Message-ID: <3D494C2A.C0067976@virgin.net>
Date: Thu, 01 Aug 2002 15:56:42 +0100
From: "Stewart Bryant" <stewart.bryant@virgin.net>
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To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: RE: Re: "Downward modulation"
References: <01C2396D.942EAAA0.g4jnt@thersgb.net>
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Do you think that we could get a tour of the station and a lecture on site?

Stewart

Andy talbot wrote:

> 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