XRef-PLL
Icom IC-756ProIII Installation Notes (Draft)
1. Overview
Most modern Amateur transceivers now generate their operating frequency from a single
internal Reference Oscillator. In many cases, this Reference Oscillator is voltage-controlled,
allowing front panel adjustment of the Reference frequency.
The XRef-PLL locks the radio’s Reference Oscillator to an external 10 MHz reference signal
from a GPS reference or other high-accuracy source. It intended to be installed internally within
the radio. When no 10 MHz reference is connected, the XRef-PLL completely disconnects from
the radio, allowing it to operate as from the factory.
In the case of the Icom IC-756ProIII, the Reference frequency is 32.0 MHz.
2. Technical Specifications
Connections to the board are shown below:
Connection Description
Specifications
Test
Do Not Connect
Lock
PLL Lock Indicator
+3.3V 20mA max
Vp
Do Not Connect
Gnd
Power Ground
Vin
Supply for XRef
5 to 16 V @ 20 mA
Ref
10 MHz Reference Input
0 to +15 dBm
(0.5V to 3.6V p-p)
RF
Reference frequency from Radio.
Radio dependent
Ctl
Control output to Reference VCXO
0 to +3.3V
Test
Lock
Vp
Gnd
Vin
Ref
Gnd
RF
Gnd
Ctl
A Word of Caution: The installation requires a small amount of soldering to very small and
fragile SMD components. If you do not have experience with SMD techniques, please seek
the assistance of someone who does. We are happy to provide any advice needed, but we
cannot take responsibility for any damage to your radio.
