Antenna questions for RF Elements


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I have need of some recommendations from you'll.  I have a link to a client that is about 1.5 miles long. It is using a Ubiquiti LTU ap with an RF UD-TP-24 for an antenna with Twist port mounted on the penthouse of a 25 story office building.  The client side is a Ubiquiti LTU-LR antenna mounted about 25' up in a big oak tree.  The trunk is still over 2 feet thick at that point so no appreciable sway.  We were using 5740 with 20db transmit power and do to some interferance on that channel tried to switch down to 5170 as an alternate channel.  However when we did the link lost about 5-6 db on one polarity and 7-8 db on the other, with the loss being about the same on both side of the link.  The link is already degraded considerably due to an intervening tree we were unable to get around at time of install.  But nothing changed power wise or aim wise on the link only the frequency.  Now the Ultradish we are using is a unit we purchased for eval if I remember correctly not long after they were first released.  My questions are the following.  I remember several years ago RF announced larger frequency capabilities for their antennas, adding the ability to go up into 6 ghz but i don't remember how low they went. The current specs say 5180-6400, but if you look at the gain charts, the gain is still only down maybe .5db by the time you reach 5100.  So if that chart is accurate does it also apply to the Ultra Dishes when they were first released. If not, what were the specs and would that account for the large signal drop trying to go to 5170.  Second moving forward we are thinking to up the antenna at the ap.  Looking at current specs we were thinking of going to the ultra horn for the better isolation but then noticed that the UD-TP-27 beam is narrower still and gives more gain for punching through the tree.  Would that be a better choice then the horn even with the side lobes the 27 has vs the ultrahorn at 24 with essentially no side lobes at all but a larger total beamwidth in general.  Thanks for your thoughts.

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Hi, as you correctly assumed, the UD-TP-24 has almost flat gain across the useful bandwidth so the 7 - 8 dB drop in signal strength is strange. To your questions:

1. May be that due to different frequency the reflections add up destructively at the CPE, I'd try to move either AP or CPE (including antenna) up/down a little to see if it improves. 

2. For 1.5 mi distance a 24 dBi AP and 26 dBi LTU-LR antenna are more than enough. You can use the UD27-TP if you want, but if the noise is an issue, UltraHorn will increase the SNR more than the 3 dB difference in gain comparing UD24-TP an UD27-TP. Beam efficiency of UD24-TP is 40% while Ultrahorn has 99% beam efficiency

Regarding beam width - unless you have noise sources within the 15 deg beam width angle of UH vs. 12 deg of UD24-TP, you should be ok. 

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