Motorola Bag Phone RF Info

Overview

Finally got a chance to look at an old Motorola bag-style cellular phone on an IFR-1200S service monitor.

RF power output and a spectrum analyzer shot are shown before.  The phone was in "test mode," with pin 21 on the DB-25 tied to ground.

The test frequency was 837.000 MHz.  Enter 110400# on the keypad while in test mode to set the phone to that frequency.  The phone's RF output power is set with the 12x# keypad entry.  Where "x" is either 0, 1, 2, 3, or 4.  Highest output power is with the "120#" option.  The RF output seemed unstable while on the "124#" option, so stick with "123#" and pad down the RF power level with a resistive attenuator pad.  Most commerical double-balanced mixers needs a +7, +10, +13, or +17 dBm input LO signal, if you use the phone for this application.

Motorola Test Mode Command RF Output Power (Watts) RF Output Power (dBm)
120# 2.57 +34.1
121# 0.85 +29.3
122# 0.30 +24.8
123# 0.10 +20.0
124# 0.02 +13
125# No RF Output No RF Output
126# No RF Output No RF Output
127# No RF Output No RF Output
128# No RF Output No RF Output
129# No RF Output No RF Output

Spectrum analyzer screen capture of a Motorola bag-style cellular phone, in testmode, transmitting at 837 MHz.  The horizontal setting is 20 kHz per division.  Vertical is 10 dB per division.