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I am using GnuRadio Companion (GRC) 3.75 and I am trying to use the Frequency Xlating FIR Filter (FXFF) block to perform some filtering.

All the tutorials I've seen had this FXFF block take in only 1 input (such as this), which is the complex signal (blue in colour).

However, my version of the GRC has the FXFF block take in an additional "freq" input (grey in colour).

I have totally no idea what to feed into this new input and there is not much documentation out there.

Can anyone help?

Is this "freq" input some carrier wave at the baseband frequency?

If so, what block should I use to create this?

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freq is a message queue that allows you to change the center frequency of the filter. You should create a pmt pair containing (intern("freq"), double(frequency) where frequency is the new frequency in Hz. When the new frequency is applied the block will produce a new tag to inform downstream items where the frequency change was applied.

If you do not need to change the frequency during the execution of your flow-graph you can leave this port disconnected.

于 2015-05-07T14:16:51.490 回答