[RTTY] The Problem with AFSK ...

[Joe Subich, W4TV]

 > This is why I always advised against using the mic input for AFSK.
 > By the time you saturate the mic pre-amp, it is game over.  You are
 > most likely to present a non-symmetrical signal to the balanced
 > modulator, and we know what that does.

Unfortunately West Mountain Radio and Signalink both do exactly this by 
default.  For example - Signalink cables:
   SLUSB4R - For 4-Pin Round Mic Connector
   SLUSB8R - For 8-Pin Round Mic Connector
   SLUSBRJ1 - For RJ-11 Mic Connector
   SLUSBRJ4 - For RJ-45 Mic Connector
   SLUSBKX3 - For the Elecraft KX3's Mic and Phones jacks
Yes, they also have them for the DATA/PACKET/LINE/etc. jacks but
they're "down the list".  WMR does not even offer cables for the
"Line" jacks.  Those two are not alone, look at the information
on the internet from folks with their "interface kits" almost all
of them simply show connections to the mic connector and headphone
jack.  Even Icom presents a mic jack option in their Instruction
Manuals.

 > Like I have personally discussed with a few folks, the problem with
 > FSK keyclicks is that we have to wait for the manufacturers to get
 > off their behinds and do something about it (just look at how long it
 > took Yaesu to remove CW keyclicks from their contest grade rigs).

Not only do we need to wait for the manufacturers to get off their
duff and do something about the wider than necessary FSK signals, then
we will need to wait for the existing inventory to age out of the ham
shacks.  How many "clicky" FT-1000D, FT-1000MP and FT-1000MP MKV
transceivers (and their Icom counterparts) are still in regular use
today even though they are 15, 20 even 30 years old?

73,

    ... Joe, W4TV


On 1/19/2013 2:43 PM, Kok Chen wrote:
>
> On Jan 19, 2013, at 10:51 AM, Joe Subich, W4TV wrote:
>
>> Doesn't mean a thing if the level going into the mic jack is
>> already too high for the microphone preamplifier.
>
> This is why I always advised against using the mic input for AFSK.
> By the time you saturate the mic pre-amp, it is game over.  You are
> most likely to present a non-symmetrical signal to the balanced
> modulator, and we know what that does.
>
> The other, less obvious (but equally important) reason is this: the
> cable between the sound card and the radio now has to carry a tiny
> signal.  This means that any noise and hum pickup is much larger by
> proportion.
>
> To do good AFSK, send as large a signal as possible on the cable to
> the radio and if needed, add two resistors to attenuate it at the
> radio itself.  But be sure not to saturate any transformer that is in
> the large signal.
>
> On something like the Elecraft K3, as example, use as large a line
> level in the menu as your sound card will deliver cleanly.
> Typically, I have found that -3 dB of the sound card full scale
> output is a good value to use.  You then adjust the line level menu
> in the rig to accept that.  Only back off the sound card output if
> that is still too much for the line level menu to compensate.
>
> Even on something like the Kenwood TS-590 with its built in sound
> card, you should still use a good sized signal from the modem, just
> in case there is ground noise within the rig itself.
>
> It is really not hard to produce good AFSK, as Andy K0SM's spectrum
> captures showed.  All those clean AFSK signals in Andy's spectra
> showed that it is not just theoretical possible, but it is quite
> practical to produce pleasant AFSK RTTY signals that are friendly to
> neighbors.  And quite a few contesters are using it.  With something
> like a K3 or a TS-590, there is almost no reason not to.
>
> Like I have personally discussed with a few folks, the problem with
> FSK keyclicks is that we have to wait for the manufacturers to get
> off their behinds and do something about it (just look at how long it
> took Yaesu to remove CW keyclicks from their contest grade rigs).  It
> is not going to happen overnight, even though it is really simple to
> accomplish for rigs that generate FSK signals in their DSP stages.
> In the meantime, we already have means today to generate a clean
> signal instead of waiting on manufacturers.  With CW keyclicks,
> responsible people also took matters in their own hands and modified
> the FT-1000s and other rigs to make them acceptable.
>
> 73
 > Chen, W7AY
>
>