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Re: LF: RE: 500 kHz report / Great expectations

To: <[email protected]>
Subject: Re: LF: RE: 500 kHz report / Great expectations
From: "Graham" <[email protected]>
Date: Fri, 2 Nov 2007 00:03:56 -0000
References: <[email protected]><[email protected]><[email protected]><[email protected]><[email protected]> <[email protected]> <[email protected]> <[email protected]>
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----- 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 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 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 if

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 will see how the ground wave fades with decreasing power level. Those of us 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 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 power
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 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.

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 level ,

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
very effective.

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. 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 "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.


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

Graham ..

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