Mike Dennison wrote:
It did, however, surprise me that in a weekend that saw more 136kHz
contacts
at 1500km+ than ever before, and many 'firsts' and personal bests (thanks
to
the excellent Russian expedition), together with more 73kHz stations than
ever before being copied in the USA, the reflector was dominated by
academic
puzzles.
I guess everyone was off working the DX and too busy to post to the
reflector!
I don't have a problem with this kind of thing either, as it's good for
exercising the grey matter - as long as it doesn't result in the "true LF
posts" (for want of a better term) being engulfed to an extent that those
who aren't interested in the puzzles find it difficult to extract the stuff
they want from a long list of emails. If everyone uses "puzzle" in the
subject line then the disinterested could set up a mail rule to delete them
accordingly.
Talking of mental exercise, I'm a sucker for punishment in more ways than
one: I'm currently trying to work out a way of getting more audio filtering
into my latest 136kHz regenerative receiver without increasing the number of
active devices (3 x BC550C transistors + 1 x OA91). This receiver is based
on a reflex architecture ("Spontaflex" circuit by Sir Douglas Hall) and
appeals to my "KISS" instincts. It has surprising sensitivity (<0.1uV CW
signal is easily readable in the absence of QRM/N) and very low supply
current (300uA) - although at these currents we won't mention dynamic
range.... it hears things on 136kHz, which is what matters, although a
directional loop antenna is probably "de rigeur" to null out DCF39.
I think the only answer is going to be to add another BC550C configured as a
Sallen-Key bandpass filter (darn - another active device). Could configure
the audio output device as such, I suppose, but this would probably result
in too much loss of gain.
Ideas invited (but please don't suggest I go out and buy an AR7030 or
whatever, or add a DSP filter on the end - that would be missing the point!)
73, Kevin G1HDQ
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