Re: [Discuss-gnuradio] Interpolation in usrp_siggen

[Shyam]

hi Eric,
The daughterboard I use is RFX2400 so I set -f 2.45G ( btw my gnuradios
have been properly set up since benchmark_tx and receive  work fine for
gmsk)  . I have tried the below stated experiment using two antenna
types to see if it is due to the antennas but it is consistent across
antennas.
2400-2480 MHz ISM Band PCB Quad Patch, and

2400-2480 MHz ISM Band Vertical Antenna.

Also for the above configuration can u kindly also let me know is my
observation that 7KHz is the frequency offset due to the oscillators is
true?

Thanks in advance for ur reply
Shyam

Eric Blossom wrote:
> On Mon, Dec 11, 2006 at 08:30:25PM -0800, Shyamnath wrote:
>   
>> hi,
>> I am new to gnuradio architecture and am trying to learn about it. I was
>> using the usrp_siggen,py sample code provided with different interpolation
>> rates (4, 8,12,16,64)  since it has to be a multiple of 4.  the observations
>> are as follows (which  cannot explain)
>>
>> 1) For interpolation rates set to 4,8,12, at the sender, what I observe on
>> the receiver (directly connecting the usrp_source to a file_sink), is just
>> noise.
>>
>> 2) For a interpolation rate set to 64, I almost get the required sinuosoidal
>> at the required frequence(100khz), with the difference that the frequency of
>> the signal at the receiver for nearly 200 samples at the beginning  is
>> nearly 7KHZs. To understand this better, I just send a constant signal on
>> the sender (using usrp_siggen.py) and received a sinousoidal at the receiver
>> with a frequency of 7Khz (which I presume is because of the frequency
>> offset). Although I think the above two observations are related I could not
>> explain them.
>>
>> 3) Another interesting case is when the interpolation rate is set to 16. the
>> output at the reciver is a signal which has a sinousoidal with the required
>> frequency(100khz) spaced with sinousoidals with a frequency of 7khzs.  This
>> observation is something I cannot understand.
>>
>>  Kindly help me out with this.
>>
>> Thanks
>> Shyam
>>     
>
> You didn't mention which daughterboard you are using, but assuming
> it's a Basic Tx, be sure to set the -f <freq> option to something like
> 10M.  Neither the Basic Tx nor Basic Rx will pass signals under about 100kHz.
>
> Eric
>