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On Fri, 27 Jan 2017 08:22:43 -0500, rickman wrote:
I had a WISP unit upgraded for better reception and they used a Yagi antenna, at least I guess it's a Yagi. Here's a photo. http://www.netwifiworks.com/images/a.../Yagi/yagi.png Ok. That's an Ubiquiti AirMax AMY-9M16 900MHz antenna. 16dBi gain and dual simultaneous polarization (i.e. not switched): https://www.ubnt.com/airmax/airmax-yagi-antenna/ https://dl.ubnt.com/datasheets/airmaxyagi/airMAX_900MHz_YAGI_Antenna.pdf You need the dual polarization to get double the normal speed by using 2x2 MIMO streams, one per polarization. This doesn't seem to fit the mold in a couple of ways. The elements are not spaced at all regularly. The spacing seems to vary around a bit. I agree. It does look weird. However, having extra aluminum near the antenna in the form of the other polarization, and getting sufficient isolation between the two polarizations, is going to do strange things to the design. Send me dimensions and I'll analyze it (time permitting), like I did with the 2.4GHz MFJ1800 yagi: http://802.11junk.com/jeffl/antennas/mfj1800/index.html But more importantly, I've read that the director elements are *insulated* from the support beam while these are all welded. That's done so that the mounting boom does not become part of the element length. Were it not insulated, half the circumference of the boom would need to be added to the element lengths. Insulating the elements also provides slightly fewer sidelobes and possibly (not sure) better isolation between polarization. Looking at the patterns on the data sheet, it looks much better than I would normally expect from a single polarization yagi. Obviously it works. Assumption, the mother of all screwups. However, the data sheet does seem to show that they actually made some measurements. I'm getting about 6 dB stronger signal than before although it's a bit hard to compare as the location changed and I measured about a 3 dB gain with the old unit in that location. But more importantly, with the signal rising by 6 dB, the reported background noise also rose 6 dB. Isn't SNR what is important that the antenna should have improved? Yep. You want to maximize the SNR. Increasing both equally is about what I would expect if your antenna were also pointed at other sources of interference. The 900MHz smartmeters are a likely culprit. Plenty of other possibilities. Can you move your new yagi around a little to see if you can minimize the background noise? This Yagi claims something like 20 or 25 degree beam while the old antenna had a 60 degree beam. A narrow beamwidth is good for reducing interference coming from off axis interference sources. However, if the source of interference is along the antenna axis, or in your case, within less than +/-10 degrees off axis, you can easily make things worse. Got a 900MHz spectrum analyzer handy? Any of the USB RTL-SDR (RTL2832U) dongles should do the trick, although a 900MHz RF amp will probably be needed. Use it to see what you're dealing with. http://www.rtl-sdr.com/?s=spectrum+analyzer -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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