[Elecraft] K2 RTTY

[Don Wilhelm]

Logan,

What you say is true and quite workable *except* for the times when 
there is a strong undesired signal inside the IF passband.  That strong 
signal takes over the AGC and reduces the receive gain causing all 
signals (including your desired signal) to become weaker.

The solution is to set up the RTTY set of filters so one can narrow the 
receive IF bandwidth when a strong undesired signal is present.  I set 
the RTTY filter widths as follows: FL1 = OP1; FL2 = 1.00; FL3 = 0.70; 
and FL4 = 0.40.  I use Spectrogram to center the narrow filters at 1000 
Hz (you can simply copy the SSB FL1 BFO frequencies to the RTTY FL1 
settings.

In use, tune the desired signal using the K2 VFO to the vicinity of 1000 
Hz (your narrow filter center) and enjoy the QSO.  Should an undesired 
signal enter the passband, you may switch to a narrow filter to reduce 
the AGC pumping effect.

A great advantage for using the RTTY filter set instead of the SSB 
filters for data modes is that there is a compression setting 
independent of the SSB compression setting - you can use any compression 
for SSB and set the RTTY compression to 1:1 for best transmit IMD.

The only problem with this approach is that there may be a slight shift 
in the audio frequency of the received signal when you change to a 
narrow filter (up to 20 Hz).  One can easily counter that shift by 
clicking on the "Lock Transmit Frequency" in the software before 
switching filters - that will keep the QSO from 'walking the band'.

73,
Don W3FPR

Logan Zintsmaster wrote:
> I hope the group will pardon me while I engage in a bit of RTTY heresy.....
>
> When you use a PC sound card for decoding RTTY, the center frequency is no
> longer important, just the tone spacings.  With MTTY, I can pick any center
> frequency I want to use (typically 1000 Hz so I stay away from the roll-off)
> and tune until I see it in the MTTY spectrum window.  I make any fine
> adjustments with the cursor to pick the signal I want if there are multiple
> signals shown.  If I want a bandpass filter, I use the bandpass function in
> MTTY.  MTTY uses the same audio frequency for encode as it used for decode
> so the signal is inherently locked to the received signal.  It even has an
> AFC function to track any drift.
>
> Using just the SSB filter for receive and transmit avoids the problem of
> center frequency tracking between the SSB filter that is always used on
> transmit and whatever receive filter has been selected.  
>
> It also has the advantage of allowing you to hear what is happening across
> the audio bandwidth so you know whether to go higher or lower for the next
> signal.  Very useful in a contest.
>
> I use Writelog with the MTTY decoder for contests and the whole setup works
> very well.  Using the mouse wheel for tuning and macros for the exchange, I
> rarely touch the K2 at all.
>
> Hope this helps.
> 73
> Logan, KZ6O
>   
>