Hey Guys, I have an ePMP network for a CCTV system. I am currently using an ePMP 1000 connectorised access point with a 120 degree sector antenna. I need to add an additional SM location 180 degree (behind the current ePMP 1000 AP).
I wanted to connect a Force 180 to the AUX port of the ePMP 1000. Is there any problems doing this? Can the ePMP psu power both the ePMP 1000 and Force 180?
thats the exactly what those are for!
you'll need to enable POE passthrough in the config>system menu to power it up via POE through that port
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Would i be able to get away with mounting the force 180 behind the epmp1000 (same mounting pole) facing 180 degrees opposite direction? FYI my epmp1000 is not syncronized. Would that likely cause interference issues?
My transmit power would be lowered and frequency used would be far from the epmp1000 frequency.
that should work (and i have setups like that);
BUT you should try to separate them by every centimeter(or inch) you can. a one meter separation means 10 times less coupled signal than at 10cm ;
a two meter separation is just 2x better than 1m; so, this first meter of separation, if possible, buys you A LOT in terms of the radios not desensitizing each other.
Both the force180 and the original Epmp1000 have a front/back ratio of about 20db, as per their datasheets.
That means that with zero separation, they will listen to each other at this level:
E1000 / F180
<) -||- (>
13dbi 16dbi
interference = (power+gainA - F/B_A -F/B_B +gainB -distance_loss)
that will be <powerA/B>+16+13-20-20-free_space_loss = -11db for 0db power and 0 distance.
or -1db at 10dbm tx power, and +9db!! at +20dbm tx power and 0 distance
(considering the radios are really back/back).
this is enough signal to "desensitize" the reciever at and near the operating frequency, causing retransmits and low troughput / high jitter.
The moral to the story is: try to get as much distance you can between the radios, for the best possible perfirmance. it should work provided you use low TX power at both radios.
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Great Info thanks. I wont risk it and will install the device with a couple meteres of seperation.
@Guilherme wrote:that should work (and i have setups like that);
BUT you should try to separate them by every centimeter(or inch) you can. a one meter separation means 10 times less coupled signal than at 10cm ;
a two meter separation is just 2x better than 1m; so, this first meter of separation, if possible, buys you A LOT in terms of the radios not desensitizing each other.
I do not disagree with you one bit on having as much separation as possible between units. There are some descrepancies in your math that will cause some large errors. Radio obeys the inverse square law. Doubling the distance reduces strength by a factor of 4 or by 6db. Increasing the distance by a factor of 10 drops received power 100 times (not 10 times) or by 20db.
This also works in reverse. While it is true that if you want to double the signal level at a receiver, you can double transmit power, or increase antenna gain by 3db, that is not true for doubling range/distance. if you want to double your distance, the power or gain of antenna must increase by a factor of 4 (6db), not by a factor of 2.
The example you gave with the1000's and 180's is a little more complicated due to the radio being mounted directly to the back of the antenna. There is a shield over the top of the receiver section of the PCB, but not on the bottom of the PCB. In other words, anything strong coming from the back hits the receiver pretty hard, harder than the math adds up using the F/B ratio. Would be nice if the entire PCB was in a metal shield, but...these are $100 radios, can't be too picky.
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I was not trying to be exactly precise in the maths there, just trying to make the point that these radios are not meant to operate back-to-back.
Adding 1/d² of a log scale in there would add an unnecessary complication that would distract more than everything.
For completion, everything inside a couple of lambdas of the radiator is "near field", and is even more representative in this scenario.
Maybe i shouldn't have posted the math, as calculating the actual coupled signal in a "back to back" scenario would gonna have to account for fuzzy RF effects, the actual pole, how much is leaked in the back of the PCB.. (and Cambium did a great job there.. the epmp1000 and the force180 have about 0.5cm of signal lines between the point they exit the shield-can and drop down to the other side of the aluminum plate)
The objective here was to showcase that there is a very significant advantage in putting some 2 meters of separation between the two radios.
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