Roger,
> I have the Yaesu FT1000MP and the 250Hz filter is stated as
> being 250z at -6dB and 700Hz at -60dB. I also have the 500Hz
> which is again stated as being 500Hz at -6dB and 1.8kHz at
> -60dB.
Are you using the cascaded filters (both 2nd and 3rd IF) or
in the case of the "250" only one? Yaesu's bandwidth specs
are a bit misleading since they are for both filters in
cascade. For 500 Hz, the 2nd IF (8 MHz) filter is close to
500 Hz with the 3rd IF filter (particularly the "Collins"
version) providing additional skirt sharpening but not a
lot of narrowing At "250 Hz" the each filter is only -3 dB
at 250 Hz wide but when cascaded the overall selectivity
becomes -6dB at 250 Hz.
> I can honestly say that I can copy 75 Baud RTTY very well
> using the 250Hz filter.
I have no doubt of that if you are using only one of the
two "250 Hz" filters since the real -6 ddB bandwidth will
be more like 350 Hz. Even if the filters are slightly
narrow, as long as the skirts don't have excessive phase
issues the effect of a "too narrow" filter will only be
a bit more attenuation. The problems with excessively
narrow filters will be much most obvious with multi-path
and weak signals rather than a strong signal in crowded
conditions.
> I would not advocate using any faster speeds anyway, because
> with the vagaries of propagation, especially over an auroral
> path and with QSB etc., too many characters will be lost.
> Not only that, but as someone mentioned, the difficulty comes
> with typing, unless a pre-prepared text is sent from the bottom
> window.
If operation is to transition to 75 baud, I like the idea of
combining it with a move to ASCII (e.g., 75 8N2) vs. BAUDOT
(45.45 5N1.5). Throughput will be about 15% higher due to the
combination of higher bit rate and elimination of the LTRS/FIGS
overhead but will still be within reach of the keyboarder.
73,
... Joe, W4TV
> -----Original Message-----
> From: rtty-bounces@contesting.com
> [mailto:rtty-bounces@contesting.com] On Behalf Of Roger Cooke
> Sent: Friday, January 29, 2010 5:21 AM
> To: lists@subich.com
> Cc: roger@g3ldi.co.uk; bartg@bartg.org.uk; 'rtty contesting
> rttycontesting'
> Subject: Re: [RTTY] High Speed RTTY again
>
>
>
>
> Joe Subich, W4TV wrote:
> >> In fact I have tried up to 110 Baud. Using 170Hz shift within
> >> a 250Hz filter width errors start creeping in at 110 Bauds and
> >> even at 100 Bauds, but 75 seems a good standard to aim for.
> >>
> >
> > If your filter is truly 250 Hz at -6dB, it is too narrow for
> > even 45.45 baud 170 Hz shift RTTY as the required bandwidth
> > is roughly 270 Hz. Most "250 Hz" filters are actually wider
> > - often between 300 and 350 Hz which results in an effective
> > bandwidth of 250 Hz when cascaded with a 280 - 300 Hz wide
> > filter at 455 KHz (e.g., INRAD #186 or #704).
> >
> > The required bandwidth for 75 baud/170 Hz shift RTTY is about
> > 350 Hz. 100 baud represents about 420 Hz and 110 baud gets
> > to about 450 baud although the onset of bandwidth issues may
> > be masked by QRM, QRN, multipath and selective fading.
> >
> >
>
> I have the Yaesu FT1000MP and the 250Hz filter is stated as
> being 250z
> at -6dB
> and 700Hz at -60dB. I also have the 500Hz which is again
> stated as being
> 500Hz at
> -6dB and 1.8kHz at -60dB. I can honestly say that I can
> copy 75 Baud
> RTTY very
> well using the 250Hz filter. I would not advocate using any faster
> speeds anyway,
> because with the vagaries of propagation, especially over an auroral
> path and with
> QSB etc., too many characters will be lost. Not only that, but as
> someone mentioned,
> the difficulty comes with typing, unless a pre-prepared text is sent
> from the bottom
> window.
> Phil, GU0SUP, mentioned PSK faster speeds, but I think that is a
> different case. The
> bandwidth used by PSK is limited to the USB audio bandwidth
> and to see a
> PSK125
> signal in there is being too greedy. It was never the
> intention of Peter
> Martinez, G3PLX
> to have anything other than PSK31 in the first place.
