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 Subject :dual antennas, questions or ideas.. 2013-11-24- 11:32:20 
kj4yzi
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Joined: 2013-10-16- 10:21:44
Posts: 6
Location: 

Could i run one antenna port to an amplifier then  to my dish for transmit, and have an omni on the other antenna port? could i run a dish facing north on one, and a dish facing south on the other? so i can cover twice as much area??
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 Subject :Re:dual antennas, questions or ideas.. 2013-11-24- 16:05:16 
K5KTF
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Joined: 2010-01-18- 23:04:04
Posts: 266
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YES (to both questions)

We are doing that right now on several stations.

At my personal QTH, I have a dish on one and an omni on another (see Menu-APPLICATIONS-Towercam over mesh for pictures).

At a hospital, we have 2 nodes, one with an omni and dish, the other node with 2 dishes, tied together via CAT5 LAN to LAN. Plans are to possibly add a 3rd node for 2 more dishes to reach additional destinations.

Happy Meshing!

KTF
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B-) Jim K5KTF EM10bm Cedar Park, TX :star:
 Subject :Re:dual antennas, questions or ideas.. 2013-12-10- 02:13:16 
F5SFU
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Joined: 2013-10-28- 14:36:22
Posts: 2
Location: 
One question then ! the hardware switching is such that only one antenna is selected at a given time. If the 2 antenna cover, say 2 independent area, can we estimate the bandwidth loss if the firmware has to send data from one area to the other ? I'm guessing that firmware has no mean to know when a not heard node (belonging to the not selected antenna) will talk and then firmware has no way to anticipate antenna selection. I expect a ratio of much less than 0.5. Am I correct ? Anyway this is great we can do this, even the cost of bandwidth loss. 73, Alexandre
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 Subject :Re:dual antennas, questions or ideas.. 2013-12-16- 22:12:07 
W5LMM
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Joined: 2012-02-13- 18:18:04
Posts: 126
Location: Albuquerque, NM
 
I think the switching is done so fast it really does not matter.. Also, WiFi is a contention medium, so there are retries and collisions/drops anyway. The decision on which antenna port to use is based on signal strength at the time. I don't think it's a big issue in practice.
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 Subject :dual antennas, questions or ideas.. 2013-12-16- 23:13:25 
wx5u
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Joined: 2013-01-02- 00:30:45
Posts: 188
Location: Austin, TX

I don't think the data rate loss will be from antenna switching, it comes from the fact that your node is the relay between two other nodes.  It has to receive from one node, then transmit to the other node.   Antenna switching shouldn't matter much.

I would expect about 50% data rate when forwarding traffic from one node to another vs. originating or terminating the data.


[F5SFU 2013-12-10- 02:13:16]:

One question then ! the hardware switching is such that only one antenna is selected at a given time. If the 2 antenna cover, say 2 independent area, can we estimate the bandwidth loss if the firmware has to send data from one area to the other ? I'm guessing that firmware has no mean to know when a not heard node (belonging to the not selected antenna) will talk and then firmware has no way to anticipate antenna selection. I expect a ratio of much less than 0.5. Am I correct ? Anyway this is great we can do this, even the cost of bandwidth loss. 73, Alexandre
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I'm not part of the development team, so take what I say with a grain of salt. I'm also easily confused.

Check out the free Wireless Networking Book
 Subject :Re:dual antennas, questions or ideas.. 2014-01-04- 10:14:05 
F5SFU
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Joined: 2013-10-28- 14:36:22
Posts: 2
Location: 
thanks for ideas. Let me go further then : if we had to compare 2 situations for a node that need gain in antenna to reach 2, not aligned, neighbors (say one is in the north, the other is East or even South, they don't see each other) - case A : 2 antennas with directivity, one for each node on each port - case B : 2 same antennas on the same port, with a coupler (ratio 3db by default or to be defined according to distant nodes needs). Assuming we have sufficient margin to handle the loss of the coupler. Theoretically which one would be the best, Case A makes neighbors fully independent, collisions come mainly from switching. Case B makes neighbor as if they are aligned. collision could come from real talk at same time, but stronger node is heard better and should pass when requiring. 73, Alexandre, de F5SFU.
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 Subject :Re:dual antennas, questions or ideas.. 2014-02-01- 12:28:24 
KF7MCF
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Joined: 2013-02-09- 08:16:21
Posts: 3
Location: 
No, that will usuall not work well.. (two antennas of different types, one on each of the antenna jacks of a WRT54G at the same time) The WRT54G has a basic diversity antenna system - The unit is looking for the same signal (from the same target node)on each of the antennas. It will then choose and utilize the best signal from the source it is listening to on the strongest antenna connection. The two antenna connections can be used well in the dual antenna software mode with a dual polarity antenna (one with vertical polarity, and one with Horizontal phase tilt of 45 to 90 degrees) or distance offset dual antennas to greatly improve reception when experiancing phase problems. Phase flipping or distortion is usally caused by reflections in the Fresnel Zone, manifested by the receive signal level bounceing up and down. That is why the WRT54G comes with two antennas in its stock mode. An easy mistake to make is to assume that you can use two antenna types, for instance Omni and directional, putting one of each type on the two antenna inputs of the WRT54G. The unit can only listen on one of the antennas at at time, comparing the two, and then choosing the best signal from the target site to use. It can switch continuously back and forth very quickly, utilizeing the best signal from the target unit. The problem with using a gain directional, and a lower gain omni is that unless it sees the same target site on both antennas at the same time to compare which is best, it will not work in dual antenna mode properly. Most often, the high gain directional antenna will see signals it is pointed at that the lower gain omni can not even pick up, and the lower gain omni will see signals out of the beam width of the directional that the directional antenna can not see either, not allowing the software to compare the signals out of both antennas to choose the best one at each instant in time. Using two gain antennas aimed in two directions with a coupler on one antenna port (jack) would work but there are down sides to that, also. Comercial installs use that often with multiple sector antennas to beam a signal in specific areas, but remember, signal level is split between the two or three antennas used, and noise and competing signals will be picked up in the added directions. Hope that helps... David T. Bauman KF7MCF Magna Utah Bishop's Storehouse Emergency Response Communications
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