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## Re: [Discuss-gnuradio] Max Output Power from the LFTX

 From: khalid.el-darymli Subject: Re: [Discuss-gnuradio] Max Output Power from the LFTX Date: Tue, 6 Jan 2015 15:39:46 -0330

Yes, it is 1 Mohm, and my probe is set to 1X.

Khalid

On Tue, Jan 6, 2015 at 3:33 PM, Nick Foster wrote:
Is the input impedance of your scope 1Mohm or 50 ohms? You sure you have the voltage multiplier (1x/10x) set correctly?

On Tue, Jan 6, 2015 at 11:01 AM, khalid.el-darymli wrote:
>> Trying setting a gain in your sink block of, let's say, 20dB, with a magnitude of 0.9.  What power output do you get?   How are you measuring power?

This gives me 23.2 mV (peak to peak). This is the reading I get from a scope connected to a T. For the input ends of the T, one end is connected to a 50-ohm terminator and the other end is connected to the output from LFTX. This gives a power of: 30+10 log_10[{23.2e-03/[2*sqrt(2)]}^2/50]= -28.711 dBm.

>> What is your flow-graph actually doing?  Have you tried both connectors on the LFTX?

Simple, a signal source (Sine) block directly connected to a USRP Sink block.
Yes, both connectors on the LFTX daughterboard give the same voltage reading.

Thanks,
Khalid

On Tue, Jan 6, 2015 at 2:34 PM, Marcus D. Leech wrote:

>> Output power is determined largely by baseband signal magnitude in that case.

Yes, I understand. And I noticed that for baseband signal with an amplitude > 1,  the pass-band signal gets clipped off. So I assume that an amplitude of 1 for the baseband signal should deliver the maximum output power (for the pass-band signal).

My question was, what is the maximum power one can get for the pass-band signal output from LFTX? In your earlier reply, you said it is around +7dBm, am I getting this right? In my case, for a baseband amplitude of around 1, I am only getting -28.13dBm, much less than what you said, I am not sure, why?

Thanks,
Khalid

For a magnitude of ~1, you should see maximum amplitude signals coming out of it.

You could try setting gain, but on any platforms with VGAs in the DAC, there's only about 6dB of gain range settable.  Trying setting a gain in your
sink block of, let's say, 20dB, with a magnitude of 0.9.  What power output do you get?   How are you measuring power?  What is your flow-graph
actually doing?  Have you tried both connectors on the LFTX?

On Tue, Jan 6, 2015 at 1:56 PM, Marcus D. Leech wrote:

>> Probably somewhere in the neighborhood of +7dBm, maybe a little more.

>> The LF/BASIC series have *no* gain in either path, so you're just looked

So, ~ +7dBm is the max output power I supposed to get from the LFTX daughterboard? How do I get that?

Since I am only getting -28.13 dBm, does that mean I have some issue with my LFTX daughterboard?

Khalid

Output power is determined largely by baseband signal magnitude in that case.

Message: 2
Date: Tue, 6 Jan 2015 10:13:45 -0330
Subject: [Discuss-gnuradio] Max Output Power from the LFTX
daughterboard
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Content-Type: text/plain; charset="utf-8"

Hi,

What is the maximum output power from the LFTX daughterboard when used with
the USRP N200?

According to this datasheet [1], the N200 with the WBX daughterbaord
provide an output power of 15 dBm. However, when using the LFTX
daughterboard, I am getting a much less output power.
[1] http://www.ettus.com/content/files/07495_Ettus_N200-210_DS_Flyer_HR.pdf

In GNU Radio with the USRP N200, we use a sinusoid with a frequency of 150
kHz and an amplitude of 0.98, fed into the LFTX daughterboard for a center
frequency of 5 MHz. When the output of LFTX is plugged into a scope
terminated with a 50-ohm terminator, the scope reads 24.8 mV
(peak-to-peak). This is around -28.13 dBm.

Is this the max power one can get out of the LFTX daughterboard?

Thanks.

Best regards,
Khalid
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Message: 3
Date: Tue, 06 Jan 2015 08:48:08 -0500
Subject: Re: [Discuss-gnuradio] Max Output Power from the LFTX
daughterboard
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On 01/06/2015 08:43 AM, khalid.el-darymli wrote:
> Hi,
>
> What is the maximum output power from the LFTX daughterboard when used
> with the USRP N200?
>
> According to this datasheet [1], the N200 with the WBX daughterbaord
> provide an output power of 15 dBm. However, when using the LFTX
> daughterboard, I am getting a much less output power.
> [1]
> http://www.ettus.com/content/files/07495_Ettus_N200-210_DS_Flyer_HR.pdf
>
> In GNU Radio with the USRP N200, we use a sinusoid with a frequency of
> 150 kHz and an amplitude of 0.98, fed into the LFTX daughterboard for
> a center frequency of 5 MHz. When the output of LFTX is plugged into a
> scope terminated with a 50-ohm terminator, the scope reads 24.8 mV
> (peak-to-peak). This is around -28.13 dBm.
>
> Is this the max power one can get out of the LFTX daughterboard?
>
>
> Thanks.
>
> Best regards,
> Khalid
Probably somewhere in the neighborhood of +7dBm, maybe a little more.

The LF/BASIC series have *no* gain in either path, so you're just looked

--
Marcus Leech
Principal Investigator
http://www.sbrac.org

```--
Marcus Leech
Principal Investigator
http://www.sbrac.org
```

```--
Marcus Leech
Principal Investigator
http://www.sbrac.org
```

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