Topband: Fwd: Spot Light Effects... Beacon netwrork

[Steve Dove]

------- Start of forwarded message -------
From: topband-owner at contesting.com
To: dsp at hifidelity.com
Subject: Fwd: Spot Light Effects...  Beacon netwrork
Date: 01/03/05 20:35:29



   From:        Steve Dove <dsp at hifidelity.com>

   To:          Topband at contesting.com
   Date:        Mon, 03 Jan 2005 20:32:35 -0000
   Organization:d s p
   Subject:     Spot Light Effects... Beacon netwrork

   Hi Ford,

   Your description, with minor differences, of a multi-station beaconing
    network
   parallels an 'ad hoc' system presently in use in the 136kHz amateur band and
    at
   'Lowfer' frequencies, particularly at 185.3kHz.  The tools in the form of
    logging
   software etc. are ready to hand, and time-tested.

   The beacons at LF have *extremely* low ERPs, but are readily sensed and are
   measurable using PC-based FFT programs at levels many tens of dB below
   normal CW bandwidth ear-hole levels, and certainly well below measurable S-
   meter strengths.  They are considerably below the noise floor as 
perceived by
    a
   normal receiver.

   A principle implication of this on a similar scheme for 160m is that the
    beacon
   signals do not have to be anywhere near as potent as a normal
   'communications' level signal:  A key factor often missing in discussions
    about
   beacon networks is the high degree of involvement and hardware usage on
   behalf of the beacon-keeper;  that essentially as long as he has the beacon
   running, he is out a radio, a big antenna, and as a consequence use of the
   band.  Reducing the ERP to enough to still allow ultra-narrowband sensing
   means that the transmitter need not even be a radio (!) and the antenna need

   not be very efficient nor full-sized;  with judicious filtering, the 
beacon's
    presence
   need not preclude normal topband operation, either.

   This reduction in scale and resources reduces disincentives and could allow
    far
   more beacons to be constantly available, which would obviously be far more
   useful.

   Without getting too involved in possible operational details, a quick look
    at how
   the system works at LF may be of interest as an initial model:  the beacons,
   rather than time-share, 'stake-out' their 'own' known frequencies, but all
    within a
   fairly tight cluster a few Hertz wide, and ID repeatedly at a very low
    symbol rate
   commensurate to the very narrow measuring bandwidths (30 or 60 seconds per
   dit CW are common).  As a departure from this for a predominantly 
propagation

   beacon network, a better approach may be a simple continuous carrier,
   interrupted every few minutes by a say 10wpm legal ID;  the FFTs would
   essentially ignore the wide-spectrum ID;  knowledge of which beacon was
   which would be from their frequencies within the window.

   A couple of years ago there was a minor storm-in-a-teacup here over low
    power
   beaconing on 160m, which was resolved by an informal 'ghetto' being created
   for such in the top kHz (i.e. 1999-2000kHz);  indeed a few such low-power
    low-
   rate tests showed promise, with one-Watt and even tenth-Watt ERP signals
   being usefully detectable country-wide. N2XE's tests show that even such
   power levels could be leaning to the profligate, although 1 Watt ERP would
   make for an easy 'standard'.

   Might I humbly point to:

   http://www.w3eee.com

   where a number of real-time FFT LF beacon monitors are running;  indeed one
   has been keeping continuous track of a German data station at 138.83kHz for
    a
   number of years now.  I will gladly provide a template for 'SpectrumLab' (a
   program by DL4YHF) which will facilitate the data-logging and plotting of
    multiple
   simultaneous beacons/carriers, to you or to whomever might become the 'point

   man' on such a system on 160m.

           73

                   Steve