NT7SU-200

Date: 1 September 1998 To: Frank Coperich, FCC From: John Montgomery, Senior RF Engineer, DIVA Communications Tel: 1.510.986.6441 Fax: 1.510.986.6489 Email: [email protected] Subject: Response to Correspondence ID: 3101 Grantee Code: NT7 Product ID: SU-200 731 Confirmation Number: EA89425 Correspondence ID: 3101 1.) Response to question # 1: Sorry for the confusion, DIVA concurs with your note. This is correct. The ERP (power with respect to a dipole antenna is 2.1 dB less ). The gain of the antenna is 0 dBi or -2.1 dBd. The ERP is therefore: 27.3 dBm - 2.1 dB = 25.2 dBm or 0.33 W 2.) Response to question # 2. DIVA is assuming that the minimum user spacing referred to is the 19 cm required to meet the MPE limit. Please note that our calculation does include the use of the 9 dBi gain antenna. This calculation was given in the previous response (Correspondence ID: 1824, item 4). The calculation is repeated below: The DIVA radios can be used with the 0 dBi built-in TX/RX antenna or an external antenna with a maximum gain of 9 dBi. The power output at the antenna port is 0.8 watts +20/-50% or 0.96 watts maximum (0.8 watts + 20%). The maximum antenna gain G is 9 dBi (7.94 numeric ratio) (for the 9 dBi antenna). The Transmitter Duty Cycle DF is 33% for TDMA (used by the SU-200). The required MPE Limit is f/1500 mW/cm^2 At 824 MHz the MPE Limit is 0.549 mW/cm^2 (worst-case) At 849 MHz the MPE Limit is 0.566 mW/cm^2 The Power density S = E^2/3770 = 0.549 mW/cm^2 for the worst-case MPE. The electric field strength E = 45.5 V/m for the worst-case MPE. Since E = (300*P*G*DF)^(1/2) / d = 45.5 V/m for the worst- case MPE. Where P is in watts, G is a numeric ratio and d is in cm. Using the values given above with a 9 dBi antenna and solving for d using worst-case MPE we obtain d = 19.1 cm (for 9 dBi the external antenna). Note that the use of the built-in antenna results in d = 6.8 cm for the worst case MPE. Please note that the unit is designed to be wall mounted near the ceiling and includes an RJ-11 jack to which a standard phone line is attached. Phone line extensions are typically wired through the home or business from this RJ- 11 jack. Since generic third party telephone handsets are used, as supplied by the customer, there is no reason for the SU-200 to be in close proximity to the user during normal usage. Depending on the site requirements, either the built in antenna is used or an externally mounted higher gain antenna (e.g., the 9 dBi antenna referenced before) is used. The external antenna must be located external to the building, usually on a mast attached to the roof or an external wall of the structure. A DIVA supplied cable adapter (DIVA P/N 120-00003-01) and RF cable is used to connect the SU-200 to the external antenna. Attached is a drawing of a typical installation using an external antenna. Please Note : When external antenna is used, the built in antenna is disabled. John Montgomery Sr. RF Engineer Engineering Group Diva Communications, Inc. 1999 Harrison St., Suite 1400 Oakland, CA 94612 USA TEL: 1.510.986.6441 FAX: 1.510.986.6489