SGC SMARTUNER SG-237 Technical Information download pdf (Page 8)

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3.4 VSWR Detector

A directional coupler is made up of a current transformer T2 and a

voltage transformer T1, in conjunction with termination resistors R35,

R36 and R33, R34. The coupler is inserted in the 50-ohm transmission

line between the input connector, ST2 RF - ST3 GND, and the tuning

network. The forward power is measured across termination R33, R34

and reflected power is measured across termination R35, R36. Diode

D1 generates a positive DC voltage proportional to forward power and

D3 generates a positive DC voltage proportional to reflected power.

The forward DC output is fed to a voltage divider consisting of R19

and R14. These voltages are input to the RF power detector and to an

A to D converter port of the processor. The reflected DC output passes

through a voltage divider consisting of R29 and R16, and then it also

goes to an A to D converter port of the processor.

3.5 Phase Detector

A phase detector is formed by T3, A1, and their associated compo-

nents. This detector indicates the state of any reactance associated with

the antenna coupler as noted from the generator. A line current sample

is compared in phase with a voltage sample in a double balanced

mixer. Output polarity varies negative or positive depending on the

reactance of the antenna. The output of phase detector A1 is shifted to

a 0 to 5v range, then fed to processor’s A to D converter port and used

within micro controller.

3.6 Central Processing Unit (CPU)

A tune-up algorithm, which is contained in the memory of the micro-

processor, implements the antenna matching. It is designed around the

MC68HC711E9 CPU that features a versatile instruction set, RAM,

and EEPROM (memory which is saved after the coupler is turned off).

The antenna coupler relays are controlled by latches U6, U7, & U8

which receive serial data input directly from the CPU. During opera-

tion, data is transferred into the CPU from the A to D ports and Input

Capture port (measures RF frequency). Basically, the program moni-

tors the status of the input sensors and—starting from a preset condi-

tion—uses a built-in algorithm to achieve a tuned condition. When the

tuning algorithm is complete, the CPU saves the settings in its

EEPROM, which is addressed by the applied RF frequency. This non-

SG-237 Manual

page 8

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