What State is Your Amplifier In?

Gordon Hardman, W0RUN

The microprocessor at the core of all current Alpha products monitors and controls the amp, and it does this by moving the amp through a series of "states". While it is not necessary for the user to know the details of this process, some knowledge of what is going on under the hood can help in station planning and integration, as well as in operating the station. This brief overview of the 9500 states will concentrate on how the automatic frequency detection operates in each state, since it is at the heart of so much 9500 functionality.

The 9500 can be in one of 7 states, as in the following table.

State 0, AC power has been applied to amplifier, and a small auxiliary power supply is always on. This unit provides the 5V dc required by the microprocessors, so they are all running. All that happens in this mode is that the front panel is set to be blank, and all other important control lines are set to a "safe" condition. The amplifier is waiting for some user commands, either from the front panel or via the serial interface, to cause it to move to the next state.

State 1 (sometimes called "On 1") is provided so that the user can access any of the four antenna ports and the input wattmeter while using only the exciter.  Only those front panel switches and serial commands which are appropriate to this mode are active. The amplifier is, in effect, a four-way antenna switch with a wattmeter.

State 2 (sometimes called "On 2") is the warm-up state. The tube heater voltage is present, as is the high voltage (HV). The warmup time for the tube, as specified by the manufacturer is three minutes. While this timer is running down, the user can access the antenna ports etc. just as in State 1. When the warmup timer reaches zero, the amplifier goes into State 3 if the OPER/STBY switch is in the STBY position or it goes to State 4 if the switch is in the OPER position.

State 3, (sometimes called "Standby") the amplifier is fully warmed up, but is in standby (bypass) mode. The key line from the exciter can be activated, but the amplifier will not go into transmit mode. The antenna port selection works as before.

State 4, (Operate, un-keyed mode) the amplifier is in operate mode as a result of the front panel switch being moved to the OPER position, or as a result of a serial command.  In this mode, the amplifier is waiting for the key line from the exciter to be asserted, at which time it will move to State 5.

State 5, (Operate, keyed, no RF) the amplifier moves its T/R relays to the transmit position, and waits for RF to be sensed coming from the exciter. This is a critical time- the amplifier must determine if the Band and Tune and Load settings are appropriate for the RF that it is being asked to amplify. This is when the internal frequency counter samples the RF and compares it with a table to see if the amplifier can simply go on to State 6, or if it must briefly go back to a lower state in order to safely move the Bandswitch and Tune and Load capacitors. In this case, the amplifier will go back to state 4, and once the settings are correct, rapidly and automatically go through State 5 again and then on to State 6.

State 6 is the "fully tuned up and ready to go state"- it linearly amplifies whatever  RF is applied to it. It remains in this state until the key line from the exciter is released, or until an off-nominal operating condition  is sensed. In the latter case, the amplifier registers one of a number of faults.

In reality, the amplifier is always monitoring for anything out of the ordinary and can register a fault in other states as well. But a full discussion of all the faults is beyond the scope of this article.

You can see from the above that the amplifier can move from one state to another for many different reasons- end of a warmup timer, front panel switch action, PTT keying from the radio etc. Frequently when it does this and if there is RF coming from the radio, it will use its internal frequency counter to see if the amplifier is correctly set. 

The following discussion applies to the situation where the frequency counter is employed:

In States 0, 4 and 6, the frequency counter is not active. Obviously, in State 0 (plugged in, but front panel dark) the amplifier is not expected to do anything. The other two states deserve a bit of explanation. In State 4 (warmed up, operate, but not keyed by the radio) the user has placed the amplifier into the "ready" condition. There should be no RF until after the PTT is asserted and the amplifier moves to State 5; therefore there is no reason to run the counter. In State 6 (fully up and amplifying), the amplifier has already determined and set the band, segment, tune and load caps etc. Until the user un-keys the rig (and the amp) there is no reason to expect that these settings will need to be changed.

States 1,2 and 3 are the cases where the user may be only employing the radio, and does not need the amplifier. But the amplifier should still select the correct antenna output according to the frequency being used. So in these three states, the amplifier watches for the RF power to cross above a pre-set threshold value. When this occurs, the frequency counter goes through its routines, and then does nothing until the power has crossed below threshold and then come up above threshold again.

State 5 is the one that is normally most critical for the frequency counter. The amplifier has switched into the active, amplifying state, but has not sensed RF. When it does, it first attempts to ascertain the frequency, and if it can get a good frequency reading it compares this frequency to a large number of stored frequencies internally. The amplifier first determines if the frequency is between 1.75 and 30 MHz; it then looks to see which band within this range the frequency lies. If it is outside of any band, the amplifier will give a fault. If the frequency shows that the user has moved frequency to another valid band such that the amplifier is not correctly set up, the amplifier will briefly drop back into State 4 while the band switch and variable capacitors are moved to the settings appropriate to the new frequency. Then it goes through State 5 and immediately to State 6. Voila- we are QRV.

The current state is reported as one of the fields in the telemetry sentences from the amplifier, and can be used by external control software.

The operation of the frequency counter has been the area of the amplifier operation where we have been most influenced by input from our users. It is safe to say that our first cut at this was far from perfect. Since then we have listened to our customers to try and understand what it is that they are seeing, and then we used this information to help perfect the amplifier performance. Perhaps by explaining what is going on inside the amplifier our users can provide us with even more precise ideas on how the 9500 can be improved. Please note that this description applies accurately to the latest firmware release for the amplifier. If your amplifier is running an earlier version, there may be discrepancies between this narrative and the operation of your amplifier.

Gordon, WØRUN