[RTTY] DXP38 vs MMTTY tuning faceoff

[Kok Chen]

N6TQS wrote:
> I think we've discussed this before.  The DXP38 tuning indicator
> sucks.  I use a HAL RTTY=1 with mine, which works much better,although
> I find the cross display an affectation.

I have had moderate luck with a software tuning indicator
which resembles the KAM display.  In fact, it is my preferred
software indicator (much faster than using a spectrum display
like MMTTY).

I used to use a crossed banana display on a 5" Tektronix
instrumentation/medical CRT, until the HV went poof (that's
for buying surplus :-).

The crossed banana was best tuning indicator I have used. I
will eventually try and create one in software (no software burns
on LCD :-) or one that mimics DJ0OT's discriminator (she used
resonators which placed zeros at the mark and space, rather
than poles; there is almost no cross response when tuned
correctly and the tuning indicator show up as two lines that are
at right angles to one another, rather than two bananas.  I think
Dick's page had a photo of her discriminator.

With a KAM-like indicator, the trick is to use grayscale to
  indicate the amplitude of a frequency bin, and to display the
spectrum well beyond the 170 Hz shift.  I use 32 "segments"
over a 500 Hz spread. (64 segments over 500 Hz would
probably do better).

The grayscale modulation of each "segment" is crucial.

Without it, the mark and space regions are spread out enough
you cannot tune accurately.  The grayscale give a much faster
visual cue of the third dimension than a spectrum plot such as
that used by MMTTY.

I have two red pixels below the set of green bars to indicate
the 2125 Hz and 2296 Hz bins.

The VERY crucial thing about tuning indicators is to make the
delay from realtime as small as possible.  Many software indicators
suffer from too long a delay time.  You need to use as short a A/D
buffer as you can tolerate.  Any delay will exhibit a hysteresis or
backlash when you attempt to tune rapidly -- kinda like tuning
the old radios that used  dial cords or the cheaper planetary
reduction drives on tuning capacitors.

IMHO, an FSK tuning indicator should only be as visually complex
as it needs to be to tune a signal accurately, and no more complex
than that.  Fancy displays only distracts you from tuning something
in quickly.

73
Chen, AA6TY