Re: [Discuss-gnuradio] Boosting Output RMS Power of BasicTX Daughterboard

[Joe K]

Did you get a resolution on this issue?  We had an old app using UHD 3.5.4 that, once upgrade to 3.9.x or newer, drastically lowers the transmit power.  In our case we're using subsampling, transmitting at 130 MHz.  I don't know if that's related or not.  A while back I built a simple flowgraph with a constant source and a USRP sink.  Built/installed the old UHD, ran the flowgraph, and measured my output power on a spectrum analyzer and it was as expected (-1s of dBm).   Built/installed newer UHD, re-ran the flowgraph, and it was many 10s of dB lower.

I wanted to rerun my test, take plots and document things well, and write an email to the list, but never got around to it.  For now my "solution" has been to stick with the older UHD.

Has anybody else seen anything similar?  Michael, maybe try the older UHD, unless you've figured out your issue.

On Tue, Dec 27, 2016 at 6:29 AM, Michael Skaggs <address@hidden> wrote:

Using GRC 3.7.8, UHD 3.8.5. We had a spare BasicTX, but swapping it out provides the same effect. The o-scope is properly terminated.

It seems like it has to be some way that we've set up the GRC test. I've attached the top_block.py and the .grc file to this message, perhaps this will shed some light on the situation.

Thanks,

Michael

On Tue, Dec 27, 2016 at 5:53 AM, Marcus Müller <address@hidden> wrote:

Also: The BasicTX's source impedance is 50Ω; make sure you properly terminate either by setting your scope to 50Ω or by measuring with a high scope impedance over a 50Ω resistor.

Best regards,

Marcus

On 12/23/2016 10:50 PM, Marcus D. Leech wrote:

On 12/23/2016 01:45 PM, Michael Skaggs wrote:

1 MHz signal with a 6.25MSps rate. We just attempted a signal at 5MHz and measured it at 114mV RMS, a 10MHz signal is 56mV RMS. The voltage seems to drop as the signal frequency rises. Does this assure a hardware issue? Or is there something else we can check?

Thanks,

Michael

Thing is, there's not that much that can go wrong with a BASIC_TX.  It's all passives.

What version of UHD are you using?

On Fri, Dec 23, 2016 at 10:44 AM, Marcus D. Leech <address@hidden> wrote:

On 12/23/2016 10:26 AM, Michael Skaggs wrote:

Hi all,

We're currently working with a BasicTX daughterboard attached to a N210 USRP. We are using both outputs of the BasicTX in quadrature (I on one channel, Q on the other). The problem we are running into is that the output power of the BasicTX board seems very low. Looking at it on an o-scope, we are seeing around 166mV RMS on each channel, which seems lower than we would expect.

We are using GNURadio Companion to transmit these waveforms, and it is a very simple setup. A single "Signal Source" block generating a sine wave into a "UHD: USRP Sink" block. The "amplitude" value is at it's near max without clipping in the ADC and since the daughterboard has no gain elements, "gain" does nothing, so we're kind of at a loss here.

Any help is appreciated.

Thanks,

Michael

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What frequency?

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