Co-locating new PTP-450i with existing PTP-250

I am looking at leasing tower space on an existing 36 inch faced PiRod tower for a new PTP450i 5.8 GHz installation.  The PTP450i bearing would be 327 degrees.

Another entity has a PTP-250 operating at 5.8Ghz on the same tower with a bearing of 180 degrees. 

Other than trying to coordinate channel selection between the two PTP units, setting each on a different fixed channel,  how much physical spacing (vertical)  between the units would be required?   Or is it unwise to co-locate these PTP models?   I can choose my model but the PTP-250 is already on site.

Unless they're already doing GPS sync to begin with, and you're very friendly with them, it's going to be difficult  to do any sync with them. My guess is that if they only have one link on the site, theyr'e not doing sync.

As far as seperation between the two, this depends on the antenans that they're using and you're using and the front to back ratios on them. You'll want antennas with a high front to back ratio... shoot for 25dB or better. The nice thing is that the PTP450i already has some filtering capabilities, and it's a wide-band radio, so you have pretty much the whole 5GHz band to choose from. This should make it very easy for you to find a channel to put your 450 on.

All that being said, assuming you choose an antenna with a good F/B ratio and they're using a decent antenna with their link, you could put them very close to each other physically (like within a few feet of each other) and only have to use 20MHz band guard or possibly less.

PTP 250 doesn't support TDD synchronization, and it is not possible to synchronize the TDD frame of the PTP 250 and PTP 450i units. In that case, you need to provide enough isolation between the two units so that the transmit signal of one radio does not degrade the received signal of the other radio.

The amount of isolation you need depends on: (a) the transmitter power that you intend to use on the two units, (b) the level of noise received from other systems in the area, and (c) the modulaiton mode you need to achieve the target capacity.

This isolation will come from: (a) operating the two systems on different channels, (b) the physical separation on the mast, and (c) the antenna patterns of the two systems.

Ideally, you will install the PTP 450i at a different height on the mast, and in this case the separation distance is more or less the height difference, and the antenna response we're interested in is the gain at 90 degrees from the main lobe.

If it is not possible to install at different heights, and this is an open lattice mast, then the antenna response we're interested in is the gain at 180 degrees and, as Eric points out, this is normally specified as the front to back ratio.

If the antennas are at the same height and on opposite sides of a solid mast (like a significant size monopole), then the front-to-back ratio is less important, but it's difficult to estimate the isolation afforded by the mast structure.


Thank you for your advice.  All understood.   Project was paused but now moving forward.

Thank you Mark for the assistance.