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Re: [RTTY] High Speed RTTY again

To: lists@subich.com
Subject: Re: [RTTY] High Speed RTTY again
From: Roger Cooke <g3ldi@g3ldi.co.uk>
Reply-to: g3ldi@g3ldi.co.uk
Date: Sat, 30 Jan 2010 11:33:43 +0000
List-post: <rtty@contesting.com">mailto:rtty@contesting.com>
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@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
>>>> _______________________________________________
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>>     
>>>>     
>>>>         
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