Cobra 148GTL 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 148GTL Specifications

General

Modes	AM/SSB
Channels	40
Power Output	4 Watts AM, 12 Watts SSB
Microphone Type	Dynamic
SWR Calibration	Yes
Antenna Impedance	50 Ohms
Power Supply	13.8 VDC
Weight	4.5 lbs
Frequency Range	26.965 MHz to 27.405 MHz
Dimensions	2.25 x 7.25 x 9.25 inches

Summary

Technical Service Bulletin 10020

Problem Description and Causes

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

Troubleshooting and Action Steps

Provides four actionable steps to resolve the squealing issue, including checking SWR and adjusting components.

Post-Adjustment Checks

Instructs to check maximum modulation after changing resistor R126.

Checking Microphone Sensitivity Procedure

Step-by-step guide to measure and verify the radio's microphone sensitivity.