> With RTTY however, we do have considerably more spectrum
> and not only
> that, it
> would not increase occupancy. I certainly would not suggest
> going back
> to 850Hz
> shift, just for the sake of much higher speeds. I think 75 Bauds is a
> reasonable standard
> to aim for.
>
> Joe has a valid point however in that the Icom range of
> transceivers,
> now having RTTY
> and PSK "built-in", the users of that equipment would be
> forced to use a
> PC with MMTTY
> or N1MM, MixW, MultiPSK, or the like. But so what, how many Pro III
> users actually
> use their "built-in" RTTY for contesting? Very few I would imagine.
>
> Just more thoughts from a G3, in soggy Swardeston.
>
> 73 de Roger, G3LDI, Chairman BARTG
>
>
>
> >> It would increase Q rate in both contests and DX-pedition
> pile-ups,
> >> but it certainly is stressful on the typing!
> >>
> >
> > I have to question the wisdom of higher speeds. Even with
> > short "canned" messages like those in contests or DXpeditions
> > the overall data rate increase is not anywhere near the raw
> > difference in data rate considering transmit to receive and
> > receiver recovery times. The time "advantage" disappears
> > completely for keyboard RTTY (or paddle generated RTTY from
> > an Elecraft K3).
> >
> > It seems to me that the pursuit of higher speed RTTY is
> > speed for speed's sake without consideration of the extra
> > bandwidth (QRM) or compatibility with existing hardware
> > (e.g., Icom's "twin peak" filter, or the Elecraft paddle
> > generated RTTY) problems inherent at the higher speeds.
> >
> > 73,
> >
> > ... Joe, W4TV
> >
> >
> >
> >> -----Original Message-----
> >> From: rtty-bounces@contesting.com
> >> [mailto:rtty-bounces@contesting.com] On Behalf Of Roger Cooke
> >> Sent: Thursday, January 28, 2010 5:26 PM
> >> To: rtty contesting rttycontesting
> >> Cc: bartg@bartg.org.uk
> >> Subject: [RTTY] High Speed RTTY again
> >>
> >>
> >> Hi.
> >>
> >> Judging by the amount of emails flying about there does seem
> >> to be some
> >> interest in 75 Baud RTTY at last! I have had several QSOs
> >> at that speed
> >> both on 80 metres and 20 metres with total success. In fact I
> >> have tried up to 110 Baud. Using 170Hz shift within a 250Hz
> >> filter width errors start creeping in at 110 Bauds and even
> >> at 100 Bauds, but 75 seems a good standard to aim for. It
> >> would increase Q rate in both contests and
> >> DX-pedition
> >> pile-ups, but it certainly is stressful on the typing!
> >> I usually answer points as the other station is
> transmitting anyway
> >> and then
> >> sending at full speed it sure does rattle along. I will be
> >> calling CQ
> >> on 20 metres
> >> on Friday at around 1400z at 75 Bauds if anybody wants a QSO.
> >>
> >> John, GW4SKA certainly is giving it some thought now for a
> >> BARTG contest at that speed, possibly a short one, but as he
> >> says, although membership of BARTG is free and we would like
> >> as many as we can get, staging the contests does cost, with
> >> the certificates and plaques and things. Small donations
> >> add up
> >> so please consider making just a token donation when
> joining. It will
> >> all help
> >> sponsor the contests, plus BARTG also sponsors DX-peditions
> >> too. If you would like to sponsor a plaque too, that would be
> >> really nice! Perhaps all RTTY contests will move over to 75
> >> Bauds. :-)
> >>
> >> The next main BARTG contest is the Spring, in March. Don't
> >> forget the GB50ATG event that is on-going too. There are some
> >> nice certificates and plaques available for that. GB50ATG
> >> finishes at the end of July. Take a look on the BARTG web
> >> site, and see if it floats your boat, cocas your cola,
> >> bakes
> >> your cake, or diddles your Baud!!!
> >>
> >> www.bartg.org.uk
> >>
> >> Send some feedback. Hey, if you DO join, why not send us
> >> some pictures
> >> of your station/antennas etc., for the Gallery. You can
> >> even see the
> >> mug-shots
> >> of the committee on there if you can stand it!
> >>
> >> See you on the green keys on 75 Bauds Fri PM.
> >>
> >> 73 de Roger, G3LDI, Chairman, BARTG
> >> _______________________________________________
> >> RTTY mailing list
> >> RTTY@contesting.com
> http://lists.contesting.com/mailman/listinfo/rtty
> >>
> >
> > _______________________________________________
> > RTTY mailing list
> > RTTY@contesting.com
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> >
> >
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