Hi Moses,
I would try to reduce the task to something that >must< work and then gradually
increase the complexity.
* Maybe even start with checking the spectrum analyzer with another signal
source. Do you have a programmed calibration (power) offset?
* Put a DC block at the input of the spectrum analyzer.
* Reduce sample rate
* Reduce amplitude of the signal source in flow chart. --> Does the
spectrum change? View wider spectrum. Do you see intermodulation products,
harmonics, other spurs?
* Reduce gain of the USRP sink in flow chart --> Does increasing gain
follow a linear relation, i.e. 1 dB increase in gain value gives 1 dB increase
of output power?
* Change center frequency --> Is it the same at all center frequencies or
does it have a frequency slope?
* …
Best regards, Bernd
Sent: Dienstag, 10. November 2020 09:12
To: Moses Browne Mwakyanjala <mbkit...@gmail.com>; GNURadio Discussion List
<discuss-gnuradio@gnu.org>
Subject: Re: Measuring transmission power from USRP B210
**This email has been sent from an EXTERNAL source**
Hi
I did not tried to calibrate my USRP source up to now but I'm interesting by
this subject.
* I saw in Ettus USRP
manual<in%20%20%20%20%20%20%20%20%20%20https:/files.ettus.com/manual/page_power.html>
that :
* "The TX reference power level is defined as such: When a 0 dBFS signal
is transmitted, it will leave the RF output at the selected reference power
level. In other contexts, this value is sometimes referred to as "peak power
level", because it's the maximum power that can be transmitted."
* It seems that on some USRP, this reference power level can be
set/changed at runtime
* Given example clearly states that the source level in GRC is not
directly related to the power level at URSP output in dBm
* Looking at How to set the trasmit power of
USRP?<https://urldefense.com/v3/__https:/forums.ni.com/t5/USRP-Software-Radio/How-to-set-the-trasmit-power-of-USRP/td-p/2202190?profile.language=fr__;!!LUcoR2A!bMdMC6dkA6QgtJNBOvi1aHbim4k7ioMTl4gp0PpaZy086ea5k3FNiIpwMBQ_J4VH7iHJDg$>
on NI forum (see Sara answer)
* "Since these are uncalibrated devices, a particular gain value doesn't
correspond to a particular power level"
* take a look at Sarah's reference b200_rev4_TX_FE1.pdf 859
KB<https://urldefense.com/v3/__https:/forums.ni.com/ni/attachments/ni/500/1420/1/b200_rev4_TX_FE1.pdf__;!!LUcoR2A!bMdMC6dkA6QgtJNBOvi1aHbim4k7ioMTl4gp0PpaZy086ea5k3FNiIpwMBQ_J4W3DRwbyQ$>
page 61 : it seems that the output power for a B200 at 2.2 GHz, with 0 dB
gain (1 in linear) is close to -5 dB for a zero gain : Could that explains your
-6 dBm?
* These references do not give a clear answer. I don't clearly understand
given explanation.
Regards
On 09/11/2020 17:39, Moses Browne Mwakyanjala wrote:
Hello everyone,
I'm in the process of testing a GNU Radio transmitter. The transmitter will be
connected to a solid-state power amplifier (SSPA) for near-Earth satellite
communications. The SSPA expects an input of 0dm from the USRP TX port.
The first step is thus to measure the power from the USRP. To that end, the
flowgraph generates a complex sinusoidal signal with a unit magnitude. The
UHD:USRP Sink block is set to maximum gain (i.e. normalized gain of 1.0).
Unfortunately, the maximum power I can see from the spectrum analyzer is around
-6.93 dBm as shown below. To my understanding, the USRP can transmit up to 20
dBm as reported in the "External Connections" section at this Ettus link :
https://files.ettus.com/manual/page_usrp_b200.html<https://urldefense.com/v3/__https:/files.ettus.com/manual/page_usrp_b200.html__;!!LUcoR2A!bMdMC6dkA6QgtJNBOvi1aHbim4k7ioMTl4gp0PpaZy086ea5k3FNiIpwMBQ_J4WmUTIx6Q$>.
Could anyone explain why I can't achieve a 20 dBm (or anything around it) power
level?
[cid:image002.jpg@01D6B743.D5271B10]
Thanks in advance,
Moses.
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