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Community Member

Antenna Spiller for 2.4Ghz

Does anyone know about Antenna Splitter for 2.4 Gh I would like to try an AP with 4 Antenna ?? Does anyone know the product number of it?? so I can order it.



Cisco Employee

Re: Antenna Spiller for 2.4Ghz

Hi Israel,

I am not sure what you want 4 antenna's for, but I really dont recommend that you use a spliter as 802.11 sytems are low powered which means the received signals are very low in level, a spilter will introduce a large amount of loss into the system and will affect performance.

The dual antenna system on the Aironet product range is for spacial diversity to combat the effects of multipath loss. Adding 2 extra antenna's will not increase the affect of combating multipath loss more than the loss introduced by using the splitter.

If you are trying to cover 4 sectors, then this can only be done via 4 AP's or bridges etc. The 2 antenna ports will both receive and only the strongest signal at that point in time will be used. If you have the 2 anttenna in different sectors then it will only receive from the strongest sector and as such will not provide reliable communications to the devices in other sectors. The AP will only transmit on one antenna port and as such the client may not be in that sector and will miss that packet. The antenna port that the AP will transmit one is based on the best antenna at the point in time (normally the port last received on)

Community Member

Re: Antenna Spiller for 2.4Ghz

We install an AP with a splitter. Two directionnal antennas are connected to the splitter and directed in two different direction.

No radio problems appear at all. Of course, the throughput is divided by 2, but it's normal.

Cisco recommend to use a "good quality splitter", it mean approximatively 4db loss at each antenna (Cisco training guide, "Aironet Wireless Lan Fundamentals ver1.0", page 10-42).


Re: Antenna Spiller for 2.4Ghz

This is a really bad idea.

Between the losses at the splitter, the coupling, and the cables, your reception would be very poor. Higher gain antennas wouldn't help (from the transmit side) because the apparent gain of the antenna depends on the input signal strength and quality.

Dividing the signal and the other associated losses pretty much guarantee a marginal (at best) signal-to-noise ratio at the antenna's input (and at the AP's transceiver).

Amplifiers and the like should only be used by folks that have the necessary equipment to ensure that the system complies with the local/federal laws for output power (EIRP) and interference.



Community Member

Re: Antenna Spiller for 2.4Ghz

Would the situation be different if I wanted to build a point-to-multipoint bridge interconnection using a directional antenna for each link (that is : central bridge - splitter - 3 directional antennas - - - 3 bridges) ?

Obviously I would adjust the transmit power to take account of the augmented loss introduced by the splitter.

Would it be a mess?



Cisco Employee

Re: Antenna Spiller for 2.4Ghz

signal level would be very low. I would not recommend it.

There is not enough adjustment in transmitt power with the legal limits of 802.11b to cover the amount of loss and still have a reasonable range

You can do it but make sure you accuratly calculate your link budget and ensure the loss of the splitter is catered for still leaving your 10db fade margin

Dont forget you have modified the system and in some countries this will mean that the installer must certify compliance as the the compliance provided on the radio is no longer valid, you need to check your local laws

Community Member

Re: Antenna Spiller for 2.4Ghz

You can legally add an amplifier and power divider (more accurate term than "splitter") IF the system is professionally installed and complies with FCC (or whatever your AHJ - authority having jurisdiction - is) regulations. In the US, this is the FCC. Read FCC Part 15 regarding unlicensed operation.

Cisco's stated position has always been that it's not legal to modify their recommended installation guidelines. I think that this is because they sell to end-users who don't really know what they're doing, and are likely to build illegal systems.

As a didactic exercise, what the legal EIRP in a P2MP configuration? I can have a fixed-gain low-noise bidirectional amplifier feedinga power divider feeding multiple antenae, as long as I stay within legal EIRP at each antenna. You need to know amp gain, power divider loss, miscellaneous losses and antenna gain.

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