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Friday, 7 April 2017

I'm about there!


You'll remember last time I started modifying the 13cm PA I had acquired. Well, I think it's about done.

What we have is the modified PA, an Arduino Nano plus some software to monitor:
  • PA Temperature
  • Forward power
  • Reflected power
  • Bias current (driver, Left and Right PA MOSFETs separately)
and trip if anything goes out of bonk.

The Amplifier now looks like this:

I've just to wire up the Analogue inputs in this image. There are three "status" LEDs on the front panel; one for "All OK", one for "It's gone horribly wrong" and a final one for "TX". If you connect the serial cable to the Nano then there is a status line repeatedly output giving the details of all the inputs read and their values.

The connector on the main board of the Amp is configured like this:

and it was therefore a fairly simple case of wiring the various pins to the I/O of the Nano and writing some code. I stole a lot of the ideas for the code from Mike G0MJW - but there are quite a few differences between what I have ended up with and what Mike created a few years ago.

The 9V line to the bias and other bits of the board is permanently on; the 28V line is also enabled all the time but switched bu a FET switch under software control. This switch is the same as the one in the sequencer, it's just altered slightly for 28V:

I've stuck the source code here if anyone is interested.

Time now for some testing.....


A couple of minor software mods (updated on the link above) during testing and all seems to be OK. I am not entirely convinced about the scaling values used to convert from the ADC readings into the value units, but time will tell.

Here's the whole system - there's an IF cable from there to my IC9100 which is used on 70cm as the rig for the transverter:

**UPDATE 2**

I found that the cheap Chinese sourced FET I was using to switch the 28V line had failed, but my software didn't pick up on this. I've changed the device for a Farnell sourced component and also added an extra digital line to the Arduino to monitor the voltage on the 28V supply to the PA. There's a potential divider added to the FET switch board to provide 3.3V when the 28V line is high, this is in turn connected to pin 9 of the Arduino and the code linked above modified accordingly. There is an additional trip condition when the 28V line is High and we are in RX or the 28V line is Low and we are in TX.

Here you can see the potential divider I have added to the FET switch to monitor the 28V line status:

And here is the finished article: