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Saturday, 18 January 2014

Minima - A Song by the Muppets?


Ashhar Farhan is well known in QRP radio circles for his creation of the BITX transceiver. It's a simplistic radio that uses bi-directional amplifier components. There must, by now, be hundreds built and also hundreds of variants on the air. I am in the process of constructing a 40M version here:

Now, there's a new design by Ashhar Farhan on the block - the Minima here:

this circuit and design looks really interesting, it's very simple but covers all HF bands with software (my favourite Arduino!) control and a Si570 as the local oscillator.

I just got a built one! Rummaging round the shack today and I a pretty sure I have all the bits here already - no purchase necessary!

So, I have made a start with the low pass filters. If you look at the schematic and accompanying text at the link above you will see there are two low pass filters, one that includes a notch at 20MHz.

So, here is the finished pair of filters at G0MGX:

the toroids and inductor design that I used is as follows:

Here is a sweep of the 15MHz cut off low pass filter:

So this may need re-visiting at some point as the slope starts sooner than 15MHz. Here is the 30MHz cut off low pass before I added the traps:

and here after the three traps were added:

and an initial tune of the traps to 20MHz using the 22p trimmers:

and close up (sweeping from 18 to 22 MHz):

So, all in all, not a bad start!

The next bit to build will be the "KISS Mixer" - this looks very interesting. It's discussed in some detail in this paper:

So, we need to make one and see how it performs!

Fun, egh?

1 comment:

  1. Hi,
    Thanks for letting me in. I am Gerard Vreeswijk and my call sign is ZS5AAC.
    My QTH is in Newcastle, South Africa. My favourite passtime is home brewing QRP radios with very little electronics experience.
    73, Gerard.