Thursday, 30 January 2014

The power of menthol

How powerful is menthol? In this case, up to 2W!

Yet another empty Altoids 'curiously strong mints' tin is due to be pressed into service tomorrow, this time to accommodate a 2W QRP power meter. Using the little 250uA movement I have, it should read from about 100mW up to 2W reasonably well.

Based on a simple design by AA5TB, Ive had to recalculate the series resistor value, which meant quite a lot of first principle maths. The end result of all the calculations was a resistor value of 53.7k. Not a preferred value in anyone's book! Rounding up to 54k, also not a preferred value, I saw that the nearest available resistors were quite a ways out. So, my design will have a pair in series, a 39k and a 15k. The trick now though will be finding some suitably power rated 200 ohm resistors to build the dummy load section.

For tonight, there's little I can do, apart from paint the Altoids tin ready. This is also having a nice shade of grey, but this time in Revell Enamel.

I'll also be adding a bypass switch to my digimodes interface. This is a simple beast, a pair of 1:1 600 ohm isolation transformers for the audio and an opto-isolator for the PTT control

It is however, very customised for my station. The socket on the front is for the Alinco DX-70's microphone, a DIN socket on the back then connects via a patch lead to the Alinco's microphone socket. This means I can select between mic and audio in/out lines, the front panel switch being for that purpose. The PTT control is via RS232, but this is also fed out the back via a 3.5mm stereo jack to the CAT interface for my FRG-100 receiver, allowing computer control of that as well. The bypass switch I wil fit tomorrow will allow switching out the level control pot.

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