Technical Topics > SDR - Software Defined Radio

Neophyte to SDR- - question

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Token:
I can't get that site to run for me for some reason, seems to be a Java issue.  However from what does load it looks like that might be a relative frequency display, kind of like an unmarked bandspread on an old school reciever.  By that I mean what you are tuned to is at "0" on the bottom scale, lets say you are tuned to 18100 kHz, then something at "-25 kHz" on the scale would be 25 kHz below you, or at 18075 kHz.

However that is just a guess, as I can't get the page to correctly load and run.  I can see everything, but not make anything function.

T!

refmo:
Nice link.

With newer versions of Java, I had to add the site to the 'sitelist' in Control Panel --> Java.

The bottom window is a separate receiver.  It appears to be a satellite receiver, with 0 being the center frequency of the satellite passband.
I'm not sure which satellite is being received, so can't be sure of the frequency.  Likely, it is in either the 2 meter or 70 centimeter amateur satellite subbands.
Lots of activity, with euro hams sending their calls and 'grid-square' locators.

Token:
Ahhhh, that makes since, notice in the upper right corner of the page it lists a satellite and the uplink / downlink frequencies.  A satellite in a pass will have Doppler shift on its signal, and you can predict Doppler if you have software to track the sat.  That way, knowing your uplink freq and the Doppler shift of the sat at that particular time you can predict your downlink shift, generally done in kHz.  So the scale will show you what freq a given uplink can be found, relative to the "center" downlink freq.

So yeah, the bottom scale is a relative display, not true or absolute frequency, and in that case a signal that was 25 kHz below the downlink center would be on -25 kHz on that display.

T!

tybrad:
Makes sense.  Thanks you two!

tybrad:
OK, just heard some chatter (Papa alpha seven (repeated).  Thank you satellite" and continues on the repeating) on those –kHz listings.  I am confused again about this waterfall.

Will post a screenshot when I get home.





Also, what could the meandering frequency sweep be?  Ionosonde?  But over such a limited range (I can't even tell what the range is on this waterfall)

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