[RTTY] High Speed RTTY again

Fri Jan 29 02:20:30 PST 2010

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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