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Friday, 14 February 2020

Making a 10W "QRP" ish linear

I've started to design some software that will control a low power linear amplifier.

I plan to use the 10W Amp from QRPLabs as the main component - I can't make one for the price they sell these kits, so thats on order.

In the meantime, I've been designing some software to control the output switching, and calculate the forward and reflected power and SWR:

Initial software design is included for the STM32 "blue pill" baord.

The software can be downloaded here.

The pinoput for the STM32 board is here.

The schematic for the RF sence using AD8307 is here.

You can purchase a STM32 board here.

The TFT display with touchscreen functionality is here:

More to follow on this topic.

Here's part 2 where I look at the Low Pass Filters and the Log Amps to take accurate power readings in software:

The finsl control software is here.

The simple software based sequencer software is here.

The schematic for the transistor switches I used in the sequencer is here.

The wiring layout for the STM32 is here.

The AD8307 schematic is here.

Sunday, 2 February 2020

A STM32 Processor - really?


In my never ending desire to fiddle with Microprocessors and/or Micro controllers, I found these boards on my local Amazon with prime next day delivery:

They are called a "Blue Pill" for some reason?!?!? The boards I ordered are these. At the time of writing I could buy 5 of these boards for £15 GBP delivered.

You can use them directly with an external USB -> Serial converter, but you can also upload a bootloader and make the on-board USB port work successfully.

I followed the instructions here:

the speed of these processors is excellent and when used in conjunction with the ILI9342 displays I have been using recently they work very well indeed.

You can see an example of the processor in action in my latest musings on the BITX:

All very impressive and I still fail to believe how inexpensive these MCUs are.

** UPDATE **

There is an alternative bootloader (its much smaller) available for this board now, you can find instructions for using it below. This uses the HID method for uploading:

Back to the BITX


I wanted to do a simple (ish) construction project for my YouTube channel and decided a BITX would be just the ticket.

If you like what I am doing please subscribe to my channel and give me some support.

Thanks muchness!

** UPDATE **

Following the issues I noted in the video on balancing the Balanced Modulator, I have added some capacitance either side as highlighted in this image:

By careful adjustment of the balance pot and the trimmer I have now got excellent carrier supression:

much better, dont you think?