SRN: 1287

APC: 672, 749

Date: Sept. 1999

Deadline: March 31, 2000

Memo To: SRN Mailing List

From: Radio Product Group / CGISS

Subject: HT750 and HT1250 Buzz or Noise When Receiving a DPL Code

Symptoms:

The user may experience either of the following when listening to transmissions with DPL signaling.

The problem will be evident mostly during low level RF signals.

  1. Excessive and noticeable background 'buzz' in the receive audio.
  2. Receiver audio distortion due to the 'buzz' heard in the speaker.

Potential Problem Radios:

All Professional Series HT750 and HT1250 portables shipped prior to June 17, 1999, radio date code 9245.

Date code of the radio is listed on the serial number label on the back of the radio chassis.

Models Affected: AAH25KDC9AA2AN, AAH25KDC9AA3AN, AAH25KDG9AA4AN, AAH25RDC9AA2AN, AAH25RDC9AA3AN, AAH25RDG9AA4AN, AAH25SDC9AA2AN, AAH25SDC9AA3AN, AAH25SDG9AA4AN, AAH25KDF9AA5AN, AAH25KDH9AA6AN, AAH25RDF9AA5AN, AAH25RDH9AA6AN, AAH25SDF9AA5AN, AAH25SDH9AA6AN

Serial Numbers: 672TYWxxxx through 672TZMxxxx

749TYWxxxx through 749TZMxxxx

Cause:

A routine in the radio's programming provides suppression of the noise in the radio receiver, created when DPL signaling is present. The suppression percentage varies as the RF level changes, to provide the best sounding received signal. The radio code plug is setup to select the RF level threshold for changing the percentage of DPL noise suppression. If the RF threshold is set incorrectly, the radio user will hear excessive DPL noise in the speaker of the receiving radio.

Corrective Action:

Previously, the factory code plug settings in the radio set the RF threshold to -80 dBm. The new factory code plug (R01.05 and later) set the RF level threshold to -115 dBm. This decreases the DPL noise during all times except very weak RF signal level conditions.

To determine if the radio is defective, apply a weak to strong RF signal, on frequency, with the proper DPL code, and no voice/tone deviation. If the SINAD of the radio is between 20-30 dB, and excessive DPL buzz is heard in the speaker, the radio is considered defective.

HT750/HT1250 radios that fail the screen test must be sent to the Radio Support Center to have code plug version R01.05 or later installed. The address of the Radio Support Center appears below.

When returning the radio please reference this SRN.

 

Motorola Inc.

Radio Support Center

3761 South Central Avenue

Rockford, IL 61102

$25.00 is authorized for shipping and handling.

Warranty is authorized for the Radio Support Center at $35.00 For Work