Tuesday, August 16, 2022

500 Watt Antenna Tuner Part 7 - User Interface

 I will start my user interface analysis as a comparison between what I need to do and the LDG AT-100ProII 100 W Automatic Antenna Tuner.  This is the tuner in everyday use in my station.

It has 6 buttons and each of these buttons have three modes, a short push, a longer 2.5 second push and a longer than 2.5 second push.  The function of each of these buttons is further modified by a function button.  I will not use anything remotely resembling this in my design.  One of the buttons is the tune button, this button will be prominent in my design.

There are two LEDs, one for Antenna 2 and one for Bypass.  I am not planning to have a second antenna.  If I ever need one, I will use an external, wall mounted switch.  The bypass indicator will be incorporated in the bypass button.  There are also two bar graphs, one for power output and the other for SWR.  Both functions remain.  The two bar graphs are also used in all sorts of cryptic ways to convey one condition or another to the user.  That is out.  I will use a text display for information.

There will be no peak vs. average power output option.  I will be using a true RMS power meter from Analog Devices to measure power output and I will display that.

The tuner gives one the option of automatic (triggered by SWR threshold) or semi-automatic, triggered by pushing the tune button.  Handling high power and tuning based on SWR trigger seems to be a bit crazy, so there will be no automatic tuning in the sense of LDG.  The automatic tuning will mean that once triggered by pushing the tune button the rest will be automatic.

The LDG has memory and full cycle tuning, assuming that my algorithms works, no such a thing will be necessary.  Just one button tune.

  • No timing variation in buttons (e.g. less than 2.5 seconds, 2.5 seconds, etc.)
  • No function modifier button
  • Prominent tune button on the touch screen.
  • Prominent bypass button next to the tune button
  • No Antenna 2 button
  • Bypass indication incorporated into the bypass button
  • No cryptic bar graph encodings, use a text display for user feedback.
  • Only automatic tuning triggered by pushing the tune button
  • Pushing the tune button will measure the power output and ask for it to be adjusted if necessary
  • Pushing the antenna bypass will measure the power output and ask for it to be adjusted if necessary
  • Error indicators will be all on the text display
After some thought and investigation, it looks like I do not have well formed opinions about the user interface (UI).  I will attempt to design the full UI using a touch screen display only.  It will give me a chance to play with the user interface ideas and also modify it over time if and when I change my mind.  Next step will be testing different UI ideas.

To experiment with a touch screen user interface, I ordered an Elegoo 2.8" TFT touch screen display.  I spent a few days trying to make it work without success.  I returned it and continued looking for alternatives.  I ordered an Adafruit 3.5" TFT touch screen display and it worked as advertised.  Initial tests show that it will do the job.  The front panel might end up being a touch screen and an on-off switch.

Adjusting Amplifier Power Level

My rig is an old Ten Tec Omni D from the 1980s.  It would be good if I don't have to manually reduce the output power (putting 100 watts into a 10:1 SWR would not be great).  Below is the schematic of the Ten Tec ALC circuit (I have used the same reference designations in the Ten Tec manual).  There are two controls in the radio.  The drive which controls the level of the signal (CW or phone) applied to the low level driver and ALC which controls the threshold at which the forward power signal is used to roll back the gain of the low level driver.  The ALC signal is single to the base of Q8 is the rectified output of a Brune bridge fed through a 10K resistor.  


I will have to experiment with injecting current into the base of Q8 also from a 10K source (maybe with a diode blocker so It does not interfere with normal operation) to see if I can automate the output power adjustment.  To implement the idea, I will have to build a new enhancement box for the Ten Tec (https://ad2cc.blogspot.com/2022/04/ten-tec-transceiver-enhancements.html).  This will not be the only enhancement that needs to go in.

In the mean time, I will use the combination of power measurement in the tuner and manual adjustment of the radio to set the desired power level for tuning and for driving the power amp.



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