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Re: [RTTY] The Problem with AFSK ...

To: rtty@contesting.com
Subject: Re: [RTTY] The Problem with AFSK ...
From: Robert Chudek - K0RC <k0rc@citlink.net>
Reply-to: k0rc@citlink.net
Date: Sat, 19 Jan 2013 14:31:36 -0600
List-post: <rtty@contesting.com">mailto:rtty@contesting.com>
"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."

Here's another opportunity for all those politicians to get involved and earn their paycheck. Mandate the FCC certification program institute adherence to a IEEE standard. The problem is, there would need to be a IEEE standard created first. Another 'gumment' opportunity, just like mandating mileage and emissions standards.

73 de Bob - KØRC in MN

------------------------------------------------------------------------
On 1/19/2013 1:43 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



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