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DM780 question

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Adam Koczarski

DM780 question

I’m new to the data modes, in fact, I’m new to HF in general, so here’s my question.

When I tune the K3 to a frequency it makes sense to me that I see data streams in the waterfall that are in the side band to the right of the tuned frequency. When I tune in a CW signal and zero beat it using the tone feature of the K3, shouldn’t the CW stream be right at the left edge of the waterfall since it’s just the carrier being modulated?

TIA

Adam – ka7ark

http://ka7ark.com

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Adam Koczarski

Re: DM780 question

> -----Original Message-----
> From: Tom Hammond [mailto:[hidden email]]
> Sent: Thursday, January 08, 2009 8:20 AM
> To: Adam Koczarski
> Subject: Re: [Elecraft] DM780 question
>
> It would be IF there was no 'tone' from the CW signal. But the
> waterfall
> display is showing you a waterfall of all AUDIO TONES (not RF) within
> the
> passband of the receiver... NOT RF signals.
>
> Assuming that you have the CW note tunes to 550 Hz, the waterfall
> display
> of that signal will appear at the 550 Hz spot in the waterfall.
>
> hope this helps.
>

Makes perfect sense to me. Thanks Tom!

Adam - ka7ark

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Richard Ferch

Re: DM780 question

In reply to this post by Adam Koczarski

One other point to note about this:

In AM and FM, the frequency displayed on the K3's dial is, of course, the
carrier frequency, and the modulation sidebands will be on both sides of the
carrier in the waterfall.

In USB and LSB, the frequency that is displayed on the K3's dial is the BFO
or suppressed carrier frequency. In USB, everything you hear at audio will
be above this frequency, i.e. to the right in the waterfall. In LSB,
everything you hear at audio will be below the dial frequency. Which side
they are on in the waterfall depends on whether the waterfall is arranged
from left to right with increasing audio pitch or with increasing radio
frequency - in LSB they run in opposite directions.

In CW, however, the K3 does not display the BFO frequency. The frequency
that appears on the dial is the actual frequency you transmit on, which is
lower than the BFO frequency by your chosen sidetone pitch (CW on the K3
uses the lower sideband). Higher frequency signals will be at lower audio
pitches than your sidetone, and lower frequency signals will be at higher
audio pitches. If you prefer, you can put the radio in CW-REV, which is
upper sideband.

In data modes, it's a bit of a mixture. DATA A is just like USB: the
frequency display is the BFO frequency, and everything you hear is at higher
frequencies (to the right in the waterfall). AFSK A and FSK D are more like
CW. They are both on the lower sideband, and the frequency in the display is
the actual transmitted Mark frequency, not the BFO frequency. You can choose
one of four different values for this using the PITCH control. PSK D is
upper sideband, and the displayed frequency is the actual transmitted
frequency, which is at 1010 Hz audio.

73,
Rich VE3KI

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Adam Koczarski

Re: DM780 question

This explains all the shifting I saw on the waterfall as I switched modes. I
just ended up using DATA A during my first few forays into data modes (PSK,
RTTY), and saw the CW just to the right on the waterfall. I was able to
rationalize most of what I was seeing, but this looks like it will explain
it all.

Great email Rich! I'll print this one out and study it tonight.

Adam - ka7ark

> -----Original Message-----
> From: Richard Ferch [mailto:[hidden email]]
> Sent: Thursday, January 08, 2009 11:01 AM
> To: [hidden email]
> Cc: [hidden email]
> Subject: Re: [Elecraft] DM780 question
>
> In data modes, it's a bit of a mixture. DATA A is just like USB: the
> frequency display is the BFO frequency, and everything you hear is at
> higher
> frequencies (to the right in the waterfall). AFSK A and FSK D are more
> like
> CW. They are both on the lower sideband, and the frequency in the
> display is
> the actual transmitted Mark frequency, not the BFO frequency. You can
> choose
> one of four different values for this using the PITCH control. PSK D is
> upper sideband, and the displayed frequency is the actual transmitted
> frequency, which is at 1010 Hz audio.
>
> 73,
> Rich VE3KI

Jim Brown-10

Re: DM780 question

In reply to this post by Adam Koczarski

Not quite. Software like HRD PSK31 and DM780 (very good software) is designed to look at detected audio from a radio running in USB mode. What you'll see in a waterfall display is all of the signals that fit within the bandwidth of the radio (typically about 2.6 kHz, but adjustable to any bandwidth you choose based on what the radio itself can do). DM780 has the additional capability of reading the radio's carrier frequency, adding to it the audio frequency, and displaying that at the top of the waterfall!

If you used DM780 to for CW but had the radio set for USB, it would be like any other stream -- offset by whatever frequency that station was from the carrier, just like a PSK or RTTY signal.

When you run software like HRD PSK31 and DM780 with a radio in USB mode, you see all the noise in that 2.6 kHz bandwidth. With the K3, you would use one of the digital modes, because they are optimized for modes like RTTY and PSK. See the manual for details. The K3 has the additional capability to narrow up the the bandwidth a LOT to make a huge reduction in noise. This can really help when copying weak signals. You do this using the Width and Offset controls.

Hope this helps.

73,

Jim K9YC

--Original Message Text---
From: Adam Koczarski
Date: Thu, 8 Jan 2009 08:06:08 -0800

When I tune the K3 to a frequency it makes sense to me that I see data streams in the waterfall that are in the side band to the right of the tuned frequency. When I tune in a CW signal and zero beat it using the tone feature of the K3, shouldnt the CW stream be right at the left edge of the waterfall since its just the carrier being modulated?

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Adam Koczarski

Re: DM780 question

From: [hidden email] [mailto:[hidden email]] On Behalf Of Jim Brown
Sent: Thursday, January 08, 2009 11:58 AM
To: [hidden email]
Subject: Re: [Elecraft] DM780 question

If you used DM780 to for CW but had the radio set for USB, it would be like any other stream -- offset by whatever frequency that station was from the carrier, just like a PSK or RTTY signal.

Which I <believe> is what I was doing. My main question was the offset from the left edge in the DM789 waterfall, (the frequency the K3 was tuned too), and the fact that the CW stream was offset a “bit”. I believe Rich’s explanation is still correct??

More good info to process. Thanks!

Adam – ka7ark

Adam Koczarski

Re: DM780 question

In reply to this post by Adam Koczarski

Exactly what I found last night.

Thanks!

Adam - ka7ark

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