# Re: Max Output Power from the LFTX **URL:** \ **Category:** GNU Radio\ **Created:** [January 6, 2015, 6:23pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733 "2015-01-06T18:23:39Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [January 6, 2015, 6:23pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/1 "2015-01-06T18:23:39Z")
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 Message: 2 Date: Tue, 6 Jan 2015 10:13:45 -0330 From: “khalid.el-darymli” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) To: “removed\_email\_address@domain.invalid” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Subject: [Discuss-gnuradio] Max Output Power from the LFTX daughterboard Message-ID: \ 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](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… URL: \< [http://lists.gnu.org/archive/html/discuss-gnuradio/attachments/20150106/37846ff4/attachment.html](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” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) To: removed\_email\_address@domain.invalid Subject: Re: [Discuss-gnuradio] Max Output Power from the LFTX daughterboard Message-ID: [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Content-Type: text/plain; charset=UTF-8; format=flowed On 01/06/2015 08:43 AM, khalid.el-darymli wrote: > 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 L. Principal Investigator Shirleys Bay Radio Astronomy Consortium > **[Live Draw HK Tercepat | Result HK | HK Pools | Live HK | HK Prize Hari Ini](https://www.sbrac.org/)** > > Temukan live draw hk tercepat melalui halaman hk pools yang resmi dan dapatkan result hk prize melalui live hk secara langsung di situs kami. ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 6, 2015, 6:28pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/2 "2015-01-06T18:28:00Z")
> 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. ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 6, 2015, 7:01pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/3 "2015-01-06T19:01:25Z")
> > 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 ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 6, 2015, 7:05pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/4 "2015-01-06T19:05:45Z")
> 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? ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 6, 2015, 7:14pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/5 "2015-01-06T19:14:25Z")
> share this info since what you’re seeing might be a hardware issue > rather than something you can resolve with settings. > > -Mike > The only active component that can really fail on those boards is the > differential-to-single-ended buffer. But you have to work failry hard > to make > those fail. Like maybe driving a dead short for an extended period, > or a big ESD zap on the RF connector. ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 6, 2015, 7:10pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/6 "2015-01-06T19:10:41Z")
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 \ **Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 6, 2015, 8:02pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/7 "2015-01-06T20:02:42Z") > > 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 ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 6, 2015, 7:44pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/8 "2015-01-06T19:44:46Z")
Thanks Mike. I appreciate your comment. I’ll look into buying a new LFTX. Khalid ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 6, 2015, 8:04pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/9 "2015-01-06T20:04:33Z")
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 \ **Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 6, 2015, 8:11pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/10 "2015-01-06T20:11:22Z") Yes, it is 1 Mohm, and my probe is set to 1X. Khalid ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 6, 2015, 8:18pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/11 "2015-01-06T20:18:47Z")
> > 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. Greetings, Marcus ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 6, 2015, 8:22pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/12 "2015-01-06T20:22:30Z")
On 01/06/2015 02:17 PM, Marcus M. wrote: > significantly. > > Greetings, > Marcus > The AD8047 is designed for a max of 50mA drive current. If you do the > math, that’s plenty. I believe that Khalid was terminating in 50Ohms resistive, so with a 1Mohm impedance across that, the scope input impedance will hardly make any difference at all–it should “see” the voltage developed across that 50Ohms, without noticeably changing it. ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 6, 2015, 8:24pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/13 "2015-01-06T20:24:21Z")
On Tue, Jan 6, 2015 at 11:17 AM, Marcus Müller [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > 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 ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 16, 2015, 8:10pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/14 "2015-01-16T20:10:11Z")
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 ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 6, 2015, 11:18pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/15 "2015-01-06T23:18:09Z")
Ah ok, I was (wrongly) assuming Khalid just leaves the TX port virtually open. Greetings, Marcus ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 16, 2015, 8:12pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/16 "2015-01-16T20:12:40Z")
On 01/16/2015 02:08 PM, khalid.el-darymli wrote: > 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. ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 16, 2015, 8:44pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/17 "2015-01-16T20:44:22Z")
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)? Khalid On Fri, Jan 16, 2015 at 3:41 PM, Marcus D. Leech [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Best regards, > > > at some point. > > > > > of around 1, I am only getting _-28.13dBm_, much less than what you > > > > > > > with my LFTX daughterboard? > > > > > > > > ``` > > > > daughterboard > > > > > > > > ``` > > > > > > > > frequency of 5 MHz. When the output of LFTX is plugged into a scope > > > > -------------- next part -------------- > > > > To: [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > > > > > > > > > scope terminated with a 50-ohm terminator, the scope reads 24.8 mV - ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 16, 2015, 8:55pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/18 "2015-01-16T20:55:33Z")
I see. If you would like to diagnose the problem, we can ship you the malfunctioned daughterboard? Thanks, Khalid ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 16, 2015, 8:48pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/19 "2015-01-16T20:48:43Z")
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. ---
**Author:** ![khalide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/3bc359/32.png) [@khalide](https://www.ruby-forum.com/u/khalide)\ **Post date:** [January 16, 2015, 9:00pm UTC](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733/20 "2015-01-16T21:00:32Z")
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. [Next page](https://www.ruby-forum.com/t/re-max-output-power-from-the-lftx/233733.md?page=2)