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Re: [Discuss-gnuradio] Flummoxed!

From: liverpudd
Subject: Re: [Discuss-gnuradio] Flummoxed!
Date: Sun, 25 Sep 2016 20:56:36 +0100



I set the sampling rate on the GRC block diagram on all three devices to 1Msps. When I vary the sample rate to either side of 1Msps by a few Ksps using the resampler, the audio output start to go higher/lower in frequency and I start to get ‘UaUaUa…’ errors as you would expect.


However, I have just had a search to see what the HackRF supports and it would appear to be 2Msps to 20Msps. That being the case, I fail to see why the audio output of gr-rds is OK if it was set to 2Mbps!


With regards the USRP1, there is no UHD ‘The hardware does not support the requested TX sample rate’ warning when I run the gr-rds so I am assuming that it does support 1Msps +/- any frequency errors in the master xtal clock.


Finally, I tried gr-rds with a cheaper RTL dongle device without the 0.5ppm TXCO (I think it had a 5ppm xtal) and that worked OK with the audio and the RDS decoded OK also.


Watch this space…………………









>On 09/25/2016 01:32 AM, Cinaed Simson wrote:

>> But as strange as this might sound, it almost appears as if the RDS

>> module is configured to use RTL dongle raw I/Q data pairs and not the

>> complex I/Q pairs used by the USRP and HackRF One?


>I don't know the difference between raw I/Q and complex I/Q, but the module is supposed to work with >either source.


>>> Next adjusted the 1Msps sample rate using a Polyphase Arbitrary

>>> Respampler.  Adjusted it from 1Msps to +/- 50Ksps in small increments.

>>> RTL dongle packed in the RDS decode a few Ksps either side of the

>>> nominal centre of 1Msps. No joy from the USRP or HackRF no matter

>>> what sample rate I set it to!!!


>Maybe the better approach would be to check what sample rate is supported by the device, set the source to >that sample rate, and then resample accordingly.







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