[Discuss-gnuradio] Problems Changing USRP Sink Center Frequency During Runtime

[Sean Horton]

After about a week of debugging why I was having trouble receiving multiple AX25 packets when sent together, I've discovered the issue seems to be that if the initial center frequency of the usrp sink is not the frequency that it is changed to after it starts running, then the problem surfaces. Tweaking parameters in other blocks, like quad demod and clock recovery mm have had almost no impact.

The code is supposed to allow the center frequency (and other parameters) to be changed while running, which is why just setting the center frequency to the frequency I'm using for testing is not the best way to solve this. 

What sending multiple ax25 packets look like. There's a single 0x7E between each ax25 packet, which is allowed by the specifications. Also, an icom radio works just fine, and it's in a different room.

<~100 bytes of preamble> <AX25> <AX25> <AX25> <AX25> <postamble>

Also, if the radio is sending one ax25 packet at a time, even when the starting center frequency is 100 MHz+ away from where the radio is transmitting at.

--

Sean Horton