Technical Manual

GUARDIAN VHF 110W MOBILE 2-5
2.4.1.2 On/Off Switching
The main continuous supply 10V control is passed through a front panel on/off switch to generate 10V SW from the
main radio supply. In normal operation the on/off switching is controlled by the radio on/off rotary switch by the
control /RADON. Once switched on the main controller can hold the radio on by setting PWRHOLD. In addition
to the radio rotary on/off switch, the on/off switching can be controlled by the external line /RADOFF via the
accessory connector. This line overrides the /RADON line and can be used to force the radio off regardless of the
rotary switch setting. However, the H8 controller uses the PWRHOLD and PWROFF lines to implement a clean
controlled switch off.
Figure 2-3: RECM Power Supply
2.4.1.3 Transmit Power Switching
A single FET switch controlled by CTX is used to provide a switched 10VTX high-current supply (1.5A) for the
transmitter.
2.4.1.4 4.5V Switch Mode Power Supply
This circuit uses a switch mode power supply device to generate a 4.5V supply at 450 mA maximum for the radio
logic. The switch mode device is synchronous and uses an externally provided power supply clock at 384 kHz. The
power supply circuit includes input and output filters to limit the conduction of the fundamental switching
components and their harmonics in the VHF band, both onwards into the logic and back into the power supply.