Q1: Which port should be used for Horizontal and which for the Vertical polarization?
Makes no difference, but if you intend to put SXT 5HnD to other end of the link then chain0 (j2) should be Horizontal one.
Q2: Is this configurable through wireless interface and how?
Radio side does not know anything about antenna polarization on these devices.
Q3: Do I have to declare H as Tx and V as Rx or this assigned automatically?
How exactly those antennas are being used is not clear to me, but it is not simply Rx/Tx separation either.
Q4: Which is the actual and practical difference between HH, VV and HV?
Interference from neighbour transmitters running close bands can be mitigated somewhat better when those antennas are operating in different polarizations. If you can put various transmitters much further apart channels then you need no polarization difference.
Q5: What kind of implementations each model support?
Every one can be connected, but HV/VH should work better.
Too many questions from a beginner… >
Me too, at least to the world of 802.11n and still testing it out. Somehow my attempts to get a 2 km 2 chain (HV-antennas) link working is not too satisfactory to me - at some point all traffic will be cut despite link is still being reported as up with very good link speed and SNR numbers. 1 chain links are running fine, but I haven’t seen any actual speeds higher than 25Mbps.
I indeed use SXT 5HnD. I also read in other threads that chain 0 has to be assigned to horizontal polarity.
For SXT manual says “Dual polarization 5GHz antenna” and “Polarization Dual Linear (V-pol, H-pol)” and:
“If you want to overcome certain obstacles or interference by using only one polarization in 802.11a mode,
you can switch off chain1 of the wireless device. When chain0 is used, the device is horizontally polarized
when mounted as indicated in the Mounting section of this document. If you wish to use vertical polarization,
turn the device 90 degrees to that the mounting bracket attachment is parallel to the ground. Chain1 can’t
be used separately. Switching off chain1 to use only one polarization can be done in the RouterOS wireless
configuration menu.”
Now for AP we have:
a) j2 antenna port corresponds to chain0 (should be set to horizontal)
b) j3 antenna port corresponds to chain1 (should be set to vertical)
Because on the SXT we have:
a) chain0 which corresponds to horizontal
b) chan1 which corresponds to vertical
Thus, an HV polarized antenna (on the ap) is ideal in this case, because can take advantage of SXT dual polarization.
In RouterOS menu of the AP, we can set Tx or Rx in any directions. So the combinations are:
chain0 Tx - Chain1 Rx
chain0 Rx - Chain1 Tx
chain0 Tx & Rx - chain1 Tx & Rx
(Each of the above should be placed on both ap and SXR)
Furthermore, I think there is a method to isolate Tx & Rx on separated directions (or even antennas) to improve performance and reduce noice.
In any case all the above require deep testing in order to have a clear view of the results…
Is anyone more experianced who can help us with this?
if you use dual polarized antennas then use the 3rd option: chain0 tx/rx and chain1 tx/rx. In this case it doesn’t matter to which connector you connect which polarization.
Note that you can’t use chain1 without chain0. Chain0 always should be enabled for wireless operations.
Each time and hw/ROS combination I have used the dual chain operation is destined to fail. At some point all traffic over that link will be halted for extended periods of time (minutes). Usually it will recover by itself or a simple re-enabling of the radio will do the trick, but that is not a working option. Funny thing is that during that trafficless time the radio link numbers will be excellent. Chain0 only operation does not have that issue for me.
I’ve tried RB433AH & SXT5HnD and RB433AH & RB433AH with different cards and antennas with the same results.
On my case and all tests were successfull when using dual chain operation. I didn’t noticed such behavior.
Let me note that I didn’t have enough time to perform extensive testing and I only used nstream for my tests.
I still haven’t found some time to test nv2 but I’ll definetely schedule it for coming days.
I was very surprised with the results. SXT was able to pair with the AP even for 22Km distance giving 16mbps thoughput!
Since SXT supports dual polarity (H & V), after you enable dual chain, you ought to have also dual polarised antenna on AP side too.
So, did you used dual polarity antenna on AP side?
During my nstreme testing I disabled encryption and P Throughput jumped from ~30Mbps to ~90Mbps. I haven’t tested real performance, but it seems there is an issue with encryption of the traffic. Why?
Indeed you cannot use tkip. See below respective section from wiki:
Security in Nv2 network
Nv2 security implementation has the following features:
hardware accelerated data encryption using AES-CCM with 128 bit keys;
4-way handshake for key management (similar to that of 802.11i);
preshared key authentication method (similar to that of 802.11i);
periodically updated group keys (used for broadcast and multicast data).
I have that tkip issue in all other modes, not with NV2 which is known not to use any defined security profiles at all and has own security settings. I’ve yet to test out if I can use NV2 at all, but by turning off tkip I now can use 2 chains with nstreme mode.
