..... Today, one cannot use the same channel/polarity on the same site anyway...
Actually, you can if the azimuths are sufficiently different and you choose antennas carefully. The difference is distance. Say you built a new path between points A and B using the traditional FDD licensed equipment, and for simplicity, there are no other 11GHz systems anywhere close to your new link. Your coordinator would be free to choose any frequency pair for you because there is no interference to avoid. At 11GHz the frequency pairs generally have a 490MHz split, so at site A you may be instructed to transmit at 11015MHz which means you will also have a receiver operating at site A at 11505MHz. Your system works fine. You now decide you need a link from A to C. Once again, there are no other 11GHz systems in the area, so the only potential interference is from your A/B link. The A/C link coordinator now has an established Hi/Lo regimen at site A, with site A transmitting "Lo" to B, so he would normally pick another "Lo" frequency for transmitting to site C, which would bring along another high band receiver at site A. Doing so maximizes the frequency separation between the transmitters continually transmitting from A and the receivers continually receiving at A. The nearest receiver operating in the low half of the band would be at a distance equal to the shorter of path A/B and path A/C. Any third party link would ideally follow the established Hi/Lo regimen. Now you introduce a TDMA link between A and D. If you choose a frequency pair that follows the Hi/Lo regimen you will again go with a Lo band transmitter, but it is only a transmitter for the duty cycle of the TDMA link -- say 50% of the time. The other 50% of the time you have a low band receiver at site A with the nearest transmitter only feet away. NSMA has a paper that suggests the pattern of an 11GHz antenna isn't predictable until you get about 0.55km away from the antenna, so you probably can't assume the antenna will protect you. Polarization may help, but the systems under discussion seem to use both polarizations, so at best only one polarization may be affected. Ah, but you still have _some_ frequency separation, right? Well, when we run a frequency analysis we will look for interferers at not only the frequency of interest, but at a minimum, anything falling within the adjacent and second adjacent channels to cover the potential impact of out-of-band emissions. For a 40MHz system this means looking at everything within +/- 100MHz, and for a 80MHz system, +/- 200MHz. So again, if you are running an isolated system you shouldn't have any issues. However, given the current licensing process, if there are third parties involved and they are reviewing the PCNs that they receive, you should expect them to flag your links as unacceptable due to bucking with, perhaps, some accommodation if you agree to a post-installation test of some sort. Mike Black Black & Associates 727-773-9016 www.bamicrowave.com logo.png black & associates Frequency Coordination ● FCC Licensing ● Engineering Design From: Af [mailto:[email protected]] On Behalf Of Faisal Imtiaz Sent: Tuesday, October 20, 2015 7:07 AM To: [email protected] Subject: Re: [AFMUG] Mimosa B11: Exactly what does the mounting look like? >>>Instead, the challenge is in assessing and accepting the risk of possibly >>>bucking your own 11GHz links or other operator's 11GHz links on or near your >>>two endpoints. As there is no reliable way to calculate this type of >>>interference, you may only become aware of the problem after you have >>>installed and turned up your TDMA system. Call me stupid, and please explain how that is ......I can understand the issue of channel/polarity availability...however how is this potential interference different from current ..... Today, one cannot use the same channel/polarity on the same site anyway... The B11, actually opens up the possibility of channel reuse, on the same site with angular separtion ...(possibility being a key word). Regards Faisal Imtiaz Snappy Internet & Telecom 7266 SW 48 Street Miami, FL 33155 Tel: 305 663 5518 x 232 Help-desk: (305)663-5518 Option 2 or Email: [email protected] _____ From: "Mike Black" <[email protected]> To: [email protected] Sent: Tuesday, October 20, 2015 12:45:25 AM Subject: Re: [AFMUG] Mimosa B11: Exactly what does the mounting look like? +1 to Tim's remarks in this thread. The challenge isn't in coordinating the same frequency pair in H and V between two sites, in both directions. Instead, the challenge is in assessing and accepting the risk of possibly bucking your own 11GHz links or other operator's 11GHz links on or near your two endpoints. As there is no reliable way to calculate this type of interference, you may only become aware of the problem after you have installed and turned up your TDMA system. If there are no other 11GHz systems within about a half km of either site and you don't plan to expand either site with additional 11GHz equipment from other vendors, you may be ok. If not, then ? Mike Black Black & Associates 727-773-9016 www.bamicrowave.com logo.png black & associates Frequency Coordination ● FCC Licensing ● Engineering Design -----Original Message----- From: Af [mailto:[email protected]] On Behalf Of Hardy, Tim Sent: Monday, October 19, 2015 8:29 PM To: [email protected] Subject: Re: [AFMUG] Mimosa B11: Exactly what does the mounting look like? In the olden golden days building the MCI route with full block systems, we would have "bucks" or "bumps" in frequency plans when required, and we learned first hand how important it was to use ultra high performance antennas or better in such situations. With very little free space loss, antenna performance is key and there is very little reliable data on close-coupling antenna performance, so it is extremely difficult to accurately calculate expected interference levels in these situations. With the prevalence of 2&3' antennas these days, antenna isolation will be an even larger challenge. Sent from my iPhone > On Oct 19, 2015, at 8:03 PM, Seth Mattinen < <mailto:[email protected]> > [email protected]> wrote: > >> On 10/19/15 16:56, George Skorup wrote: >> To make Tim's point, we're co-located on a couple towers with other >> 11GHz users and using both the high and low of a channel pair at both >> ends is unpossible. (yes, that's a word :) > > It's a perfectly cromulent word. > > ~Seth
