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

[Marcus D. Leech]

On 01/16/2015 02:54 PM, khalid.el-darymli wrote:

I see. If you would like to diagnose the problem, we can ship you the malfunctioned daughterboard?

Thanks,

Khalid

Thanks.  I personally wouldn't have time/equipment to really diagnose it.  So it would be up to Ettus R&D as to whether they want it back to see
  what the failure mode is.

I've been doing Ettus support for 6 years, and LF_TX are not generally items that show up with RMA requests very often. 

On Fri, Jan 16, 2015 at 4:17 PM, Marcus D. Leech <address@hidden> wrote:

On 01/16/2015 02:42 PM, khalid.el-darymli wrote:

We were using only one Tx channel with the Subdev Spec in the USRP Sink is set to A:AB

Could the failure be due to that the other (idle) Tx channel is left open circuit (i.e., not terminated by 50 ohms)?

That seems quite unlikely.  These aren't "precious princess" RF power transistors, but reasonably-robust differential-to-unbalanced drivers.  I'd
  be very surprised if they couldn't handle an open-circuit condition.

Khalid

On Fri, Jan 16, 2015 at 3:41 PM, Marcus D. Leech <address@hidden> wrote:

On 01/16/2015 02:08 PM, khalid.el-darymli wrote:

Hi All,

Just to update you in case somebody else comes across this problem. Following Mike's advice, we replaced the LFTX daughterboard with a new one. We're getting now 1 V p-p. This is around 4 dBm.

Thanks very much for your help.

Best regards,

Khalid

Interesting.  The driver chip that's used, as a unity-gain differential-to-single-ended driver, is, according to the datasheets, pretty robust.  So, it would
  be interesting to know exactly what the failure mode is.

On Tue, Jan 6, 2015 at 2:38 PM, Michael Rahaim <address@hidden> wrote:

Hi Khalid,

I had a similar issue with an LFTX that I had been working with for about two years. I actually had two boards running on separate USRP2's and both were working fine for quite a while, but I recently noticed that one had a drastically lower output range. I ended up replacing the LFTX and all is working well now, so I'm assuming it was a hardware issue that came up at some point. 

I didn't take the time to look for the problem, but I figured I'd share this info since what you're seeing might be a hardware issue rather than something you can resolve with settings.

-Mike

On Tue, Jan 6, 2015 at 12:59 PM, khalid.el-darymli <address@hidden> 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

On Tue, Jan 6, 2015 at 1:56 PM, Marcus D. Leech <address@hidden> wrote:

Thanks Marcus for your reply.

>> 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
at buffered ADC ouput.

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
From: "khalid.el-darymli" <address@hidden>
To: "address@hidden" <address@hidden>
Subject: [Discuss-gnuradio] Max Output Power from the LFTX
        daughterboard
Message-ID:
        <CACdmG=zCHATiwrtv=wBVLwG0_

5GQr0y=address@hidden>
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
From: "Marcus D. Leech" <address@hidden>
To: address@hidden
Subject: Re: [Discuss-gnuradio] Max Output Power from the LFTX
        daughterboard
Message-ID: <address@hidden>
Content-Type: text/plain; charset=UTF-8; format=flowed

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
at buffered ADC ouput.



--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

 

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