[Elecraft] Displaying keying waveshape on Spectrogram.

Thu Sep 11 21:26:00 2003

That's the way I do it.

Have a look at W1AW doing code practice to see a proper shape.

My spectrogram settings:

Sample rate: 48k
Resolution: 16 bit
Type: Mono
Display: Line
Plot type: Signal
Averaging:  0 msec
Amplitude: 60
Palette: CB
Scroll Mem:
Freq Scale: Linear
FFT Size: 16384
Freq Resolution: 3.2 Hz (minimum)
Low Band Limit: 250 Hz
High Band Limit: 2250 Hz
Pitch Detector: Off
Cursor Frequency Offset: 0
Recording Enable: Off

Hit "OK" button

On the Display, click the "GRID" button.

On your receiver, connect the headphone jack to the Line-in jack on
your sound card. On whatever sound controls you have onscreen for your
sound card, put the Line-In setting at mid scale.

You should be hearing your receiver on the computer speakers and
seeing a display on the Spectrogram display.

Set the receiver to receive upper sideband, widest possible filter
setting. Find a loud CW signal and center it at 750 or 1250. This will
place the signal centered between the grid lines spaced every 500 Hz.
Imagine each space between grid lines as a separate channel.

Adjust the RF/Audio gain on the receiver so the keyed CW peaks at the
top of the graph. Optimally the keyed waveshape should stay within the
grid lines (carrier +/- 250 Hz). As you tune around the band, you will
find loud signals which do not. You will find some that make the
baseline jump across the ENTIRE graph.

This setup will allow you to see energy 60 db below carrier and see
what is being placed in the adjacent channel, with noise (listening on
the band) or without (listening to a close transmitter being keyed
without an antenna on the receiver).

When you do a bandwidth check on a local transmitter, adjust the
keying speed for the highest bandwidth indication on the display, to
avoid interaction between sweep and keying speeds. Hit the peak hold
button. The red line left over when you let up on the key tells you
what is going on.

Check out the W1AW code practices at 1818, 3581.5, 7047.5, 14047.5,
18097.5, 21067.5 28067.5

You will see that it is not necessary to have a "broad signal" to have
clean, crisp CW. It IS possible to stay inside +/- 250 Hz AND sound
really good.

It will also be apparent that many signals are only loud enough to
have the top 5, 10, 15 db of their waveshape above the noise. You will
never know if they have clicks or not.

I was listening to a station from Texas (!) on 40m that was 40 db over
S9 (all the lights on the K2). This is a level usually reserved for
the BC stations up the band. When he was sending, the band noise was
not visible anywhere on the display due to the AGC action. His
waveshape crossed +/- 250 Hz grids at about 52, making his sidebands
potentially S6 or S7 in the next channel.

The more power you run, the cleaner you need to be.

A friend's JI-modded FT-1000 MP is between the lines below 60 db.

I suspect that Wayne's mod for the K2 will get down there. The
approach is excellent. And it's Wayne.

73, Guy.

----- Original Message ----- 
From: <[email protected]>
To: <[email protected]>
Sent: Thursday, September 11, 2003 3:39 PM
Subject: [Elecraft] Re: K2 Key clicks

>
> Many of you guys have Spectrogram. To measure the CW transmit
bandwidth of the K2, why not listen to the K2 on a receiver opened up
to a wide SSB bandwidth and feeding its audio to Spectrogram? Transmit
a string of dots and see what the spectrum looks like.
>
> Al  W6LX
>
>
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