Signal level

Hi,
In GRC is it necessary that we give a signal to any sink having an
amplitude greater than 1?
Regards,
Ali

Hi Ali - some sinks care about the amplitude, and others do not.

For example, the instruments built into gnuradio (Scope, Frequency
display,
etc.) can examine a signal of almost any amplitude within floating-point
range because you can adjust the display scale factor.

However other sinks, such as a physical transmitter (USRP, HPSDR, etc.)
are
constrained in the amplitude that they can accept. Normally this must be
less than one, and hitting or exceeding 1.00 (even just on the peak)
can
cause problems. Also a physical transmitter might have only 12 or 16
bits
fixed point dynamic range, so there may be a minimum signal amplitude as
well.

– Tom, N5EG

On 05.06.2014 05:17, jason sam wrote:

Hi Tom,
Can you tell what is the constraint for USRP B210?

Stay well within +/-1.

M

Hi Tom,
Can you tell what is the constraint for USRP B210?

What will happen if i exceed this limit?Actually with this amplitude the
TX
power is very less…Is there any other solution?

On Thu, Jun 5, 2014 at 12:54 PM, Martin B. [email protected]

Hi Ali,

power is very less…
Of course, since power is proportional to amplitude squared.
Obviously, if you try to drive an DAC with more than it’s maximum
amplitude, you will get clipping.
This is a nonlinear thing and has very bad effects on your spectrum, and
that’s why you usually avoid it.

Greetings,

On Thu, Jun 5, 2014 at 3:54 PM, Martin B. [email protected]
wrote:

On 05.06.2014 05:17, jason sam wrote:

Hi Tom,
Can you tell what is the constraint for USRP B210?

Stay well within +/-1.

Is there any way to tell whether clipping had happened, says from
warning
message etc …?

On Thu, Jun 5, 2014 at 4:09 PM, Marcus Müller [email protected]
wrote:

Hi Ali,

power is very less…
Of course, since power is proportional to amplitude squared.
Obviously, if you try to drive an DAC with more than it’s maximum
amplitude, you will get clipping.
This is a nonlinear thing and has very bad effects on your spectrum, and
that’s why you usually avoid it.

Dear Sirs,

There is a parameter “Ch0: Gain(dB)” on both UHD Source and UHD Sink.
Does this gain apply before or after the ADC?

Meanwhile depends on daughtercards, sometime there are some built-in
“auto-gain” mechanism, is this correct?

Well, clipping definitively will occur when you leave the ±1 range;
below that, clipping can happen in the analog part, which the USRP can’t
warn you about.

On 05.06.2014 13:13, Activecat wrote:

Dear Sirs,

There is a parameter “Ch0: Gain(dB)” on both UHD Source and UHD Sink.
Does this gain apply before or after the ADC?

Meanwhile depends on daughtercards, sometime there are some built-in
“auto-gain” mechanism, is this correct?

That sort of wraps it up. However, setting the gain to max can also give
you nonlinear distortions.

M

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