Date: Sun, 4 Nov 2007 11:00:06 +0000
From: John Pumford-Green GM4SLV <gm4slv@sighthound.demon.co.uk>
To: rsgb_lf_group@blacksheep.org
Message-ID: <20071104110006.691f913f@lurcher.twatt.local>
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	<000a01c81e72$31c8b000$2a298351@w4o8m9>
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Organization: The Gammy Bird
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Subject: Re: LF: Re: 500 KHz Narrow RTTY
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Hello Gary and LF,

I'm sorry I wasn't available last night to try some decoding tests
myself. I saw the RTTY traces on the grabber as I was heading out for
the evening.

I will certainly put together a collection of captures from the night
for you. Unfortunately there are no audio captures from last night.

Conditions were good from what I saw at around 1700-1800 - I worked
G3UNT, G3XIZ and (just... as I was being dragged from the house by XYL)
G4GDR. 

The QRN levels were low enough to make it possible to copy some very
weak CW by ear.

I'll send you a zip file of screen captures for the period wou had the
RTTY running once I've had a chance to sift through them

Cheers,

John




On Sun, 4 Nov 2007 10:52:45 -0000
"Gary - G4WGT" <g4wgt@tiscali.co.uk> wrote:

> Good Morning LF,
> 
> My thanks to Graham - G0NBD, Jim - M0BMU & Dave - G3WCB for the very 
> interesting reports & comments regarding my narrow shift RTTY tests.
> It looks quite likely that this mode could be competition for normal
> CW QSO's at 20 wpm were RTTY 45 Bd gives the equivalent of 60 wpm
> without taking too much bandwidth on a small band allocation ( 23 Hz
> in this case).
> 
> The findings have surprised me in such that I believed that the
> narrow shift could be a problem but as Jim stated with a little care
> tuning to the signal a very good percentage copy can be achieved.
> 
> In Jims case the distance is 268 Km & Dave 274 Km.
> 
> During the test I was also monitoring Johns (GM4SLV Shetland) grabber
> IP90GG at 739 Km & Daves (G3YXM Birmingham) grabber IO92BK at 143 Km.
> The traces there were such that at Birmingham the qsb periods between
> dips were short & deep but at Shetland the QSB period between dips
> was much longer & dips shallower maintaining a longer readable trace.
> The traces after dark at Shetland were so strong that my RTTY signal
> was producing a solid white line so in those terms we could expect
> the narrow RTTY would have given a 100% copy.
> 
> Perhaps John could send me or make available to some captures of last
> night so I can include them on my web site at the next update, even
> better if there were a sound bite available.
> 
> Thanks to all for watching & reporting.
> 
> 73
> 
> Gary - G4WGT - IO83qp
> 
> 
> 
> 
> ----- Original Message ----- 
> From: "James Moritz" <james.moritz@btopenworld.com>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Saturday, November 03, 2007 11:35 PM
> Subject: LF: Re: Re: Re: 500 KHz Narrow RTTY
> 
> 
> > Dear Gary, LF Group,
> >
> > The attachment shows a spectrogram of the last hour or so of your
> > test, up to around 2251utc - earlier periods were similar. The
> > upper trace is G0MRF's
> > beacon, which is quite local to me, and the lower trace is G4WGT.
> > As far as
> > readability goes, the transmissions that are fairly yellow were
> > printing out
> > with few errors; this was about 20dB above the "blue" noise floor
> > on the spectrogram. I would estimate that this mode will work with
> > similar signal levels to CW - the "yellow" signals would have been
> > comfortable audible CW copy. As you can see, the periods of QSB are
> > quite variable - For a short QSO of a couple of minutes, this
> > wouldn't be a problem, but long QSO would require standing by
> > waiting for the signal level to build up after a fade -
> > also rather like CW.
> >
> > I used MMTTY for reception - with 23Hz shift, the signal has to be
> > tuned quite accurately for best reception, perhaps within 5 Hz, and
> > I found it was
> > neccessary to turn the AFC off to avoid it wandering off towards
> > G0MRF's CW/PSK31 signal - the separation between the two signal
> > carriers was only 100Hz, so not surprising I suppose. The bandwidth
> > of the narrow RTTY looks quite similar to PSK31.
> >
> > Thanks for the test,
> >
> > Cheers, Jim Moritz
> > 73 de M0BMU
> >
> > 
> 
> 


-- 
John GM4SLV
IP90gg
Clousta, Shetland