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

[Joe Subich, W4TV]

On 9/14/2015 2:55 PM, Luis V. Romero wrote:
 >
> 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

The displays generated by K0SM are frequency domain ... TX MON is
strictly a time domain (amplitude) display.  TX Mon uses a amplitude
detector driven by a directional coupler.  To do what you desire would
require an SDR tuned by frequency data (TX frequency) from the K3.

The difference between an envelope (diode) detector and a tracking SDR
is a couple of orders of magnitude in both cost and complexity.

73,

   ... Joe, W4TV


On 9/14/2015 2:55 PM, Luis V. Romero wrote:
> 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
>
>
>
>
>
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