Topband: Digital mode spurious issues

[JC N4IS]

Tom,  Mike is right, the issue with audio overload is complex for most of
new radios,  most of them  have A/D just at the MIC input, if the  A/D
overloads the RF chain is compromised. These radios have no actual filters,
everything is digital, like the IC7600. An analog radio is BW limited by the
SSB crystal filter  but SDR don't, when the A/D overloads, there are spoors
everywhere several KHz far from the carrier; enough to trash the entire
band.

Using a SDR water fall it is easy to see the signal transitions and
associate the trash with the main signal. I've seen several spoors every 10
KHz almost 100KHz up and down 1838. This is a growing problem.

73, JC
N4IS



-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Mike
Waters
Sent: Monday, December 30, 2013 1:31 PM
To: Tom W8JI
Cc: Topband
Subject: Re: Topband: Digital mode spurious issues

Tom,

I believe the mode that operates at 1873-1838 is JT65, and WSJT is needed to
decode it. I never tried it. It was developed by K1JT for weak-signal and
EME work.
http://www.physics.princeton.edu/pulsar/K1JT/wsjt.html

A common scenario with digital modes is that the audio into the mic input is
too high, causing unwanted spurs.

73, Mike
www.w0btu.com


On Mon, Dec 30, 2013 at 11:11 AM, Tom W8JI <w8ji at w8ji.com> wrote:

> ... a digimode station up roughly around 1837 came on with a LSB 
> "spurious" signal on 1833. His signal was a series of slowly changing 
> stepped tones. I don't know what mode that was. His unwanted sideband 
> suppression was about 40 dB, but that was not nearly enough. He was 15 
> dB out of noise with his unwanted sideband.
>
> Does anyone know of a universal software to decode signals? Since the 
> FCC does not require a CW ID, I think that is the only way to identify 
> stations. ...
>
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