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LF: Re: Re: RTTY Protocol

To: <[email protected]>
Subject: LF: Re: Re: RTTY Protocol
From: "Alan Melia" <[email protected]>
Date: Wed, 6 Mar 2013 19:09:30 -0000
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Hi Minto the other trick when mechanicals were around was always to transmit a figure  as fs9ls even if another figure was to follow. This ensures the machine doesnt slip into fs mode ....most text is letters so the extra char doesnt use a lot of time..
 
Alan
G3NYK
 
----- Original Message -----
Sent: Wednesday, March 06, 2013 1:57 PM
Subject: LF: Re: RTTY Protocol

My PIC software now does the following when starting a RTTY transmission:
* Start the TX (mark)
* wait 500 ms to ‘wake up’ the receiver to the mark
* send two NULL characters to get the receiver in sync (probably not necessary?)
* then (always) send a letter or figure shift depending on the first ‘real’ character to transmit.
* then send the text

 
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Ceterum censeo Carthaginem delendam esse
 
From: g3zjo
Sent: Wednesday, March 06, 2013 14:38
Subject: Re: LF: Re: RTTY Protocol
 
On 06/03/2013 13:14, Minto Witteveen wrote:
That settles it. The info I got (from an untrusworthy source it seems) told me mark is 2125 and space is 2295. See my original message below.
But it is the other way around.
 
But it is only independent of the sideband used if both sender and receiver use the same sideband.... You still have to agree.
And it seems that the current consensus is mark = highest tone = highest frequency. So USB if AFSK is used.
Yes yes.

BTW regarding missing the first character 's. In the mechanical days did we not send CR/LF first to get things going? I have seen the software have problems during the recent tests, printing Numbers instead of Letters. This can be alleviated by sending 46RY first, 46 I think being RY with LetFig set wrong.

Eddie

 
73’s Minto pa3bca
 
 
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Ceterum censeo Carthaginem delendam esse
 
From: Alan Melia
Sent: Wednesday, March 06, 2013 13:57
Subject: Re: LF: RTTY Protocol
 
From my days on HF RTTY (~1970) with mechanical 'printers, the highest RF frequency was Mark (or idle tone)  It was independent of which sideband was used. I think this was also the mode used by the commercial stations
Remember only European lines used bi-polar signalling. The US used a 20mA mark and no current for space. A mechanical machine of either type would chatter if the mechanism was not held in Mark. Timing was mechanical and stop-start was necessary to maintain character timing sync. with simple mechanical governors.
 
Alan G3NYK
----- Original Message -----
Sent: Wednesday, March 06, 2013 11:09 AM
Subject: Re: LF: RTTY Protocol
 

Hmm might this be because ‘in the old days’  (amateur) RTTY was done with the rig in LSB mode using AFSK?
With mark at 2125 Hz and space at 2295 hz and mark being the idling position, when using LSB the actual transmitted frequencies would be ‘swapped’ (reversed)
So MTTY seems to assume rig at USB, while all (all?) others assume LSB…

Still, Stefan and I seem to do RTTY wrong (i.e. amateur reversed, as in AFSK on USB).  I just checked my PIC code and I have mark at high (DDS_BASE + 85 Hz) and space at low (DDS_BASE). This then gets swapped around by fldigi because I listen (via websdr) in USB… This explains why fldigi decodes me (and Stefan) just right.

This is of course based on the assumption that ‘right’ means AFSK on LSB, that the space must be the high tone AND the low(est) frequency.
What _is_ the consensus (if any)?

73’s Minto pa3bca

 
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Ceterum censeo Carthaginem delendam esse
 
From: g3zjo
Sent: Wednesday, March 06, 2013 11:44
Subject: LF: RTTY Protocol
 
Graham

Just confirmed by test, MMTTY is backwards compared to all other Software. Others idle on the high tone MMTTY idles on the low, unless the REV is pressed.


From Wiki
the upper tone used for idle condition (MARK).


Another site says
You also have to switch the correct phase position (whether the lower or higher frequency carrier in frequency modulation corresponds to "Mark" or "space").

Mind you a Ham education site on the subject says.
Remember that bfo’s help filter out the carrier waves to allow for the original signals to come through


Eddie


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