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Audio Pulsing

Models that could be effected:
KT8900, JT6188, mini8900, UV2501
KT UV980, UV5001
Note: Does not occur in all radios
by: John  'Miklor'
December 2015


Important Note
-  Not all radios are affected by this.
-  The outdoor environment and the Receive CTCSS play a key role in this issue. 

-  When in a moving vehicle, the audio will pulse.
-  This does not occur while the car is still or when used as a base station. 

The Cause

This audio issue occurs when selecting a channel with a CTCSS tone assigned to the Receive frequency. When leaving that channel, the issue will remain, even if the new channel has no CTCSS receive tone assigned.
-  Issue is activated even if there is no activity on the CTCSS assigned channel.
-  Once activated, pulsing occurs on all channels. (CTCSS and non-CTCSS)
-  DCS does not impact this issue, only CTCSS
-  Setting squelch level to Zero does not resolve the issue.
Workaround Identified
Remove the Receive CTCSS tone from All channels when running mobile.  
-  Power cycling the radio On/Off will temporarily resolve the issue, as long as you PowerOn to a channel where receive CTCSS is not assigned. Once a channel with CTCSS assigned to the receive is selected, the issue will reappear.
-  It is possible that a line conditioner (inductor and 1000mF cap) may reduce this effect.
Miklor Note
The above conclusion was the result of the following tests:
-  Multiple (4) antennas
-  Multiple 12V sources (vehicle & stand alone battery)
-  RFI suppression using Ferrite Cores on antenna and DC lines
-  Multiple Squelch settings
-  STE setting makes no difference
-  DCS mode has no impact  (only CTCSS)
-  Full radio reset
-  Hours of drive time 
This has been resolved in the newer radios.
I hope you find this information useful.


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