[Elecraft] P3 TX Mon: FEATURE REQUEST - Monitoring of RTTY Waveform

[Luis V. Romero]

Alan:

 

You wrote:

It gets more interesting if there is a problem 

 in the RTTY transmitter that causes the two tones to come out at 

 different amplitudes, which would be easy to see on the screen.

 

In your example, you would see ripple in the flat waveform on the screen,
true enough.  The Ripple would increase with the amount of the different
amplitudes of the two tones.

 

However, I can't monitor other issues that can rear their ugly heads in
RTTY, be it modulated by FSK or AFSK with the existing functionality
available:  The reason I was looking for a better visual representation of
these issues in this tool is explained in an excellent article by Andy
Flowers, K0SM.

 

http://frontiernet.net/~aflowers/k3rtty/k3rtty.html

 

Gee, it would be nice not to have to buy a Flex rig just to monitor my K3's
output. And I already have an SDR receiver sitting inside the P3 box, locked
to my transmitter frequency.   

 

You wrote:

The traditional "plus sign" (crossed ellipses) display is normally used 

 in the FSK receiving demodulator as a tuning aid.  As you tune the 

 receiver the ellipses change their angle.  When you see the "plus sign" 

 then the receiver is tuned correctly.

 

Not just for receive, but in transmit as well.  Especially in tone modulated
RTTY (pseudo FSK) using AFSK "tone" modulation.  If one tone is off, it
would be shown in the transmission ellipsoid representation as well.  When
you see a "plus sign", both tones are in phase and in quadrature.  But if
one tone is out of quadrature?  Then you see an ellipse.  We deal with this
daily in the representation of Trellis modulation artifacts in ATV
transmitters.  There we call it "The Eye Pattern". Same display principle. 

 

While the dual ellipse waveform would be ideal, there are alternatives, In
receive, we can see similar information in the two tone demodulation
"envelope" showing two peaks with a valley in between using a single
envelope detector as described bu K0SM. Why not avail us of at least that
waveform, since you already can show it on receive in the P3
hardware/software?  With some handles on the display for gain, width, slope
and maybe a synthetic "mask", it solves this requirement!

 

You wrote:

You can also see if the transmitter has the wrong (or at least 

 different) frequency shift.  In that case the ellipses don't make a 

 right angle with each other even when the receiver is tuned correctly. 

 

True and correct.  And I agree.

 

You wrote:

 That might be useful in a transmit monitor, but it can't be done using 

  An RF coupler because it only detects the amplitude, not the frequency.

 

True: Not the *quadrature* (two ellipsoids) display. But you *can* show the
dual peak/valley display. You already show it on receive!  It is an
equivalent 2-D representation that can be used in addition to the flat
envelope display.  But, alas, I can't see it in transmit (yes, I could
unplug the control cable to see IF "bleedthrough", but what a pain!). The
way it is now, I can only tell folks I am receiving that they are having
problems.  I can't proactively solve my own problems before I transmit with
my monitoring tool!

 

I don't know. Maybe I'm just old fashioned, but I'm really disappointed to
have waited 5 years and paid $200 for this simple envelope sampler
functionality using a repurposed WM2 sampling bridge.  I sort of expected
more. Maybe not in hardware, but in the application software, as all
hardware for this type of measurement is synthesized in apps anymore.  For
$200 more I could have gotten a Wavenode WN-2, but then I have wasted the
wattmeter again and I would need another PC to run the app software.  But
the funniest thing is that the P3 can display an equivalent waveform today
in receive that does what I need for transmission monitoring!     

 

I'm still no better off and $200 poorer than where I was with my Bench
Oscilloscope and a 17 inch piece of hook up wire, and that is the issue.
It's the first time I have been disappointed by an Elecraft product.  

 

 

Lu - W4LT