From: "Mike Dennison" <mike.dennison@rsgb.org.uk>
To: rsgb_lf_group@blacksheep.org
Date: Mon, 22 May 2000 12:02:36 +0100
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII; format=flowed
Content-Transfer-Encoding: 8bit
Subject: Re: LF: Re: Best tone for aural copy
In-reply-to: <002b01bfc239$ea9019e0$2546b28f@w8k3f0>
Message-ID: <E12tqES-0002AE-00@mserv1c.u-net.net>
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

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