Date: Thu, 4 Nov 2010 07:58:07 +0000
From: John P-G <gm4slv@sighthound.demon.co.uk>
To: rsgb_lf_group@blacksheep.org
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Organization: The Gammy Bird
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Subject: Re: LF: WSPR window
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On Wed, 3 Nov 2010 20:25:38 -0400
<jrusgrove@comcast.net> wrote:


> Good discussion.

Jay, LF 

Some interesting points to consider! I understand your basic thrust,
and would, in general, agree that WSPR won't really work under the
conditions you're describing, but I've put some thoughts down
nonetheless :-)

> 
>  Many US stations run 'large' antennas and appreciable power
> compounding the problem. Local (out to a few hundred miles)
> groundwave signals can be well over S9 here and completely lock up
> WSPR.

I'd hope that they wouldn't be on high duty cycle transmit, so there
should still be gaps where weak signals can be detected.

If it's true that there will be too many S9+ signals received by each
Stateside WSPR operator, in each and every 2-minute timeslot, in
effect wiping out all small signals, then how are these same stations
going to be able to receive anything from other, more distant USA
stations? All they'll see is the strong locals. Which means that all
that power is being transmitted for no reason, if it's just going to
wipe out the WSPR receiving capability of everyone within groundwave
range, and you're saying that everyone will be within groundwave range
of at least one high power station?

You seem to be saying that it isn't possible to use WSPR in the form
intended because there will be continuous self-generated QRM preventing
the reception of any weak signals - including the ones your're trying
to study on trans-USA overground paths.

Or is it simply that the high power USA stations on 499.6 are
only interested in T/A reception reports, and don't care about
receiving other USA-based signals? 

In which case, then yes - we could run semi-duplex split frequency and
care only about T/A reception. 

I thought the point was to observe propagation wherever it appeared,
and I also thought the WD and WE experimental stations were interested
in observing the vaguaries of MF propagation over land.

> 
> Don't believe there is a direct comparison between 40/30/20m
> operation and LF / MF. Most of the stations using WSPR on 40/30/20m,
> with little to no groundwave,


Agreed, 

however

> may never even audibly hear another WSPR station let alone have to
> contend with S9 plus mega signals.

Not sure this is the case. On 20m, 30m and 40m there can be many strong
signals, not all of them WSPR, within the IF passband and also within
the 200Hz WSPR window, and there can be dozens of WSPR stations, some
of them very strong due to good propagation and, at times, high TX
power. Admittedly they probably aren't "bending the needle" to
S9+ though, but the overall effect can be of a very full and noisy
part of the band.
 

> There's no reason that US stations can't listen on 502.4 while
> transmitting on 499.6. 

But would that mean they won't be listening on 499.6 for their "own
kind"? That kind of defeats the object? 

> Alternatively, E > W could occupy a designated time slot
> and W>E a different designated time slot to alleviate the
> interference problem.

WSPR, in its current form, can't do this - it picks slots at random to
yeild an average "on air" ratio as set by the user, but there's no way
of designating which slots are used.

> 
> It just seems that some sort of a coherent plan would yield better
> results than an ocassional 'luck of the draw' spot because a number
> of stations happened *not* to be transmitting.

That's the way it's supposed to work though :-)

I think that another mode needs to be considered to achieve the kind of
thing you're suggesting, with rigid time slots and split frequency
built in, but with the super-convenience of web-based instant reporting
as used by WSPR.

I think we've exhausted this one, now. I guess the proof will be when
the spots dry up, or we get bored and try something else!

Best regards from Shetland,

John
GM4SLV