question about 'useable' bandwidth

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I've been doing a lot of wsht-x lately.
Just curious about bandwidth.

I normally start wsjt with the flag on the left side, butted up to the edge of the useable band grid.
I then select DIGU and 3.0K
Now this highlights a good portion of the right side of the screen where hopefully the wsjtx stations will be seen/heard.
A small portion of the screen is still available on the far right side of the 3.0K passband.
I can grab the right edge, and drag it farther to the right.

My question is, once I exceed the 3.0K, does resizing the band cause any rolloff in response?
Does it exceed the limits of the 6K's 'useable' bandwidth for this mode?

In legacy receivers, it sure would, but so far I don't see any loss, although I'm only increasing it to maybe 3.02K width.

Just curious.
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Bill-W9OL

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  • embarrisingly stupid

Posted 4 years ago

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Tim - W4TME, Customer Experience Manager

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"My question is, once I exceed the 3.0K, does resizing the band cause any rolloff in response?"

In your case with a 3K filter, the sharpness of the filter skirts does not change as you expand the filter out wider.

In SmartSDR, the filters in DIGx modes have dynamic shirt characteristics.  With any DSP filter, the sharper the skirts, the greater the latency or the amount of time it takes for the signal to propagate through the filter and higher DSP computational overhead.  For narrow digital modes, very sharp skirts are a requirement, so the narrower filters have very sharp skirts and and consequently higher latency.  As you expand the filter out to a wider value, really sharp skirts are not really needed, as they are relaxed and the filter has a lower latency and less DSP computational overhead..  At 3k wide, you are no longer within the range where the skirts would be narrow, hence the answer, "in your case the shape of the filter does not change".


"Does it exceed the limits of the 6K's 'useable' bandwidth for this mode?"

No, it does not.
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Bill-W9OL

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Thank you Tim.
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KY6LA - Howard, Elmer

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I usually run 4K or5k. With WSJT-X so I. Can work both JT65 and.JT9

You can save the4K and 5K in profiles


No issues. With rolloff
(Edited)
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DrTeeth

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I am using WSJT-X a lot too. Yet to have my first JT9 QSO however. Never heard a signal and no answers to CQs. Mainly on 1700-0000z during the week and any daytime hours I can snag at the weekends; XYL and taxi service for my teenage children permitting. It is spooky to see how far the signals travel on PSK Reporter - much further then the QSOs sadly.
(Edited)

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