----- Original Message -----
From: "Alan Melia" <[email protected]>
To: <[email protected]>
Sent: Thursday, November 01, 2007 10:42 PM
Subject: Re: LF: RE: 500 kHz report / Great expectations
Ø Hi Graham, ah but yes it will!!. The skip you talk about is due to
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
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
Ø That distance is the zone where no use can be made of the signal due
to severe , constant multi path propagation ? , well out side the 'uk' and
our 100 mW erp !
you plug the figures into to the late Reg Edwards GRNDWAV4 program you
see how the ground wave fades with decreasing power level. Those of us
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
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
would give some fade margin so the signals didnt go right out.
Ø That's a disputable area , the point I was making , was that , from
observation , power levels of stations inside the uk look to have little
effect on the 'peak to dip' ratio of the qsb , I think the early beacon's
proved one thing , that's when 'in range' power is not a problem , If I can
'see' my signal at Bham, ~75 miles , just outside what , could be called the
'service area' dropping the tx power as low as can , makes very little
change to the pk/dip ratio , Increasing the level will 'enable' a contact
, but the ratio still looks to 'hold' ?
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
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.
Ø I ran some propagation 'observations' using 3 carrier spaced 100 Hz
apart , that showed quite a marked 'fade pattern' with the highest frequency
displaying a longer pk/dip ratio than the lower frequency , I would say
20/30 p/c longer , and during a 50 Hz qsy , hf , the top trace was totally
lost at Shetland, leaving just the lower 2 showing , totally un-expected !
Ø NB : It was the out come of theses that prompted , me to suggest
that 85 Hz shift be used on rtty , 200/170 being vulnerable to carrier
loss and in tests with Gary , 25 Hz did not perform well in the high noise
Ø 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
Ø Yes , amtor would provide one of the reliable data mode , HF 110
baud packet may also work , but these modes require a 'decodable' signal ,
at range signal levels rarely reach this level , oddly packet may provide
the answer, but the bandwith use is a little high , The Olivia system gave
'good' results when I ran a test a while ago , the wider version may prove
quite robust but would take 'too much' band space .
Ø 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.
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
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.
Ø These modes look interesting, but require 'linear' system's ,
unfortunately a lot of work has been undertaken with non-linear system's
hopefully Jim's EER system may roll out as a retro-fit
Ø A digital band . you can hear them or you cannot hihi