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[Linrad] Re: Best waterfall settings for viewing JT65b

Hi Jeff,

> I've been using Linrad to monitor the 2M band with one receiver 
> and using a second receiver with WSJT.  With the default settings 
> for SSB, the waterfall display doesn't seem very sensitive to the 
> JT65B signal.
Sure. The waterfall bandwidth would be around 200Hz, two orders of
magnitude too large.

> I've tried playing with 2nd FFT BW factor and averaging on the 
> waterfall and EME signals that show up crystal clear on the WSJT 
> screen looks very faint on the linrad display.
Make the second fft bandwidth something between 2 and 5 Hz.
It may be a good idea to make the fft1 bandwidth 20Hz or so
to avoid a very large ratio between the bandwidths in case you
also have very strong signals present.

Since you have a total span of something like 40 kHz over the screen
with perhaps 10000 fft bins, you must average over at least 10
transforms with a sin squared window. (Higher order windows will 
require even more averaging but there is no point in using them
with such large transforms.)

The waterfall gain should be at least 3 to allow you to see the 
grainy structure of the noise floor.

> I could have problems with DEMI downconverter and Softrock, 
> but it has good noise figure, gain and sensitivity on test 
> equipment.
Do you mean you measured the noise floor on the output from 

Try to remove the DC voltage to your 144 MHz preamplifier.
The noise floor should fall by something like 17 dB. You
should see the same result on both your receivers (AGC off
on the conventional one)

> On another point, it would also seem convenient to set 
> the scrolling speed to produce 30 second or 1 
> minute time stamps on the left hand side of the waterfall.  
> Does anyone have settings for that?
There are no settings to control this.

Time stamps are written each time twice as many lines as the
height of the currently selected font have been written.
The code is in screen.c, the functions are:
void wg_waterf_line(void)
void redraw_wg_waterfall(void)

The asci and its associated time are stored in
wg_waterf_times[0].text and wg_waterf_times[0].line
It would be possible to do it after a 30 second or 
1 minute intervall has passed, but one would have to
allow for a very large number of intervals. 0.2 seconds
up to 10 hours or so. Would take some time to do but
if someone writes the code I will happily include it.


Leif / SM5BSZ

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