PA0SE wrote:
But when I am busy in my shack doing other jobs I often leave the receiver
on with a wide IF-filter selected, no audiofilter and such high volume
that the headphones function as speaker. I have noted several times that
I could detect a weak signal this way. After putting on the headphones and
switching on the 30Hz audio filter it was often very difficult to read the
signal! It again goes to show that the ear-brain combination acts as
tracking bandpass filter that should not be "assisted" by too much
pre-filtering.
I have often noticed that I can read a signal better on the tiny
speaker in the lid of my IC-706 Mk1 than I can when I put on
headphones. In fact I use phones only to exclude external noise,
not to improve readability.
Another phenomenon is that a signal will be more readable right on
the edge of a filter passband, even slighly down the slope, than in
the middle. Is this perhaps because noise very close to the signal
is the main problem with the 'filter between the ears' and at least
one sideband is attenuated using this method? Is there a clue to
DSP designers here in that it isn't the signal that should be
peaked, but the noise either side that should be notched?
Dick will no doubt also be familar with the old technique of turning
headphones up so loud that the diaphragm rattled with the Morse
code.
Totally off-topic but still with loud headphones, my father told me
that in the early days of radio only a few sets could drive a
loudspeaker and it would difficult to dance to music with phones on
(I'll pause here whilst you make a mental picture of that)!
So it was common practice to put the phones in a washing up bowl
(enamelled metal in the days before plastic) and this enahanced
the volume like the cone on a wind-up gramphone. Hi-fi it wasn't.
Mike, G3XDV (IO91VT)
http://www.dennison.demon.co.uk/activity.htm
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