Thank you all for clearing up that matter.
Mario Filippi
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Today's Topics:
1. Re: Swlfest Digest, Vol 39, Issue 11 (Richard Cuff)
2. Re: Swlfest Digest, Vol 39, Issue 11 (Eric A. Cottrell)
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Message: 1
Date: Tue, 19 Feb 2008 15:30:11 -0500
From: "Richard Cuff"
Subject: Re: [Swlfest] Swlfest Digest, Vol 39, Issue 11
To: "Discussion list for the Winter SWL Fest"
Message-ID:
<[EMAIL PROTECTED]>
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I remember my dad in the 1960s telling me it was some type of teletype
operation.
Rich Cuff
On Feb 19, 2008 3:21 PM, Fred Zalupski wrote:
>
> As a boy I imagined that to be sound of the engines heard through the open
> door of a military cargo plane with the mic stuck in the open position.
> Rather I think it was actually some type of image transmission.
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Message: 2
Date: Tue, 19 Feb 2008 23:35:05 -0500
From: "Eric A. Cottrell"
Subject: Re: [Swlfest] Swlfest Digest, Vol 39, Issue 11
To: Discussion list for the Winter SWL Fest
Message-ID: <[EMAIL PROTECTED]>
Content-Type: text/plain; charset=ISO-8859-1
Mario Filippi wrote:
> The idea to play SW noises sounds great. As long as I can remember
> there was the sound of something like an airplane engine on shortwave,
> never could figure out what that was, maybe when I attend the 'fest
> someone will know what it is.
>
> */s/*
Hello,
It is a Voice Frequency Telegraphy. I know it as FDM for Frequency
Division Multiplex. It sounds like a aircraft engine when tuned on AM.
Most of the activity in the US is Military for point-to-point links.
It is a method of transmitting multiple RadioTeletype channels within a
3 KHz voice radio channel. It uses very narrow shifts for the RTTY
signals and up to about 12 channels can be sent. Most of the military
signals are encrypted but on some FDM there is one channel of Aviation
Weather or News in the clear.
This web page has a good description.
http://crackmonkey.org/pipermail/crackmonkey/2001-July/021165.html
I copied some FDM in my time. It takes a very stable receiver, good
audio filter, good RTTY demodulator, and a steady hand on the tuning
knob. 10 Hertz off frequency can turn good copy into bad.
73 Eric
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End of Swlfest Digest, Vol 39, Issue 13
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