Message-ID: <003401c28afd$99622420$f9997ad5@laptop>
From: "Kevin Ravenhill" <hdq@btinternet.com>
To: "LF Group" <rsgb_lf_group@blacksheep.org>
References: <001901c28af1$aa0faa60$9d740450@oemcomputer>
Date: Wed, 13 Nov 2002 10:11:44 -0000
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Subject: LF: Re: Puzzles and DX
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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