How to Change Bandwidth

[rchrdmParticipant]

Looking at the 80 meter ham band, as an example, I see that the bandwidth that first comes up goes from about 3480 KHz to 4020 KHz. This is about 540 KHz. (Span in the data below the spectrum is 555.6 KHz.)

I have searched the manual for how to control the span, but can’t find anything except a reference to the displayed span data.

Is the span locked into the band displayed?

What if I want to, for example, see the WWV signal at 5 MHz? I can tune to that frequency by entering it into the digital readout, of course, but I’d like to be able to just scroll up the band as if I was turning a tuning knob.

Richard

[Andy2Participant]

If you use the ‘band’ buttons, the chosen band will be ‘framed’ ie the span and the LO will be fixed. If you want to have access to variable span etc, then you should enter the frequency via the keyboard/keypad. Once you have done this, you can set the sample rate and decimation to get the span you require.

[rchrdmParticipant]

Thanks.

I set the frequency for WWV at 5 MHz. The span is 333.3 KHz. How do I change the span and decimation? What is decimation? (There is a discussion of it in 2017 on the old SDRplay forum board.

The only reference in the manual to decimation no page 38 and it does not say how to change it.

It does mention about “bands wider than 10 MHz cannot be framed.” How would I set a band to 10 MHz wide?

Sorry if I am overlooking something.

Richard

[Andy2Participant]

OK Richard. I’ve been using my Winradio SDR recently and have left my RSP2 disconnected for a while. I’ve just plugged it back in and downloaded Uno 1.33 to make sure I’m up to date.
All the buttons you need are in the small MAIN RX CONTROL panel, the one with the RF gain slider.
First of all, change the mode to ZIF (zero IF). This will give you access to the Sample Rate (SR) and Decimation boxes. You should see these roughly central in the panel. The lowest SR is 2 MHz, so if you want a smaller span you should click in the Decimation box to bring up a division number. Choose a number that gives you something close to the span you want.
Note you cannot do this if you are using the ‘band’ buttons, as this fixes the SR and DEC selections.
If you select LIF (Low IF) you cannot choose the SR, only the DEC.
Hope this helps.

[rchrdmParticipant]

Thanks, Andy. That worked! What is the relationship of span and decimation settings?

It would be good to add this to the manual, unless I overlooked it.

That Winradio SDR looks pretty nice!

Richard

[Andy2Participant]

Glad it’s sorted. BTW, I forgot to mention that to get a 10 MHz span, just press the SR button and select 10 MHz from the menu. Then press the DEC button and select 1. To get a 5 Mhz span, use a 10 MHz SR and select a DEC of 2.
Once you’ve seen how the numbers interact you’ll be able to work it out. The final span is the result of dividing the SR by the Decimation figure.
The Winradio Excelsior is very nice, but it should be at the price! It came my way after it reached the end of a long trip around several reviewers. I put a derisory bid in and got it for a song. Sadly, the supplied software lacks some features that Uno has as standard. There is no way of slowing down the waterfall displays, so spotting satellite Doppler shifts is difficult, and there’s no ‘asymmetric’ IF filter available, which is very handy if you are trying to hear a weak AM signal right next to a big unwanted one. Being able to ‘roll off’ one side of the response is very useful, but the s/w on the Excelsior doesn’t do it. You can do something similar by using SSSync AM or even SSB, but asymmetric would have been nice.
I feel your pain about the Uno manual. It’s been constantly updated as new versions of UNO have come out and it’s ended up a bit fragmented and sometimes contradictory.

[wb900Participant]

Ultimately it is the Sample Rate that gives you the span. Think of decimation as throwing away samples (a bit more complicated than this) thus further reducing the sample rate and therefore the bandwidth.
e.g A decimation value of 2 would throw every other sample away

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