[RTTY] High Speed RTTY again
Roger Cooke
g3ldi at g3ldi.co.uk
Sat Jan 30 03:33:43 PST 2010
HI Joe.
My FT1000MP is fully fitted with filters - both IFs -
plus I have the Inrad roofing filter too.
I had two contacts yesterday, KK5OQ for 25 minutes, and
also K4HBM about five minutes. The first one, with Charles
was solid copy for about 98% of the time with the occasional
character lost due to QRM mainly. The path was good however
with no multi-path or auroral flutter etc. It will be interesting to
see how 75 Bauds reacts under those conditions. I shall have to
look for a West Coast station to do some tests.
The second QSO with Joe, K4HBM, was shorter but solid again.
Probably the 500Hz filters would be a better choice, but I use the
250Hz nearly all the time on RTTY.
Anyway, it looks very encouraging, so I just hope more people
will give it a try. Hunt and Peck are definitely out though for this
speed! :-)
73 de Roger, G3LDI BARTG Chairman
Joe Subich, W4TV wrote:
> 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 at contesting.com
>> [mailto:rtty-bounces at contesting.com] On Behalf Of Roger Cooke
>> Sent: Friday, January 29, 2010 5:21 AM
>> To: lists at subich.com
>> Cc: roger at g3ldi.co.uk; bartg at 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 at contesting.com
>>>> [mailto:rtty-bounces at contesting.com] On Behalf Of Roger Cooke
>>>> Sent: Thursday, January 28, 2010 5:26 PM
>>>> To: rtty contesting rttycontesting
>>>> Cc: bartg at 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
>>>> _______________________________________________
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>>>>
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>>
>>>>
>>>>
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