Re: [RTTY] Scopes

[Kok Chen <chen@mac.com>]

On Jan 21, 2004, at 9:03 PM, K4SB wrote:
> Would like to buy a scope for use with my P38. What types are you guys
> using.
>
> Want to run RTTY in two windows.

Hi Ed,

I use a laptop, with my own home brew program to display crossed 
bananas.

The mark and space filters are in the program so I don't need a special 
TU, and it uses the stereo sound channels to process signals from two 
receivers (in my case, the A and B outputs from an FT-1000MP) to create 
a side by side display, which I can reduce to a single channel display 
using a menu.

The biggest advantage is there is no CRT burnouts, and adjustable 
bandwidths and phase delays to get perfectly orthogonal bananas and of 
the fatness I choose.  Fatter bananas is easier to tune on S&P when you 
are approaching the signal from far away, narrower bananas is more 
precise -- I am tempted to do an adaptive filter where the bananas 
automatically narrow down as you tune closer to center).

The display size  I ended up choosing is two squares about 2 inches to 
3 inches on a side (depends on which LCD display I run it on).

I used to use (back in the early 1990s) a Tektronics instrumentation 
scope that I'd picked up at a surplus store and a KAM Plus as the 
filter.  But the HV on it eventually died and I was without a scope 
until I went the software approach, which I now prefer (the KAM Plus 
produces a non-orthogonal banana display with a 170 Hz shift is tuned 
in unless you go in and tweak the switched capacitor filters a little).

In the MacOS 9 days, the sampling delay through the OS's sound system 
calls was troublesome (need to tune slowly to not overshoot), but MacOS 
X is basically instantaneous.  I don't know what the delay through a 
modern Windows OS is.

If anyone wants to adapt something like this to Windows, I am willing 
to shoot the source code over (warning, there is a bunch of MacOS X 
Cocoa [Objective C] calls for the graphics, but the filter 
implementation is straight C code).  And if you are running MacOS X on 
a machine that has sound input, just drop me an email and I will shoot 
the application back.  Sorry, it won't run on MacOS 9 anymore since I 
went to Cocoa.  I have used both an old laptop with built-in sound and 
also an external USB based A/D converter.

Vy 73
Chen, W7AY

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