Re: [Discuss-gnuradio] Power，Band width and spectrum switch problems

[Johnson_lu]

Thanks for the reply. 
I tested the parameter tx_amplitude=0.001 and I can get little transmit
power I wanted.
I can observe the bandwidth from the spectrum analyser. I also changed the
bitrate and modulation to get different bandwidth. But I still have some
questions about the difference of the transmit bandwidth and the filter
bandwidth.

Marcus D. Leech wrote:
> 
> On 06/30/2010 08:05 PM, Eric Blossom wrote:
>> On Tue, Jun 29, 2010 at 11:23:36PM -0700, Johnson_lu wrote:
>>   
>>> Hi guys，
>>> Could anybody can help me for these problems？
>>> 1、I varied Tx_amplitude from 0.1 to 1 and measured the output with a
>>> spectrum analyzer. But the changes are very little. The output is almost
>>> the
>>> same when Tx_amplitude is 0.1 and 1.  How can I reduce the transmit
>>> power to
>>> a very little value?
>>>     
> All else being equal that should produce a 10dB change in signal power,
> unless *something* in the
>   chain is already at saturation due to other factors in the Tx chain. 
> Keep in mind that a 10dB change
>   on a logarithmic scale isn't very much.
> 
>>> 2、How do I know bandwidth of transmission and reception channels in
>>> tunnel.py? 
>>>     
> There seem to be *two* versions of tunnel.py in the examples--which one
> are you talking about?
>   Have you put the output of the transmit side on a spectrum analyser? 
> That would tell you
>   unambiguously what the bandwidth is, but also careful and
> knowledgeable inspection of the
>   code will tell you what the theoretical bandwidth is.
> 
> 
> 
> -- 
> Marcus Leech
> Principal Investigator
> Shirleys Bay Radio Astronomy Consortium
> http://www.sbrac.org
> 
> 
> 
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> 
> 

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