Message-ID: <3BF960B4.FFF55445@netscapeonline.co.uk>
Date: Mon, 19 Nov 2001 19:42:44 +0000
From: "gii3kev" <gii3kev@netscapeonline.co.uk>
Organization: Netscape Online member
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To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Long-Baseline Phased Arrays on LF
References: <E165s4B-0007KS-00@mail1.isys.net>
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Klaus von der Heide wrote:

> Dear all,
>
> nearly two years ago we had a discussion about Phased Arrays
> and Diversity on this reflector.
>
> Diversity is a method to choose the temporarily best signal
> from receivers that are many wavelength apart from each other.
> Especially when the antenna must be omnidirectional, this is
> advantageous.  The 10 m relay in Hamburg is a well known example.
>
> Phased Arrays combine several antennas coherently. For an
> acceptable antenna pattern the distances of the individual
> antennas should be about a quarter of a wavelength (as in a Yagi).
>
> The combination can be done in several ways:
>
> 1. Direct combination of the antenna feeds as in Yagi-groups
>
> 2. Combination after preamplification
>
> 3. Combination after conversion
>
> The first way is not possible on LF because of the distances.
> The third way needs coherent oscillators at all wide spread
> receiver frontends or a sufficiently strong pilot signal
> in the LF band that could be used later to make all converted
> signals coherent. Since, in any way, the signals must be combined
> from distances of some hundred meters to a few kilometers
> the optimum choice are IR-links that can transmit the 136 kHz
> bands directly to a central station (way 2.).
>
> The combination at the central station can be done in two ways:
>
> a. Delaying the individual signals appropriately to realize
>    one directional pattern, then adding them and receiving with
>    a conventional receiver.
>
> b. Downconverting all signals in parallel using the same
>    oscillator (which in this case is no problem), digitize
>    the signals and implement delay patterns for all directions
>    you want in parallel by a DSP. This is equivalent to a
>    strongly directional antenna with high gain that simultaneously

What radio amateur is going to go to all this trouble for an occasionl
QSO. At present there are only 7 active radio amateurs on 136 khz. Get
real, learn the morse code, operating procedures, get the best antenna
installed on your property that you can manage and that is all you need.
The rest is just patience, listen and work what you can hear.
>>From the radio amateur point of view that is all that is required,
except you intend to shift vast volumes of radio traffic. The commercial
operators on LF have invented it all and RE-INVENTED it
Years ago the radio amateur was ahead in his garden shed but today he is
so far behind in the same shed, it seems some people never learn.
G3KEV


>
>    looks in many directions.
>
> 73 de Klaus, DJ5HG
>
>