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FLEX-6000 Signature Series – Maestro User Guide

Page 88

21 HOW TO OPERATE THE ATU

The antenna tuning unit (ATU) is a device in the RF signal path that improves power transfer from

the transmitter to the antenna by transforming the apparent antenna impedance seen by the

transmitter to a value compatible with the transceiver’s power amplifier (PA). An ATU is useful when

the antenna’s feedline impedance is unknown, complex, or otherwise different from the

transceiver’s. It's important to remember that the ATU has no effect on the actual SWR of the

antenna and feedline. It does however change the impedance presented to the transmitter by the

ATU.

Note that the radio software automatically folds back transmitter power so that the power reflected

by the antenna and tuner system does not exceed 25 watts. This feature protects the Power

Amplifier but should not be relied upon when operating with a mismatched antenna. Use of the ATU

or an external tuner is recommended to match the transmitter to the antenna and minimized power

reflected to the Power Amplifier.

The FLEX-6000 ATU is a standard feature of the FLEX-6700 and FLEX-6500 and an option for the FLEX-

6300. The operation of the ATU is controlled by the Maestro software.

21.1 MODES OF OPERATION

There are two modes of ATU operation, Manual and Memory. In Manual mode, the user initiates an

ATU tuning operation to attempt to find a better match between the PA and the antenna system,

but the inductance (L) and capacitance (C) values that are found are not retained and the ATU will

revert to Bypass mode if the frequency or band is changed. Memory mode is an extension of Manual

mode in which the L/C values are retained and automatically used when the frequency of the

transmit Slice is within the ATU Match Frequency Range.

The ATU will try to impedance match the load to as close to a 1.1:1 SWR as possible. If the ATU

measures an SWR of 1.1:1 or better at the beginning of the matching process, the ATU stops

searching and remains in Bypass mode.

A successful ATU tuning on 6m occurs when the SWR is improved from the initial SWR determined in

the Bypass state and is better than 2.32:1. On other bands, a successful ATU match is one where the

SWR is improved from the bypass SWR reading and is better than 1.7:1.

The ATU will stay enabled but the ATU button will not be lit if the SWR improved from Bypass but

does not meet the SWR criteria described above. If the resulting SWR after an ATU tuning operation

is not better than when in Bypass and the above SWR criteria is not met, the ATU goes into Bypass

mode and the ATU button will not be lit.

21.2 ATU MATCH FREQUENCY RANGE

After the ATU has found a successful match, the inductance (L) and capacitance (C) values are valid

for a 200 kHz frequency span centered at the frequency the ATU tuning operation was initiated, or

+/- 100 KHz. Once you tune the frequency of the transmit Slice beyond that range, the ATU will be

put into Bypass mode unless there is a previously saved ATU memory at the new frequency.

FlexRadio FLEX-6000 Signature Series User Manual

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