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.  There will be a bypass button and a bypassed indicator.  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.  Also, I have noticed that my antennas behave differently during the day and night and on sunny and rainy days.  An antenna tune memory will not be helpful under these conditions.  Just one button tune.

I have decided not to have any displays on the tuner interface.  I will integrate it with my stationmaster software and all user interactions will be done through its web interface.

  • No timing variation in buttons (e.g. less than 2.5 seconds, 2.5 seconds, etc.)
  • No function modifier button
  • Prominent tune button.
  • Prominent bypass button.
  • No Antenna 2 button
  • Bypass indicator
  • No cryptic bar graph encodings, use a text display for user feedback.
  • Only automatic tuning triggered by pushing the tune button
  • There will be a "Measure Power" 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 use text display
I designed and prototyped the full UI using a touch screen display only.  I have since decided to abandon this design and switch to integration with my Stationmaster software.  But I will include the write up of this prototype at the end of these series of blog posts for anyone who is interested.

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.  

In the Stationmaster software, the tuner will have its own web page with a link on the navigation bar.  The tune, bypass, test (see the SWR with some power applied) and measure power buttons will be on this page (plus anything else that I have not thought of yet).  All the interactive text during the tuning and bypass process like power is not in the right range will be on this page.

The SWR and Power meters and the bypassed indicator will be on the "Contest", "Logger" and "VFO" pages in addition to the tuner page.

Adjusting Amplifier Power Level


I have two radios, a modern Yaesu FTDX10 and an old Ten Tec Omni D from the 1980s.  The case for the Yaesu radio is simple, it has a nice API that I am currently using for the contesting interface so I will not discuss it anymore.  For the Ten Tec, 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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