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LF: Morse tones and spacial filters

To: "rsgb_lf_group" <[email protected]>
Subject: LF: Morse tones and spacial filters
From: "Alan Melia" <[email protected]>
Date: Sun, 21 May 2000 23:05:33 +0100
Reply-to: [email protected]
Sender: <[email protected]>
Dave and Larry raise an interesting effect, that I noticed myself when idly
monitoring the band on the speaker (move your head around to select the
signal you want to copy). The effect is caused, I think, by the selection of
a position of the ear where multiple audio paths add in phase for the
required tone. The noise is not affected or may even have it high and low
frequencies attenuated by the size of nearby objects in relation to the
wavelength and absorption by furnishings (or tent walls on FD). I believe
the effect is an analogue of the technique used in digital filtering called
Finite Impulse Reponse  (FIR) filters, where delayed copies of a signal are
added together can produce a very selective output.

I have noticed that whilst I often copy signals at tone frequencies up to
1800Hz, if I find the going difficult I can read the same signals better at
around 600-800Hz. Strangely enough this is not where the ear is supposed to
be the most sensitive (1000 Hz to 1400Hz I seem to remember) which may be
why the is a lot of reference to 1000Hz tones.

In the case of static-crashes I agree that getting as much as possible over
between the crashes with repetitions is undoubtably the best way, but I
don't think you work really weak stations under those conditions. I have
listened to pairs of continental stations late in the evening who are
probably good strength with each other pushing along at a reasonable speed.
They were down in the normal band noise (not crashes) with me making copy
very difficult as I seemed to miss the 'dots'. In these conditions I find
the slow deliberate sending easier to read, and I use a pencil. (BUT then I
am not by any stretch of the imagination a morse operator..... but I do
try!) The problem I found with Jim was that having the AGC on to give an
S-meter reading, meant the crashes carved up the copy (with the AOR 7030 it
is not easy to flip the AGC on and off....ergonomics is not one of its
strong points)

All the comments have been most instructive, it keeps me trying, and maybe
my ability is improving slightly ( I hope). I look forward to learning more
from the Thesis that Dick mentioned.
Cheers de Alan G3NYK
[email protected]

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