On Tue, Jan 6, 2015 at 11:17 AM, Marcus Müller <marcus.muel...@ettus.com>
wrote:
> >Is the input impedance of your scope 1Mohm or 50 ohms?
>
> Yes, it is 1 Mohm,
>
>
> Well, in that case, your power consideration is not really correct; the
> LFTX is designed for 50 Ohm load impedance; so, for meaningful
> measurements, you'd have to measure the voltage over 50 Ohm.
> I'm not really sure how much current the opamp on the LFTX is designed to
> source, but I think adding a 50 Ohm load would reduce the current through
> the negative feedback resistors R4/R7 (and in turn reduce the bias over
> R33-R3/R35-R6) , which might change your measurements significantly.
>
>
With a 50ohm term hanging off the other end of a tee, the effective
impedance is 50ohm, so I'd expect to see the rated 7dBm or so coming out of
his setup.
Just for reference, I'm currently getting 5mW (7dBm, 700mV P-P) out of an
LFTX into a 50 ohm load for another project.
--n
> Greetings,
> Marcus
>
>
> On 01/06/2015 08:09 PM, khalid.el-darymli wrote:
>
> Yes, it is 1 Mohm, and my probe is set to 1X.
>
> Khalid
>
>
> On Tue, Jan 6, 2015 at 3:33 PM, Nick Foster <bistrom...@gmail.com> 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 <
>> khalid.el-dary...@mun.ca> 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 <mle...@ripnet.com>
>>> 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 <mle...@ripnet.com>
>>>> 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" <khalid.el-dary...@mun.ca>
>>>>> To: "Discuss-gnuradio@gnu.org" <discuss-gnuradio@gnu.org>
>>>>> Subject: [Discuss-gnuradio] Max Output Power from the LFTX
>>>>> daughterboard
>>>>> Message-ID:
>>>>> <CACdmG=zCHATiwrtv=wBVLwG0_
>>>>> 5GQr0y=wksequrcajrtuv5...@mail.gmail.com>
>>>>> 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
>>>>> -------------- next part --------------
>>>>> An HTML attachment was scrubbed...
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>>>>> http://lists.gnu.org/archive/html/discuss-gnuradio/attachments/20150106/37846ff4/attachment.html
>>>>> >
>>>>>
>>>>> ------------------------------
>>>>>
>>>>> Message: 3
>>>>> Date: Tue, 06 Jan 2015 08:48:08 -0500
>>>>> From: "Marcus D. Leech" <mle...@ripnet.com>
>>>>> To: discuss-gnuradio@gnu.org
>>>>> Subject: Re: [Discuss-gnuradio] Max Output Power from the LFTX
>>>>> daughterboard
>>>>> Message-ID: <54abe798.5060...@ripnet.com>
>>>>> 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 Consortiumhttp://www.sbrac.org
>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Marcus Leech
>>>> Principal Investigator
>>>> Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org
>>>>
>>>>
>>>
>>>
>>>
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>>
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