Cobra 148NWST User Manual

Consumer Response Group
6500 W. Cortland Street * Chicago, IL 60707 * Phone: 773-889-8870 * FAX: 773-622-2269
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June 3, 2003 Page 1 of 2
TECHNICAL SERVICE BULLETIN
10020
MODEL(S): 148GTL, 148NWST
DESCRIPTION: Squealing on transmit. Possible causes:
• High SWR
• Inadequate ground
• Microphone sensitivity of radio is too high. Specification:
− From 1 to 2mV for 50% modulation with Soundtracker off
− From 0.5 to 1mV for 50% modulation with Soundtracker on
ACTION: One of the following suggestions should solve the problem:
1. Check the SWR of the antenna, make sure it is below 3.
2. Connect a ground wire to a screw on the side of the radio, to ground the
chassis of the radio.
3. Remove the top cover plate and tighten all the screws around the edge of the
circuit board.
4. If the radio still squeals, the microphone sensitivity of the radio is too high.
Change R126 to a 12K resistor.
ADJUSTMENTS: If R126 was changed, check maximum modulation.
NOTES: Page 2 contains a procedure for checking microphone sensitivity.

Cobra 148NWST Specifications

General

Brand	Cobra
Model	148NWST
Category	Two-Way Radio
Language	English

Summary

Technical Service Bulletin 10020

Model Identification

Lists the specific Cobra radio models affected by this bulletin.

Problem Description and Causes

Details the issue of squealing on transmit and lists potential causes like high SWR or inadequate ground.

Troubleshooting and Action Steps

Provides a sequence of recommended actions to resolve the squealing issue.

Adjustment and Verification

Outlines checks and adjustments related to microphone sensitivity and modulation.

Checking Microphone Sensitivity

Procedure for Sensitivity Test

Details the steps to test and adjust microphone sensitivity using audio and modulation meters.