Message-ID: <007801c81ce3$dd9a4cd0$0d00000a@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <001c01c81c0b$ef981a80$2201a8c0@PC2><E1InMCb-0006LO-Ae@post.thorcom.com><47297997.1208.1CCA4C@dave.davesergeant.com><20071101082740.18172494@lurcher.twatt.local><000d01c81c8e$85911230$0d00000a@AGB> <20071101143241.7af5f29e@saluki.ngw.uk.com> <003c01c81cca$6c685ed0$0d00000a@AGB> <007201c81cd8$882ca500$0900a8c0@Lark>
Date: Fri, 2 Nov 2007 00:03:56 -0000
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Subject: Re: LF: RE: 500 kHz report /  Great expectations
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----- Original Message -----=20

From: "Alan Melia" <alan.melia@btinternet.com>

To: <rsgb_lf_group@blacksheep.org>

Sent: Thursday, November 01, 2007 10:42 PM

Subject: Re: LF: RE: 500 kHz report / Great expectations



=D8      Hi Graham, ah but yes it will!!. The skip you talk about is due to=20
the
> ground wave fading below the noise qrm at ranges before the skywave starts
> to come in at good strength. This is well known in the Lowfer (160 to=20
> 180kHz
> 1 Watt DC) fraternity in the States. the higher power Part 5 stations dont
> get this problem. On the commercial station power levels the ground wave
> equals the skywave strength at somewhere around 700 km (CCIR reccs), and=20
> if

=D8

=D8      That distance is the zone where no use can be made of the signal du=
e=20
to  severe , constant multi path propagation ? ,  well out side the 'uk' and=
=20
our   100 mW erp !

=D8
> you plug the figures into to the late Reg Edwards GRNDWAV4 program you=20
> will
> see how the ground wave fades with decreasing power level. Those of us=20
> that
> live in domestic areas have to put up with a higher level of blanketing
> noise than John, which make the situation far worse.
>
> A little bit more power could enable us to achieve better groundwave=20
> ranges
> in daytime than are possible on top-band. Then add to that the possibility
> of daytime skywave at longer distances and it could well help. There will
> always be a rapid fading at shortish distances (100 to300km) but more=20
> power
> would give some fade margin so the signals didnt go right out.

=D8

=D8      That's a disputable  area , the point I was making , was that , fro=
m=20
observation , power levels of stations inside the uk look to  have little=20
effect on the 'peak to dip' ratio of the qsb , I think the  early beacon's=20
proved one thing , that's when 'in range' power is not a problem , If I can=20
'see' my signal at Bham, ~75 miles , just outside what , could be called the=
=20
'service area' dropping the  tx power as low as can , makes very little=20
change to  the pk/dip ratio ,  Increasing the level will  'enable' a contact=
=20
, but the ratio still looks to  'hold' ?

=D8

=D8

=D8
>
> On the data, a "locked" signal should be somewhere around at least 6dB
> better under fading but it has to flywheel its parameters through the=20
> fade,
> not suddenly start hunting for them again when the signal disappears. Much
> data software is not written for these LF type conditions, Amtor ARQ would
> be good with some error correction and longer bursts than 3 chars....
> possibly adaptive to match the fading conditions. The origin SITOR was
> designed for HF conditions which have different problems. Selective fading
> is not really an issue at LF.

=D8

=D8      I ran some propagation 'observations' using 3 carrier spaced 100 Hz=
=20
apart , that showed quite a marked 'fade pattern' with the highest frequency=
=20
displaying a longer  pk/dip  ratio than the lower frequency , I would  say=20
20/30 p/c longer , and during a 50 Hz qsy , hf , the top trace was totally=20
lost at Shetland, leaving just the lower 2 showing , totally un-expected !

=D8

=D8      NB : It was the out come of theses that prompted , me to  suggest=20
that 85 Hz shift be used on rtty ,  200/170 being vulnerable to  carrier=20
loss and in tests with Gary , 25 Hz did not perform well in the high noise=20
level ,

=D8

=D8      I was involved (at work) in a kite fly about
> a Marine Radio data protocol that would have used  an (A)X25 type of
> protocol with narrow bandwidth and a packet handshake that would have been
> very effective.

=D8

=D8      Yes ,  amtor would provide one of the  reliable data mode ,  HF 110=
=20
baud packet may also work , but these modes require a 'decodable' signal ,=20
at range signal levels rarely reach this level , oddly packet may provide=20
the answer, but the bandwith use is a little high ,  The Olivia system gave=20
'good' results when I ran a test a while ago , the wider version may prove=20
quite robust but  would take 'too much' band space .

=D8

=D8

=D8

=D8       The ultimate is GPS locked and that is very effective. If
> you want to see the the effectiveness of a locked system look at WOLF.=20
> This
> is not designed for "conditions adaptive" operation though, but I have
> copies signals way below the level QRSS can be seen on 136kHz. Even the=20
> "QSO
> mode" Wolf B put in does not make it friendy for qso work. A good system
> should go quickly when conditions are good and slow down, integrating the
> repeats, in bad spells, until the packet checksums agree.
>

=D8

=D8      These modes look interesting, but require 'linear' system's ,=20
unfortunately a lot of work has been undertaken with non-linear system's=20
hopefully Jim's  EER system may roll out as a retro-fit

=D8

=D8      A digital band . you can hear them or you cannot  hihi





Graham ..