Question about 1242AG AP

Unanswered Question
Sep 2nd, 2008

HI, I have an AIR-LAP1242AG AP, I don't understand why they have two RF ports (Left / Primary )for A and B, do you know why ?.

I have this problem too.
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Overall Rating: 5 (3 ratings)
ericgarnel Tue, 09/02/2008 - 06:39


Dual RP-TNC antenna connectors for 2.4-GHz radios

Antenna connectors support a variety of Cisco 2.4-GHz antennas, providing range and coverage versatility.

lveraza Tue, 09/02/2008 - 07:15

Can I use one port (Left) for Access Point and the second port (Right) for a bridge connection ?,with diferent antennas.

I don't understand it.

Thank you.

rob.huffman Tue, 09/02/2008 - 07:35

Hi Luis,

Just to add a note to the good tips from Eric (+5 points here Eric)

"Can I use one port (Left) for Access Point and the second port (Right) for a bridge connection?"

This is NOT supported :( Have a close look at the attached docs (especially the Golf Course Case Study);

The use of two Antennas on these AP's is used for "Diversity Mode" this is why there are 2 connectors. You can connect an Antenna like a 5959 which has 2 Cables or 2 x 1728's which have 1 Cable each. In most cases only the Primary connector is used. Here is an explanation for the use of two Antennas :)

This describes the use of 2 **Identical Antennas in "Diversity" Mode;

The purpose of diversity is to overcome multipath reflections. Diversity antennas that share the same physical housing are placed at an optimum distance apart. The maker of the particular antenna determines that distance based on the characteristics of the antenna. When you use a pair of antennas with matching characteristics to provide diversity for cell coverage in your facility, the guideline is to put those matched antennas at a distance apart from each other that is equal to a multiple of the wavelength of the frequency that is being transmitted. The 2.4 GHz wavelength is approximately 4.92 inches. Therefore, to support diversity on a 2.4 GHz radio with two separate antennas, the antennas should be spaced approximately 5 inches apart. The antenna pair could also be spaced at multiples of 5 inches, but the distance between should not exceed 4 multiples: reflected waves farther apart than that are likely to be so distorted and different in delay spread that the radio could not work with them.Because each antenna is selected by itself, both antennas must have the same radiation characteristics and be positioned to provide similar cell coverage.

**** Two antennas connected to the same access point must not be used to cover two different cells.****

From this good doc;

Multipath and Diversity

A diversity antenna system can be compared to a switch that selects one antenna or another, never both at the same time. The radio in receive mode will continually switch between antennas listening for a valid radio packet. After the beginning sync of a valid packet is heard, the radio will evaluate the sync signal of the packet on one antenna, then switch to the other antenna and evaluate. Then the radio will select the best antenna and use only that antenna for the remaining portion of that packet.

On transmit, the radio will select the same antenna it used the last time it communicated to that given radio. If a packet fails, it will switch to the other antenna and retry the packet.

One caution with diversity, it is not designed for using two antennas covering two different coverage cells. The problem in using it this way is that, if antenna no. 1 is communicating to device no. 1 while device no. 2 (which is in the antenna no. 2 cell) tries to communicate, antenna no. 2 is not connected (due to the position of the switch), and the communication fails. Diversity antennas should cover the same area from only a slightly different location."

Diversity Antenna Systems

Diversity antenna systems are used to overcome a phenomenon known as multipath distortion of multipath fading. It uses two **identical antennas, located a small distance apart, to provide coverage to the same physical area.

From this Antenna reference guide;

Hope this helps!


lveraza Mon, 09/08/2008 - 08:06

Hi Rob,

Thank you by yours answers.

I have one question, I need to make a Point to point link, but It's small, like 50 meters, can I use the next antennas AIR-ANT5195P-R ?.

Thank you.

rob.huffman Mon, 09/08/2008 - 12:04

Hi Luis,

You are most welcome my friend! I am not that familiar with setting up Point to Point Bridges but I don't think the "patch" Antenna like the 5195 will be your best choice. Something more "directional" like a Yagi is probably better suited even for a short run :)

Take care,


lveraza Wed, 09/10/2008 - 06:37

Hi Rob,

The problem here that I can't find more antennas for 5.0Gh frecuency.

Do you know the antennas that I can use for point to point link at 5.0 frecuency.

They use RP-TNC Connectors.

Thank you !.

talmadari Wed, 09/10/2008 - 22:54


For this length of distance you can surely use the patch antennas or even use the built-in antennas.

I have deployed several links with this kind of setup and it's working fine!



lveraza Thu, 09/11/2008 - 06:20

Hi Tal, thank you.

I'm thinking to install them for the point to point link and I'll have at both sides access point clients with the 2.4 frecuency, I see that It's possible.

Do you have it installed ?


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