1200W HF Linear Amplifier from budget parts - 2
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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