1200W HF Linear Amplifier from budget parts - 2

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While I'm waiting for the rest of the parts to turn up, I have started working out how to automate band-switching on the Low-Pass Filter module.  To do this, I am relying on the output of my IC-7300 transceiver to control this.

If you want to skip ahead, the source code is located on my GitHub page:

 https://github.com/au-chrismor/arduino7300

As noted in part 1 of this series, the IC-7300 outputs a voltage from 0 - 8V depending on the band selected.  The approximate values (from IC-7300 forums) are listed below:

630m    7.41V

160m    7.41V

80m      6.07V

60m      5.07V

40m      5.07V

30m      0.03V

20m      4.07V

17m      3.18V

15m      3.18V

12m      2.22V

10m      2.22V

6m        1.88V

 

My LPF has switch inputs for:

10/12m

17/15m

30/20m

40m

80m

Fortunately a lot of these will line up, at least for my usual bands.

However there seems to be a bit of dispute about the actual voltages.  Icom don't publish anything, which is not entirely surprising.  My first step therefore, is to verify what my transceiver is putting out.  Yours will probably be similar, but make sure you verify it first.

Also remember that at best, an arduino's ADC can cope with 5V, so we have to use a divider of some kind to reduce the input voltage.  I decided to err on the side of safety and make sure we could not exceed the ratings of the device so I assumed a maximum of 9V.  By using a 10K and a 12K resistor I fall nicely in the range.

If you can't remember how to calculate a divider, Digi-Key have a nice calculator you can use:


With that out of the way, let's run our first test and output the reading from the ADC for each band.  You will find this first module in "7300vin.ino"

But how do I connect it to my IC-7300?  Simple, the owner's manual gives you the pinouts for the ACC connector, and the wiring colour codes.  They even gave you a little breakout cable with the radio.


On my system, I got the following values from the ADC:

630m    766

160m    766

80m      627

60m      524

40m      524

30m      2

20m      420

17m      330

15m      330

12m      230

10m      230

6m        193


Based on these measurements, I have the following decision tree:

if vBand < 100

    band="30m";

else if vBand >= 100 < 200

    band = "6m";

else if vBand >= 200 < 250

    band = "15m";

else if vBand >= 250 < 350

    band = "12m";

else if vBand >= 350 < 450

    band = "20m"

else if vBand >=450 < 550

    band = "40m"

else if vBand <= 550 < 650

    band = "80m"


If nothing else, we now have the makings of a clever little display tool.


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