Ethernet crystal harmonics. The crystal on Ethernet is 25MHz. So your hitting them with the 9th harmonics. This bleeding is worst with PoE powered devices because it couples into the DC power over the cat5 cabling and if the power supply is not nice and clean it will couple into the AC system as well. I have been involved in certifying 4 radios in a FCC certification lab. Each time we ran into this problem especially when powered by PoE. A different power supply could make a huge difference but also installing ferried beads on the cat5 cabling (close to the radio port, directly after the poe device out port and directly on the poe data in port) cleaned up this emission. Using shielded cable will help on equipment that is picking up this radiated signal directly from the cat5 cabling but if it's bad enough and the powersupply isn't good enough the harmonics signal will go out into the AC source unless ferried beads been installed properly.
On one of these devices I helped getting certified we had to make it mandatory to have these beads installed to be able to pass (product never made it to market). / Eje CTO WISP-Router, Inc. -----Original Message----- From: wireless-boun...@wispa.org [mailto:wireless-boun...@wispa.org] On Behalf Of Steve Barnes Sent: Wednesday, April 29, 2009 10:02 AM To: WISPA General List Subject: [WISPA] Noise by me on a tower I have an odd situation, I have 2-2.4 180* sectors MT RB411 and 5-5.8 StarOS War1 backhaul radios and a RB600 router at the top of a 265ft old AT&T microwave tower. The top has a grounded NEMA metal box and POE powered by an Allen Bradley converter. I have an AC and an Ethernet run to the base where I have a APC UPS. The owner just leased space to another client 20 Feet away on same level from me. It is a local REMC doing meter reading on 221Mhz. They were having problems with receiving they brought in a spectrum analyzer and there was a noise floor of -71 at 220Mhz. The tower owner being an radio guy not a wireless guy just killed power on the ups. (taking down all my stuff and locking up 1 one of the radios for an hour GRRR) When our equipment was off the noise floor went to -108. As soon as he powered me back up the noise returned. They actually said that there was noise from around 150Mhz to 240Mhz. Everything is grounded and cased in metal except the LMR that goes to the Antennas, the AC wire is in flex and the shielded Ethernet down the tower. Ideas? there might be a little noise off the oscillators of the War-1 boards but that's 175Mhz. The Ethernet is 100Mhz, RB411 300Mhz and RB600 266 MHz Steve Barnes RCWiFi Wireless Internet Service ---------------------------------------------------------------------------- ---- WISPA Wants You! Join today! http://signup.wispa.org/ ---------------------------------------------------------------------------- ---- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ -------------------------------------------------------------------------------- WISPA Wants You! Join today! http://signup.wispa.org/ -------------------------------------------------------------------------------- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
