This map is showing propagation characteristics on a VHF channel amateur radio operators use for their tactical mapping and vehicle tracking network call APRS (http://aprs.org/). While it will show some enhanced propagations when the band/frequency conditions are better than other times, it's not necessarily going to indicate ducting. This system uses a single VHF frequency of 144.390 MHz. I have been working with this network for over 25 years. The differences in this range compared to 2.5 GHz is significant. I am not saying you don't have that happening but you want to keep these differences in mind. I would also compare the sunrise times to the times of their interference. There might be chances that you are getting noise from the sun as well.
I am wondering if they could possibly pick up what the interfering system is broadcasting? If it's a cellular carrier like Sprint maybe you can detect the LTE signal or something. Maybe they can put a CPE on the tower in the direction of the problem and use it as a spectrum analyzer? Learning more about the interfering signal could possibly help in mitigation of the problem. Thank You, Brian Webster www.wirelessmapping.com www.Broadband-Mapping.com -----Original Message----- From: AF [mailto:[email protected]] On Behalf Of Adam Moffett Sent: Thursday, April 25, 2019 1:21 PM To: [email protected] Subject: Re: [AFMUG] Ducting mitigation It is licensed, yes. If I knew where the signal came from, could I figure out the angle of incidence? It seems like the warm air layer is above you so it has to be coming from above. Maybe we just put a climber on the tower in the AM and have him tilt down 0.5 degree at a time until it goes away. There's a null right above the main lobe, so I feel like if we tilt down slowly we can put the signal in that null. This is the map they're looking at by the way: http://aprs.mennolink.org/ -Adam On 4/25/2019 12:48 PM, [email protected] wrote: > Downtilt will help assuming it is coming in at a particular sky angle, > but you may lose coverage by doing it. Be interesting if you could > actually find the source of the interference. 2.5 is licensed right? > If you could get a real accurate bearing on the interference you ought > to be able to look up who is on that line. > > -----Original Message----- From: Adam Moffett > Sent: Thursday, April 25, 2019 10:40 AM > To: [email protected] > Subject: Re: [AFMUG] Ducting mitigation > > Hmm....couldn't say. In the example they showed me it was clearly > coming from the west, but I don't know if it's the same every time. > Does the fact that it affects more than one tower at the same time tell > us anything? I couldn't get more separation than a separate tower. > > Is down tilt likely to help at all or is that just chasing our tail? > > On 4/25/2019 12:22 PM, [email protected] wrote: >> Spatial diversity would work if the interference is always coming at >> the exact same angle. >> Is the interference always coming from one direction? >> >> >> -----Original Message----- From: Adam Moffett >> Sent: Thursday, April 25, 2019 10:01 AM >> To: AnimalFarm Microwave Users Group >> Subject: [AFMUG] Ducting mitigation >> >> I'm trying to help some associates in the Southeast who seem to have an >> issue with ducting. >> >> They have a number of 2.5ghz Telrad base stations. During the mornings >> in the springtime they'll get an interfering signal on multiple base >> stations at the same time. The strength of this signal is pretty >> ridiculous whatever it is. Last spring they struggled to explain where >> this was coming from, and initially were exploring things like return >> loss on cables or self interference. They found an online map of >> tropospheric ducting conditions and apparently they find that whenever >> the issue pops up they can pull up this ducting map and see a big red >> blob on top of their locations. This spring they're getting about the >> same experience. The fact that it happens like clockwork every morning >> and that it can be reliably predicted by this online tropospheric >> ducting map has them pretty convinced. >> >> The question is what can they do about it? >> >> My first thought was increase down tilt until the sector can't see over >> the horizon. They could try spatial diversity, but I don't know how far >> apart the antennas would have to be to make a difference. Any thoughts >> on that? Any thoughts on other solutions? The problem will go away in >> mid may (until next year), so whatever they try has to be done in the >> next couple of weeks. >> >> -Adam >> >> > > -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list [email protected] http://af.afmug.com/mailman/listinfo/af_af.afmug.com
