Re: [Tlf-devel] Few modification for RTTY

[Martin Kratoska]

Hi Ervin,

on your radio you have a FSK input which allows you to key (mark/space) 
your RTTY without AF modulation chain. No overdrive, no issues with 
badly suppressed oposite sideband *and* you can use the *full power*, 
assuming that your (additional) cooling system is capable to hold the 
temperature of the final (PA) withn acceptable limits. Of course, some 
older radios do not have the FSK input.

There is nothing good on AFSK use. To keep distortion acceptably low, 
you have to turn the mic gain (or equivalent) low resulting in very low 
output, a 100W radio delivers mostly ~10-20 Watts. BTW this is the 
reason why I hate soundcard modes, every "digimode" presumes to switch 
your radio to SSB and modulate with the output from the sound card. RTTY 
is *only* mode which does not require SSB modulating chain, it can be 
simply switched (from spaces to marks and vice versa) via dedicated input.

More info:
http://www.aa5au.com/gettingstarted/rtty_start_intro.htm

however probably thwe best info source is the MMTTY help file:
http://hamsoft.ca/pages/mmtty.php

I was active on RTTY many years ago. No AFSK again! AFSK can be a good 
start point but not the option you want to meet in a pile up!

73,
Martin, OK1RR

P.S. MMTTY is capable to key the FSK, also probably Digipan (I need to 
fill the gaps in my memory) but AFAIK NO LINUX software! The very 
popular fldigi uses "pseudo FSK" which is an AF signal which is 
rectified and switching the radio FSK input via transistor switch. The 
problem is the rectifier, its filtering capacity is rather critical. BTW 
when I cooperated with Tony, VE6YP on the YPLOG we developed a CW keying 
system capable to key you TX up to 200 WPM - it was a very unique 
option. Also I collected a lot of experience with such rectifiers and 
can say, it is very tricky! Anyway, we need to beat the timing (latency) 
issues to get an useful FSK program.



Dne 11.2.2014 11:02, Ervin Hegedüs napsal(a):
> Hello Martin,
>
> On Tue, Feb 11, 2014 at 09:47:10AM +0100, Martin Kratoska wrote:
> > Hi,
> >
> > a brief question: what RTTY modem software would you recommend to
> > use with tlf? I am in search of a program capable to transmit true
> > FSK (like MMTTY does), no AFSK or similar gimmick. Bands are quite
> > full of overdriven signals, also the reduced power is no option. Any
> > ideas?
>
> why is better the native FSK than AFSK?
>
> I tought on receive side would be better, because then the
> soundcard should be skipped (if RIG support the FSK output,
> and/or you have a real RTTY modem). But on transmit side, I don't
> understand that.
>
> (This isn't an offense :), I'm really interested)
>
>
> 73,
>
> Ervin
> HA2OS