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Wednesday, December 2, 2015

Colchester Mighty Mite


GM Bill,

So, I got round to making my Michigan Mighty Mite!

The crystal arrived almost safe and sound, thanks to the USPS’ mail crusher. Perhaps they think that because email and packets can be compressed they can do the same with parcels? (the photo really doesn’t do it justice - the orange area is a large dent…):


No 2 son, Cameron (12), got involved - The extremely neat tank coil is his handywork :


And so to the video: Not only does it oscillate on the correct frequency as shown here, it also has the added bonuses of oscillating around 21.5Mhz (which is the number my frequency counter gives - which caused a great deal of head-scratching on first smoke), and muting the FM broadcast receiver on 96.1MHz on the shelf 3 feet away!. The dummy load is the 3w metal film resistor suspended in mid air.

video

You might notice more resistors in the circuit itself than the diagram calls for. I chose to have 2 x  20K resistors in parallel to produce a single 10K resistance that could handle .6W. And the poor old 27R .3W resistor got really hot and discoloured before rapidly increasing its resistance ( !! ), so I used 4 (2 serial pairs in parallel) to handle the current. They still get hot, but survive. And the 2N2222a has a bulldog clip heatsink.

Please excuse the uncorrected error at the end of the CQ call!!

This is the second transmitter I have ever built - the other one is a 30m Hans Summers QRSS kit which you also get the ‘blame’ for :-)

Thank-you, Bill. Keep up the good work.

73’s de G7TAT, Colchester, England.







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