# How can I make WBFM receiver without using WBFM Receive block?

I'm trying to make a WBFM receiver without using WBFM Receive block. So I've tried this way

But it won't work. The problem is

RuntimeError: flow graph has loops!

and I need to use loop feedback for implement FM demodulation.

Very pleasure for any suggestions and advises.

• You wrote “transmitter” in your text on one place, do you mean “receiver” there? – Kevin Reid AG6YO Jan 31 '18 at 15:04
• Yeah, sorry for the mistake – Yondonjamts Ganzorig Feb 1 '18 at 17:00

However, you do not need feedback to implement a FM demodulator. The key block to FM demodulation in GNU Radio is the Quadrature Demod (gnuradio.analog.quadrature_demod_cf) block. This block takes in a complex signal and outputs the phase difference — or instantaneous frequency — of every successive pair of samples, which is exactly the core of FM demodulation.