Basic Full Tuning Cycle; What A Full Tuning Cycle Does - Acom AOM 04AT User Manual

User's Manual | ACOM 04AT | Remote Automatic Antenna Tuner and Switch

5. BASIC FULL TUNING CYCLE

5.1. What a Full Tuning Cycle Does

The impedance matching is a transformation to resistive 50 Ohm of the complex RF impedance, presented
to the selected antenna output. This is typically done with a residual SWR allowance under 1.3:1 in the
ACOM 04AT. A full tuning cycle is the "seek and find" process for a combination of tuner relays that leads to
this impedance matching condition.
The necessary relay combination depends on the frequency and the complex impedance, presented to the
selected antenna output. Searching for the suitable combination is performed following a specific algorithm.
A series of impedance measurements is performed during the cycle and the results are used to determine
both the necessary configuration of the matching circuit (L or reversed L-shape matching network), and the
necessary values of the coils and capacitors in it.
A full tuning cycle is started by briefly pressing the TUNE button. Next, an RF signal has to be applied from
the transceiver - 25 W continuous carrier at the operating frequency (when using transceivers with CAT this
is automatically done). The RF signal is used to activate the impedance sensors of the tuner.
The automatic tuning process consists of a series of steps, in each one performing measurement and
evaluation of the RF impedance transformed by the matching circuit (L-network). With more than 20 RF
relays, coils and capacitors of various values are added to the circuit or excluded from it. Each switching is
completed with no RF power, to prevent relay contacts from burning. For this purpose, the tuner has a built-
in electronic switch for local enabling and blocking of the RF power at the required moment (synchronously
with the algorithm steps), while the transceiver power is maintained continuous during the entire tuning
cycle.
In each algorithm step, a short pulse of RF power (a few milliseconds) is emitted to activate the tuner
impedance sensor and evaluate the current state of the antenna impedance transformed by the matching
circuit. At the end of the pulse, data from the sensor is read and RF power is blocked. The result of the step
is evaluated by analyzing the measured data - R, G, PH, the forward and reflected power at the matching
circuit input. Upon evaluation, the tuner controller makes a decision what switching combination to be
applied at the next step, following the tuning algorithm stored in its program memory. The algorithm is
designed in such a way, that the time needed for seeking is substantially reduced - the combinations checked
are tens of thousands of times fewer than all 2 million possible relay combinations.
The "measurement - evaluation - switching" cycles continue, each subsequent switching decision being made
according to the algorithm logic and accumulated changes of the impedance transformation by the matching
circuit.
Further, the algorithm is designed in such a way that it unambiguously leads the impedance, transformed by
the matching circuit (L-network), to the goal (50 Ohm). This process is complete when the impedance is close
to 50 Ohm with a tolerance less than SWR of 1.3:1, or if the possible steps of the algorithm are exhausted.
October 2023 S e c t i o n BASIC FULL TUNING CYCLE | Page 53 of 88