900Mhz Relay site interference

I could use some advice!

I recently bought and deployed 900Mhz Canopy equipment for a repeater site. I am receiving signal from my primary 900Mhz tower using a 900Mhz (915Mhz) SMC with a Ya9-11 yagi antenna. Then about 45 feet in front of the SM and about 5 feet to the side of it, I have a 900Mhz AP (924Mhz) connected to a Til-Tek 120 antenna to re-broadcast into a shadowed area. I am running a sync cable from the SM to the AP to carry sync and then have an Ethernet cable going from the AP to a switch where the SM connects as well. None of these cables are shielded (as of yet). I can only get the Transmitter Output Power level to about 15dBm on the AP … anything higher and the SM quits responding. I’m assuming the power of the AP is squashing the SM’s sensitivity.

What do you recommend … I would like to crank the Transmitter Output Power to 28 dBM. Do you think shielded cables (sync cable, Ethernet cable for the AP and Ethernet cable for the SM) will make a difference? Is there some type of shielding I can do behind the Til-Tel antenna so it doesn’t radiate back to the SM? Other thoughts?

Gregg Smith

According to Motorola:
To put an SM near an AP in the same frequency band you need either 100ft of vertical separation or 1000ft of horizontal separation.

There seem to be ways around this with other frequencies. I have found that with 900 this pretty much applies. I use 2.4 Canopy AP/SM pairs as Backhauls to link Site A with Site B both running 900 APs. 2.4 will go through a few trees as well. Put a stinger on the AP and a dish on the SM to make the link very solid.

mattmann72 is right… separation is critical with the 900 setup… 100ft vertical or 1000ft horizontal will alleviate the self interference, or you may need to utilize different Color Code and Frequency… I still think you will need the separation to successfully deploy this configuration.

Good Luck.

Frequency alone will not do it from my experience.