Fri Apr 23, 2010 11:08 pm
wirelesswaves
I too am a ham and have run this RB433AH/2-XR5 config. Without spectrum analyzers, just intuition--and just plain old RF experience DXing and running VHF/UHF and above contest stations that have come in #1 or close to it (AA9D) I have come to some conclusions. I worried about the use of two high power, especially XR5's, cards in the same box before I even powered it up. It just felt wrong--and certainly doesnt work.
Some in this thread seem to want to squeeze more blood out of this rock than could possibly be available. I think many are trying to solve the wrong problem, my opinion only.
The first hint at what I am taking an educated guess on is IF connectivity. I had two XR3 cards connect on a 5GHz frequency, i.e. one not convertable to the offset 3.65GHz frequency. Seems like simple proximity allowed connectivity between the two cards. Who knows at what frequency? Dont even want to know. What would you possibly expect with two or more stacked cards? I too was contemplating putting in a 'ham engineered' shield of aluminum foil inside of the static bags that cards or boards come in. Seemed a little too rigged up before I proceeded. Of course that begs the question, why are there three mini-pci slots. Another topic all together.
However......I already had two XR5's in the top and bottom slot to separate them by a slot (wow). Trying to get something out of a config that was mounted in a place not readily accessible, AND, coincidentally I had the cards connected to a dual-pol Gabriel 2ft 'drum' dish I surmised that a workable config could be had. The cards have pretty good receive characteristics, and ample power for sure, and I if I operated with only one of them transmitting, maybe I had a chance. Two cards transmitting produced the expected results--de-reg, de-reg. Of course you know where I am going. Dual Nstreme with 220MHz separation actually worked--to a fashion. A short 7 mile link, more than 700ft off the ground at each end with nothing in between was able to connect.
Where is the catch? Band was pretty crowded, so results must be interpreted with a grain or more of salt. Attempting to config the correct polarity/frequency/direction combo is very critical in the ability to obtain reasonable bitrates and stability of the link of course. I was able to operate turbo in one direction (downstream the desirable direction if you can make it work), and 20MHz channel on the other. The isolated feedhorn collared dish provided excellent near field ingress from many other co-located APs. However, putting out copius power into the cross-pol feedhorn has the expected effect. Lowering power (1dBm increments) gave me the best possible compromise.......
Now, for the real world performance of this highly utilized backhaul. The more traffic either direction sustained, had a direct relation to the CCQ of the 'other' direction. CCQ of course is estimated by performance and jitter only, since it doesnt seem to be a metric available in dual-nstreme. This was expected, and could even make this config unusable, but I believe it provides some empirical evidence that multiple cards can be used in thee 433 class environment, with the caveat that you might not get maximum bitrate. However again[!], I was able to run the turbo channel at 54Mbps@2, with the cost of lowered stable bandwith in the other direction. With careful tuning of power and micro adjustment of channel (5MHz increments), a full-duplex, albeit asymmetric backhaul can be operated. Many times the asymmetry matches the real world bandwidth requirement.
The moral of this verbose ham-engineered story is that I got what I expected out of something that was deployed with a useless second card. As with DXing and contesting, it all seemed to be in the antenna guys. Put up 4-18el beams on 144MHz, and you know its going to burn through a lot more distance than the same EIRP obtained using a single 18el beam with 6dB more output power. Im sure that could be disputed. Thats why we used 4 different yagis on six meters. Some could hear a certain distant station, while other antennas could not hear a peep out of the same station....
Bottom line is that I believe IMHO that the wrong problem was attempting to be solved. For those that just want it to work with all three slots filled, eventually the stress will beat you.....BTW, an RB600 with two cards doing the same thing doesnt have these problems...Hmmm....Is there a significant null to the side of the cards that takes you below the threshold of pain?
Thats my story, and Im stickin to it...Hope this in some way helps someone leverage what they have invested and obtains the benefit of an asymmetric--and very fast (done properly) backhaul that leverages just the benefits and good characteristics of each component of the total link........If I missed something obvious, forum, or helped in any way, please advise...