Message-ID: <01C2396D.942EAAA0.g4jnt@thersgb.net>
From: "Andy talbot" <g4jnt@thersgb.net>
To: rsgb_lf_group@blacksheep.org
Subject: LF: RE: Re: "Downward modulation"
Date: Thu, 1 Aug 2002 15:10:29 +0100
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Well, I think that solves the problem.   Makes sense, and Droitwich is 
certainly a 'very high power transmitter'.    But a lot has been mentioned over 
the last few days about the technology of high power transmitters.  Techniques, 
I for one, knew nothing about.  Would be very  interesting if those in the know 
could put together some sort of treatise on these.  Or an idea for a lecture at 
a future LF Meeting.   Just a hint ;-)

I went to take a look at Droitwich a few days ago and noticed something a bit 
odd.  The Tee top section is not symmetrical.  One end seems to have an extra 
bit of wire attached to it that the other end does not have.  A legacy of the 
move from 200 to 198kHz perhaps ?

Andy  G4JNT


-----Original Message-----
From:	Prof. Arnaldo Coro Antich [SMTP:inforhc@ip.etecsa.cu]
Sent:	2002/08/01 12:31
To:	rsgb_lf_group@blacksheep.org
Subject:	LF: Re: "Downward modulation"

You are certainly talking about DAM...
Dynamic Amplitude Modulation....
a process that is used with very high power
transmitters to save energy.....
When there is no modulation, the carrier
level is moved UP, in order to keep the
signal to noise ratio on the channel at
a better level for the listener ( i.e. no background
noise or co-channel stations... you require
26 dB signal to noise ratio on an AM system
that has between 4 and 5 kiloHertz bandwidth
in order to provide full quieting ...)
AND YES.... there are many high power
AM transmitters nowadays that are facing
very poor operation !!!
73 and DX
Arnie Coro
CO2KK