Also, remember that some radios have the ability to sync, so one radio
is not transmitting while the other is receiving.
-Matt
Jason Wallace wrote:
Bob,
Item 4 is what I am talking about. If your radios have very good
adjacent channel rejection, are not transmitting at high levels, and
the antenna has minimized any of the coupling I mentioned, then they
may be able to listen through the "noise" from the other transmitter.
A lot of this depends on output power; it is possible to just totally
swamp one receiver with another transmitter and create a noise floor
too high to listen through. In my last post I was thinking like a HAM
operator (theory-wise) that deals with much greater power levels.
With 802.11 power levels, it may work better. It has to be designed
right, like you said. No one should think that you can just hang a
dual pol and do anything with it.
Jason Wallace
Bob Moldashel wrote:
Sorry but this whole thread is going sour fast.....
1. Dual Polarity antennas work for transmit and receive. They are not
TX only or RX only in configuration.
2. The normal isolation between vertical polarity and horizontal
polarity can range from 10-30 dB depending on the operating frequency.
3. The biggest issues to using 2 radios on the same dual polarity
antenna is the adjacent channel rejection, x-pole polarity, TX power
levels and Receiver sensitivity..
4. 802.XX radios will not work on the same channel because while one
radio is transmitting on 5825 GHz. the radio on the other polarity is
receiving on the same channel. Considering there is only 10-30 dB of
seperation, the radio RX levels will only be reduced by that amount
causing receive interference.
5. We have more than 20 dual polarity links running FD radios such as
Proxim Tsunamis operating in the same band. Granted, they have much
better filtering than the basic 802.XX radio but they work flawlessly..
6. We presently have 2 DP links in place with 802 style radios. One
of the links consists of WRAP/CM9's operating in 5.7-5.8 Ghz. The
other has a Proxim MP.11a on one plane and Tranzeo TR-5a on the
other. One link is 6.5 miles, the other is 7 miles. There is no
desense between radios and both operate fine without interference
issues.
7. While Tom may be experiencing the tower rental issues regarding
antennas, we have not seen this in the NE. Most leases we have
negotiated are based around wind loading on the tower.
Like everything, dual polarity antennas have a place like all other
equipment. The link just needs to be engineered to operate properly.
-B-
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