RA-38M "JU" jumper settings:


Header - Jumper Summary:

JU1 - Selects between active high and active low COS logic signal.
JU2 - Selects between audio biased COS, Hardware COS signal, or no COS.
JU3 - Install this jumper to enable CTCSS hardware logic signal.
JU4 - Install this jumper to disable PTT LED falsing protection.
JU5 - Selects between Left or Right TX audio channel.
PTT - One of two jumpers to select transistor or relay PTT keying. See NOTE below.
PTT - Two of two jumpers to select transistor or relay PTT keying. See NOTE below.

NOTE:
The PTT keying method is selectable by two mechanical jumpers. You choose between Transistor or
Relay keying.  The selection between transistor and relay keying is done with a pair of 
two - 2-pin headers in a square arrangement.  These headers are red and require two jumpers 
to be placed in either a up/down or back/forth (vertical or horizontal) side-by-side orientation.
Both jumpers are required for the option to work correctly.  The up/down position selects the 
relay, while the back/forth position selects the transistor.  These headers are located in a 
square box labeled "PTT" near the relay.  If the relay position is selected - it's best to 
also place JU4 - but not required.  In the transistor position - select the position of JU4
as required and detailed below.


R12 (the larger blue pot) controls the receiver audio level.
R14 and R16 (the smaller blue pots) control the TX audio level Right & Left.

Detailed explanation of these headers and jumpers:

JU1 - This jumper selects the polarity of the COS signal.  The choices are 
active low and active high.  Baofeng portable radios produce an active high
signal.
A = Active Low.
B = Active High - Use with Baofeng portable.
Default is B.

JU2 - This jumper has three valid positions, A - B - None. 
This jumper selects the type of COS signal that the RA-38 will use, or none at all.   
The choices are Conventional hardware logic signal, Audio biased COS, or None (disabled).
Baofeng portable radios produce an audio biased COS that "rides" on the receive 
audio line.
A = Conventional hardware COS logic (active low or high depending on JU1).
B = Audio biased COS - Use with Baofeng portable / ASL.
None = NO COS (COS is disabled - necessary with Windows applications like VARA FM).
Default is B.

JU3 - Install to enable the conventional hardware CTCSS logic signal.
Default is removed - (CTCSS is disabled).

JU4 - False PTT LED illumination protection:
Jumper JU4 is removed to enable this illumination protection.  The jumper can be 
placed if this option should it create a problem for a particular installation. 
The jumper simply shorts out the diode.
Default is removed - False illumination protection is enabled.

JU5 - LEFT or RIGHT Channel TX Audio Output Selection
Left and Right channel audio is available on the RA-38.  You can select which 
one feeds the transmitter by the position of JU5.  L is for Left and R is Right.
R14 adjusts the Right channel TX audio and R16 adjusts the Left.
Default is Left (main) Channel.

What is JU4 for, and why is it necessary?
Partial (or full) illumination of the Red PTT LED can happen if the radio adapter is
connected to a radio that has a PTT switching voltage (bias) of less than 5 volts.
This is the case with many portable radios.  When the radio is receiving, the low 
keying voltage condition can cause the red PTT LED to partially illuminate. False 
illumination can also happen with just about any radio when the radio's power is 
turned off, but the radio interface is still powered, falsely indicating the radio
is transmitting when its not.  
Placing JU4 disables protection.

For analog - (ASL) by default, we recommend NOT installing the jumpers on JU3 and JU4.

For digital (VARA etc.) we recommend NOT installing the jumpers on JU2 and JU3.