Re: [Discuss-gnuradio] Fwd: Problem in uhd_fft

[Josh Blum]

On 07/04/2013 01:41 AM, Karan Talasila wrote:
> Hi Josh,
>             we tried using the same grc flowgraph and tried transmitting at
> frequencies 33Mhz and 35 Mhz. Though we could see a constant source output
> on the fft, the frequency at which that was occuring was at -31Mhz and
> -29Mhz. The output log is shown below for frequency of 33 Mhz. I have
> attached a screenshot of my grc too.
> 

That sounds correct. The receive chain performs frequency translation
with a CORDIC running at 64MHz. So -31MHz is an alias of 33MHz and
-29Mhz is an alias of 35MHz

-josh

> 
> enerating: "/home/anrc/Downloads/top_block.py"
> 
> Generating: "/home/anrc/Downloads/top_block.py"
> 
> Executing: "/home/anrc/Downloads/top_block.py"
> 
> linux; GNU C++ version 4.6.3; Boost_104800; UHD_003.004.005-0-unknown
> 
> Using Volk machine: sse4_1_64
> -- Opening a USRP1 device...
> -- Using FPGA clock rate of 64.000000MHz...
> 
> UHD Warning:
>     The hardware does not support the requested RX frequency:
>     Target frequency: 33.000000 MHz
>     Actual frequency: -31.000000 MHz
> -- Opening a USRP1 device...
> -- Using FPGA clock rate of 64.000000MHz...
> U
>>>> Done
> 
> 
> 
> On Thu, Jul 4, 2013 at 6:36 AM, Josh Blum <address@hidden> wrote:
> 
>>
>>
>> On 06/29/2013 09:14 AM, Karan Talasila wrote:
>>> ---------- Forwarded message ----------
>>> From: Karan Talasila <address@hidden>
>>> Date: Sat, Jun 29, 2013 at 6:44 PM
>>> Subject: Re: [Discuss-gnuradio] Problem in uhd_fft
>>> To: "address@hidden" <address@hidden>
>>>
>>>
>>> Hi Josh,
>>>             I am using USRP 1.   I am using a sma-bulkhead cable from
>> Tx_A
>>> of basic tx daughter board and similarly a sma-bulkhead cable from Rx_A
>>> terminal of the Basic Rx daughter board. and then i am connecting a
>> sma-sma
>>> cable from usrp transmitter to a coupler on powerline cable. Similarly I
>> am
>>> connecting a sma-sma cable from usrp receiver to another coupler on the
>>> powerline cable.
>>>
>>> so in all I am using 2 usrp 1, 2 sma-sma cables, 2 sma-bulkhead cable and
>>> two couplers. Please let me know if i am not clear with the description.
>>> Thank you.
>>>
>>
>> Seems to work OK for me. I used a single USRP1, BasicRX, BasicTX. RXA is
>> connected to TXA and RXB is connected to TXB. Attached is a GRC flow
>> graph. Hope that helps.
>>
>> -josh
>>
>>>
>>> On Sat, Jun 29, 2013 at 11:24 AM, Josh Blum <address@hidden> wrote:
>>>
>>>>
>>>>
>>>> On 06/27/2013 09:44 AM, Karan Talasila wrote:
>>>>> Hi,
>>>>>       I am using a basic tx and basic rx daughterboard for transmission
>>>> and
>>>>> reception. The spec says basic tx and basic rx run from 0 to 250 MHz.
>> But
>>>>> when i run transmitter and check the uhd_fft at receiver, after 32 Mhz,
>>>>> there is no signal. If i set the transmitter frequency in my flowgraph
>> as
>>>>> 33 MHz, I don't get a signal at 33 Mhz, But when i enter frequency as
>>>>> -31Mhz in the uhd_fft i get a received signal on my fft. why does this
>>>>> happen? If it's in the range of daughter board it should be receiving
>> it
>>>> at
>>>>> that particular frequency right.
>>>>>
>>>>>
>>>>
>>>> Can you tell me more about the cabling setup? Which ports of the Basic
>>>> TX and RX are you using, and how are they connected via SMA cable?
>>>>
>>>> -josh
>>>>
>>>>>
>>>>> _______________________________________________
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>>>>>
>>>>
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>>>
>>>
>>>
>>>
>>>
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>>
> 
> 
>