Power，Bandwi dth and spectrum switch problems

GNU Radio
1

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?

2、How do I know bandwidth of transmission and reception channels in
tunnel.py?

3、I am using an USRP2 with Gnu Radio and XCVR2450 as daughterboard. I
want
to switch frequency among different channels 2.4G~2.5G. However, I find
that
switch only can succeed about 20 times, then fails.
The python code is:
self.tb.lock()
ok = self.tb.txpath.set_freq(new_freq)
if not ok:
print “Failed to set Tx frequency”
raise SystemExit
ok = self.tb.rxpath.set_freq(new_freq)
if not ok:
print “Failed to set Rx frequency”
raise SystemExit
self.tb.unlock()

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2

  1. Change tx-gain if you are using tunnel.py. The default value is set
    to
    the mid value. Use -h to find out more.

  2. Spectrum analyzer would help you to observe. I believe you can also
    “calculate” based on your settings. Maybe someone can point out where in
    the
    code the bandwidth relationship is determined.

  3. Not sure why. I thought someone had implemented a FH system.

An

3

On Tue, Jun 29, 2010 at 11:23:36PM -0700, Johnson_lu wrote:

    if not ok: 
        print "Failed to set Rx frequency" 
        raise SystemExit                     
    self.tb.unlock()

FWIW, there’s no need to use lock/unlock to change the frequency.
You only need to use those when you are reconfiguring the topology of
the graph.

Try it without those and see if it works.

Eric

4

On 06/30/2010 08:05 PM, Eric B. 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 L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

5

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:

power to

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6

Thanks for Eric’s reply. I tried the frequency switch without
lock/unlock,
the switches works well, no failures happen again.

Eric B. wrote:

a very little value?
self.tb.lock()
FWIW, there’s no need to use lock/unlock to change the frequency.
Discuss-gnuradio Info Page

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