What's the settling time after new frequency set to dongle?

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Nikos Balkanas nikos.balkanas at eyeonix.com
Tue Jan 14 19:26:37 UTC 2014


We forgot the most important parameter. The frequency "jump". If the
frequency change is large, i.e. from 10 Khz to 1 Ghz, then of course it
will take longer for the tuner to equilibrate. In my scanner, when I
approach a target I take 10 baby steps of 2 Khz each to zero in. Drift is
negligible. I tried using the 5000 us in my scanner, and the results were
the same as without it, except for the delay of an additional 50 s. I
promptly removed it.

The way I see it, tuner needs some time to settle in a new frequency, but
there is no fixed delay. It is situation specific and depends highly on the
amount of frequency change.

HTH,
Nikos


On Tue, Jan 14, 2014 at 6:47 PM, Nikos Balkanas
<nikos.balkanas at eyeonix.com>wrote:

>
>
>
> On Tue, Jan 14, 2014 at 5:50 PM, <steve at steve-m.de> wrote:
>
>> Hi,
>>
>>
>> On 2014-01-14 15:23, Jiao Xianjun wrote:
>>
>>> Is there any information or hint on the settling time after new
>>> frequency set to dongle?
>>>
>>
>> That depends a bit on the tuner and the sample FIFO of the RTL2832,
>> but you need to drop a few buffers, as the PLL of the tuner takes
>> some time to lock and stabilize.
>>
>> Sample FiFO should be full at all times in a DVB-T. I have never seen it
> empty due to interfernce, noise, etc.
>
>>
>>  Can I immediately read samples after new frequency is set by
>>> rtlsdr_set_center_freq? If so, will the samples quality be degraded?
>>>
>>
>> Kyle Keen did some experiments for his scanning application
>> (rtl_power), and he settled for waiting a few milliseconds and
>> flushing the buffer to get optimal results. See here:
>>
>> http://cgit.osmocom.org/rtl-sdr/tree/src/rtl_power.c#n626
>>
>> Regards,
>> Steve
>>
>> That's a little too long, making large spectrum tuners inoperable. In my
> scanner I use a read immediately after the frequency
> set without any problems. Of course I cannot vouch for correct frequency,
> but I have noticed that the frequency doesn't drift
> appreciably when resetting frequency and locking to a band.
>
> BR,
> Nikos
>
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