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Home » Knowledge Base » FLEX-3000 Transceiver » Antenna Tuning Unit (ATU) » FLEX-3000 ATU Operation with PowerSDR 1.x

FLEX-3000 ATU Operation with PowerSDR 1.x

FLEX-3000 ATU Operation with PowerSDR 1.x

FLEX-3000 ATU Operation with PowerSDR 1.x

System Dependencies
Minimum PowerSDR Version:	1.18.0
Applicable Hardware:	FLEX-3000

Content provided by: FlexRadio Systems Engineering

The FLEX-3000 has an integrated Antenna Tuning Unit (ATU) is a standard feature. The ATU will tune a variety of unbalanced antenna systems (coax) that facilitates its use with multi-band antennas where the SWR is less than 3.0:1. When used with an appropriate balun, balanced antenna systems can be utilized also. The ATU, when tuned and enabled, is also in the RX signal path further enhancing reception acting as a preselector. An ATU bypass function will completely remove the ATU from both the TX and RX signal paths. All ATU functions are automatically controlled using FlexRadio PowerSDR as well as having manual control of the ATU.

FLEX-3000 ATU Specifications

Network Type: Switched "L"
Impedance Range: 17 to 150 ohms
Power Rating: 100 watts 160-6m
Maximum SWR 3.0:1

There are two PowerSDR 1.x front panel controls used with the FLEX-3000 ATU. The are the Bypass control (BYP) and the ATU enable control (ATU).

To initiate the tuning processes, click on the ATU button. The ATU, TUN (tune) and MOX (PTT) buttons will all turn yellow indicating that the ATU tuning process has started.

The first step in the ATU tuning is to measure the actual impedance of the antenna system to determine the baseline SWR. If the baseline SWR is greater than 1.1:1 and less than 3.0:1, then the ATU begins the tuning process. You will hear a series of relay clicks and the transmitter will send a low power signal to the antenna as the ATU switches in different values of inductance and capacitance trying to compensate for a complex impedance that varies from 50 ohms resistive. This activity should only take several seconds to complete.

If a better impedance match was found within the operational range of the ATU (1:1 to 3:1), the ATU button will turn from YELLOW to GREEN, indicating that the ATU is operational and in the RF signal path (both TX and RX).

If the ATU could *not* find a better match than the baseline SWR and it is within the operational range of the ATU (1:1 to 3:1), the ATU button will turn from YELLOW to off and the BYP button will turn YELLOW, indicating that the ATU has been bypassed and is *not* in the RF signal path (both TX and RX).

If the ATU determines that the baseline SWR is greater than 3.0:1, the ATU button will immediately turn RED indicating an error condition. The error condition is that a SWR greater than 3.0:1 exceeds the operational parameters of the power amplified (PA) The ATU is *not* engaged and is *not* in the RF signal path. In essence, it is in BYPASS mode, but the ATU button remains RED to provide a visual cue that you should not transmit using this antenna system until the SWR is less than 3.0:1.

NOTE: The TUN button is used for manually generating a low RF signal used for external ATUs and is not utilized with the FLEX-3000 internal ATU.

To fully illustrate the FLEX-3000 ATU, a few examples are provided below.

ATU Tuning Examples:

#1: The baseline impedance of the antenna system is 1.4:1
You engage the ATU and it can not add inductance or capacitance to produce a better match than 1.4:1. Since the final impedance is less than 3:1 and is within the normal operating range of the PA, the BYPASS button will be yellow, indicating that the ATU is in bypass mode.

#2: The baseline impedance of the antenna system is 1.7:1
You engage the ATU and it *can* add inductance or capacitance to produce a better match, say 1.1:1. The ATU button will be green indicating that the ATU found a match and is operation (in the RF signal path).

#3: The baseline impedance of the antenna system is 3.5:1
You engage the ATU and it cannot add inductance or capacitance to produce a better match. Since the baseline impedance is greater than 3:1 and is *not* within the normal operating range of the PA, the ATU button is RED, indicating the there is a high SWR error condition. The ATU is actually in bypass mode and is not in the RF signal path nor it the signal path "blocked" due to the excessive SWR that the ATU determined. You can still transmit, but the SWR exceeds what is acceptable for the PA.

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