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From: 0004133373@mcimail.com (Donald E. Kimberlin)
Newsgroups: comp.dcom.telecom
Subject: Re: Tones on Mideast Broadcasts
Message-ID: <16445@accuvax.nwu.edu>
Date: 26 Jan 91 14:59:00 GMT
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X-Telecom-Digest: Volume 11, Issue 69, Message 3 of 7


    A post and some comments on here remark about tones of the region
of 10 Khz and up are heard or radio broadcasts of Mideast dial-up
connections.  It is utterly impossible for these to be coming from the
source, as any dial connection passes through at least one and
probably several sets of channel bank filters and digital carrier
channels that cannot pass anything beyond 4 Khz, most often no more
than 3 Khz.

     However, high-pitched noises and crosstalk on local telephone
cable pairs are often and readily passed by broadcast equipment and
transmitters.  AM stations in the US can often pass 12 Khz, and most
can pass 10 Khz, while FMs are regulatorily required to pass 15 Khz.
Experienced broadcasters avoid this by placing their own low-pass
filter in the dial line output to air so as to avoid these problems.

     If the source of what is being broadcast was taken from an inter-
national shortwave broadcast, high-pitched noises and whistles caused
by adjacent channel transmissions on the High Frequency bands are
rather common.  These could likewise be filtered out at the station,
but frequently the news people grab such material and air it in a rush
without any prepping for air.

     I really suspect the latter is more often what people hear now-
adays.