wirelessrudy

VVH / VHH versus HV sector antennas

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Is there really an advantage in using triple chain VVH (or VHH) antenna in a network presently consisting out of a mixture of V-pol single chain antennas with V+H-pol antennas?

(Network consists of Groove's on 24-25dBi or higher Mesh/panel antenna and some SXT's and SEXTANTS and the first RF Basebox XL5's)

We use Mikrotik radio's only and to us it seems the radio only uses these chains that give best signal. In our opinion it is not like a VVH-polantenna on AP side will increase signal at V-pol client with 3dB (or 1,5dB in case of the use of duo chain antena at client).

Now to make a transition to full duo chain network we have to change these 1xCH ones one by one for dual chain CPE's antenna. For budget reasons we are planning to use Basebox XL5 with rb911's.

But gain is 19dBi where the duo chain setup gives us 3dB extra. So compared to a 25dBi mesh we still loose 3dB signal (halve the energy!).

In the 'old' days we worked with signal levels at CPE (Rx) up to -81dB but we now try to maintain -70 or better to sustain the higher mcs rates. (Clients want more speed than 2 years ago!)

We already increase the Tx at the AP from 25dBm to 30 or 31dBm and will use either RF carrier class or the Simper cone antennas to bring more, and 'cleaner' signal to the CPE.

But we are still not sure if a triple chain sector would give us any benefit above a duo chain sector. (On the moment the triple chain NetMetals are actaully cheaper than the duo chain units!)

 

Anybody has any say in this?

 

 

 

 

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Wirelessrudy,

The use of our 3x3 sector could help.  Most likely with 2x2 cpe.  You don't always see better signal, but it could help with packet delivery in higher multi-path areas.  The 3rd chain has the ability to potentially receive signals that the other pol's may drop.  You would have to decide if you will use a HHV or a VVH.  Since you have many single pol devices, and I assume they are Vpol so VVH might be best.

 

Here is a representation of how it may help.  You can see the 3rd chain might receive packets that the other 2 miss. 

3x3mimo.jpg

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Hi, good to get this forum starting...

We are coming from a V-pol network (like most WISP's I would think) so a VVH would be the one I'd pick.

Although your theory is that 3rd chain might received a V-pol package that is not picked up (in the same strenght) by the 1st V-pol chain I have some doubts:

1. To get the higher MCS values we need mimo to work. Thus the H-pol chain needs to work too otherwise we only have a single chain connection with related low (50%) throughputs. Only if the signal of either one of the V-pol chains has similar signal as the H-pol we have mimo. The chance now one V-pol chain reception is much lower than the H-pol where the 2nd V-pol could now would come to the aid to still get a high V-pol signal is very rare. After all, on relative longer distances (> 1km) multipath receipt for similar polorized signals leaving same antenna is almost un noticable. Same theory prevents full triple chain links (3x3) to get much advantage over 2x2 when distances are more than 300-500 meters.

2. When we have a field of single chain or duo chain CPE's a triple chain (VVH) might improve signal receipt a little on the AP side. But in the day to day practise the bulk of the traffic is AP >> CPE. Here the only chance a VVH sector might improve CPE's receipt is if one of the V-pol chains would be poor compared to the H-pol and the 2nd V-pol chain's signal could now come to the rescue. How big is the chance this is ever happening?

3. We actually learned that in a P2P 3x3 link (H+V+45ªslant) link the 3rd chain did not produce any gain improvement on a 8 km link. On the contrary, the CCQ dropped meaning the 3rd chain actually made the link worse. We have done this setup on 2 separate P2P links and for both we had the same 'dissapointing' results. 2x2 actualy worked better.

So again, I am really not pursuaded on the advantages of 3x2 P2mP networks. Unless you have other info or inside (or real world tests) to spare... ^_^

 

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