move the Peplink closer to egress than to extend its antennas with longer cables.
Ethernet can get you 300ft or by using intermediate switches connected via Fiber you could extend beyond 300ft.
Get the antenna on the roof or the side of the building. That will be orders of magnitude better than anything you do from only inside the building.
To build on the comments of others:
- Keep the co-ax/antenna cable short. You can mitigate a longer run with a better cable. One tool we use is at co-ax cable run calculator. When reasonable, trade a short antenna run for a longer ethernet run (e.g., using PoE to a router). Note that high-quality cables are very stiff - no sharp turns.
- But long runs can still be OK. We have a 100 feet LMR-400 run from antennas to an HD2 LTEA inside a Faraday cage (long story) and it works well enough.
- But, don’t discount using an enclosure to mount the router outside. For the above set-up we have an additional router (a Transit Duo CAT-12 - lovely!) hanging off the pole where the antennas are. It beats the [expletive deleted] out of the HD2, and in a rather basic box it has survived a winter in the mountains.
Just the usual $0.02
Cheers,
Z