interference with vhf pager system

well 911 has blowed a cog with me eventently i understood them to have only a vhf 2 way radio system and we tested to make sure it worked and it was fine but to my surprise they had a vhf pager system that relays through a phone line to key a repeater anyway my stuff was interfering with it they never even called me to go fix it and they call there technitions and they unplugged my stuff now i go tto pay there bills hehe anyway no problem i understand the rules .
But my question is what do i need to prevent this from happening what kind of filter etc… here is my equipment i have there.

1 900 ap connnectorized with the 900 mhz horizontal polorized omni antenna from lastmile. located about 30 ft from there vertical polorized omni about the same height. i think there pager system pages at 154.490 or close to that.
the technition that services there equipment said it shouldn’t interfere with the wide separation of frequencies but that harmonics could be playing a role in this how can i test the harmonics to see?

oh and all there equipment is motorola to lol help me moto

Info-Ed Inc…

The chances of your 900 MHz stuff interfering with their 154.49 MHz paging transmitter (controlled by phone lines, you say) is slim to none. However, some paging transmitters are controlled (or used to be) by 900 MHz directional links - if they have one of those links, you may have an issue where you’re actually impairing their link…

Their technician’s comment about harmonics is far more likely referring to the chance of their 154.49 harmonics that hit 900 MHz and interfere with you. Many/most paging transmitters are high power units, with up to 250-300W output power, so even a 6th harmonic of 154 MHz that’s 120 dB below their carrier power might be noticeable to your 900 MHz stuff.

As always, it’s good practice regardless to use shielded cable to feed the Canopy unit (and their tech might have mistaken that cable for RF coax, rather than the Cat5 ethernet cable it actually is), and ensure good grounding practice at your antenna and at your equipment’s location.

Regardless, your description of your antenna’s location relative to theirs should give plenty of isolation (although I’m talking about isolating YOUR stuff from their high-power VHF tx) - again, it’s highly unlikely, to the point of near-impossible, for your stuff to interfere with their OTA paging signal.

A current Motorolan may expand on this - I’m merely an ex-Motorola land-mobile tech with 20 years’ experience…

Sorry to disagree with you Kwatson but it is a known fact that the 900 Canopy units interfere with VHF radios. Motorola’s recommendation is 10ft vertical seperation of antennas. I would go 20ft to be safe. I have experienced this first hand by doing the same.

well i was using 910 mhz and they said it hit the 6 octave dead on so if i change the frequency to something different do you think i will be ok ? and they do know it is cat 5 wire and it is strapped on the oppsite side of the ladder coming down the tower which is about 12-18 inches apart.
here is a pic of the tower you cannot see our antenna but it is top dead center of the tank and you can see to the left on the little tower is there equipment this is on a 230 ft tank. i am sure it is more than 10 ft from there stuff but what do you all think?