Author: Ken Wells - NM9P Date: April 12, 2023
Using the ATU on the FlexRadio 6000 Series
This is an operational summary of the 6000 Series Internal ATU
For more in-depth details, please consult pages 98-100 of the SmartSDR Software User Guide:
https://edge.flexradio.com/www/uploads/20200818184951/SmartSDR-Software-User-Guide.pdf
The FlexRadio Internal ATU has a nominal tuning range of 3:1. Which means that it is capable of tuning antenna mismatches up to about 3:1 SWR. We say "about" because the actual effective range can vary, depending upon frequency and the particular makeup of the capacitive and inductive reactance of the load presented to the tuner.
In SmartSDR, there are two buttons in the TX Control Panel that manage the ATU: The ATU Button and the MEM button.
There is also a status indicator that shows "Success" "Byp" (Bypass), and "Mem."
THE ATU BUTTON:
The ATU Button turns the Tuner ON and OFF and initiates the ATU Tune function
The first press of the ATU button enables the ATU and begins a tuning sequence.
This initiates a "tuning" transmission with 10 Watts at the carrier frequency of the "Active TX Slice" of the radio. You will hear the relays rapidly stepping through the appropriate combinations of inductance and capacitance in the ATU as it searches for a match for the load.
This will result in one of three outcomes:
- If the ATU is able to find a good match for the load, then it will stop, and will display "Success" in the status indicator. Indicating that it was successful in finding a good match for the load.
- If the ATU is unable to find a better match than is already presented to it, and the current match is acceptable to the radio, then the ATU will stop and will display BOTH "Success" AND Byp" in the status indicator. The ATU Button will also turn GRAY. This indicates that the load presented to the radio is good, and the ATU cannot improve on it and has bypassed itself, since it is not necessary at this time.
- If the ATU is unable to find an acceptable match to the load, it will stop and display "Byp" WITHOUT the "Success" indicator, indicating that it could not find an acceptable match for the load.
The second press of the ATU Button:
If you press the ATU button while "Success" is showing on the status indicator, it will disengage the ATU, remove the "Success" Indicator, and display "Byp" on the Status Indicator. This is what is referred to at putting the ATU into "Bypass Mode."
What are acceptable matches for the ATU?
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.
6 Meters: 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.
How to test the match on your radio:
If you wish to check the quality of match currently provided by the antenna and ATU, press the TUNE Button. This initiates a transmission at the carrier frequency of the "Active TX Slice" of the radio.
(The power level for the TUNE operation is set by the TUNE Power slider.)
Observe the RF Power output and the SWR on the meters.
When you are finished getting your readings, click the TUNE Button again to stop the transmission.
The MEM Button:
The Internal ATU has a Memory function. If the MEM button is enabled (Blue) the ATU will remember the tuning solutions for different frequencies across the band - everywhere you have successfully tuned the ATU.
As you tune around the band, if you come close to the frequency for which there is a successful tuning solution, the ATU will automatically recall the ATU settings for that frequency. You will not need to hit the ATU button again to tune the antenna.
ATU Memories are stored separately for each of the two antenna ports (ANT1 and ANT2).
If you have two antennas connected and in use for the same band (for example a dipole on ANT1 and a vertical on ANT2) the ATU will remember the tuning solutions separately for each antenna on each band.
Clearing your ATU Memories:
If you wish to clear the ATU Memories and start over, for example after changing to a different antenna, simply right-click on the ATU or MEM Button and select "Clear ATU Memories."
What if you are using an amplifier or an external tuner?
The internal ATU will only match the load that is immediately presented to it. If you have another device, such as an amplifier or external antenna tuner, it will only match the load presented to it by the amplifier or external antenna tuner.
For example: You cannot match an antenna that is on the OTHER SIDE of your amplifier. You must place the radio's Internal ATU into Bypass mode, and use an external antenna tuner that is between the antenna and the amplifier. (The internal ATU would only be tuning the input to the amplifier, which can cause issues with some amplifier/radio combinations).
Do NOT use the internal ATU and an external ATU at the same time. If you are using an external ATU, put the radio ATU into Bypass Mode and let the external ATU do the work.
If you are using an M-Model Front Panel or a Maestro:
This is covered in greater detail on pages 108 and following in the 6400M/6600M User Guide:
https://edge.flexradio.com/www/uploads/20200818185014/FLEX-6400M-and-FLEX-6600M-User-Guide-v3.x.pdf
All of the functions available from SmartSDR for Windows are also available from the Radio Front Panel or Maestro. However there are some variations in how the functions are accessed.
The ATU Status Indicator is incorporated into the Background LED of the ATU Button:
- The ATU Button shows GREEN if it was able to find a successful match, or cannot find a better match than the one already presented.
- The ATU Button shows WHITE if the ATU is in Bypass Mode.
- The ATU Button will be unlit if the ATU is not able to find an acceptable match.
The ATU Button:
If the ATU is in Bypass mode (WHITE) pressing the ATU button will initiate a tuning cycle. If the ATU is able to find a good match, it will stop and turn the ATU Button Green.
Pressing and Holding the ATU Button will place the ATU into Standby Mode. This turns the ATU Button WHITE and a momentary information window will flash on the screen saying: "ATU: Byp"
The MEM Button:
In order to save space on the Front Panel/Maestro, the MEM button has been moved to the TX Menu , which is opened by pressing the Mic Gain/CW Speed knob above the VFO B knob.
Look for the "ATU MEM" button in the lower left of the screen.
Clearing ATU Memories:
Press and Hold the ATU MEM button for about a second and release it. This will bring up an option button called "Clear ATU Memories." Tap that and it will clear the ATU Memories.