Question about Transmission Power and Number of Antennae

[Brawn]

Hi,

I want to know the max FCC-legal transmission power i can use on the n66u (each antenna is 3.5dbi for each band)

I understand that multiple antennae help the router to receive data
But what is the point of having multiple antennae with regards to sending data?

From what I understand, multiple antennae does not increase range (at least not much)

The FCC restricts the total EIRP (Equivalent isotropically radiated power)
I assume that the n66u's transmission power (Settings>Wireless>Professional>Transmission Power) is split equally among the 3 dual-band antennae

Therefore, since the EIRP (as I understand it) is tripled with 3 antennae, the amount of power that you can legally send to each antenna is 1/3rd of what you could have instead sent to 1 antenna

Wouldn't having 1 antenna radiating at 3x the power have much better range than if it were 3 antennae each radiating at 1/3rd the power?

 

[wh7qq]

Hi,
Therefore, since the EIRP (as I understand it) is tripled with 3 antennae, the amount of power that you can legally send to each antenna is 1/3rd of what you could have instead sent to 1 antenna

Wouldn't having 1 antenna radiating at 3x the power have much better range than if it were 3 antennae each radiating at 1/3rd the power?

Without actually looking at the schematics, I suspect that the antennae are fed from a single amplifier and the energy is divided between them more or less equally so you are not getting 3 x 3.5dbi on output. I also suspect that on the transmit side, the advantage is minimal. Reception, on the other hand, needs to maximize antenna surface area, more so on the 5GHz band. There is also the potential advantage of more favorable distribution depending on orientation of the 3 antennae. I think, though, that the primary advantage accrues to the marketing department who can tout the three appendages as being better than one.

Range on two way systems is going to depend as much on reception as on transmission. As your client devices tend to have tiny antennas buried in plastic and probably minimal transmission power, they don't produce a huge signal and their orientation tends to be random. If both ends of the signal path can't suck as well as they blow..... Trying to optimize router output power beyond a certain point is generally masturbatory.

 

[huotg01]

Hi,

I want to know the max FCC-legal transmission power i can use on the n66u (each antenna is 3.5dbi for each band)

I understand that multiple antennae help the router to receive data
But what is the point of having multiple antennae with regards to sending data?

From what I understand, multiple antennae does not increase range (at least not much)

The FCC restricts the total EIRP (Equivalent isotropically radiated power)
I assume that the n66u's transmission power (Settings>Wireless>Professional>Transmission Power) is split equally among the 3 dual-band antennae

Therefore, since the EIRP (as I understand it) is tripled with 3 antennae, the amount of power that you can legally send to each antenna is 1/3rd of what you could have instead sent to 1 antenna

Wouldn't having 1 antenna radiating at 3x the power have much better range than if it were 3 antennae each radiating at 1/3rd the power?

I'm not sure you are serious with your question. If you are, you should read a little more on the subjetc. It is a lot more than just a question of power (MIMO, etc).

Regarding the power, let's take the case of 3 directional transmission antennas, and compare with 3 guns. Let's take the case of the gun. For a specific bullet strength, having in front of you 1, 2, 3, 4 guns won't change anything for you as long as you are out of reach of one. Their power don't add. On the other side, if you are within the range of one gun, the more guns, the more chances to be hit by a bullet. Basically, for a specific frequency, for a specific power, it is the same thing for antennas. But within the defined range, the coverage will be a lot better if you have many antennas (and if you are out of range, you will not be reached by more antennas). Therefore, having many antennas allows the router manufacturers to use many strategies to better target, within range, the other side of the communication. In fact, when using the wireless AC standard, the end result is completely dependent of the amount of antennas.

Don't take that for granted. I could be wrong, and I'm not an electrical engineer.

 

[Brawn]

thanks wh7qq and huotg01!

i think i get it now

i also believe that i have calculated the maximum transmission power to be 1786 mw, but setting it to that does pretty much nothing to connection strength

there's the chance that the software doesn't recognize that number, or there is some code that i'm unaware of that limits the power, or the hardware does not support it

or maybe the extra power is just creating more noise.. who knows. guess there's no point in increasing it to that level!

thanks again

 

[wouterv]

With 802.11n the technique is a little more complex then simply one signal with one or more antenna's, or one or more guns to make sure a bullet hit the target.

802.11n (2.4 GHz and 5 GHz) uses MIMO technique, Multiple Input and Multiple Output. Each antenne in a 802.11n system can send or receive a maximum of 150 Mbps of data, with a channel bandwidth of 40 MHz. If both ends, router and client, have 3 antenna's, the maximum throughput is theorethically 450 Mbps.

The 802.11ac standard uses 5 GHz only, the specificaton allows up to 8 data streams and a channel bandwidth of 160 MHz. Current 802.11ac routers do not utilise the full 802.11ac specification, due to lack of the hardware (the wireless chips). New 802.11ac routers step by step become more advanced and get closer to what the standard allows. On the other hand the world start to recognise that also the 5 GHz frequency band has reached its limits. New developments are in progress. The 2.4 GHz band allready reached its limits, mainly due to neighbor disturbance.

Old style 802.11g (2.4 GHz only) was closer to "more guns to hit the target", here it was one data stream with multiple antennas that you could configure as Rx or Tx or both, with "both" it was expected that different antenna orientations could help to optimize the data link to various clients.

Do not worry much about Tx power, this is allready discussed so often.
Increasing the router Tx power only helps if you also increase the client Tx power. And increasing power only helps if you significantly increase the power (e.g. double it), next you may hope that the radio circuits can deal with this higher power.
Distance and free line of sight between router and client are more important, avoid obstacles (walls, floors).
Also try to match the router and clients: a 3 antenna 802.11n router works the best with a 3 antenna 802.11n client. The weakest link determines the final result for the total network: mixing your network with an old 802.11g client "destroys" your throughput.
Home use Wireless networking is not intended to bridge long distance.
A licence free SOHO (small office, home office) router shall be able to cover an average family home on 2.4 GHz and one room or one floor at 5 GHz.
For best coverage you shall install an accesspoint in every room.